Monday, January 21, 2008

3. Nikon TTL-BL Flash


The most advanced flash mode on the Nikon flash is TTL-BL. Originally, the BL meant BackLit, but Nikon marketing gurus changed it to mean BaLanced Fill. (Why didn't they change the initials to TTL-BF?). The word BackLit suggests the situation for which this mode is most useful.

The photo on the left is a good example of a subject being backlit by a brighter scene.

I have discussed in the previous blog entry that in the TTL mode the Camera Metering System is entirely separate from the Flash Metering System, and that they work independently. Well, in TTL-BL, the same two metering systems do communication with each other.

First, let's discuss what Fill Flash is and when it is needed.

Fill Flash is needed any time the background (also called ambient) is brighter than the subject and this often occurs outdoors on a bright day. In this situation, if you look closely at the subject's face, you will see shadows in the eye sockets, under the nose, and under the chin. When you shoot this type of shot, it will look much much better if the flash is used to 'fill' the shadows. Another situation would be if the background behind the subject was the bright sky. Again, flash should be used to 'fill' the subjects face and make it balance with the bright sky. One more situation would be when indoors during the daytime, and you want to shoot the subject in front of a window with a beautiful brightly lit scene behind (like the picture above). Again, the flash should be used to brighten the subject's face to balance with the bright scene behind.

These are the situations where Nikon's TTL-BL mode works best.




In the above example image the subjects are in front of a window and I wanted the outside to be exposed properly by bright ambient light, while I needed lots of fill to bring their faces up to be slightly less bright than the outdoors. I put my D200 in Manual mode, ISO 200, and used the built-in light meter to set f/3.5, 1/160th, and TTL-BL with -1.7 ev worked great in this situation to just bring up their faces to what seems a natural brightness.

Here are the steps that the camera and flash do for you as you push the shutter:

Given: Flash in TTL-BL, Camera in P mode, matrix metering, and AF-S focusing.

1. As the shutter is half-pushed, the focus system becomes active, the focus is achieved, and the overall scene is metered by the camera.

2. The data from the camera metering system and, the focal distance from the D or G lens are sent to the flash metering system. This is the only communication that takes place between the camera metering system and the flash metering system.

3. As the shutter is pushed down the rest of the way, the flash fires the preflashes, and the flash metering system measures the reflected light. This reflected energy is a secondary factor to the distance reported from the D lens in the TTL-BL equations. If a D lens is not being used, the preflash reflected power assumes a more important role in the TTL-BL equations. When using a D lens, the main purpose of the preflash is to set the white balance.

4. The flash metering system (which actually resides in the camera) then uses the distance information from the D lens and the data from the camera metering system, to determine the amount of added power required to make the subject brightness equal to the overall scene brightness. In other words, it adds light from the flash to balance the brightness of the subject with the ambient.

5. The shutter opens, the flash fires at the power level determined above, and the shutter closes.
Now, for this all to work well, a couple of key things must be considered. First, the subject (obviously) can only be brightened by the flash. There have been several advancements to TTL-BL since I originally wrote this, and now TTL-BL handles the situation fairly well when the subject starts out brighter than the background in low ambient. However, it is still best not to use TTL-BL if the subject is already brighter than the overall scene. Regular TTL usually works better.

Second, flash pictures usually look really odd when the subject is just as bright as the background. The subject seems to jump off the page unnaturally and it is obvious you used flash. Fill flash is supposed to be subtle, and when looking at the print it is usually best that you cannot even tell that flash is used at all. Consequently, it is often best to turn down the flash compensation by -.3 ev to -0.7 ev, so the fill is just enough to lift the darkest shadows on the face without looking obvious.

Notice that the flash never tells the camera anything about the power setting it has chosen. The camera sets its f/ stop and shutter (in auto modes) as if the flash wasn't even attached (with the exception of limits on shutter speed). The only coupling between the camera metering system and the flash metering systems is when the camera sends its metering information and focal distance (if using a D or G lens) to the flash metering system.

If you are using camera Manual mode, the flash system is not even told what f/stop or shutter you have selected. It assumes that you have zeroed the light meter in the camera and sets the flash power accordingly. It only receives the metering data from the camera metering system and uses that as the 'background' brightness. This is why it is often best to use camera P or S modes when shooting fill flash. They automatically zero the light meter in the camera using the aperture which avoids the overexposure that often occurs when using A mode.

Of course the flash also knows the f/ stop and ISO from the camera settings which are sent through the hot shoe.

Next: Flash Value Lock

186 comments:

ram said...

Hi Russ,
This TTL/ BL and TTL explanation has been really helpful ,
Sir,i thank you for this info,
Looking forward to your further blogs.
Ram Mohan.R

Russ MacDonald said...

Ram,

I appreciate the feedback.

Thanks, Russ

Anonymous said...

Finally, something I can understand, thank you!

Anonymous said...

"I put my D200 in Manual mode, ISO 200, and used the built-in light meter to set f/3.5, 1/160th"

Hi Russ,
After putting the camera in manual, how exactly did you figure out these numbers using the built-in light meter? Thank you.
Walter

Russ MacDonald said...

Walter,
I used the built-in lightmeter to meter the scene outdoors. I moved up close to the couple and pointed the camera outdoors and it metered at 1/160th and f/3.5. So I set that into the camera and backed up and used TTL-BL to make the couple match that outdoor brightness (and down by -1.7 ev).

Russ

Anonymous said...

Hi Russ,

I understand what you did, but not how. In order to meter after setting ISO 200, did you use, for example, program or aperture mode and then set the results in manual? The DOF outside the window is great; I would have expected to see less of it with f/3.5.

I've found your blog through a link at Planet Neil. All your topics are extremely well written, interesting and enlightening, I really appreciate you taking the time to write and to answer our questions as well.

Thanks a lot.

Walter Rojter
Miami, FL

Russ MacDonald said...

Hi Walter,

I simply used the camera in Manual mode and used the built-in light meter. You can watch the meter through the viewfinder (or from the top LCD) as you change the f/ stop and shutter speeds until the dots collapse into the center.

I like to use the built-in meter whenever I have the time. It's a little slower than the auto modes, but you can meter different parts of the picture (by pointing the camera at different places) to see the range of f/ stops and shutter speeds in the scene.

Manual metering works best when using Spot metering mode, but In the image we are discussing, I think I just left it in Matrix mode, because you cannot select TTL-BL when in Spot mode, and I wanted to use TTL-BL.

There are other ways to get the desired f/ stop and shutter speed, and lots of people do as you suggested where they use one of the Auto modes and half-press while pointed at various parts of the scene and read what f/ stop and shutter is selected, and then set that in manually. I prefer to use the built-in manual meter.

Russ

Anonymous said...

Hi Russ,

Thank you for your explanation. It has been very helpful.

Walter

koss said...

Great post, thank you

Remi said...

Again, in depth step-by step explanation how the flash and the camera works and communicate. I can finally imagine in my head the data transfer (in 1 and 0) between the camera and flash. One question, in your example of the couple standing beside the window, did you use any flash modifier and did you bounce the flash?

Russ MacDonald said...

Remi,

I can't remember for sure, but I think I used a Gary Fong Light Sphere II with the Chrome Dome option to throw more light forward. I couldn't bounce it, because it was in the church with 50 foot high and dark ceilings.

Russ

Anonymous said...

Russ,

It would *seem* like the fact that one cannot use TTL-BL while in wireless mode is a drawback. Can you give your thoughts on that and how big a deal it is? Is a SC-xx cord the only way around it?

Russ MacDonald said...

Anonymous,

TTL-BL is not available for wireless CLS. However, the reason is that you don't want to use TTL-BL when using wireless.

TTL-BL is designed for adjusting fill flash in bright ambient conditions. It depends on the matrix metering in the camera to determine the ambient, and then it sets the flash to match that, so that your subject will be the same brightness as the ambient.

TTL is designed for when you want the flash to be primary (ie, not just fill). Indoor dim ambient is the main place where you use TTL.

In wireless CLS you normally are indoors in dim ambient so you want to use TTL anyway. Then, the flash will be primary on the subject.

I can't think of any situation where you would ever want to use TTL-BL from a remote flash.

Russ

Dundee Pham said...

Thanks a lot for your information. I used Nikon system since the day of F90 until D300 here and never understand their flash technology.

Just read your blog once and grab my camera to practice, I can have a wonderful picture out of my home window with both exterior and interior properly exposed using TTL-BL.

I have to read your blog the third time to absorb all of the little details about the flash system. My flash pictures were unpredictable until now. What a great piece of information!

Dundee Pham.

Russ MacDonald said...

Dundee,

I am happy that you found my articles useful. Thanks for the very nice feedback.

Russ

Anonymous said...

Immensely useful blog, scientific and didactic. Unfortunately, unrivaled in French language. Many thanks.
Pascal from Poitiers (France)

Russ MacDonald said...

To Anonymous,

Thanks for the feedback!

Russ

billmoris said...

Hi Russ, you said in the 5th post above this one, "I can't think of any situation where you would ever want to use TTL-BL from a remote flash."

How about when you shoot out door with an umbrella or soft box to diffuse the light. Won't you want to use ttl-bl then?

Russ MacDonald said...

Bill,

TTL-BL is not available when the flash is in Remote mode.

You can't have TTL-BL when the flash is not on the camera, because the camera could be pointed at a different angle than where the flash is pointed, and that would mess up the balancing equations.

Russ

Bill said...

Russ...very helpful info. I shoot outdoors at sunise/sunset and often get mixed exposure results, so I'm going to try a new gameplan.

I've recently set up the D300 for AE-L only on the AE-L & AF-L button and using the AF-ON button for focusing. I'm also using the Fn button for FV Lock.

Now...do I have this gameplan "right" ?

1) Meter on background/sky & press AE-L button.
2) Press AF-ON (while focusing on model) and press Fn button to lock FV
3) Recompose (to get the beach, water & sun in the frame)
4) Shoot!!!

Also...do i have to half-press for each step or is it unnecessary ?

Bill

Russ MacDonald said...

Bill,

What you describe should work if you push and hold the AE-L button, but then you won't have a free finger to push the AF-ON button later. To avoid this problem, you can set the AE-L/AF-L button for 'AE Lock Hold'. Then, you don't have to keep it pressed. It will be reset after each shot.

Also, you have press AND HOLD the AF-ON button to allow you to recompose without refocusing. If you aim at the model and push AF-ON and release it, it will focus on the model, but when you recompose and press the shutter, it will refocus on whatever is in the selected focus area. When holding the AF-ON button, the half-press on the shutter does nothing.

You can change this by removing the focus function from the shutter button in the AF-ON menu, so that when you push AF-ON to focus, you can release it, and it will not refocus when pushing the shutter.

However, I am not a fan of the AF-ON button for this situation. In fact, I only use the AF-ON button (decoupled from the shutter button) for focusing when using AF-C mode, so that I have the ability to recompose in AF-C mode.

You didn't mention what metering mode you plan to set the camera to, or what mode the flash will be in. I always use TTL-BL mode and matrix metering to let the camera automatically balance the fill flash to the ambient.

My preference is to do this in one of the two following ways without using the AF-ON or AE-L buttons:

AUTOMATIC:
In this mode, the camera uses Matrix metering to set the shutter and f/stop to the ambient, and the flash uses TTL-BL to automatically give the correct fill.

1. Camera P,S, or A mode, and Matrix metering (be careful of A mode as you can easily get overexposure, since the shutter is limited to 1/250th).

2. Flash in TTL-BL mode.

3. Aim at model.

4. Push FV Lock to lock in fill flash. Note: This step is not necessary if using the flash in TTL-BL mode with the head pointed straight forward, since the flash will use the focus distance as reported by the lens to set its power rather than the preflashes.

5. Half-press shutter to lock in focus on the model.

6. Recompose and complete shutter button press. Matrix metering will automatically meter the whole frame after recomposing and normally does a good job of protecting the colors and highlights in the sky.

SEMI-AUTOMATIC (Camera manual to set ambient, Auto fill flash):
1. Set Camera to Manual mode and Matrix metering.

2. Set Flash in TTL-BL.

3. Aim at sky to the right or left of the model, and use the in-camera meter to set the camera aperture and shutter manually to underexpose by one stop. Matrix metering usually does a good job of giving you an accurate ambient exposure that protects the highlights in the sky. This step is essentially the same thing as when you use AE-L, except that it lets you adjust to underexpose the sky just a bit, and when you use AE-L, it sets the camera right on. Of course, you can then use the camera ev to adjust that, but that also affects the flash power, so then you have to adjust flash ev to compensate. I find it simpler to use Camera Manual.

4. Aim at model.

5. Press FV-Lock to fire preflashes if necessary (see above comment).

6. Half-press the shutter button to lock focus.

7. Recompose and complete the shutter release.

If flash is too bright or weak, adjust flash ev.

Please let me know if this is helpful.

Russ

John Meyer said...

Hi Russ

Your blogs are great!

One thing you may be able to clarify for me is whether the camera's metering mode has any affect on CLS.

I read somewhere that Nikon's CLS prefers Matrix. True?

Hope you can help.

Regards

John

Russ MacDonald said...

Hi John,

Thanks for the compliment!

The choice of camera metering (matrix, center-weighted, spot) affects the CLS flash system differently depending on which TTL mode you are using.

In regular TTL mode the camera metering is not used by the flash system, so it has absolutely no effect on the flash power.

However, in TTL-BL mode the camera metering information is used in combination with the CLS reflected preflash data. Therefore, when in TTL-BL mode, the choice of camera metering can change the result of the flash power computation.

In TTL-BL mode the flash computer assumes the information received from the camera metering is an accurate proxy for the average ambient brightness in the frame - which turns out to be the same as the background brightness in a flash picture, assuming the subject is significantly closer to the camera than the background (typical for outdoor shots, which is where you use TTL-BL 99% of the time).

The flash computer also assumes that all of the reflected preflash energy is coming from the subject, which means that that data is a proxy for the brightness of the subject.

