So, what are the A and AA modes are on the SB800?
Well, first, there are actually three non-TTL modes that use this technology: 1) A mode flash in hot shoe, 2) AA Mode, flash in hot shoe, 3) Commander AA Mode, wireless flash in Remote Mode.
These are all 'automatic' modes on the flash that do not use TTL (Through The Lens) technology. Instead, these modes use a small clear window in the flash itself to determine when the reflected light from the subject is correct. Take a look at your SB800 from the front. You will see the small round clear window on the lower left side pointed straight forward.
A Mode, Flash in Hot Shoe:
The A Mode with the flash in the hot shoe is the oldest and simplest technology used for non-TTL automatic flash control. I first used an 'Automatic' Vivitar flash in the early 70's, and it worked extremely well. This technology still works extremely well today in the SB800.
The SB800 flash defaults to AA mode, which I will discuss in a moment, so to put the SB800 flash in A mode you have to go into the menu on the flash and choose A mode. Press ON/OFF to exit leaving the flash in A mode.
The concept of the A Mode is very simple. The main flash pulse fires (turns ON) when the shutter is pushed, and there is a thyrister circuit inside the flash that measures the reflected light from the the subject through the little clear window. The flash pulse stays ON until that reflected light accumulates to a certain amount, and then the circuit turns the flash OFF.
Of course the flash needs additional information about the camera settings in order to work. In the older Automatic flashes, you had to enter the ISO and f/ stop manually into the flash. With the SB800 in A Mode, the ISO is picked up automatically from the camera through the hot shoe, but you still have to enter the f/ stop manually using the rocker switch on the back of the flash.
Then you simply aim and shoot. The flash takes care of the exposure automatically.
One very nice thing about the A Mode on the SB800 is that there is no preflash pulse sequence to cause people or especially animals to blink.
NOTE: If you want to observe the preflash pulse sequence separately from the main flash pulse, simply put your camera in flash Rear Sync, and set a long shutter, say 1.6 sec, and push the shutter. The preflash sequence will occur at the instant the shutter is pushed, and the main flash pulse will occur at the end of the shutter sequence right before the curtain closes. This is handy for verifying what I am explaining about no preflash pulses when using A Mode.
AA Mode, Flash in Hot Shoe:
The AA Mode is the default mode for the 'Automatic' non-TTL flash modes. If your flash is sitting in the hot shoe, and you cycle through all the modes, you will see AA in the list unless you have changed it to A.
The AA mode is similar to A mode except for two things: 1) the flash automatically picks up both the aperture and the ISO that you have set on the camera, so AA mode is really fully automatic, and 2) a preflash pulse sequence is used.
To use AA mode, simply select it on the flash, point and shoot. The flash measures the amount of reflected energy from the Preflash through the small clear thyrister window. In this mode the flash does not used the main pulse to set the power.
The preflash is also used by the camera in AA mode to calculate the white balance.
Another useful byproduct of the fact that the AA flash uses a preflash is that you can use the Flash Value Lock (FV Lock) function. This helps with the fast blinkers when taking group shots.
In addition, there is another way use AA mode that eliminates the preflash sequence. You simply put the flash in SU-4 Mode, while in the hot shoe, and when AA mode is selected, it works by measuring the main flash through the thryrister window just like the A mode does.
Commander AA Mode, Flash in Remote:
The third 'automatic' flash mode is the Wireless AA Mode. The flash is set to Remote Mode and placed separate from the camera with the small round red IR window facing the commander. Then AA Mode is selected on the Commander menu on the camera. In this mode, the Commander sends a preflash pulse to the flash telling it to use its internal AA mode followed by the command to fire the main pulse. The remote flash also fires a preflash pulse which is used for setting its own power via the thyrister 'eye' as previously discussed.
So, When would you use these modes?
Flash A mode or SU-4 AA mode are useful when shooting pets. These modes eliminate the problem of pets who can close their eyes so quickly that they are closed by the time the main flash fires. The alternatve is to use TTL mode and FV Lock. I use both techniques. Some animals are greatly bothered by the flash, so I use A or SU-4 AA mode just to reduce the flashes the animal has to put up with.
