A poll about Auto ISO action with hot shoe TTL flash

[WayneF]

I too am confused. Why would you want to use auto ISO with flash? As a manual shooter, maybe I'm missing out on something. I have used Auto ISO outdoors without flash when I'm shooting in varying light conditions, but when I'm shooting with flash, I want total control.

Uh Oh. Don't get my rant started.

I fully agree with you, and I never would consider using Auto ISO with flash. But the real world is, many do turn on Auto ISO, or use camera Auto mode which does, and don't know any other way, and they never get any clue about turning Auto ISO off. However, then they may ask questions about how Auto ISO works with flash, and it's hard to answer without knowing how their camera treats it. There have been three different Nikon plans about it, in the last several years.

Nikons original plan which I call Group A was sane, and it agrees with you and me. Then Auto ISO never advanced with TTL flash, it always used only Minimum ISO with TTL flash (up until the D300S model in 2009). If TTL flash was present, it treated Auto ISO as if it were Off (menu still said On, but it would not do anything).

Of course, all manual flash (then and now) absolutely cannot deal with Auto ISO changing, so this question is about TTL flash. All camera models always remain at Minimum ISO if a manual flash is detected present (but remote flashes are not detected). Auto ISO must be Off with manual flash (else we see surprises). Likewise, all models of the Commanders always force Minimum ISO.

Then about 2009, Nikon got the idea to allow Auto ISO to go high with TTL flash (my Group B). Actually, the camera meters for the ambient to set ISO, at whatever high ISO ambient needs. I think this change may have been related to the concept of balanced flash, TTL BL, which is the Nikon default, with the flash to become fill flash then. Of course, in bright sun, Auto ISO should stay at minimum. However, the system cannot use ISO 3200 with flash, which would blow the exposure to kingdom come (well, minimum 1/128 flash power at 24 mm might be ONLY Guide Number 48 at ISO 3200, which could be usable in some situations, not less than f/4.8 at 10 feet. But it leaves no range to deal with things.) But ISO is allowed to go pretty high (group B). So at the instant when TTL preflash is metered, ISO is lowered from the ambient value to be a usable flash value. But lowering ISO from the 3200 that the ambient metered and set the camera exposure for, to whatever lower ISO value the flash can deal with... underexposes the ambient. Which is probably good, because incandescent ambient that shows up is orange. And the flash does add illumination. Nikon started adding filter holders to the flashes then though, so we could correct it with CTO filters. Forcing fill flash seems to be the plan. It just gets crazy. Or of course, we could always turn Auto ISO off with flash if we knew to.

But a little of this was too much, it did not last long, and Nikon wised up again, and newer group C model only allows Auto ISO to advance two stops, to 4x Minimum ISO, if with TTL flash. And ISO 400 is quite reasonable with bounce flash, so this return to normalcy was a good thing. Speaking of hot shoe flash, but the Group C internal flash still does high ISO like group B.

The vast seven stop range of the TTL flash mostly only sees ISO 400 then. But if the distance is very short with TTL flash (2 or 3 feet) or a wide aperture, even ISO 400 may be too much, and when true, Auto ISO will be reduced below 400, as necessary. And if the reverse, when the flash power is insufficient, the Auto ISO will be raised above 400. These ISO changes will also surprise the ambient which metered for 400. It does seem prudent to turn Auto ISO OFF with flash, and actually plan for the surprises. But not everyone cares.

But people do ask questions about sometimes bizarre Auto ISO action, and my goal is to learn how each model works to help advise them. Nikon does not mention this Auto ISO action with TTL flash. There are just the three groups, so the concept is clear, but the exact model dividing lines are not fully known.

I was hoping the many users here, with many camera models, could help clarify this with the simple test. I'm not sure myself how to make the test parameters failsafe, but if seeing an ISO lower than expected, try again with like 12 feet distance, or f/11, or maybe both.

 

[litrattonijuan]

Thanks very much John. The D7000 is one I was very much interested in (near group division lines), and your data obviously shows (now) group C is correct, so it shows my assumption about it was wrong. The D800 is the one that caused so much commotion about this change (for the better), so I assumed it was first, but your data shows the D7000 (18 months earlier) had it first. I'm surprised it did not cause attention then?

Your screen shot suggests your subject distance was fairly close, maybe 3 or 4 feet? That could cause different results. Could I please ask that you repeat this, same thing, but at more like 10 feet, just to be certain? I would very much appreciate knowing for sure for the D7000.