Then, the flash computer calculates the flash power that will make the reflected flash energy (assumed to be the subject) equal to the camera metering energy (assumed to be the background).

Since camera matrix metering analyzes the entire frame, that often results in the best proxy for the ambient (background), and consequently it usually does the best job with TTL-BL.

You can also use Center Weighted metering with TTL-BL, but it doesn't measue the whole frame, so it usually will not give the best proxy for the average background brightness. CW usually works best in special situations when there is an unusually bright spot in the background located near the edge of the frame (like a small white building on a bright day).

Spot Metering is not allowed when using TTL-BL for the obvious reason that it only measures the brightness of the subject, so the TTL-BL flash computer would have nothing to balance the flash power against.

Hope that helps.

Russ

John Meyer said...

Thanks, Russ, for taking the time to explain that. It's much clearer to me now.

But what about Exposure MODES (manual, aperture, etc? Do these have any effect on what CLS decides to do?

Regards

John

Russ MacDonald said...

Hi again John,

First, to repeat one very key point: The camera settings adjust only the ambient portion of the exposure and not the flash portion. The flash portion of the exposure (flash power) is set by the flash metering system.

The various exposure modes (A, S, M, P) do not affect the flash portion of the exposure. They do not affect the way the flash computer calculates its flash power.

However, camera A and P modes do restrict certain settings on the camera to give you a better chance of a good flash picture. To say this another way, the A and P modes provide some automatic restrictions on the ambient part of the exposure.

For instance, when in A mode, the shutter is restricted to a minimum speed of 1/60th sec (by default). This helps you get a good flash picture in low ambient light, by helping you avoid camera motion, which keeps the background from being blurred. You can decrease this minimum shutter speed to whatever you want in the menu, but then the background is likely to become blurred.

Additional info: The reason for the 1/60th default limit is that this is the slowest shutter speed that most people can hold the camera still enough to avoid motion blur. The only time the camera runs into this limit is when taking pictures in a low ambient condition (like indoors) where the camera needs actually a lower speed to get a proper background exposure, but then the background would be blurred if the camera were allowed to select it.

Since the shutter limit of 1/60th will obviously cause the background to be underexposed in low ambient conditions, most people counteract this by setting a higher ISO which brightens the background.

In P mode, the shutter has the same 1/60th default limit, and in addition, the aperture is limited by the program in the camera. The actual limitations on the aperture are not well documented, but it tries to keep the aperture at a setting that will optimize the quality of the flash picture.

In M and S modes, there are no restrictions on the camera settings, except the max shutter speed as dictated by the speed of the mechanical shutter itself (called the Flash Sync Speed).

In M mode you can set the shutter and aperture to whatever you want them to be, and you are fully responsible for the ambient portion of the exposure. However, you can use the built-in meter in the camera to help you set the shutter and aperture correctly.

In S mode, with or without flash, you can choose whatever shutter speed you want (up to the flash sync speed) and the camera will choose the proper aperture for the ambient portion of the exposure.

One more important point. If you happen to set the aperture and/or shutter wrong, and the ambient portion of the image becomes over or underexposed, that doesn't affect the flash power. The flash uses the metering data from the camera, but it does not factor in what aperture/shutter you set on the camera. This is why you can change the ambient portion of the exposure without affecting the flash portion.

So, in summary, the A,S,M,P modes of the camera do not affect the flash power. They simply put various restrictions on what other camera settings are allowed.

Let me know if that helps,

Russ

John Meyer said...

Russ, you're a star!

I'm now all clued-up and ready to go! All thanks to you. Keep up the good work.

A few more actual lighting scenarios and graphically illustrated or photographed setups would, for me, be a nice addition to your 'collection' of technical CLS topics. Just a thought...

Regards

John

Russ MacDonald said...

Hi John,

I'm glad I could help!

I have been thinking of adding more illustrations and graphics to my blogs. I'm just not sure what types of illustrations would help. I'll keep working on it.

Thanks,

Russ

Anonymous said...

Absolutely Fantastic Blog!! I've read countless articles and manuals on this subject and felt more and more confused after each one. After spending ONLY an hour reading your blog, things are finally starting to click in my brain. Thank you so much for explaining things in such a simple and straightforward way. I appreciate it more than you could ever imagine.
IW

Russ MacDonald said...

To Anonymous,

Thanks very much for the great feedback!

Please let me know if anything is unclear. I use that information to add information to the blog to make it better.

Russ

Anonymous said...

This has explained things more clearly than anyting I have read Thank You

I do have one question as I am new to the CLS System. When you the FV -1.07, where did you do that the camera or the flash my SB800 adjust in 1/3 increments and cannot fiqure as of yey how to adjust FV om my D80.

Russ MacDonald said...

Hi Anonymous,

Well, the FV I mentioned is -1.7 and not -1.07.

-1.7 is the same as -1 and 2/3, so that's how you set it.

FYI: -1.3 is the same as -1 and 1/3

You can set the flash compensation in two places: 1) on the camera and 2) on the flash.

Whatever you set on the camera adds to what you set on the flash. For instance, if you set the flash to -1.0 and the camera to -2/3, then you have a total of
-1 and 2/3.

If you set -1.0 on the flash and
+ 1.0 on the camera, you add the two and the flash will be set to 0.0.

Let me know if that is clear,

Russ

Anonymous said...

Thanks that does go a little deeper for me and does help. Do you know if you can adjust the flash output on the remote flash units if you set one as a commander and use skyport remotes or does ttl still work when using them?

Russ MacDonald said...

To Anonymous,

The Skyport triggers are simple slaves. They do not do any CLS functions, so there is no way to adjust the power remotely for any slave that is triggered by the Skyport trigger.

The only way to use the Skyport triggers in conjunction with CLS is to connect them by PC Sync cable to the camera. However, you have to use an external commander (like an SB-800 in the hot shoe) to do this, because the camera does not put out a PC Sync pulse when the pop-up flash is used as the commander.

The slave flash that is connected to the Skyport trigger will have to be in Manual mode, and you will have to adjust its power using the rocker switch on the back of the flash itself.

Then, you would be able to control the power of the remote CLS flashes from the commander, while any Skyport flashes remain fully manual.

Russ

Anonymous said...

Russ:

I am just a weekend photographer and don't do events or weddings. I do photograph a lot of nature stuff where subjects are outdoors and either front or side lighted most of the time. In these situations, I have used TTL-BL most of the time with ev at -1.7 or so to add a catchlight and fill in contrasty shadows. Although not backlighted, TTL-BL seems to work pretty good here too. Would you suggest that straight TTL would work better?
Gene

Russ MacDonald said...

To anonymous,

Those are some of the most difficult situations to add fill.

Any time there is side lighting, or any direct lighting on the subject, you have to realize that whatever flash you use will add to that light and tend to blow out those areas.

Therefore, TTL-BL is definitely the right mode to use and keep it turned down as you are doing.

Also, underexpose the ambient a bit (using shutter/aperture), to reduce the risk of overexposure in the highlights regardless of how low you set the flash.

Hope that helps,

Russ

Anonymous said...

Thank you Russ. I Have picked up a lot of useful info here. Appreciate your efforts and commentary.
I was using the auto modes, but have switched this year to manual metering for the very reason you suggest...overexposure on occasion. I now watch my blinkies and histogram. I used to go nuts because I left compensation on from previous shoots and forgot to change it back. Now I leave comp. at 0.0 and just underexpose via the shutter or aperture. Much easier and better, more consistent exposures.

Thanks again
Gene

Russ MacDonald said...

To Anonymous again,

You just need to make sure that you realize that the shutter and aperture will adjust only the ambient part of the exposure.

The camera eve adjusts both the camera and the flash portion.

The flash ev adjusts only the flash portion.

Russ

Anonymous said...

Hi Russ, just found your blog. very helpful indeed.
Just want to know what settings should i use in a large hall (no way of bouncing from the ceilings), with the flash (SB800)head at maybe 70-80 degrees + the attached bounce card (or is it better to use the included diffuser?).
1. if D80 in manual mode, would the auto iso limit works? i usually set the auto iso between 100 - 400 & shutter limit to 1/100.
2. should i just set to A + auto iso? i prefer to set the aperture accordingly.
3. flash set to TTL?
My flash exposures (especially where i cannot bounce off the ceilings)so far are quite inconsistent.
Always thought that one can set anything on the camera, SB800 TTL, & the image will be properly exposed!

Thanks.
Din

Russ MacDonald said...

Hi Din,

A large dimly lit hall that doesn't have much bounce is the absolute worst case for shooting with flash. It is best to use a large diffuser like the Gary Fong Light Sphere if you have one.

If you don't have an LS, then next best is to use the white pull-out bounce card with the head of the flash pointed at 60 degrees. However, the resulting light will only be a tiny bit better than direct flash. Most photographers I know either use an LS or they just point the flash straight at the subject and underexpose a bit.

The small snap-on diffuser will do absolutely nothing for you in a large hall without bounce. All it will do is waste your flash batteries.

The bounce card will get some of the light higher above the lens which adds another angle and helps to soften it a slight bit.

I don't own a D80, so I can't comment on the auto ISO mode. I never use auto-ISO on my D200.

For a large low ambient room (like a church) I usually use my D200 in Manual mode set to ISO 400 and 1/80th and f/2.8 - 4.0.

Remember that the camera metering mode never has any effect on the flash power. It only sets the camera aperture and/or shutter based on the ambient conditions. Therefore when shooting flash with the camera in Manual mode, the camera Manual mode (matrix, spot, or cw) has absolutely no effect on either the flash or the camera, so it doesn't matter what you have that set to.

If the ambient will be contributing to the exposure, then the camera metering will have an effect on the image, because it will adjust the amount of ambient.

The flash should always be set to TTL in low ambient conditions so it will be primary on the subject and the ambient won't contribute.

If you are doing all that and still getting inconsistencies, then something else is causing the problem.

For instance, you might be allowing the ambient to contribute to the exposure. That would tend to cause overexposure.

Or, you may not be close enough to your subject for CLS to work well. The subject needs to fill a fairly large percentage of the frame and should be a significant distance from the background. If one of these is the case, then the surroundings will affect the flash power.

Also, the subject needs to be centered in the frame, since the flash metering is always center weighted. When I shoot weddings, I normally use raw and center my subject and crop the image to place the subject properly, later. That allows the flash metering to work the best.

Another trick that works well, is to zoom in on the subject and hit FV Lock to fire the preflash. That locks in the computed flash power. Then, zoom back out and frame the shot however you want to. Of course, this takes time.

Hope this helps,

Russ

Anonymous said...

Hi Russ,

Thank you very much.
In future I'll try fixing the iso & shutter speed, then play with the aperture for depth of field.
I doubt I'll try the LS, since i feel it makes me look like a gadget freak of sorts (though I know it works - cost quite a bit over here in Malaysia).
Again thanks & keep the articles coming.

Din

Ovidiu said...

Dear Russ. Reading your blog makes me feel like I found the Holy Grail of flash photography. For the last few months, since I got the SB900, I have been searching and searching...and reading trying to understand the mechanics behind flash photography but only with a partial success. Your blog is perfectly written and most of all very easy to understand. THANK YOU.

Now. The question. I use a Nikon D700 + SB900. One thing I noticed in most of the portraits I took, is that the skin has always a strange orange color and is overexposed. I always shoot in manual, iTTL indoor or iTTL BL outdoor. The flash head is 60 degree vertically orientated, bouncing card out or bouncing of the ceiling or wall behind me. Do you have any idea why this strange "skin effect"?
Many thanks
Ovidiu

Russ MacDonald said...

Hi Ovidiu,

Thanks for the nice compliments on my blog!

Well, if the faces are overexposed, and you are sure you are overpowering the ambient, then your flash is too hot. You just need to turn it down. I'd suggest -0.7ev to start.

The orange color of the skin is probably one of two things. Either your white balance is off or your saturation is turned up too much.

I don't own a D700 (yet), but with my D200, I find it best to shoot with the flash at -0.7 ev and the white balance on flash.

Now, saturation settings in the camera are only used when shooting jpegs. If you shoot raw, none of the image processing settings on the camera are used except white balance. And even the white balance can be changed later in post processing if you want to.

So, assuming you are shooting jpegs, you should use Color mode I and not III. Mode III is for scenery and inanimate things. Mode I gives the best skin tone (on my D200).

Some people use Color Mode II which is for Adobe RGB color space. I have found that sRGB is best for portraits, so I never use aRGB.

Then, on my D200 I use the Optimize Image settings to set sharpening to medium high and saturation and tone on normal - never auto.

I encourage you to learn to shoot raw. It is a lot easier than most people think, especially with Capture NX or Lightroom software.

Hope that helps.

Russ

I never add any saturation when shooting portraits!

Ovidiu said...

Russ. Many thanks for your answer.
I should have mention that I shot only Raw. If you check my blog you will see that I am a bit advocate of the Raw file.
You mentioned that I should dial down the flash by -0.7EV. Is not this against the theory recommending that for dark surfaces we should dial down (-EV) the flash and for bright we should dial up (+EV)? I am just thinking that if the face is bright then is it correct to dial down the EV?
I am going to try the flash compensation once the weather improves (bit difficult to see that in Ireland). Many thanks again for your answer.
Ovidiu

Russ MacDonald said...

Hi again Ovidiu,

The reason for turning the flash down a bit when shooting faces is that the flash system tends to try to push everything all the way to the right on the histogram. With faces, this never looks good. Caucasian face pixels should never be much farther to the right than about the middle of the 4th quartile. The face pixels of very dark-skinned people should never be farther right than the middle of the 3rd quartile.

You are right that light colors cause the flash to underexpose and that dark colors cause the flash to overexpose.

However, the color of an average Caucasian face is not really that light, and is normally not enough to cause this to happen. In fact, the average Caucasian face seems almost perfectly balanced to our flash system, and the face pixels are normally placed at the very right hand edge of the histogram, which, as I mentioned, doesn't look good.

Now, when shooting people with dark skin, our flashes will sometimes cause overexposure, so you have to turn the flash down even farther; say -1.0ev.