It turns out that Flash A and SU-4 AA modes measure the reflected energy quite evenly across the frame, so it is useful for group shots as well.
Flash A and SU-4 AA modes do a very good job of setting the flash to the correct power most of the time, but these modes still suffer from the same problems as TTL, ie the flash power is set too high when the subject is black (or dark colored) and too low when the subject is white (or light colored).
One 'gotcha' to remember for both AA and A mode, especially if you use them in an umbrella, is that you must always turn the body so the thyrister 'Eye' is pointed at the subject.
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28 comments:
Once again, you gave us more insight to the SB-800 flash gun; great article, Russ! Thumbs up!
Russ, thank you very, very much for your work and for the very helpful blog!
I am using the SB900 together with the D300. (I own also a D200 and a SB800/SB600). Concerning the AA/A modes: The SB900 has 4 different A modes:
1) AA - with Pre Flashes
2) AA - without pre Flashes
3) A - with Pre Flashes
4) A - without pre Flashes
The reason why there are Pre Flashes used - in my understanding - is, because this enables the SB800/SB900 to use all the CLS features (color temperature for Auto WB, FP, AF light, Flash Value Lock and AWL)
I think this is the answer why the pre flashes are needed. (see discussion with @Bob Walters)
One thing I realized is, that the AA mode works very well [robust] in almost all conditions. Also in the AWL environment the AA mode works INDEPENDENT and is not influenced by the TTL mode. The technology ist 40 years old!
Russ, please help, is TTL for the cats or for the horses? (an Austrian proverb). Do you think, that there is a serious situation (except the pre flashes of course), where the AA mode works much better than the TTL mode?
Thank you again,
gottfried (Austria, Salzburg)
Hi gottfried,
Where can I find the discussion about preflashes with Bob Walters? I searched Nikonians, but I didn't find it.
I can see how preflashes might help with Auto WB, but I can't see any way preflashes could affect FP, AF light, Flash Value Lock, or AWL.
In addition, FV Lock has no meaning when using A or AA modes.
I can't think of any time when AA would be better than TTL. However, I have been told by some of my fellow wedding shooters that they use AA when shooting the bride in her white dress, because they think it meters her better than TTL, but I can't confirm this, since I have not studied it.
Russ
Hi Russ,
thank you for your answer!
I have asked you, because Nikon has implemented 4 different A/AA modes in the SB900.
I thought, maybe there is a very important reason for this.
But your answer is very clear and it makes sense for me!
thank you
gottfried
just for info:
You can find the discussion under this topic 'SB800 A and AA modes', (on September 8, 2008), you answerd Bob:
"So, if a preflash is needed for AA mode, why is not needed for the A mode?"
and in the SB900 manual, Nikon always say: In AA/A mode you can only use FV-Lock and FP when you turn on preflashes.
Hi again gottfried,
I don't own an SB-900, but I have a copy of the manual, and I see the statements about preflash in Auto Aperture mode.
It is possible that my SB800 also works the same way and it simply was not documented. I will investigate and try to find out.
Thank you for bringing that statement to my attention. That may be the missing information from the SB800 manual that I was trying to figure out related to preflashes and the AA/A modes.
Once I understand and verify this, I will explain it more clearly in my blog.
Thanks,
Russ
about preflash in AA mode,you said it youself without making the connection to why.In A mode the sensor in flash is used,ie the flash works on its own,in AA mode the camera sensor is used hence preflash is required.
To Anonymous,
I did not say that the camera sensor was used in AA mode to set the flash power. In fact, I said the small sensor in the flash is used to set flash power in all A and AA modes.
I have received several comments that suggest that the preflash pulse is used for the camera to measure white balance on the subject, and possibly to allow FV Lock to work. I plan to try to devise some sort of tests to confirm this.
Although I don't own an SB-900, comments in its manual explain more details about this.
Russ
Hi Russ,
I'm not the other anonymous with the SB900,I only own the SB80DX.