The 1/100 second is your Auto ISO menu setting of Minimum Shutter Speed. It is the threshold where (in falling light), falling shutter speed stops and holds there, and instead, Auto ISO starts increasing. Your Auto ISO without flash was 1/60, which implies that 1/100 second was not sufficient even at ISO 6400 (without flash), so shutter speed had to continue its fall then. In that way, the 1/100 is not an absolute limit, but it is the shutter speed that will be used with Auto ISO, that is, when between minimum and maximum ISO. But if "AT" minimum or maximum ISO, those are limits, and shutter speed may have other values.

Hi Wayne,
I repeated the procedure as you suggest at a farther target distance of more than 10 feet and got the same results(iso 3200 w/o flash, and iso 400 with external flash att TTL). So it's consistent. I've also tried it with my D70s and you're correct, Group A. The iso did not change with external TTL flash, it remains at iso 200.

Then i tried D7000 with the internal flash and it showed the same iso of 3200, same as w/o flash, resulting in a somewhat wash out result. While with the D70s, iso remains at 200 with the internal flash.

Hope this will help

 

[WayneF]

Hi Wayne,
I repeated the procedure as you suggest at a farther target distance of more than 10 feet and got the same results(iso 3200 w/o flash, and iso 400 with external flash att TTL). So it's consistent. I've also tried it with my D70s and you're correct, Group A. The iso did not change with external TTL flash, it remains at iso 200.

Then i tried D7000 with the internal flash and it showed the same iso of 3200, same as w/o flash, resulting in a somewhat wash out result. While with the D70s, iso remains at 200 with the internal flash.

Hope this will help

Thank you John, I appreciate that very much. It makes it very clear, except that it makes my notions wrong. But clearly Group C must have been implemented in 2010, a couple of years earlier than I thought. The D800 got lots of attention in 2012, but it was the first I heard about the change.

Yes, the internal flash continues to use high ISO. And probably its lower power is helped by it.

D3100 Aug 2010 ?

D7000 Sep 2010
D5100 Apr 2011
D3200 Apr 2012
D5200 Nov 2012

So I assume now that all of these are Group C also (Auto ISO 400 maximum with hot shoe TTL flash).

I sure would like to hear reports about those too. Surely others here have those models.
​

 

[Fat Fingers]

When testing your camera you must do this in a reasonably dim room ....under bright condition the ISO will not go up 2 stops but stay at base and in very dark conditions will go higher than 2x. For indoor situations with room lighting you get the 2 stop rise. I use auto iso base 200-6400 in Aperture mode F8 all the time. Don't forget to set the flash to FP 1/320 or you will get in nasty trouble if you leave your flash on outside by mistake with the shutter locked at 1/60 .( ~FP means flash programme)

 

[WayneF]

When testing your camera you must do this in a reasonably dim room ....under bright condition the ISO will not go up 2 stops but stay at base and in very dark conditions will go higher than 2x. For indoor situations with room lighting you get the 2 stop rise. I use auto iso base 200-6400 in Aperture mode F8 all the time.

Yes, I have discovered the problem of describing a failsafe test situation to avoid too close, too far, etc. One concern is that not all flashes are the same power level.

Don't forget to set the flash to FP 1/320 or you will get in nasty trouble if you leave your flash on outside by mistake with the shutter locked at 1/60 .( ~FP means flash programme)

I always assumed FP here referred to Focal Plane shutter sync issues. Same name and purpose as the FP sync flash bulbs we used in the good old days. At least we thought it was fun then.

I didn't follow this part though. In camera modes A and P, the 1/60 second shutter we see indoors is the default Minimum Shutter Speed With Flash (E2 menu on some), seen in dim ambient, and this Minimum shutter speed is not likely to show up outdoors in sunlight (unless unusually high fstop or unusually low ISO, maybe). The only way to get a faster shutter with flash in A mode is to go out into brighter ambient. That higher shutter speed answer indoors is camera M mode. We can set the same aperture, and can set any usable shutter speed of our choice, and (again, speaking indoors in dim ambient), it will do anything camera A mode can do.

The FP 1/320 is not a shutter setting, instead it describes the threshold when, if the actual shutter speed is higher than this, the flash will shift into FP HSS mode. That does change the game, and gives shutter speed importance in the flash exposure.

FWIW, the nasty trouble that I know about is Auto FP in camera A mode in outdoor fill flash situations and settings when the shutter speed can vary slightly either side of this 1/320 threshold. Then one flash shot to the next of same thing can vary EXTREMELY.

So that is one plus of camera P mode. It will allow forced HSS, but its automation will first use the absolute highest possible f/stop before it will allow switching into automatic HSS action.