It is always best to underexpose a raw image rather than overexpose. You can recover a much better picture from a raw image that is 1 ev under rather than 1 ev overexposed.

Russ

Anonymous said...

Hi Russ,
after reading few times and try to understand technical things, I come back with two questions here;

as you said "flash pictures usually look really odd when the subject is just as bright as the background. The subject seems to jump off the page unnaturally... "

and then "Fill flash is supposed to be subtle, and when looking at the print it is usually best that you cannot even tell that flash is used at all"
Aren't that the above two sentences quoted from you contradict or I may misinterpret it ?

will the pre flash system / flash metering works the same for non nikon lens ?

Many thanks Russ

hanif

Russ MacDonald said...

To Anonymous,

Let me see if I can rephrase what I am trying to say more clearly.

I think that you may not understand is that the flash tends to be too powerful to look natural. Left alone, the TTL-BL flash system will try to make the subject equal to the brightness of the background. However, to look natural, the subject should be slightly darker than the background.

So, when you shoot fill flash (TTL-BL), you have to turn the flash down with compensation (reduce its power) to avoid the subject looking unnatural.

I recommend using between -1.0 ev and 1.7 ev as a starting point when shooting fill flash.

Hope that is clearer,

Russ

Russ MacDonald said...

Hanif,

I re-read your last question, and maybe the point you are missing is that it is possible to add just a small amount of fill flash and brighten the subject just a small amount. Then, if you do it just right, you can't tell that you used a flash to brighten the subject. It looks like natural light was used.

In fact, as a general rule, you should never be able to tell when you use fill flash. It should always look like natural light.

That makes the whole picture look more natural.

Russ

Anonymous said...

Thanks Russ, its more clearer know. Just another question here.

1. Using this setting (TTL BL), do we have to dial down flash power if we move closer to the subject and did vice versa if go further away ? or just SB600/800 doing good enough compensating its self ?

2. Doing stop down to make ambience darker, will the flash also reduce its power to balance ambience light ?


Hanif

Russ MacDonald said...

Hi again Hanif,

Normally you do not need to change the flash compensation when you move closer or farther from your subject. This is true for both TTL and TTL BL. The system adjusts the power for you automatically.

Regards,

Russ

Chun Man said...

Hi Russ,

I had forgoten to read this page before I took a set of photos with my girl friend in outdoor yesterday, so.. most of photos are over-exposure on her face :(
I found you told ue TTL-BL in outdoor for fill in should set -1.7ev in flash, I felt strange then when should use TTL-BL in 0ev? I always think when I use TTL-BL(Not use TTL), flash system should know i am shooting in outdoor and use the flash in 'fill in shadow' only, why I still have to manual decrease the EV?(I think in outdoor, use TTL will easier to over-exposure as ambient light, so TTL-BL was designed to overcome that!) If I set -1.7EV in TTL-BL, will it same as I set -1.7EV in TTL?
Please help me.. thanks

Russ MacDonald said...

Hi Chun Man,

Yes, TTL-BL is usually the best choice when shooting outdoors in daytime.

The compensation setting on the flash really should be set to your taste. If you set it to 0.0ev then your flash will try to make your subject the same brightness as the background.

I chose -1.7ev in my example, because I didn't want the flash to be obvious. I often use -0.3 in bright daylight conditions where it takes a lot more flash power to lift shadows.

Some people like the look of flash and leave it at 0.0 ev when shooting fill.

Another thing to really watch out for when shooting fill in bright sunlight is don't let the face have any direct sunlight hitting it. If there is direct sunlight, the camera will adjust for that exposure, and then if you add flash, that area will be blown out. If you have to shoot in direct sunlight, get the subject to face you with the sun behind her. Then, use the flash at 0.0 ev to brighten her as much as possible. That way, there is no place on her face where the flash will add to the sunlight.

In TTL mode on the flash, the compensation setting works exactly the same way as in TTL-BL. It sinply increases or decreases the power that the camera chooses. The difference with TTL is that it only looks at the reflected energy from the monitor preflash; i.e. TTL doesn't consider the background brightness. TTL-BL considers both the monitor preflash and the ambient brightness.

Russ

Chun Man said...

Thanks Russ,
I wanna ask one more question. If I use TTL-BL in outdoor, and the subject in not at the center(at very side position in frame), so should I use poin to subject and use FV-LOCK firstly? If I used Fv-lock, will it became TTL instead of TTL-BL?
thanks again.

Russ MacDonald said...

Chun man,

If your subject is not centered, you can use FV Lock when using TTL-BL. It doesn't make it TTL.

When you point at your subject and press FV, the flash power is determined the same way as it is when the subject is in the center.

When you press FV Lock, the monitor preflashes are fired, the reflected energy from the center of the frame is measured, and the camera meter (ambient) is read (matrix metering is usually best). Then the system compares the two metered values and sets the flash to the power that will make the subject equal brightness to the ambient.

Russ

Bill said...

Russ, please note my Sept. 16, 2008 question.

I think I've got the settings, but I'm still not completely clear on things.

This is how I've got the camera set up...

Manual mode
Matrix metering
Flash set to TTL-BL
AE-L/AF-L button set to AE Lock (reset on release)
to lock ambient exposure until shutter is pressed
AF-On button to focus (shutter decoupled)
AF-S (I'm shooting a pretty much stationary
subject)


1) Aim at the sky/water and press/release
AE-L/AF-L button

2) Aim at model and press/release AF-On button

3) Recompose and shoot...

Although I know your preference is to not use AF-On for focus (with shutter decoupled), but I've become accustomed to it ; )

Have I got the settings and sequence right?

Thanks in advance for your continuing input,

Bill

Russ MacDonald said...

Hi Bill,

That should work, except that there is no purpose for using the AE-L if you have the camera set in Manual mode. The purpose of AE-L is to lock the camera exposure when in one of the auto modes. In Manual mode, you set the aperture and shutter manually.

Also, remember that the AE-L will only stay locked until the meter times out, which is only 6 seconds by default. You have to go into the menus and change the timeout period to as long as possible when using AE-L or FV-Lock.

Russ

SpookiePower said...

I just bought my SB-900 one month ago, and takes a lot of photos to learn how to use a flash. I have been reading your blog many times now, and really like it :)

The last few days I have tried to put a person in front of a bright window and took some pictures. You say that in this situation it is best to use the TTL-BL mode, but I think that all my photos in the TTL-BL mode has a cold light, compared to the TTL-mode where the color is more warm. How can that be ?

I shoot in M mode and use the same aperture/shutter setting, when I switch between TTL and TTL_BL.

Russ MacDonald said...

To SpookiePower,

First, any time you see a color change between images that both use flash, it is because the flash and the ambient are not matched in color, and you are allowed a different percentage of contribution between the flash and the ambient light into the image.

The flash is always the same color, and it is matched to sunlight. However, it can often warmer than the daylight when you are using soft light from an overcast or from a north window.

For example, in the case of the north window, as you increase the percentage of flash the image will get warmer.

That explains what happened; now how do you fix it?

Important:

When using TTL-BL, you should also use one of the camera Auto modes (A,S, or P), so the camera f/ stop and shutter will get set automatically according to the matrix metering. The TTL-BL flash will always adjust its power based on what the Matrix Metering is telling the camera to do. So, if you have the camera in Manual, and you are not setting it per the light meter, then the flash will be balancing to the wrong thing.

So, when using TTL-BL with a backlighted situation, make sure to set the camera in one of the auto modes so the camera will match what the flash is doing. This is also true for outdoors in daylight.

Indoors, under dim artificial light, use TTL and set the camera in Manual. Then the flash will light the subject to a 'standard' brightness, regardless of what the background is.

Hope that makes sense,

Russ

SpookiePower said...

Thanks Russ :)

So the TTL-BL should be used mostly when there is a bright background, like a window or outdoor against the sun, and always in A,S,P mode. Indoor, away from the window I should use TTL - so far so good :) I'll try it later today.

Russ MacDonald said...

Hi Spookie,

Yes, that is correct! When I am shooting indoors during the daytime, I keep the camera in P mode, and I watch the background closely. If I see a window back there, I switch to TTL-BL and stay in camera P mode, so the window will not blow out (as much).

In addition, TTL-BL (and camera P mode) also works well outdoors even when not against the sun. If you look closely at your subject's face, outdoors in daylight, you will usually see slight shadows, especially in the eye sockets and under the nose and chin. TTL-BL will eliminate those shadows very nicely. That's where the definition of 'Fill Flash' comes from; it fills in the shadows.

Russ

Anonymous said...

Hi there,
do I have the right impression that in TTL BL with the flash in the forward position the flash metering does not care much for the meter and uses distance only? If I put a sheet of paper in front as difussor, the power seems to stay the same and the exposure decreases. However this is not the case in the bouncing position, with the diffusor on (microswitch) or with FV lock. (D90)
BR, Sem

Russ MacDonald said...

Hi Sem,

You are right!

In fact I wrote a separate blog about it here:
http://nikonclspracticalguide.blogspot.com/2008/03/ttl-and-ttl-bl-study.html.

Russ

Anonymous said...

When you say -1.7 ev in your post, do you mean exposure comp on the camera, or by adjusting the SB800?
Thanks
Jerry

Russ MacDonald said...

Hi Jerry,

I mean to adjust the flash exposure compensation to -1.7ev.

That is usually done on the flash, but on cameras with a built-in flash, there is also a flash exposure compensation button on the camera. This works identically to the one of the flash and, in fact, adds to whetever you set on the flash itself.

For this reason, I always leave flash exposure compensation setting on the camera at 0.0 ev. That way I don't forget it and wonder what is going on.

The camera exposure compensation affects both the flash and the camera. When shooting indoors in camera manual mode, I always make sure the camera ev is set to 0.0 ev to avoid confusion.

I should also mention that with my new D3 camera (Wow, what a camera!), I get the best results with the flash set to -0.3 ev. So, it definitely makes a difference what camera you are using. You have to experiment with your own camera to determine what works best for you.

Hope this helps,

Russ

Anonymous said...

Thanks Russ
I'm am intrigued that you reduce flash output in order to balance with ambient. This is what is confusing me. I will need test this out - and vary flash EV as your suggest. I made shots last fall - there was a of chimping (//www.flickr.com/photos/ranchjp/3063006820/in/set-72157610243492646/ plus others in he set). But I need to develop a much deeper understading. When the ambient is waning, you need to know what you are doing and why..you can't chimp too much or you'll miss the shot.
Jerry

Anonymous said...

Russ
BTW..this is why I need to learn to use TTLBL..the images I sent via that were shot with TTL (I used a SU800)..maybe that's why I had to chimp so much..TTL BL would have been more friendly?
Jerry

Russ MacDonald said...

Hi again Jerry,

What I have found is that when using the flash in TTL-BL mode, it will balance the brightness of the subject to be just about equal to the background. However, this doesn't look natural. It makes the subject look like he/she is jumping out of the picture. When you decrease the flash power by a stop or so, the subject returns to looking normal and if you do it right, it will look like no flash was used at all.

Shooting at dusk is one of the most difficult times to shoot, because the sky is still very bright and the ground is very dark. The dynamic range gets extremely large, far beyond what the camera can capture. This is when fill flash must be used and it must be done right for the image to look natural.

Now, some people like that 'jumping out of the picture' look, so they make the flash fire at normal power on purpose. This is 'art' and is always heavily influenced by personal preference.

I looked at your senior portrait. I think it was done very well! The lighting is nice and warm, matching the 'golden hour' sunset. The only thing I might have done differently was to open up the camera a bit to get some detail into that black area in the background. Of course, that's personal preference as well.

TTL-BL just does a lot of the work for you. You won't have to play around with the flash power as much. It will nail it for you nearly every time once you learn how to use it. I always use TTL-BL at dusk if there will be any sky in the picture at all.

Russ

Anonymous said...

Thanks Russ
Your insight and experience helps with this impoirtant exposure issue. The whole article is worth reading and over..great nuggets. I'm gonna' get back to you later as I have a question on FV-lock.
Best
Jerry Ranch

Abe said...

Russ,
Thanks for your blog!
In the last three days since learning of your site I have learnt more than in the past year. The information and clarity in which it is expressed is invaluable.

I just finished reading the section on TTL BL and its comments. I think I understand it, now it's just a matter of using it in combo with the knowledge. I am using a D300 + SB-800. But one area is still very dark for me:
When not using the SB-800, instead using the camera's flash does it function as TTL BL or TTL? Or is there a setting? And what is the Rear mode of the internal flash?

Russ MacDonald said...

Hi Abe,

Thanks for the nice feedback!

The pop-up flash has no switch on is or any way to switch it back and forth between TTL-BL and TTL.

The only way to do it is to use the camera metering mode.

The pop-up flash works in TTL-BL whenever the camera metering is in Matrix or Center Weighted modes. If you switch to Spot Metering mode, the flash will switch to regular TTL.

So, to make the best shots indoors in normal artificial ambient light, always switch to spot metering mode. Your flash shots will all be more consistant.

Outdoors, whenever the ambient is bright, use Matrix mode to get the best balanced fill flash shots.

Hope that helps,

Russ

Abe said...

Thanks for clarifying.
But I allways had this concern about using spot metering with flash since in order for the flash to satisfy this metering only one spot has to be lit correctly. Is this a valid concern, how would you handle this?

thanks again for your most outstanding bastion of light

Abe said...

I just tried this:
Indoors, I set camera to M mode, 60/4.0 which was showing as at least 2 stops under exposed (Low). then I popup the internal flash and took the picture and the flahs lit up the whole scene where nothing was under exposed. I tried this both with spot and matrix.
My quetion is - if TTL BL just brings the forground to where the ambien light setting is (in this case at least -2 stops) how would the result be correctly exposed picture?

Russ MacDonald said...

Hi again Abe,

When you use spot metering, the only things that are affected by the metering data are the camera settings; ie, aperture and shutter (and ISO if in Auto ISO). The power of the flash is never affected by the camera metering.