Just to clear things up a little I'll elaborate.In A mode the flash sets power level itself with onboard sensor in real time like you said ,ie mirror up,shutter opens,flash fires,onboard sensor measures light output then flash turns off,shutter closes,mirror downs,but in AA mode the camera controls everything.Digital cameras' TTL is done with preflash because image sensors don't reflect light like film so metering is done beforehand instead of real time like the good old days(light sensor in camera is relocated from below mirror in film days to above mirror in digital cameras).
Hope that helps
To anonymous with 80DX:
I'm sorry, but I think you are a bit confused.
AA Mode is NOT TTL. In AA mode, the camera does not contribute to the flash power calculations. The power is set internally in the flash just like in A mode, using the small clear window in the front of the flash. In fact, AA mode works exactly like A mode, except that the f/ stop is sent to the flash so that you don't have to enter it manually on the back of the flash like you do in A mode.
This explains why the preflash sequence that is sent to the flash is longer than in A mode, because the f/ stop is being sent, but it still deosn't explain why the remote flash also sends out its own preflash sequence. That's what the mystery is about.
In TTL mode the preflash pulses are used to determine the flash power, and that calculation is done in the camera and sent to the flash.
Russ
@Russ, I have read all your blog entries over the last two days and I want to thank you for your time and effort you put into this blog so that we can benefit from your knowledge. Like all the others I have read manuals (SB800, D700, including the additional docs from Nikon about the SB800/600 examples) and various other information but I still couldn't figure out why some of my photos didn't come out like I wanted. I have learned a lot in the last two days. BTW, the combination D700/SB800 seems to over-expose pictures with "red" subjects a lot. I shot some pictures (in a hurry) of a couple (he in black suit and she in a red dress) and guess what, the faces were blown out...
@anonymous (the one with the SB80DX): you can easily test yourself that the flash is doing the whole metering in AA mode. Set up your camera and flash in remote mode accordingly. Then take the flash into your hand and shoot. For the second shot you make sure you cover the sensor on the flash unit (the small clear window Russ was talking about) with one of your fingers. You will see that the second picture is extremely over-exposed because the flash is trying it's best to light up the scene but cannot "read" the light which is reflected.
Bernhard
Bernhard,
Thanks for the nice feedback!
Black is the worst color for flash. The flash tries to brighten anything that is black to be gray. This greatly increases flash power and causes faces to blow out.
Red is the second worst color for this same problem. In fact, whenever I am shooting an event and I come across a redhead or a person with reddish skin, I always dial down the flash one whole stop (-1 ev) from where I have been shooting.
Then, if I come across someone with red hair and reddish skin in black clothing, I dial the flash down to about -1.7 to -2.0 ev.
One person dressed in black and another in red will also cause the flash to fire about 2 stops too high, easily blowing out faces.
I have noticed that in addition to increasing flash power, Nikon cameras are more sensitive to reds, and that also adds to the problem of overexposure.
And, since this blog is primarilly about A & AA mode, I will point out that this flash power problem exists when using A and AA modes exactly the same as when using TTL modes.
I have learned to notice these color combinations as I am shooting and automatically reach for the Flash Exposure Compensation to fix them.
Thanks again for your comments.
Russ
Hi guys! Sorry English is not first my language. I hope you are understand my post:)
Thank you very much for this really useful blog. I find answer on many of my questions in work with CLS and TTL flash. Maybe I have one question how TTL work when flash direct to back of object, or on background, or when you shoot big object, when you use a few flash, not all of which direct on center of object. In this situation I think TTL work unpredictable, more accuracy in this situation use А/AA mode, when flash to measure own light.
I think about reason of preflash. I see a few reasons and write all my ideas, even those I consider incorrect, maybe it suggest you to correct answer:)
1. Construction reason. Flash need to correct impulse power regard to aperture value. Maybe while preflash happen, flash to measure impulse for 1 f/stop, and only after recalculate impulse power for given f/stop.
But in su-4 mode flash work without preflash, maybe it’s incorrect idea.