 

[voxmagna]

Rather than post a new thread, I'd like to ask a question here because I'm a little confused. I'm using a Speedlight Mk910 on the D750 hotshoe set for TTL mode. For daytime shots I've got autoISO set with my max limit and use aperture priority. I watch what ISO and shutter speed are doing as I set aperture. My problem comes with the hotshoe flash. I thought the camera would know it had a flash on in the shoe and keep my ISO to around 400? Worst case I try a test shot in semi darkness, the camera seem to think it is a daylight shot, winds the ISO to over 1000 and keeps it there when the flash fires. I check the EXIF and it has used ISO 1000. At the short distances I was testing in semi darkness, focus was held and the flash had plenty of light to get the shot at ISO 200.

Am I doing something wrong, or should I just turn off autoISO? That would be a shame because I've got used to using it now and I want to switch back and forth between outdoor and indoor shots with flash.

I've repeated my tests since posting and even tried manually forcing ISO low, but with autoISO enabled the D750 has its own mind. I think I'm resigned to turning off autoISO so I don't get flash pictures with noise. In the ideal world I'd like the D750 to recognize the shoe flash is powered on then auto adjust its ISO over a limited range say from ISO100 to ISO400. Any other ideas?

 

[Fat Fingers]

With a flash in the shoe it will go to 4x the base iso you have set ,,that's for what most would call normal use of flash ie interiors ..if its daylight..you forgot the turn the flash off ...it will stick to the base iso. If its very dark and 4x is not enough it will drift up the iso range .
for normal flash use it sticks to 4x 99% of the time

I have taken tens of thousands of photos with auto iso 200-6400 min 1/60 1/320 FP and a sb400 and never had a problem ..most are at iso 800

 

[voxmagna]

Thanks, I'm going to prove it for the shoe flash, but I thought there was always a pre-flash? Therefore shooting in a dark room should be o.k because the pre-flash should modify what the metering does before the flash(es) fire.

O.K I think I know where my problem is. The test is Aperture priority light room normal shots, then move into dark room, turn on flash. I have autoISO minimum set to 100 and max 3500 in the menu. In addition I use EasyISO to modify the ISO using the back command wheel. If I set the D750 minimum ISO100 in the menus, turn it on then frame a shot in the light room I get a daylight exposure at ISO100. Move to the dark room and ISO gets set to 400 4X, which is what I read.

However if I'm changing ISO on the fly in the light room, when I move to the dark room, flash off, the camera initially uses the last ISO setting up to the maximum set in the menu. Turn the flash on and it goes to 4X the last setting (which you forgot) hence being puzzled by seeing 2 different high ISO values. With flash turned on I then have to rotate the command wheel and watch the ISO update but it will never be less than ISO400.

I think when you use easyISO on the command wheel you are changing the base ISO and flash 'on' in the dark room will set to 4X that value. If I go in the dark room and rotate the command wheel down to ISO100 I then see the ISO400 setting for flash. If I want to use flash at ISO100 I have to turn off autoISO.

These cameras are too damn clever!

 

[WayneF]

My problem comes with the hotshoe flash. I thought the camera would know it had a flash on in the shoe and keep my ISO to around 400? Worst case I try a test shot in semi darkness, the camera seem to think it is a daylight shot, winds the ISO to over 1000 and keeps it there when the flash fires. I check the EXIF and it has used ISO 1000. At the short distances I was testing in semi darkness, focus was held and the flash had plenty of light to get the shot at ISO 200.

There are several ifs and buts about Auto ISO. Generally flash is best with the lowest usable ISO. Increasing the ambient with ISO to show the incandescent orange is not the best idea mixed with flash.

1. First, the Auto ISO being limited with flash to 4x Minimum ISO (or usually to ISO 400) applies only to relatively late model camera models.

Older iTTL cameras (D70 to D300 era) never increased Auto ISO above Minimum if flash was involved (because we were using flash instead). Seemed right. Point is, there is no one correct answer about how cameras use Auto ISO. Which camera?

Intermediate age iTTL (D300S and after, for awhile, not sure of this boundary, but before the D800) ALWAYS increased Auto ISO as much as necessary for the ambient, regardless if flash or not. Was a poor idea for flash.

Later models (roughly D800 and after) fixed that, and started the 4X Minimum ISO limit (often ISO 400) for a hot shoe flash. ISO 400 is often about right for bounce flash.

2. And 4x Minimum ISO applies only to hot shoe flash, the internal flash will still advance Auto ISO for the ambient level, regardless if the flash used or not. Because it is such a tiny flash I suppose.