Flash metering is a separate system that sets the power of the flash, and it does not consider the data from the camera metering system when in regular TTL mode.

Then, if you are in camera Manual mode, Spot metering has absolutely no effect on anything. You are setting the aperture, shutter, and ISO manually, so the only thing camera metering does is show you in the viewfinder (and on the top LCD) a scale to help you set the camera settings.

Russ

Russ MacDonald said...

And for your second question, Abe,

First, indoors, the subject is usually brighter than the background, and there is no way the flash can darken the subject (obviously). The best it can do is to go to minimum power and light the subject the least it can. This is why TTL-BL often leaves an indoor shot dark. But, any specular highlight in the background can cause the flash power to increase; like a light or window or a reflection. Then TTL-BL mode will increase the flash power to try to match that highlight. This is why TTL-BL is so inconsistant when in dim ambient light.

TTL-BL mode uses the metering data from the camera in addition to the monitoring preflashes to set the flash power. It does not use the camera settings themselves - only the data from the meter. You can set the camera aperture, shutter, and ISO to any setting you want and it will not affect the flash power. The camera settings only change the ambient light portion of the exposure.

Then, you have to remember that the flash always adds to the ambient portion of the exposure. If you underexpose the ambient by two stops, then the flash is providing essentially the entire exposure of the subject. If you were to use 0.0 ev on the camera compensation, then the subject would be exposed correctly by the ambient, and the flash would add to that, leading to likely overexposure on the subject.

Russ

Abe said...

>>When you use spot metering, the only things that are affected by the metering data are the camera settings; ie, aperture and shutter (and ISO if in Auto ISO). The power of the flash is never affected by the camera metering.

When I'm in A or P and I just pop the Flash the speed setting changes. Wouldn't that indicate that there is a corrolation between camera flash and metering?

Russ MacDonald said...

Hi again Abe,

The reason that the shutter speed changes when you pop up the flash is that there is a minimum (longest) shutter setting in the menu called 'Flash Shutter Speed'. This is set to 1/60th by default, and it limits the the shutter to this speed as a minimum when the flash is deployed in A or P modes. You can set this speed faster (like 1/160th) but not slower. This limit is used to minimize ghosting or blurring of the background when handholding. 1/60th is commonly accepted as the lowest speed that you can handhold without bluring.

This 'flash shutter speed' is not related to the metering in any way.

Also, don't get this minimum shutter speed confused with the Flash Sync Speed, which is the fastest speed shutter you can use with flash. On the D200 that speed is 1/250th sec.

Russ

Barry said...

I read a post where you advised using one of the automatic modes when using TTL-BL for backlit and outdoor situations that need BL services of the flash.

Between you and Neil (planet Neil) I’ve learned not to rely on automatic modes in order achieve the results that “I” want and to keep the pictures more consistent during a shoot.

Can you “prescribe” an alternate method, step-by-step, in which to use full manual mode where I can achieve the same results as if using an auto mode while using TTL-BL.

Thank you,
Barry

Russ MacDonald said...

Hi Barry,

Yes, you can use the camera in Manual mode while shooting fill using the flash in TTL-BL mode.

It is normally best to use Matrix metering, because it ususally sends the best representation of the ambient brightness to the flash.

Then, point at the subject and adjust the aperture and shutter to collapse the light meter in the camera to the mid-point. Then, reframe and click the shutter.

If the background is too bright or too dark, adjust the aperture and/or shutter. Changing the aperture/shutter does not change the brightness of the subject. That is controlled by the flash system when it balances the data from the camera light meter with the subject. The flash computer doesn't use the aperture or shutter settings in its calculations; only the data from the light meter (that's why Matrix metering is best).

If the subject is too bright or too dark, adjust the flash ev.

Don't adjust the camera ev, because that changes both the subject brightness and the background brightness, and then after the balancing takes place, the result can be very unpredictable.

All that said, with TTL-BL it's usually better to use one of the camera Auto modes, because you've already given up a lot of control to the flash system by selecting TTL-BL.

If you want more manual control of fill, it is best to use regular TTL and adjust camera ev for overall image brightness and flash ev for subject brightness. The flash ev will normally be best for fill at around -1.7 ev for most ambient situations. Remember that in regular TTL the flash adds to the ambient, so you want to slightly underexpose the subject and let the fill bring the subject back to normal brightness. If you fully expose the subject with the ambient, the flash will add to that and overexposure on the subject will occur.

Hope that helps,

Russ

Maurizio said...

Hi Russ,
thanks for your study and your explanations about flash system metering.Your studies explain me a lot of things that I never understood.
Just one question about new system DLighting use in new Nikon's Camera: using TTL-BL flah is better set it Auto or Off? Or it never influence system metering? Thanks again.

Russ MacDonald said...

Hi Maurizio,

I have not studied D-Lighting in detail. All I know for sure is that D-Lighting affects both jpegs and raw data. That tells me that the processing is probably applied before the data is converted to jpeg.

I don't know if it influences metering, but I suspect it does. I just haven't studied it yet.

I have shot with and without D-Lighting. It seems to widen the effective dynamic range of the camera without undesireable side effects. So, at this point, and until I learn of negative side effects, I am leaving it ON on my D3 (set to Normal).

Russ

reddy040 said...

Hey Russ,
I didnt know you live in Richmond Hill, Ga. I live here in Hinesville as you know where that is. :) I'm a photography for Fort Stewart, Ga. Not too far from where we are. I was just surfing the net excatly what I was looking for and saw what you say about the place. Sheesh!!!! lol

Russ MacDonald said...

Hi there reddy040,

Small world! I know where Hinesville is , and my son is in the Army stationed at Ft. Stewart.

Hey contact me at my email: rkmacdonald@gmail.com so we can compare notes. I'd love to know about your photography job at Ft. Stewart.

Best regards,

Russ

Gary said...

Great information and a great site. It is very helpful. Keep up the good work!

Russ MacDonald said...

Hi Gary,

Great feedback!

Thanks!

Russ

Anonymous said...

Hi Russ,
I think between you and Neil Van Niekirk I will finally grasp this flash photogrphy lark! Just one question. If the flash gun can work out how much flash is needed in TTL BL mode, why did you reduce the power by 1.7?
Thanks again

Russ MacDonald said...

Hi Anonymous,

It is really a personal preference. I don't like the look when the subject is as bright as the background. It makes it look like the subject is jumping out of the picture.

However, with my D200 camera I need much more negative compensation than with my D3, so I think the amount of negative compensation, if any, is also strongly influenced by the particular camera you own.

Basically, just try it and see what brightness you like for the subject with respect to the background.

Russ

Anonymous said...

Thanks for your prompt reply. So it's a case of chimping to a certain extent and seeing what you like.
Thanks again for the useful info on all your blogs. It's very generous of you.
Nick

Russ MacDonald said...

Hi Nick,

That's about it. That coupled with personal preference.

Russ

Anonymous said...

Hi Russ,
I found your link in a german Nikon forum, very helpful in explaining the technical context and the design points of the CLS system. Some questions to you:
Assuming i want to shoot outdoor with fill flash and matrix metering.
case 1, manual mode: I use the internal meter to set up shutter and aperture, maybe i under /overexpose a little. I half-press the shutter to focus and then i recompose. You say that the matrix metering will be read AFTER recomposing and when pressing the shutter fully. So when ambient has changed by recomposing, no problem. Is that right?
case 2, auto mode (A): I halfpress, recompose and release. Again, the matrix metering is measured after recomposing when pressing the shutter fully? Again, no problem with the different ambient values? What if i used AE-L, will these data be used by the flash calc?
Is there any transmission of metering data when i press halfways?
Other question: You say in this chapter that the flash power calculation does not care about the specified shutter and speed values, it takes the metering brightness data instead. What is this, is this the overall ev-value? A little bit confused.
The last question (for the moment): If i have no subject or foreground (e.g. paintings on a wall), i cannot use BL, i have to go to TTL, right?
Thanks, Wolfgang

Russ MacDonald said...

Hi Wolfgang,

case 1: Yes, when you half-press the shutter, the focus will be locked, but the exposure metering will not. If you are using manual mode, then the aperture and shutter will be set manually. When you recompose, the exposure will be recalculated by the camera metering and sent to the flash computer to balance with. However, when you use Matrix metering, it averages the background and subject together, so most of the time, the change in exposure metering is minimal, and it will not affect the overall image. The matrix metering is simply supplying the flash with a proxy for the ambient light.

case 2: I'm not totally sure I understand what you mean by "Auto Mode (A)". There is an Auto mode on the flash and there is an A mode on the camera that stands for Aperture Priority, not Auto.

Assuming you are talking about A Mode (Aperture priority) on the camera, when you half-press, the focus is locked, but the exposure is not. As you recompose, the exposure can change, and that will cause a change in shutter speed and a change in the ambient data that is sent to the flash.

On my D200 and D3, the AE-L button is actually AE-L/AF-L and its functionality can be changed in the menu. In the default mode, when you press and hold this button before recomposing, it will lock both the focus and the exposure. Then, when you recompose, the original exposure is used from before you recomposed, and the flash receives the original ambient data as well.

However, if the subject is now way off-center, the flash power may end up being wrong, since it always uses the reflected energy from the center of the frame to set the brightness of the subject. If the subject is way to one edge of the frame, the flash power could increase as it tries to bring up the background to the same brightness as the ambient (depending on how bright or dark the background is in the center of the frame). This is when you would want to use FV Lock to lock in the flash power for when the subject was centered. Then, recomposing will not affect the flash power, and the AE-L/AF-L button will only affect the camera aperture and shutter.

Hope that helps,

Russ

Anonymous said...

Hi Russ,
thanks for clarifying. To make the picture complete, pls confirm/correct the following.
My point is, WHEN will the ambient (which is used to balance the reflected energy for an BL picture) be measured:
In case 1 (manual camera mode) it is when the shutter is finally pressed - AFTER recompose, the f-stop and shutter values are not used for flash calculation.
In case 2 (aperture automode) the ambient data are taken from the AE storage which is BEFORE recomposing. (i assume when i do not use AE, it is the same as in case 1: AFTER recomposing).
Additional question: what are the ambient data which are used for flash power calc, aperture/shutter values or a global exposure (EV) value ?
Your last paragraph explains the off-center problem, where i have to use FV lock. But this is true for both cases, right?
Thanks for your help
Wolfgang

Russ MacDonald said...

Hi again Wolfgang,

Sorry for not being clear.

Case 1, Camera Manual Mode: The ambient is measured for a BL flash picture AFTER recomposing.

Case 2, Camera A Mode: The ambient is measured for a BL flash picture AFTER recomposing, UNLESS the AE-L button is pressed. If the AE-L button is pressed, the locked value is used for the BL flash equations.

The data that is used by the BL equations comes directly from the meter and it represents ambient ev (modified by the camera ev setting). The balancing equations don't use the f/ stop or shutter settings. This is why, when using camera Manual mode, changing the aperture or shutter does not change flash power.

The off-center problem occurs for both cases. However, in TTL-BL mode, IF the flash head is pointed straight forward, the distance information from a D or DX lens is used as the dominant factor in computing flash power. So, if the flash is pointed straight forward, the off-center problem is greatly reduced, since the focus (distance to the subject) will be locked in by the half-press before recomposing. If you are bouncing the flash or using a diffuser (that pushes the small switch on the flash head), the distance information from the lens is not used in the TTL-BL equations. This works this way, because when using TTL-BL in extremely bright light, the monitor preflash method is not as reliable.

Russ

Anonymous said...

Russ,
again, thanks for your explanation, now it is perfectly clear.
Regards, Wolfgang

Macovei Tinel said...

when i first say "nikonians.org" in the description on your profile, i was on the verge of hitting "ctrl-w" (to close the window)...lol. I was expecting a "if you wish the know the rest, you gotta pay $$ for it". lol.
Glad to see that it's free. :)
Cheers!

Russ MacDonald said...

Hi Macovei,

Yes, my blogs are free. Lots of people have suggested that I should make them into a book, but that would be way too much like work. I write these for fun. Keeps the mind sharp to answer all the questions they generate, too.

In a former life I designed IC's for flashes and cameras, and I like to share what I learned.

I don't think Nikon publishes enough of the details.

Russ

Anonymous said...

Russ,

Fantastic blog! I'm a little less scared of the SB-800 sitting in my bag now!

The SB-800 needs to be mounted on the hotshoe to engage the TTL-BL setting as you have clearly stated. However, if you use a flash bracket (obviously with the sync cord attached) with the flash significantly higher, would the same fill flash effect be maintained?

Thanks much,

Brian

David said...

Hi Russ,
thanks for putting up this very interesting information, i keep on coming back to these pages.
The manuals and the broshures that accompany the Nikon flashes aren't very helpful at explaining anything but how to change the settings, so i got a bit frustrated at using TTL and have always preferred to use manual mode (i use my strobes off camera).
Again, thanks!
David

Russ MacDonald said...

Hi David,

You're most welcome!

Russ

Desmond Downs said...

Hi Russ , I see you commented on my video . With regard to statement "3" wireless CLS uses TTL/BL metering mode unless you are using spot metering mode .
Perhaps we should discuss the matter on 'neutral ground' where you can't shut the site down when I win ?
You suggest a forum .

Kemal Sirin said...

Hi Russ

Your blog is amazing and I haven't read all of the 16 blogs so far. I have one question nonetheless... I have a speedlight and a D700... It is a SB900.
Can I use the SB 900 as an external unit without havin to trigger the build-in flash on the camera?
I mean' do i have to buy a second unit just to do that? Thanks !
Kemal

Russ MacDonald said...

Hi Kemal,

Thanks for the nice feedback.

Your question is way off topic for this blog, but since I don't have a blog for wireless operation, I will answer it here.

First, its best to be very careful with all the terminology. When you use a Nikon flash wirelessly it is called a 'Remote' and it has to be set in its 'Remote' mode to work. Also, the thing that controls it is called a Commander.