2. White balance, I'm sure what flash don't change color while change power of impulse (flash change power of impulse by impulse length). It's main reason of my friends pro photographers which use impulse light, instead halogen unit. They can change light power, without changing color balance and position of units. But SB800, SB900 can use colored filters, maybe it's important for camera, and camera need preflash to determine color of flash, to correct determine of WB.
3. In wireless mode, all group flashes one by one. Maybe preflash use like signal for next group, what they can make preflash, if it will in TTL mode, for example. But I don't know how work group in “off(--)” mode and M mode. Maybe group use time separate method for preflashes.
4.1 All new Nikon flashes can fire without waiting of full charge. Maybe preflash need to guaranty of enough of power for selected F/stop.
4.2 Flash have signal about not enough charge. How flash determine out of power, in preflash stage, or every times then it fire on full power. Maybe preflash need for determinate what power not enough?
5. FV Lock. You are use FV lock for reframing, but it's should work with change of shooting objects too. Then you press FV Lock, flash must make the same impulse regardless of changing of main object. So they make preflash, and remember flash power, and use this power value again and again for next shoot.
I make test, when flash in SU-4 mode and AA, we can't use FV Lock, maybe because flash don't make preflash.
:)So… When I write this big post, and on another language for me, I think I find answer:)
Main reason of preflash:
1. FV Lock function
2. Auto WB for working with Color filters.
I hope somebody can decode (understand) what I write:))) And sorry for this hard work:)))
Thank you again for really useful information about Flash working, and practice example. Bye Bye!
Hi Russ,
A Mode.
When I turn on the camera I can't get the sb-800 into the A mode. I can set it to A mode when the camera is off but as soon as I turn on the camera it changes back to AA or some other mode.
Also:
>You simply put the flash in SU-4 Mode
How can I change the flash to this mode?
Do you cover the RPT mode somewhere?
thanks again for your awesome site.
Hi Golikov,
I am having trouble understanding your comments, but I will try to answer.
I'm not sure I know what you mean by "impulse power". The word "impulse" is not normally used in flash system engineering. In engineering mathemetics, "impulse" means an infinitely short pulse of infinite power used to exciting a network and measuring its response. I think you are talking about the main flash pulse.
I think your numbered comments are your speculation about why there is a preflash pulse in AA mode.
Then, I think at the end of your comments you have concluded that you know the reason for the preflash in AA mode: FV Lock function and Auto WB.
You may be right! If I get some time, I'll see if I can devise an experiment to prove it.
Thanks,
Russ
Hi Abe,
You have to go into the menu on the SB-800 for chosing these modes.
There is a choice in the menu for whether you want A or AA mode to appear on the list of modes that appear during use.
There is another menu choice for SU-4 mode.
No, I haven't ever found any practical uses for RPT Flash, so I haven't written about it.
Russ
Great blog!
Set the camera to rear curtain mode at 2 seconds . Block the sensor in front of the flash and then take your hand away and see how strong it fires - it's using the built in sensor to read its preflash which I imagine gives it more control over its final output rather than cutting the flash off as it happens .
Hi Desmond,
I will try that and report in my blog the results.
Thanks,
Russ
Hi, Russ. Thank you for great work!
Have you ever heard about Better Beamer(BB)? This is a flash extender for use with telephoto lenses of 300mm or longer mainly for wildlife shooting. It's recommended to set flash head at 50mm when using it. It seems that AA mode is very useful with BB - with SU-4 it doesn't give preflashes that could scare off a bird or a pet. How do you think what mode is better for BB (AA or TTL)?
And another question: what does "SU-4" stand for? I couldn't find clear information about it in the instruction manual for SB-800.
To Anonymous,
Yes, I've used the Better Beamer. It works very well if you can keep it secured to the flash. Also, be careful not to let direct sunlight fall on it while attached to the flash. It will act like a magnifying glass and melt the flash.
I think I used A mode to eliminate the preflashes when I used the BB. At that time, I hadn't yet discovered that SU-4 AA mode also eliminates the preflashes, and today, I would use that mode, so I wouldn't have to manually set the aperture on the flash.