3. And 4x Minimum ISO applies only to TTL flash mode. Auto ISO will never increase if a manual mode flash is detected. Because Manual flash cannot react to Auto ISO changing.

4. And Commander flash use never increases Auto ISO above Minimum.

5. But your issue: Any of them, newest models (and even including the older first models that "never advanced Auto ISO if with flash") would increase Auto ISO even more, as high as necessary if the preflash indicated the low ISO was going to be insufficient for the flash power available (for hot shoe flash, NOT with the Commander remotes). So in situations needing a lot of flash power, you can see more than 4x Minimum Auto ISO, simply because it is needed for the available flash power.

5b. But this "more than 4x Minimum" part seems untrue of 3rd party flashes like Yongnuo, I suspect because the camera has no knowledge of the available maximum flash power of unknown flash models. TTL measures a weak preflash, and then says "give me X EV more... It does not work with absolute flash power levels. Viewfinder may indicate the higher amount in advance, but Exif says 4x (or 400) then. Similarly, if NOT Auto ISO where ISO cannot increase, in insufficient power situations, the camera metering displays (on the flash LCD) how much more flash power was needed, on Nikon flash models, but not on 3rd party flash. I suppose 3rd party are not designed to display it?

As you imply, it is a good thing to watch and be aware, and to control ISO to be our own preference.

 

[voxmagna]

The camera is a D750 which puts it in the later model range. Yes, as I said it does follow the X4 ASA rule. My trap seems to be I use autoISO enabled for outdoors and change it with the command wheel, which I find useful in A priority. But when I move to much darker indoors the ISO setting may not be what I expect and I have to be really careful to check what it is doing and force it down to 400, unless I really need a much higher ISO setting. If I have previously set the low ISO limit to 100, switch the camera on in autoISO without changing ISO, then turn on the flash for a dark room shot, it does stay set at 400 which is o.k. It's almost as if the camera grabs the exposure for non-flash on a half shutter press setting a high ISO, then says, 'this is my low threshold' so I will X4 on that.

 

[WayneF]

There are details, not always obvious.

What you are calling Easy ISO is slightly conceptually different. It cannot only affect ISO, that would change exposure. What the wheels actually adjust is shutter speed or aperture, pretty much in the regular way, which then just causes Auto ISO to react with a different number. But the shutter speed or aperture was the change, requiring a different ISO. This is assuming the camera settings still have range to change. If they are at limits and cannot change, then Auto ISO will not change either. So it's also good to pay attention to shutter speed and aperture.

In the situation with flash when ISO goes above 4x Minimum (on these more recent camera models), if you can recreate the same situation (camera on a tripod ensures no surprises in how it is pointed after we make changes), then assuming camera Manual mode for fixed shutter speed and aperture, then if you force manual ISO 400 instead of the higher number, then you see that your TTL flash picture will be underexposed by the difference. TTL does always try to do automatic flash, regardless of camera settings, but it only has so much power available. The camera will try to limit Auto ISO to 4x Minimum with a hot shoe flash, but when necessary, ISO otherwise increases above 4x (400) to maintain the flash exposure with the maximum power it has available.

Camera mode A is actually similar to manual mode in this case (indoor flash), because we are setting aperture, which is then fixed, same as Manual. And indoors in A mode, the camera Minimum Shutter Speed With Flash is limited at 1/60 second (menu E2), so it is fixed, meaning we are not really concerned about ambient. The only difference in dim places where we need flash is that A mode fixes the shutter speed at 1/60 second, but M mode could use other desired shutter speeds. With Indoor flash, camera mode A normally just implies we are setting shutter speed to 1/60.

(Qualification: the Minimum Shutter Speed in the Auto ISO menu can be a factor too. It is allowed to go slower when ISO hits Maximum, but the E2 menu may enforce its own limit with in A or P modes. Generally both limits apply, but I think models may vary slightly).

(Qualification: Menu E2 allows this shutter limit to be set slower, and Slow Sync or Rear Curtain Sync will allow it to be the actual slow metered value of the dim indoor ambient. But the only way to get it faster in camera A mode is to go out into brighter light.)

In practice, it doesn't take us long to realize there is no magic in every indoor flash picture always being 1/60 second, and for flash indoors, camera M mode has strong advantages (same aperture setting, but it allows other shutter speeds).
The flash exposure does not care about shutter speed, but shutter does affect the ambient exposure. So in camera Manual mode indoors, we have additional control over the effect of ambient, to allow ambient in, or to keep it out. Incandescent ambient is typically orange.