On the D700, the built-in flash can function as the Commander. It has to send commands to the Remote SB-900 using the only means it has - its flash.

So, to answer your question, no, there is no way to fire the Remote SB-900 without firing the built-in flash.

However, one of the modes you can choose in the commander menu allows you to fire only the command flashes and then the built-in flash will not contribute to the exposure (much).

Lastly, you buy a low cost Nikon SG-3IR filter that attaches to the camera that filters the flash signal from the built-in flash, allowing only the IR wavelengths to get through. These are not visible, so you can at least prevent the visible flash from bothering people.

Please send follow-ups to this question directly to my email at rkmacdonald@gmail.com.

Russ

Sarah said...

Hi Russ

I am finding your posts incredibly helpful! I have had my SB800 for a few months and up until now I have had varying results with it. I am finally beginning to feel a bit more confident after reading your advice!

I wanted to ask your advice on taking outdoor portraits with flash. I have started taking family and children portraits. I have always used Aperture Priority for my shots and I use the SB800 for fill. I take quite a lot of pictures of kids when they're going about their own thing - playing, kicking leaves, on a swing etc and I am getting motion blur/ghosting effect. What settings would you use to freeze this? Should I put the camera in M mode and bring the shutter speed up and use TTL-BL flash? Apologies if you have covered this in one of your posts already.

Thanks again!
Sarah

Russ MacDonald said...

Hi Sarah,

If you are using Aperture priority outdoors in bright light, then you may also be getting overexposure in addition to the motion blur, because the maximum shutter speed will be limited to the Flash Sync Speed (usually around 1/200th sec). So, if you set set your aperture too wide, the shutter needs to go up higher than 1/200th, but it can't, so you blow out your image. Then, you have to reset the aperture to a smaller f/ stop to prevent the overexposure. This is why it is much easier to use Shutter Priority and just set the shutter to 1/200th and leave it. This will stop most of the motion blur, and it will allow the aperture to close down as needed to control the exposure.

To stop all motion blur when shooting fill flash in daylight, you have to use a higher shutter speed. The flash won't do it, because it cannot overpower such bright ambient.

So, (assuming your camera has this feature) the answer is to switch the camera to Auto FP Sync and put the camera in Shutter priority. This will will allow you to select a high shutter speed to stop the action.

However, the downside to Auto FP Sync is that the flash power now becomes a function of shutter speed (in addition to aperture) and as shutter speed is increased, the flash power drops to much less than its normal power, so the range becomes very limited. Still, it will usually have enough power to lift the shadows on the subject's face if you can stay close enough (within 12 feet or so).

I have written more about Auto FP Sync here: http://nikonclspracticalguide.blogspot.com/2008/03/10-auto-fp-high-speed-sync-explained.html

If your camera does not have Auto FP High Speed Sync, then the only way to freeze action in daylight is to turn off the flash and use a high shutter speed.

Hope this helps,

Russ

SoftFocus said...

Hello Russ,
I have read almost all your articles and found them so fascinating that I went out and bought my first flash gun to learn more about flash photography - a Nikon SB400 to go with D90.

I immediately have a question:
The manual says the SB400 works in iTTL mode but I infer from the blogs that in fact there are two modes, TTL and TTL-BL. As the SB400 does not have a mode switch, my question is:

Does the SB400 work in TTL mode if I put the camera (D90)in Manual + spot metering and in TTL/BL in the other modes with matrix metering, such as, Aperture/Shutter priority?

I have experimented to some degree and noted differences in the exposures but can't be certain. I have verified that the exposure compensation works as you described.

I posted a similar question on nikonian.org but it occurs to me that I better ask the expert.

Thanks for sharing your knowledge of this topic.

Rod

Russ MacDonald said...

Hi Rod,

Your question is one that I have been asked before, but I don't know the answer for sure. I may have even answered you on Nikonians (I'm Arkayem there).

I don't own an SB400, so I can't test it. I think you already know that the instruction manual only mentions iTTL and not iTTL-BL mode. However, I believe that is just an error in the manual, and it really does have both modes, but I think you could help us find out for sure.

We know that the pop-up flash works in iTTL when in Spot metering and iTTL-BL when in Matrix metering. What I'd like you to do is compare the pop-up to the SB-400.

Do the following with both the pop-up and the SB400. Keep the SB400 pointed forward for this test.

Conditions: outdoors, bright sun, subject in the shade.

Position a neutral colored subject (like a person, statue, doll, etc) so that there is a bright background behind.

Adjust the zoom to make the subject fill only the center portion of the frame; ie, leave plenty of frame area for Matrix metering to make a good measurement of the background.

Camera P mode (at first), ISO 200, FEC 0ev

Do not focus and recompose (because the camera meter uses whatever is under the focus point at the time the shutter press is completed).

Take two control pictures of subject without flash.

Control Picture 1: Flash OFF, Camera Matrix Metering. Expected results: background exposed correctly, subject underexposed by an amount determined by the amount of ambient light in the shade. Write down the f/ stop and shutter values for this picture. We'll call them the 'Matrix Metering Settings' for use later.

Control Picture 2: Flash OFF, camera Spot Metering, spot on middle of subject. Expected Results: background overexposed (blown out), subject exposed correctly. Write down the f/ stop and shutter settings the camera chose for each. We'll call these the 'Spot Metering Settings' for use later.

Camera Manual Mode.

Note: If you leave the camera in one of the auto modes, the minimum shutter speed will be fixed at 1/60th when the flash is turned on. We don't want to introduce another variable.

Turn Flash ON, 'Spot Metering Settings', spot on middle of subject. Expected results: background overexposed (blown out), subject too bright and probably blown out a bit depending on how much ambient there is.

Flash ON, Matrix Metering Settings. Expected Results: background exposed correctly, subject exposed correctly (significantly darker than it was in Spot metering mode).

Run the same tests for the pop-up flash and the SB400. The results will be identical if the SB400 has iTTL-BL mode.

If these things all happen as I have indicated, then the SB400 indeed does have iTTL-BL mode, and it is enabled by Matrix Metering and disabled by Spot Metering.

Contact me by email to send me the resulting images. I will publish the results in a separate blog (giving you credit) later: rkmacdonald@gmail.com.

Regards,

Russ

SoftFocus said...

Hi Russ,
Will try your steps over Xmas and report back.
Best wishes for the New Year and Happy Christmas,
Rod

Barb said...

Russ,
I am learning a lot from reading your blog. I have a Nikon D60 and SB400 flash. Did you ever receive the test results from the person who was going to test the SB400 over Christmas break to see if it has TTL-BL?
Barb

Russ MacDonald said...

Hi Barb,

I did receive a more information that all indicates that the SB-400 does indeed have TTL-BL and it works the way I thought it did.

TTL-BL is its default mode, and there is no way on the flash itself to change it to regular TTL, but it can be forced it into regular TTL by selecting Spot metering on the camera.

I'm now about 99.9% sure that is how it works. I wish I had one to test so I could erase that last 1/10 of a percent of doubt.

Russ

Desmond Downs said...

I have an SB400 and it does work in TTL/BL mode :) .

Russ MacDonald said...

Thanks Desmond!

Russ

Alessandro (rome) said...

Dear Russel,

Fantastic info and blog. Really Thanks.

I love the Fill-in with Matrix from my old Nikon F801s (N8008s in USA), then F100 ..... till D90.

With my D90 i dont get very good results. I dont like how the D90 handle the autoiso with Flash and slowsync or rear.

In simple, autoiso works only if the light of flash is no enough , so the Nikon push up the iso to increase the light of flash. But when we use slow sync or rear it means we would like get a good background, and than the flash fill the subject.
No way to get a good background increasing iso with autoiso.

Autoiso remain "fixed", i mean remain at 200 iso (or the minum value i have choosen) and in rear and slow sync camera use only the speed and aperture to get a good pic with balanced Background.
It use autoiso only if the light of flash is no enough for the subject.


Look at this pic. I was in a restaurant. 2 friends in front of me.
I used rear and slow sync (same result), and camera gave me 2.5" of exposure, with iso fixed at 200 (when my autoiso could gain till 3200)

http://img8.imageshack.us/img8/3977/dsc0544d90.jpg

In other forum somebody suggested this way..... .tell me if i can improve something.

- TTL flash mode
- matrix metering
- M-mode ( i choose Shutterspeed and Aperture myself , eg S = 1/100
sec to freese motion, A = high enough for needed DOF )
- base iso to eg 400 ( capture some ambient light )
- set auto iso ON -> set max ISO ( eg 800 or 1600 ).

I got good pics, but the "problem" is that often when i shot those types of pics, i cant do many test, normaly i do many "street pics" where i cant wait too much... that's all


Many tkanks again for your wonderful blog and sorry for my poor english

ciao

Alessandro

Russ MacDonald said...

Hi Alessando,

Thanks you for the compliment on my blogs! And your English is fine!

I never use Auto ISO very much, and I especially never use it when shooting flash. To me it just doesn't make any sense.

For indoors I use the camera in Manual mode, ISO 400, 1/80th, and f/4. Those settings work about 95% of the time indoors.

I normally don't like to allow too much ambient into my indoor shots, because it doesn't match the flash and it gives you bad colorcasts on the subject.

Regards,

Russ

Larry said...

What a wealth of info on this site...Recently started shooting at a kids indoor soccer field, bad indoor lighting etc..Nikon D300 with SB800 flash..Set camera to M, shutter @ 250th, F4 and SB800 to TTL-BL, Matrix. Lens was a Nikon 17 to 55 2.8
Caught all the action perfectly without any ambient light motion ghost. Thanks to info I saw on your website..Thanks

Russ MacDonald said...

Hi Larry,

Thanks for the great compliment!

Even though I am not a sports shooter, all the principles are the same for all photography. I'm glad you were able to use my information!

Russ

Anonymous said...

Shooting moving athletes in bright outdoor, I like them to pop a bit and thus, reduce the exposure of the camera manually 1 stop underexposed.

In TTL-BL do I need to change the flash ev (from your recommended -.3?)

I understand if i change the ev on the camera I have to compensate, but if i change the exposure 1 stop under manually on the camera, does it affect the flash output at all?

Anonymous said...

Also, if its cloudy outdoor and not so bright, use TTL_BL or should i use TTL?

I need to stop action with flash, so I want to make sure flash is always overpowering the ambiant. This is why I always underexpose ambiant. Correct?

Ulf said...

Hi!
Thanks a lot. this is the important part by using Nikon i-TTL.
And this is my main problem.
When shoud I use BL -i-TTL and what situation is the correct one for standard i-TTL?
I know the stuff BL is Fill light and standard i-TTL is if my subjekct is main lighted with the flash.

BUT:

If The sun is in front of me (backlight) it shoud be BL Mode. But if I reduce the ambilight (in M Mode by reducing ISO, The aperture or the shutter speed) don’t I have a TTL-situation?)
At which time I use which mode??

The problem I don’t understand is that:
In standard i-TTL mode. Is it right that the flash power is always set as strong as the ambilight would be very very dark?
So If I make the shutter longer (or the iso higher or the aperture wider open) I have to reuce the flash exposer?? This could not be becuase of TTL I thought.
BUT in i-TTL the flash ignores the ambilight. And when I make higher ISO, longer Time or bigger aperture there will fall ambilight on my subject even more and influencs the light on my subject too. And in standard TTL Mode in the manual there stands that the ambilight on my subjekct does not influence the flash power.
So what is true??

In i-TTL BL this situation should be solved (I thought). BUT (again)
very often the flash is to weak. so it knows when I make the exposere (the ambilight and ambilight on my subject) brighter but why often too dark the flash?

I mean the aim should be to have a correct lighted subject right?
But onetimes with ambient light and onetimes without.
And when using ambilight there are 2 things important.
1.) not overexposer
2.) ambilight will influence the subject too. and this must correct the flash power.
Is this right?

Thanks a lot for yout help

Russ MacDonald said...

Ulf,

You are asking too many questions to answer here. In fact, you are asking questions that I have answered already in my blogs.

I suggest you start with my first blog and read them in order. All your questions are answered:
http://nikonclspracticalguide.blogspot.com/2008/01/nikon-flash-two-separate-metering.html

Especially read my 'flash cookbook' here: http://nikonclspracticalguide.blogspot.com/2009/12/camera-flash-cookbook-for-any-lighting.html

Russ

Ulf said...

Hi! Russ. thank you so much for your help.
I frightened that I ask to much sorry.

Of course I read all of your tutorials. And the manuals too.

The problem is just this BL or not BL problem.
And I'm very sad to to don not understand it.

I thought BL is used when Ambilight is important. Butif i have less light the hole picture is too dark. I thought just the amount of ambilight will be detected. so that if I manually increase the ambillight (ISO suhtter apertre) is will be recognised and so the amount of Flash will decrease.
But this is not true.
And iin standard TTL it is neither.
because in this mode manually increasing the ambiligth (again this 3 paramerters) will lead to an overexposer.

And special in mixed situations.

Sorry I do not understand. But thank you very very much for your help (the great tutorials and the personally tries.)
That's really great from you. ;-)

Russ MacDonald said...

Ulf,

Email me at rkmacdonald@gmail.com and I will continue to help you. I just don't want to do it on the blog.

Russ

Tim said...

Hello Russ!
I have a question.
When I have a nice light situation (no strict backlight) but I would like to fill a bit of shadows and improve the light situation just a bit. shoud I use BL or normal TTL with dramatic encreases flash exposion?
Cause Bl Mode ist just for backlight. Isn't it?

2 specific situations.
a)
So i I just wand fill Light additional to my light situation (maybe the sun is light and my model is in the shadow. I would have correct settings (1/200 and f/3,5 and my ambient light is ok. I just want make the person a lot brighter.
When just using ttl, is would be overexposerd beacuse the situation is very bright without the flash. But not darker than the background so no BL (Right or not)

b) in the 2nd situation i just have one sight of the face to dark (for example the sun comes from the sight. Need fill light. so BL mode or not?

Thanks for taking time

Russ MacDonald said...