About the term SU-4. The name comes from a special device called the SU-4 Wireless TTL Flash Controller that you can actually still buy: http://www.nikonusa.com/Find-Your-Nikon/Product/Flashes/3070/SU-4-Wireless-Remote-TTL-Flash-Controller.html
Of course the TTL in its title is film TTL, so when used with our digital cameras TTL cannot be used.
The Nikon abbreviations don't make a lot of common sense. The S stands for Speedlight, but the U is simply the next letter they decided to use. The 4 is because it is the fourth such controller. The newest one is the SU-800 that will control all CLS flashes in iTTL mode.
The SU-4 mode in our speedlights makes them into simple slaves that fire when they see any other flash fire.
Russ
I just found your guide and am blown away by what is here. I, also, am an engineer and like to understand how it all works so that I, in turn, can make it work for me... instead of following rules of thumb from others.
Anyway, I have a question for you that relates to the thyristor A mode... as it applies to the leaders through the years (probably Nikon, Metz and maybe Vivitar).
The question is this. What is the pattern of measure for the thyristor... in contrast to the TTL center weighted and the Matrix broad spread?
Thanks in advance.
Jim
Hi Jim,
Thanks for the great feedback!
The coverage pattern for the thyristor is not contolled. It basically measures all the light that is reflected back through the small clear lens, and that comes from the entire scene. It is somewhat effectively center weighted, due to the fact that the center part of the scene is usually closer (since subjects are usually placed on the focus plane which is farther away at the edges of the frame. Also, light reflects more efficiently from directly in front of the flash (no angle of incidence).
Regards,
Russ
Hi Russ
Thanks for the quick reply.
Does that mean that the area measured, as a percentage of the captured image, doesn't change much with the change in lens focal length?
Also, does it mean the there really isn't a need for the FV function when using the A mode?
Thanks again
Jim
Hi again Jim,
When you zoom the lens to its tele end, the flash zooms, too, and its beam becomes narrower. This means that whereever the flash is concentrated will have the most effect on the Thyrister Eye.
So, no matter whether you zoom wide or long, the flash beam will follow, and the flash power will still be spread fairly evenly across the frame, with a slight center weighting due to incidence angle.
I also wanted to mention a bit of new information that I have learned since I wrote my blog.
I now understand the reason for the preflashes in AA mode. It is the preflash that is measured by the thyristor eye when in AA mode on the SB-800. This is indicated by the double lightning bolt on the display on the back of the flash. The main flash is not measured in this case.
I will update my blog to incorporate this information.
Regards,
Russ
Hi Russ,
Quick question, in A mode, how do you adjust flash power? It seems like the flash figures out the power automatically. I can think of changing flash ISO to different value from camera ISO to fake it out. But is there a better way?
Thanks,
John
Hi John,
These comments are for the SB-800:
In flash A mode you have to enter the f/ stop manually with the rocker switch on the back of the flash. Normally you set that to be the same as the camera, but if you want to adjust flash power up or down, you set a different f/ stop on the flash.
For instance, if you have f/5.6 set on your camera and flash, and the pictures dark, you can increase the flash power by one stop by setting f/8 on the flash.
Note: in AA mode, you have the normal flash compensation adjustment using the rocker switch on the back of the flash.
Hope that helps,
Russ
Hi again, Russ, as I continue my journey through your blog. You explained possible reasons for using A mode or SU-4 AA mode in the main body. What's a reason for using wireless AA mode? I am having trouble imagining a situation where I would prefer that over iTTL remote. (I have used SU-4 in remote M mode when I needed 3 groups and had to use the pop-up on my D300 as the commander but that's a whole different thing). I just don't see what remote AA gets me. Your thoughts?
Hi Richard,
You have posed a good question.
I think that wireless TTL is far superior in every way to wireless AA mode.
The only use for wireless AA mode that I can see is for non-TTL cameras. I have an old Minolta film camera that would probably work just fine with the SB-800s in wireless AA mode.
Russ
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