Hi Tim,

TTL-BL is designed to add fill to an image that is primarilly exposed by ambient light. The flash will adjust itself to make the subject brightness match the ambient brightness.

The most obvious use of BL mode is when the subject is backlighted.

However, if you are exposing your subject with a very slow shutter and wide aperture to allow lots of ambient, like you often get with Slow Sync for instance, then TTL-BL is a good choice.

Think of TTL-BL for Fill Flash and regular TTL for flash primary shots.

One more thing; if your subject has bright sun hitting her face on one side and dark on the onter side, any flash at all will add where the sun is hitting and you will get overexposure. You have to get rid of any direct sun hitting your subject before Fill Flash will work. So, move the subject into the shade, and then TTL-BL works great.

Russ

JackW said...

Russ,

I just discovered your blog - primarily I'm sure because I have only recently started to explore the CLS - and I wanted to add my appreciation to the myriad of others who have found this information so useful, well presented, detailed, but clear. Thanks for taking the time to do it, and for doing it so well! I am posting this here, because this entry, with the one before it, finally gave me the key to clear up my confusion about the difference between TTL and TTL-BL.

Some background: I bought an SB-400 with my D300, and blithely shot away for 18 months never knowing there were two TTL modes. Then I got an SB-600, discovered the difference, started doing some research, and ... got confused. Specifically, I got leery of using TTL-BL. Like yourself, I always shoot fill flash with an FV compensation at least -1.0. My reading suggested this might not work consistently in TTL-BL mode because of the camera doing its' own fiddling with flash compensation to do the 'balancing' thing. My experiments, plus the experience using the SB-400, all seemed to indicate that it worked fine, so clearly I didn't understand something. Now, I have the key:
BL == "Back Light"
In other words, TTL-BL is for "Balanced F-I-L-L Flash", and as long as that is what I am doing, it should work fine. When I am doing something more than fill flash (part of the reason I got the SB-600), then I should consider switching to TTL only.

Final note: my reading suggests that Nikon improved the TTL-BL mode in the D300 over the earlier cameras. Supposedly, it now does a better job of recognizing dimly lit scenes and doesn't try to "balance" them. Since the D300 is my first DSLR, I have no prior referent, but using the SB-400 as a primary light in situations such as restaurants seemed to work pretty good - as long as I stay within its power limitations. So, these days I leave it in TTL-BL (for the SB-400), but try both with the SB-600, and go with whichever seems to work the best.

Russ MacDonald said...

Hi Jack,

Great feedback! Thanks!

And everything you wrote is correct!

Yes, Nikon is working hard to make TTL-BL work better in low ambient conditions. In newer cameras it works much better, but still not fully reliable.

I still use regular TTL when the flash will be primary and TTL-BL when the flash will only be adding fill. Works great when you do that!

Thanks again,

Russ

Russ MacDonald said...

Jack,

I forgot to mention one more thing.

Do you realize that the SB400 also can be used in both modes? Most people don't.

You switch it between TTL and TTL-BL with the camera metering mode.

If you select Matrix or Center Weighted metering, it will operate in TTL-BL mode. If you select Spot metering, it will operate in regular TTL mode.

Russ

Jack said...

Russ,

I know (now) that the SB-400 can be used in both modes - as can the camera's internal flash (switching to 'spot' metering switches to TTL).

I did not know this until I got the SB-600 and started trying to figure out its' options. Up to that point, whenever I read / heard TTL or Balanced flash, I thought they were the same thing. Fortunately, fill flash is the primary thing you use the SB-400 for, so the default TTL-BL mode works fine most of the time. Likewise (even more so) for the internal flash (until you get other CLS components, whereupon it becomes a commander - so cool). I live, I learn, I take better pictures.

Jack

Frank said...

Hi Russ

Here's a question for you:

When in p-mode the camera chooses an aperture of f4 and a shutter of 1/60.

Now for the same scene: When I go to aperture-mode and select the same aperture, f4, the camera also gives me a shutterspeed of 1/60.

What I dont understand is, that the meter (in aperture priority) also tells me, that the photo is underexposed by one stop.

If its underexposed, why doesnt the camera choose a bigger aperture when in p-mode? Is it to prevent overexposure?

(I use a D50, flash on, in TTL-BL)

Best regards
Frank

Russ MacDonald said...

Hi Frank,

Whenever you are shooting flash in dim ambient light, and you are using either P or A mode, the camera prevents the shutter speed from going slower than the 'Flash Shutter Speed'. This is done to prevent motion blur in the background. 1/60th is the default and the slowest shutter speed that most people can handhold the camera and not get motion blur.

If you want to use a slower shutter speed, it is best to switch to camera Manual mode, which is usually best when shooting flash in low ambient light, anyway.

Russ

Frank said...

Thanks for your reply Russ.

I properbly did a bad job explaining, what I ment.

I understand, what you are telling me. The thing I dont understand is why the aperture does not change (to a larger one) in p-mode.

I mean, when 1/60 and f4 gives me an underexposure of 1 stop in aperture priority - wouldnt it be logic for the camera when switched to p-mode, to choose a bigger aperture instead of giving me an exposure, where the ambient is underexposed by 1 stop?
(I know it cant do anything to the shutter)

Do you understand, what I mean?


I realy apreciate your help.

Regards
Frank

Russ MacDonald said...

Hi Frank,

Yes, I think I understand now.

In P mode, the 'Program' selects the aperture based on several things including the characteristics of the lens. The lens is usually not opened up to its maximum aperture (smallest f/ stop, like f/2.8) unless it is a pro lens, because consumer lenses are not always sharp when opened fully. Also, the 'program' assumes that if you are using a consumer lens, you may not be aware of the narrow depth of field that a wide aperture gives you. Also, the lens is not stopped all the way down (like f/22), because the image gets soft due to refraction distortion.

You may also be aware of the feature called 'Variable Program'. It allows you to select alternate apertures/shutter speeds when using the P mode. However, the 'program' will still prevent you from chosing the widest or narrowest apertures.

If you want to use a wider or narrower aperture than P mode will select, you have to switch to A, or M mode and select what you want. However, if you do this while using flash, you have to guard against overexposure in bright ambient light. I usually select Auto FP High Speed Sync mode when I want to shoot flash in camera A mode. Then I can select whatever aperture I want, and the shutter will increase as high as necessary to control the exposure. The negative to doing this, however, is that the maximum flash power that is available in FP Sync mode is usually less than half of what is available in regular sync mode, so you have to be closer to your subject.

Hope that helps,

Russ

Russ MacDonald said...

Hi Frank,

Another thought occured to me after I published my response.

If you want to increase the ambient in your flash pictures, and you don't want to use camera M mode, you can use Slow or Rear sync. Then the shutter will decrease to a setting way slower than 1/60th to allow the ambient to mix with the flash.

I don't normally like to do this, however, because I have no control over the shutter, and it will go as slow as necessary to achieve the balance no matter how much motion blur it causes. It is usually best to use a tripod if you use Slow or Rear sync.

Russ

Russ

Frank said...

I see, I got it now, thanks a lot!

Is it allright, that I keep on asking questions?

Hope it's not too much of topic here.
Im trying to understand the logic behind freezing a movement with shutterspeed and/or with flash.

We touched on this earlier, maybe you can tell me, if I got it right now.

My understanding of flashphotography in low ambient:

In order to owerpower the ambient, so that you will not get ghosting, you can:

1. Use a high shutterspeed. That will eliminate some of the ambient light, depending of how much you underexpose.
In some cases what is back of the ambient will cause ghosting.

2. In order to eliminate the ghosting that is left, you can use the flash to "burn away" the ghosting (or burn in the flash exposure, you might say). This will only work, if the ambient exposure wasnt too strong.

Also, some times the flash cant do this, because the subject is too far away, and the flashlight therefor is too weak.

Is this right?

When you say, that you in some situations wasnt able to overpower the ambient (for example a shot at the beach), it means, that the ambient exposure made by the sun was so "strong" and made too much of an impact on your sensor, so that your flash wasnt able to burn that exposure away and be dominant?

If this is right I might better understand what a photographer who was shooting at the beach told me. He used a very big ringflash, and said, that it was convinient, when he had to "compete with the sun".

I guess he wanted to underexpose the bright ambient a lot, and by doing so, he also gave his flash a hard time. Because of that, it had to big and powerfull...?

Am I getting it right, or have I totaly misunderstod the concept?

Thanks!

Frank

Russ MacDonald said...

Hi Frank,

Yes, everything you said is correct!

I enjoy answering all your questions, but if you want to go way off-topic, it's best to just send me an email at russ@russmacdonaldphotos.com.

I answer all my emails.

Russ

SteveUK said...

Russ,

Thanks for the easy explanation.

2 questions:-

I use a hand-held light meter so would it be right to assume I take an AMBIENT reading, rather than FLASH one and just let the flash add TTL-BL according to the ambient camera settings?

If I use a diffuser or the popup white strip on the flash do I need to amend any settings on flash output etc or do I really need to use them at all?

Thanks, Steve.

Russ MacDonald said...

Hi Steve,

All light meters will measure ambient, and some will measure flash strength. However, the way you worded your question makes me think you are using your meter to only measure the ambient.

So, the decision of how to use your flash depends on the amount of ambient you will let contribute to the image.

Most of the time, for low ambient light, you want to set your camera to unerexpose the ambient by about three stops on the subject, and then use regular TTL flash to expose the image.

TTL-BL is for bright ambient light, like outdoors in daylight, for fill.

The diffuser doesn't affect the exposure of the subject. The flash metering goes through the lens of the camera, and everything between the flash and the subject is automatically taken into account. Even if you bounce the flash off the wall behind you, that is handled automatically by the regular TTL metering.

The only thing you have to watch out for is running out of flash power. If you put too much diffusion between the flash and the subject, there might be so much attenuation that the flash cannot produce enough power to make a proper exposure.

Hope that helps,

Russ

StevesUk said...

Sorry didn't explain myself properly (I always do that!).

Yes, I am using the light meter to test ambient although, as you know, I can test it with the flash too.

So I have the option to dial into the camera the settings after a test flash in TTL-BL mode or no test flash just using settings from the ambient light meter mode.

I'll be outside, probably in bright sunlight, but I'll be taking the group photos under a tree with some shade (still with bright ambient hence TTL-BL).

Steve.

photoartist said...

Hi Russ,

Thanks a lot for your very informative information on flash setting and metering. I take my hat off for your patience in replying to all the Nikon users like me, who keep on asking you similar questions and yet you answer each person indivually(even if that means repeating that info).

Anyway to my question: In addition to the example of out door shots can you provide setting and examples for two type indoor situations?

I often have great difficulty getting the exposure right in hotels (weddings or reception), and also low light (dance event wehre we have coloring lighs on side of walls or spots and you want to take a picure of couple).

I find that it is easier to meter in manual in broad daylight and get the shuuter and fstop adjusted to get the exposure dot in the middle. But in low light inddors you cannot do the same so the metering in manual will always show under exposed unless i set it to high ISO, but the I risk images being grainy. So can you give me an idea of what bet way to handdle 90% of indoor shooting in a good ambientlight and poor ambient light.

Anonymous said...

Hi Russ,

A lot of posting on this area have been on TTL_BL.

When should one use he "A" (auto) flash setting on the SB800 and "AA" setting? How do these setting work?

Russ MacDonald said...

Hi photoartist,

Whenever there is any lighting that doesn't match the color balance of the flash, I normally increase the shutter speed to block all of the ambient out and then let the flash provide all of the exposure. Then, the colored lights along the side will not affect the exposure. Of course, if you do this, the background will darken, but that cannot be helped.

I sometimes take several shots at different shutter speeds to see what it looks like to allow a small amount of the colored light into the image.

When you are in low ambient, you normally don't want the ambient to contribute to the exposure. That is why the camera should be set to underexpose.

I wonder if you have read my other blogs, especially my cookbook here:
http://nikonclspracticalguide.blogspot.com/2009/12/camera-flash-cookbook-for-any-lighting.html

Russ

Russ MacDonald said...

To anonymous (wish you would sign your name),

Yes, the article you posted your question after is the TTL-BL article.

I wrote another article about A and AA here:
http://nikonclspracticalguide.blogspot.com/2008/07/13-sb800-and-aa-modes.html

Please read that and if you still have more questions, post them following that article.

Thanks,

Russ

Anonymous said...

Hi Russ,

I've just about got a grip on the differences between TTL and BL TTL flash and have made some improvements in my work. On a recent holiday I took a lot of outdoor pics of my girlfriend in various outdoor settings in bright ambient light. I used B-TTL on my D300 (pop-up flash with Matrix metering set) and got nicely exposed pictures of her without lots of shadows. I did notice however a somewhat warm balance to the resulting pics and am wondering if the camera should be set to manual WB sunlight to over-ride the flash setting. Some advice for using fill flash for daylight exposure would be appreciated.

THANKS

PAUL

Russ MacDonald said...

Hi Paul,

One of the prices you have to pay when balancing the ambient and the flash is getting the white balance to be acceptable.

Auto White Balance usually works great with the flash alone.

However, when using TTL-BL you are allowing the ambient to get into the picture. The warmness you are seeing is not from the flash. It is from the ambient.

If you don't like the warmness, then you should probably use regular TTL and increase the shutter to remove most of the ambient. Then the white balance will be correct.

I tend to like the warm effect of the ambient light, so I leave the white balance alone.

Have you read my 'Cookbook'? It is post 18 here: http://nikonclspracticalguide.blogspot.com/2009/12/camera-flash-cookbook-for-any-lighting.html

That one might help you.

Russ

w said...

Hi Russ,
Thanks for your great blog.
I'll appreciate if you could answer this question.
I would like to compare two modes:

1. Matrix measuring and manual exposure on the camera and iTTL in the flash (not iTTL-BL!).
2. Spot measuring and manual exposure on the camera and iTTL in the flash.

(Actually, the only difference is with the Matrix/Spot setting)

If in the both, I have the same exposure values (aperture/shutter/ISO manually, I decided according to the camera meter display for the same exposure) were set, will be any differences with the shot? Ambient and subject? Logically, as I understand it will be exactly the same. Am I right?

Now the strange thing, lets say that I change only the setup on the flash to TTL-BL, still the same exposure setup in the camera, I think the shot will exactly the same as before when the flash was set on i-TTL (not BL). Is it right?

In this case, what is the meaning of this setup on the flash?
If I use the manual exposure in the camera, no matter what the flash was set to?

I think I'm missing something (and sorry for my bad English)..

Thanks,
Willie.

w said...

Hi Russ,
One more question,
I've just ordered a SB-700.
I see now that it cannot be set to iTTL with Matrix/CW and iTTL-BL with spot. Do you think any disadvantages of that?
Actually, I think I would like to shot most of the time with manual metering and iTTL + manually compensation the flash. I know that I'm limited by the metering (cannot go to Matrix or CW). I hope that is the only "penalty".
Thanks,
Willie.

Russ MacDonald said...

Hi Willie,

The purpose of Spot or Matrix metering is to set the aperture and shutter automatically.

So, if the camera is in Manual mode, the choice of Matrix or Spot metering has no effect on the camera. The aperture and shutter are selected manually.

If the flash is in regular TTL mode, then the metering mode on the camera has no effect on the flash. So, if the camera is in manual mode, and the flash is in regular TTL mode, then switching between spot and matrix metering has absolutely no effect.

If the flash is in TTL-BL mode, then the metering has to be in Matrix (or Center Weighted) mode. If you switch the metering to Spot mode, it will force the flash into Regular TTL.

Now to your specific questions:
"If in the both, I have the same exposure values (aperture/shutter/ISO manually, I decided according to the camera meter display for the same exposure) were set, will be any differences with the shot? Ambient and subject? Logically, as I understand it will be exactly the same. Am I right?"
Yes you are right.

"Now the strange thing, lets say that I change only the setup on the flash to TTL-BL, still the same exposure setup in the camera, I think the shot will exactly the same as before when the flash was set on i-TTL (not BL). Is it right? "
No. When the flash is in TTL-BL mode, it will set its power based on the METER and not the camera aperture and shutter. For TTL-BL mode to work properly, the meter must be centered. This is one reason why I recommend to always use one of the camera automatic modes, usually P mode, when using TTL-BL mode on the flash. Then, the meter will automatically center itself. If the meter is not centered (ie, you leave the camera in Manual mode and do not center the meter), then TTL-BL won't work right. The meter MUST be centered.

Hope that helps,

Russ

timothy au photography said...
This comment has been removed by the author.
Anonymous said...

Hi Russ, i'm new in digital so wanna ask is the ttl-bl not available on some model? cause i can't find it on my d7000 setting, it only have ittl and manual mode and commander mode. can you explain more? thanks

Russ MacDonald said...

Hi Timothy,

You have TTL-BL when using the pop-up flash. You just don't know it, and it doesn't tell you.

I wrote a separate blog about that here:
http://nikonclspracticalguide.blogspot.com/2008/02/8-how-buit-in-flash-metering-works.html

Read that and then see if it answers all your questions.

Russ

Anonymous said...

Hi Ross,
First, I think your blog is a "must" for everyone who wants to understand how the CLS system works. I so appreciate that you are participating your knowledge and experience.
Thanks for the answer to my question, Probably, I have to read again your blogs and discussions again in order to understand some aspects more in deep (specially blogs #5 and #9).
I would like to understand how the following combinations work in practice:
1. Matrix/CW in camera and TTL on the flash.
2. Spot in the camera and TTL-BL on the flash.
I'm trying also to understand what it means that the SB-700 lacks these combinations.
Thanks again,
Willie

Russ MacDonald said...

Hi Willie,

This is very similar to your previous question that I tried to answer. Let me try again.

The TTL-BL mode sets the flash to a power that matches the background of the entire frame.

This system is not perfect, but the way it works is that it looks at the metering data around the edges of the frame while ignoring the center. It ignores the center because that is where the subect ius supposed to be, and it wants to match the background.

In order to look at the metering data from the edges of the frame, the metering MUST be in either Matrix or CW. It usually works better in Matrix, because in CW mode the edges are attenuated.

Spot metering cannot work with TTL-BL mode, because there is no data coming from the edge of the frame. All the metering data in spot mode comes from the subject. So, there is no way that the flash could set its power to the background.

The other requirement for TTL-BL to work correctly is that the camera must be set to expose the frame correctly; ie, the meter must be centered. This is why I recommend to use P mode when using TTL-BL mode.

You should now be able to see that your number 2 mode selection is impossible. TTL-BL cannot be selected when in Spot metering for the reasons I explained above.

But, in regular TTL mode, the flash does not use any information from the camera meter. It sets the power of the flash totally based on the reflected power of the monitor preflash as it bounces off the subject. The monitor preflash system is center weighted, so it works best when the subject is centered. But this has nothing to do with the camera meter. In regular TTL mode, the camera meter has absolutely no effect.

This is why I recommend using the camera in Manual mode when using regular TTL.

This is how all the Nikon flashes work, including the SB700.

I hope that helps.

Russ

w said...

Hi Russ,
Thanks for your answer and patience.
I've read your answer and some of your topics again and again and it's all clear. I can understand where was my confusion.
I appreciate your help.
Willie.

falke said...

Hi Russ,
I have read your blog over and over again, and I must say this is the best place on the Internet to learn how the Nikon CLS system works. As many others already have done, I want to thank you for your great articles.

I think that I have figured out the difference between TTL and TTL-BL. In essence:

TTL: The flash computer inside the camera calculates the flash amount totally independent of the F/ and shutter settings, program mode or metering mode (spot, CW or matrix). The calculation is done by measuring the reflected light from the preflash using CW mode.

TTL-BL: The ambient light resulting from the F/ and shutter speed is sent to the flash computer, which tries to make the subject (if placed in the center) equal bright.

This difference makes we wonder, why TTL-BL still works when I try to take a picture in total darkness? If I understand the difference correctly, TTL-BL tries to make the subject just as bright as the overall ambient, but since there is absolutely no ambient, there is nothing to balance with.

If there is no ambient or just very little ambient, does the TTL-BL default to TTL?

This question is just to clarify the difference between the two programs. Under very dim lightning I would prefer to use regular TTL.

I use a Nikon D300 and SB900.

Thanks again from Thomas Munch Falkeborg, Denmark.

Russ MacDonald said...

Hi Thomas,

This is a very astute observation, and one that has occupied many Nikon engineering hours.

TTL-BL is a very very complex system, and over the years it has evolved into a general purpose flash system that works pretty well for all lighting conditions.

Nikon engineers have worked very hard to make TTL-BL work in all situations. With each generation camera, they are getting closer and closer to a perfect solution

However, regular TTL still works better for most low ambient situations.

The TTL-BL system on the D300 and SB-900 is very advanced and works very well under most lighting conditions most of the time.

In fact, TTL-BL has become so good that the pop-up flashes default to TTL-BL mode and can only be changed to regular TTL by selecting spot metering.

In the specific case you mentioned; ie, completely dark, latest generation TTL-BL works quite well. When the metering detects a completely dark edge around the frame, it assumes that the ambient is zero, so it switches to a pseudo-Regular TTL mode and selects a flash brightness to make the flash primary based mostly on the distance. It doesn't work so well in this situation if you use a non-D lens.

Hope that helps,

Russ

Jacques.K said...

Hi Russ.
This is one the best explanations of how a flash works, TTL and TTL-BL. You have a gift to explain it to those of us just starting out. I have done two courses and its never been explained to me like this. Well done please keep it going.

Ragards

Jacques Krog

Russ MacDonald said...

Hi Jacques,

Thank you for the nice feedback.

One of the reasons I wrote my articles was that no one was writing about how the flash really works.

Russ

Hitoshi Ujiie said...

Russ:

Your blog is very helpful. I have one question to ask.

In the TTL-BL situation, where the subject is backlit and darker than ambient. Could you break it down using light meter in stead of Nikon automated sytem?

Russ MacDonald said...

Hi Hitoshi,

Your question is actually a lot more complicated than you realize.

There are two basicly different light meters needed for flash photography: 1) one that measures the ambient (either reflective or incidence) and 2) one that measures the power of the flash.

To measure the ambient, the light meter is placed either at the camera location where it measures the reflected light from the subject or at the subject pointed at the light source, where it measures the strength of the light source.

To measure the flash strength, the flash meter is placed at the location of the subject and pointed at the flash. Then the flash strength is measured by the meter.

The most common situation is taking flash pictures indoors in low ambient conditions with your exposures dominated by the flash. In this situation you only have to measure the strength of the flash.

To measure the power of the flash, the light meter is set at the ISO that you are using, and it tells you the f/ stop to use. The shutter speed must be at flash sync speed or lower.

There is a lot more to this, but maybe these few comments will help.

Russ

Hitoshi Ujiie said...

Russ:

Thank you very much for the reply. I would like to restate my question. I know this is a little far from this blog but would like to ask it for a specialist like you. My question is that if you use only flashmeter (eg Sekonic 358 incident / 758 incident and spot reflective) to figure out fill flash (not TTL but manual mode) in the situation where the object is placed in bright sun (TTL BL situation, where the sun is behind the object), what strategy would you take?

If you can give me some thoughts, I would appreciate.

Frank said...

Hello Russ,

you answered at June 39, 2008 "TTL-BL is not available for wireless CLS".
For me all your explanations on this topic makes sense, I can follow your arguments.

But my result of the experiment with TTL / TTL-BL with sb900 in remote mode point that it is more ttl bl than TTL. (Maybe I made a mistake)
At an german nikon forum we have had the same discussion resulting in an formal request to the Nikon Europe Support.

The answer is: in Matrix Mode it is always TTL-BL if the flash is remote used. (here the link to the request and answer http://www.nikon-fotografie.de/vbulletin/1495021-post33.html)

Now I'm confused.

Russ MacDonald said...

Hi Frank,

To answer this question you have to understand how TTL-BL works.

First, in TTL-BL mode the flash metering system makes two metering measurements: 1) it measures the ambient across the whole frame with the standard meter in the camera. This is why the camera must be in either Matrix or Center Weighted metering mode. If it were in Spot metering mode, it wouldn't be able to measure the whole frame. This is why Spot metering disables TTL-BL mode. 2) The monitor preflash and distance are used to determine the normal flash power as if the mode were TTL.

Second, the flash computer compares the two metered measurements and subtracts the brightness of the ambient from the brightness of the flash. In other words, the flash computer reduces the power of the flash according to how bright the ambient is.

Now, if you understand this, you can immediately see that the flash and the camera must be at the same location or this scheme won't work. The measurement that the camera makes must be oriented in the same direction as the flash and at the same distance or the flash power will not be calculated correctly. This means that the flash cannot possibly be in TTL-BL mode when in Remote mode, because it wouldn't work properly.

Nikon makes a related comment about this when using the SC-29 flash cable (which will allow you to use TTL-BL). Nikon says that in order for TTL-BL to work properly when using a flash cable, you must make sure the flash and camera are pointed in the same direction and that the flash is at the same distance from the subject as the camera.

The reason that Nikon allows TTL-BL when using a flash cable is that photographers want to be able to shoot fill flash when using a flash bracket, and since a flash bracket does meet the requirements for TTL-BL, they allow it.

So, there is no way that TTL-BL could function properly when the flash is in Remote mode.

Now, you can prove this very easily. Take a person out in bright sunlight and take three identical shots using a tripod: 1) flash on camera in Regular TTL, 2) Flash on-camera in TTL-BL mode, and 3) flash off camera in Remote mode at same distance and pointed at subject. Use Matrix metering and 0 ev flash and camera compensation for all three shots.

You will see that the one with the flash in Remote will be similar to the regular TTL with the flash on-camera. You will also see that in bright ambient Regular TTL will almost always cause the subject to be overexposed and possibly 'blown out'.

Hope that helps,

Russ

Samuel said...

Hi Russ

Thanks for a great guide.

1. Why does TTL-BL uses focal distance information for its flash power calculation? It could assume the subject is centered (as regular TTL assumes), and match the flash power reflected at the center of frame to the matrix ambient light.

2. Why does regular TTL not use distance information? After all, it may lead to better flash exposures indoors (low ambient conditions) when subject is off-centered.

3. What happens when using TTL-BL on a non-D lens?

Thanks,
Samuel

Russ MacDonald said...

Hi Samuel,

The key is the amount of ambient light that is available.

TTL-BL mode is normally used for adding fill flash in bright ambient conditions (ie, outdoors in daylight). Both the monitor preflash and distance are used, but distance is primary when the ambient is bright, because the monitor preflash doesn't work as well in bright ambient.

If the ambient light is lower, and you are still using TTL-BL, the system senses this, and the monitor preflash is given a higher priority. If it is completely dark, the system switches almost entirely to the monitor preflash. However, in completely dark conditions, the system no longer tries to balance the flash to the ambient, so it works more like regular TTL.

If you are using TTL-BL with a non-D lens, then the system is forced to rely entirely on the monitor preflash which is not as reliable for setting a proper balance in bright ambient conditions as the distance method.

Regular TTL is normally used in low ambient conditions, so it does not use distance, because the monitor preflash works best in low ambient conditions.

Hope this is clear,

Russ

Samuel said...

Thanks Russ,

I clearly understand now why TTL-BL uses focal distance info - the preflash reading is less reliable in bright ambient light.

However, regarding regular TTL used in low ambient (where monitor pre-flash reading is reliable), I still don't understand why the implementors CHOSE NOT to include distance info in the calculation - as it seems beneficial:
It would result in better flash output when subject is off-centered; so the photographer won't be forced to use FV-Lock in such conditions.

Thanks
Samuel

Russ MacDonald said...

Hi Samuel,

An early system that Nikon tried was D-TTL which relied only on distance. However, it did not work that well and was abandoned in favor of the monitor flash system that regular TTL uses today. I'm not sure why it didn't work well, but it didn't. Msybe it was due to the fact that it didn't work with non-D lenses.

Russ MacDonald said...

Hi Samuel,

I was reading your question closer, and wanted to more directly address it.

The reason the designers did not want to include distance as well as preflash in regular TTL is that it wouldn't work too well.

Think about the situation where you are focused on the background, but you have a person in the foreground. How would such a system decide whether to use the distance or the monitor preflash to determine the flash power?

I'm sure there is some way to define it, but regular TTL is supposed to be simple and basic. All photographers know how to use regular TTL in its traditional form.

TTL-BL is where all the fancy decision making takes place. In fact TTL-BL works so well on the newest crop of cameras and flashes that it is the default standard. Regular TTL still works better in medium ambient conditions (parties, receptions, weddings, etc.), but someday TTL-BL may be able to equal it.

Of course the key to successful flash with regular TTL requires total understanding of how it works. One of the key things is that regular TTL does not take the ambient into consideration, so you have to increase shutter speed to eliminate the ambient.

Russ

Samuel said...

Hi Russ,

Reading your answer and giving it some more thought, I think the winning argument is "TTL is supposed to be simple and basic".

TTL-BL MUST use distance info, as solely counting on the monitor pre-flash readings was probably found to be problematic (due to inaccurate readings in bright ambient).

However this has nothing to do with the TTL design which is kept "basic and simple".

Again, many many thanks for a great guide - a wonderful resource which I keep visiting once in a while.

Maurizio said...

Thank you very much. I'am Italian and live in Trieste. I have a D90 with SB900. Yours explications open a new world and it's more easy understand the different flash use. i always read your post. (sorry for my english). Good bye.

Russ MacDonald said...

Hi criticpapa,

Thanks for the kind feedback!

Russ

Russ MacDonald said...

Hi Maurizio,

I'm glad you find my articles helpful.

Russ

Honk said...

Hello Russ,

you've heard this at least a thousand times, but once more: Your blog is the best information about all tech. specs and background to Nikon flash/CLS system! McNally is like Jamie Oliver for photography, Chris Orwig the philosopher and you are the first who explain all the background, the fundamentals.

After all these words, one question for understanding:
In chapter 3 of your blog, you say at April 5, 2011, 1:04PM as reply to "Thomas Munch" (he asked why TTL-BL result to a good pic, even when the background is completely dark and there is nothing to fill):
"In the specific case you mentioned; ie, completely dark, latest generation TTL-BL works quite well. When the metering detects a completely dark edge around the frame, it assumes that the ambient is zero, so it switches to a pseudo-Regular TTL mode and selects a flash brightness to make the flash primary based mostly on the distance."

In chapter 4 you write:
"TTL-BL is for fill flash ONLY, like outdoors in bright ambient light. TTL-BL is not designed for use as primary light.
(...)
If you use TTL-BL in low ambient conditions, you will get unpredictable results, usually underexposed. Using FV Lock in this situation would only make things worse."

I think I don't understand the difference between the two statements deeply.
I mean, why I can't or shouldn't use TTL-BL in dark conditions.
Like explained in chapter 3, I would leave the flash in TTL-BL (as in former times and the results are quite OK) due to the "pseudo TTL-mode" which the flash will choose. But with the info from chapter 4 I get confused :-)

But maybe the second sentence ("unpredictable results") is for older cams like my D200, due to newer ones use a more sophisticated TTL-BL measurement?

Servus,
Honk

Russ MacDonald said...

Hi Honk,

Yes, the whole issue of when to use TTL-BL is confusing. I wrote my blog #4 based on my D200, and at that time TTL-BL gave truely horrible results if used in low ambient conditions. However, as time has passed, TTL-BL has been improved.

In each new camera, TTL-BL comes closer and closer to a general purpose mode. However, even in the newest of cameras, TTL-BL is not as consistant as regular TTL, when you want the flash to be primary. TTL-BL still underexposes quite often under those conditions.

The original purpose of TTL-BL was to balance the flash with the ambient, and that is what it still does best. Balancing the flash with the ambient is just another way of saying that you are adding fill, which is most often done outdoors in daylight. That is when TTL-BL really works great.

Thanks for the nice feedback, and I will try to find some time to work on blogs 3 and 4 to clarify this issue.

Russ

Honk said...

Hello Russ,

thank you very much for fast reply.
The last days I'm reading (and testing/writing down in my scrapbook) a lot and I'm sorry to have another question about influence of light-meter adjustments to TTL-BL:

On "Sep. 29, 2008 8:00 AM" you wrote in the part "SEMI-AUTOMATIC", (pic should be: model in front of a bright sky), 'use M, TTL-BL, aim at the sky and underexpose one stop' (I think you mean via light-meter).

On Apr. 2, 2009 6:49 AM, you wrote:
"So, if you have the camera in Manual, and you are not setting it per the light meter, then the flash will be balancing to the wrong thing."

What I understand till now:
When I adjust the meter to 0, the TTL-BL will work "as expected" (like in P, A ..).
When I adjust the meter to minus or plus, the TTL-BL will try to balance foreground and background, so the foreground (the subject) will getting darker, when I put a minus correction to the meter.

My question (also referring to Nov. 30, 2008 3:15 PM): When e.g. a minus 'correction' to the meter will influence the TTL-BL to decrease the power (like -ev in the cam will do), is't it better to use TTL instead of TTL-BL due to unpredictable results? When TTL-BL will be adjusted automatically to the manual light-meter adjustment, I always have to correct TTL-BL (+ or -). In TTL not (except of the influence of ambient light).

But, could this be the answer: Maybe standard TTL is not a good choice, because it doesn't know anything about the ambient(-influence), so TTL-BL is "safer" (less risk for overexposing the subject).

And allow me one technically question for better understanding: You wrote that TTL-BL assumes in M the light-meter is zeroed. It has no info about aperture nor shutter. What kind of info is send to the flash computer with "light-meter zero"? The whole ambient EV, say "overall brightness is xy ev?

Greetings,
Honk

Anonymous said...

Hi Russ!

Thanks to this blog I learned to understand Nikon's flash reasoning and how to improve my photography as a result. The problem I am now having occurs as a result of upgrading my camera from a D80 to the new D7000 and I also upgraded my flash from a SB600 to an SB700. I still kept my D80 and SB600 as I still want to use them.

There are some issues however.
1. The SB700 is not compatible with older cameras such as the D80 in CLS off camera mode.
2. The FV compensation on the SB700 is not the same as the compensation on the SB600. TTL-BL is my favourite mode and I often set it to -1.7ev for fill flash. This setting is 1.0 stop to bright with my D80 and 11/3 stops brighter on my D7000. No matter if you are in aperture mode or manual, the SB700 flash seems to bias the exposure of both the ambient and the flash. I find myself having to use a fill flash setting of -2.7 to -3.00 for my Sb700 to be equivalent to my former -1.7 ev.
3.The new SB700 defaults to TTL-BL and cannot be changed to straight TTL as unless you switch to spot metering. The new SB700 therefore automatically switches from TTL-BL to TTL as it sees fit according to some new algorithm but never lets you know what mode it is in as TTL-BL is continually displayed.
Soooo...Do you have any info which explains what is going on with this obvious change in the method of calculating exposure for the new flashes.
Hope you understand my gibberish here and thanks for keeping such a great resource for us amateurs

Russ MacDonald said...

Hi Honk,

'use M, TTL-BL, aim at the sky and underexpose one stop' means to use the light meter inside the camera and adjust the aperture and/or shutter to underexpose by one stop.

When you do this, the effective flash power does NOT change. The flash assumes the camera light meter is zeroed. This means that the sky will darken a bit while allowing the subject to remain at the same brightness.

I say 'effective' flash power, because as you change the aperture the flash power changes to keep the subject exposed at the same level. Changing the shutter does not affect the flash power in any respect.

The reason you have to darken the sky this is that the camera tends to overexpose the sky in Matrix metering in an attempt to bring out the subject which is always much darker than the sky. By underexposing the sky, it ends up at about the correct brightness. However, this should only be considered a starting point. In different situations, you might need up to two stops underexposed to get the image that looks most natural.

The important point to understand is that if you are in camera manual mode and you change the shutter or aperture, the meter in the camera will change, but the effective flash power remains exactly the same.

However, if you change the camera ev it will cause the effective flash power to change by the same amount as the camera.

Then, if you change the ev on the flash, only the flash power will change.

Russ

Russ MacDonald said...

To anonymous (wish you would sign your name):

I don't have an SB-700 to try, but as far as I know, it is fully compatible with the D80, both on and off camera. You have a commander buit-in to your D80 that will fire your SB-700 and your SB-600 exactly the same way. You just have to put them in 'Remote' mode. They both use the same CLS system. Where did you get the idea that the SB-700 is not compatible with the D80?

Also the FV on the SB-700 is exactly them same as the FV on the SB-600. They both change the effective flash power by one stop. That means they are the same.

The reason that there is no selector on the SB-700 to change it from TTL to TTL-BL, is for simplification. When you are in Matrix or center weighted metering mode, TTL-BL is automatically selected. When you are in Spot metering mode, regular TTL is selected. The SB-600 works exactly the same way if you set it to TTL-BL to start with while in Spot metering mode.

So, the way you use this is that when you want the flash to be the primary light source (ie, low ambient conditions), you select Spot metering. When you want the flash to add fill, you select Matrix metering.

However, as I have mentioned, Nikon has improved the TTL-BL mode in the newer cameras to the point that it comes close to being a universal mode. The D80 still has some of the older system, so it won't work as well in TTL-BL as a newer camera when in low ambient conditions. If you want the best pictures possible, switch the camera to spot mode and manual whenever in low ambient conditions.

Russ

Honk said...

Hi Russ,

I'm almost completely with you:

Does the sentence "as you change the aperture the flash power changes to KEEP the subject exposed at the SAME LEVEL" say:

a) ligth-meter is shifted from zero to, let's say, -2 f-stops = flash-power will automatically shift the same way (-2 f-stops to *balance fore-/background*: Subject may be underexposed)

b) ligth-meter is shifted from zero to -2 f-stops = flash-power will counterbalance the changed aperture and background is darker but subject is lighted as with light meter in zero position/"as before" (= "effective" power on the subject is always the same {same=as in light meter zero position})

When (b) is correct (I tested yesterday and I assume), isn't the following conclusion an antagonism to the conclusion above?

"So, if you have the camera in Manual, and you are not setting {comment by Honk: to zero? Or is Cam ev-correction meant?} it per the light meter, then the flash will be balancing to the wrong thing." -> I think, TTL-BL will always assume the meter is zeroed or rather in/decrease the power? So "balancing to the wrong think" is my stumbling block.

PS: TTL-BL is like law code. Every tiny word from your blog has to be analyzed or the chance getting wrong is big.

Servus,
Honk

Russ MacDonald said...

Hi again Honk,

My comment about the flash power changing as the aperture changes is common to all TTL. It has no special significance to TTL-BL. In other words, what ever power the flash decides it needs to light the subject at its chosen value must change if all you do is change the aperture. If you close down the aperture, the TTL or TTL-BL flash will increase flash power to attain the same amount of lighting on the subject.

The flash power has nothing to do with the light meter indicator in the camera. The light meter indicator has no connection to the flash. The light meter indicator measures only the ambient light and that will also change as you change the aperture (and the shutter).

It can be confusing when you change the aperture. Assume you stop it down two stops. That will decrease the ambient contribution to the image by two stops but the flash will increase power to apply the same flash contribution to THE SUBJECT. Now, if the subject was receiving some ambient to start with, and the ambient decreased by two stops, that will make the subject darker as well as the background. The flash will still add exactly the same amount of light, but the end result will be that the subject becomes darker.

The only exposure control on the camera that affects both the flash and the exposure is the camera EV button.

TTL-BL doesn't not receive information from the camera meter indicator. It receives information from the meter measurement circuit inside the camera prior to the point where it goes to the meter. Changes to the aperture and shutter affect the meter indicator but they do not affect the flash power. Changes to the EV affect the meter measurement circuit and therefore affect both the flash and the meter indicator (which in turn affect the aperture and shutter to make the meter center).

Maybe that is clearer.

Russ

Honk said...

Hi Russ,

bow! Absolutely perfect.
The difference between light-meter and meter measurement circuit and it's impact to the flash was (for me) not clear (enough) till now.

PS: Some wish a book. But this blog is far better due to the direct response from a flash guru to questions. Incredible blog.

Regards,
Honk

Russ MacDonald said...

Hi Honk,

I'm glad it's clear now!

Thanks for the nice feedback!

Russ

mel said...
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mel said...

Sorry I thought the system was broken

mel said...

Hi Russ,
I have been practising your methods since the day I discovered your website with success and joy.
Thx again for these great explanations about the flash photography and making such a complex topic easier and fun.
I have learned a lot from your blogs and continue learning...

Some (not every) of my flash photos lack sharpness which I have just realized and I wanted to get your opinion about the possible reasons for that.

below is the exif data of a flash photo which I found it soft although it had to be very sharp with the settings below...

nikon d7000
on a tripod
vr off
35mm nikkor lens

f9
1/250s
programmed auto
matrix metering
iso 100
af-s
wide area

sb600
i-ttl-bl
front curtain
-0.3ev

april
17:19 pm
sunny and bright weather
sun is behind the camera

the only possible reason that I can think of is:
I set the camera to self timer mode and set it to 8 photos with a 2 second delay.
(But I am pretty sure that the flash triggered on each 8 photos)
and I can say 5 or 6 of the 8 are not sharp enough.

can this lack of sharpness be bec of this self timer settings or not?
I really wonder what causes this?

thx, take care
Melih Cavli

missumlaut said...

Thank you for making your expertise available.
If you ever make a synthetic documentation about Nikon Flash system, that would definitively be a great hit, and more practical to read than blog entries and comments... (And yes, I will preorder one for me, and volunteer to create a french translation, too).
But if your are aware of such a booklet existing already that summarise it all, that would be nice, too.
Thank you for sharing your knowledge.