A poll about Auto ISO action with hot shoe TTL flash

[WayneF]

This is like a poll. I would appreciate your doing this simple little test, and letting me know your Auto ISO result with flash for your Nikon DSLR camera model... either with response here or via PM. Just two quickie pictures, then look at ISO. I don't need to see any pictures.

This can only use a hot shoe flash in TTL mode... NOT the internal flash, and NOT a manual flash.

With Auto ISO on, a Minimum ISO 100 or 200, and Maximum like ISO 2000 or 3200 would be great.
And Normal camera settings, just something like f/4 in camera A mode. Exact values not critical.

Take a quick snapshot of any regular indoor picture (regular room lighting, but not bright, fairly dim), without flash (with hot shoe TTL flash turned off ... no flash). Of anything, a chair or wall or something, the picture itself is of no importance, it should just be high ISO (in room not too bright).

Then reach up and turn TTL flash on and take the same picture.

Then the actual ISO used can be seen on the camera rear LCD in the data (see note about seeing ISO below at bottom).

High ISO is expected in the first picture without flash. The goal is a not too bright place so it will be a high ISO.

Then for the second picture with TTL flash, Nikon DSLR are in three groups (groups are a name I made up) about what the Auto ISO with hot shoe TTL flash will do.

• Group A - ISO with flash will remain at Minimum ISO. Auto ISO will not increase if hot shoe TTL flash is present.
• Group B - ISO with flash will be high with flash, about same high maximum ISO with or without flash.
• Group C - ISO with flash will increase only two stops... to 4x minimum ISO value, if with flash. For example Minimum ISO 100 will go only to ISO 400 if TTL hot shoe flash is present.

I'd really like to hear your model and results of this group. And if it is a correction, then more details would be great, about modes and settings and flash, just to be very clear.

This list is my notion of what will happen. I think the list is near correct, but I hope to verify several models in the list, via your test result, particularly near group divisions. Certainly any corrections are of extreme interest. Any help will be greatly appreciated. Nikon does not put this action in the specs, and they have changed it a couple of times, so I have guessed at a bit of it.


Nikon DSLR - Auto ISO action with TTL hot shoe flash indoors

Group A - ISO stays at Minimum ISO with hot shoe TTL flash.

D2H Jul 2003
D70 Feb 2004
D70S May 2005
D200 Nov 2005
D80 Aug 2006
D40 Nov 2006
D300 Jul 2007
D3 Jul 2007
D60 Jan 2008
D700 Jul 2008
D90 Aug 2008

Group B - ISO stays at high ISO for dim ambient with hot shoe TTL flash.

D5000 Apr 2009 ?
D300S Jul 2009
D3000 Jul 2009
D3S Oct 2009
D3100 Aug 2010 ?

EDIT: moved a few to Group C.

Group C - Auto ISO increases 2 stops (to 4x Minimum ISO), with hot shoe TTL flash

D7000 Sep 2010 * moved
D5100 Apr 2011 *
D3200 Apr 2012 *
D5200 Nov 2012 *
D4 Jan 2012
D800 Mar 2012
D600 Sep 2012
D7100 Feb 2013 *
D610 Oct 2013
D5300 Oct 2013 *
D3300 Jan 2014 *
D810 Jun 2014
D750 Sep 2014
D5500 Jan 2015 *
D810A Feb 2015
D7200 Apr 2015 *


If any question about seeing ISO: ISO is seen on rear LCD in playback. Show the previous picture, then the selector up/down arrows scroll though several data screens (camera manual shows them under Playback). A couple of these screens show data including ISO. Auto ISO value is probably Red. Here is what one of mine looks like, it shows camera A mode, ISO 3200. And f/4, etc. This was a picture of a closet door in a not very bright room, without flash. The goal is a high ISO without flash, and then to see ISO when TTL flash is turned on and used.

Thanks very much for your help.

FWIW, some ifs and buts about other cases.

The internal TTL flash is same ISO action for group A and B, but internal flash Auto ISO stays high in group C. Lower power needs it I suppose.

Manual flash can never increase ISO (assuming the camera can recognize it is present). Manual flash cannot react to Auto ISO changes.

Likewise, use of Commander in any model never increases ISO, TTL or Manual.

An off camera flash, or a flash brand that is not recognized present by the camera, will not prevent Auto ISO increases. Auto ISO must be turned off for manual flash.

Group A can increase ISO, but only at last instant if it deems the flash has insufficient power for the exposure. Like doomed bounce attempts at f/22 probably will increase ISO. So I suggest f/4 direct flash for this test.

And note that the single gray histogram shown on this screen is the B&W luminance histogram, which will not show clipping, so is totally useless in that regard. We should ONLY look at the three RGB histograms if concerning clipping (on a different screen here).

 

[Fat Fingers]

D7100 and D7200 should be in group C.
The other consideration is that some 3rd party guns assume an iso of 100 thus when used in group C need to be set at -2 stops...Meike for one.
I personally shoot base iso 200 which goes to 800 for the flash increasing battery life and reducing flash brightness in peoples eyes.

 

[Danno]

Wayne, I took the shot this morning...
D7200 with min ISO 100 and max 3200

Flash mounted but turned off ISO was 3200
Flash mounted but turned on ISO was 400

Seems the D7200 fits in group C

 

[JH Foto]

I am confused...:ambivalence:

 

[RocketCowboy]

I'll give this a try with both the D5300 and D7100. I ran into Auto ISO issues on the D5300 recently, so I'm curious to see if the two bodies perform differently.

 

[WayneF]

Thanks so much. So I edited to move a few from Group B to Group C, based your reports and on model introduction date. I think I had an earlier wrong report, which was my suspicion and concern, and is why I'm asking how it actually is.

Thanks, and please keep them coming.

 

[Blade Canyon]

One of my only complaints about the D600 was that auto-ISO with a TTL flash was terrible. It always picked an insanely high ISO, thus making the D600 Group B. You have it in Group C, which was not my experience. I will test again later today, plus I will test my D800.

 

[Blacktop]

I'll test the D7100 and the D750 later when I get home from work.

 

[Blade Canyon]

Okay, I tested both the D600 and D800, and both surprised me by increasing the base ISO a maximum of 2x as you predicted. So why did I think the D600 was so wonky in this regard? I took off the hot shoe TTL flash and did the same experiment with the TTL pop up flash, which easily could have illuminated the shot at ISO 200. Instead, with the pop-flash the auto-ISO choice was 4000!

 

[WayneF]

Okay, I tested both the D600 and D800, and both surprised me by increasing the base ISO a maximum of 2x as you predicted. So why did I think the D600 was so wonky in this regard? I took off the hot shoe TTL flash and did the same experiment with the TTL pop up flash, which easily could have illuminated the shot at ISO 200. Instead, with the pop-flash the auto-ISO choice was 4000!

Thanks. Yes, group C internal flash still acts like group B - Auto ISO stays high, based only on the ambient metering. And maybe the little internal flash does often need the ISO.

My own notion is that group A did it right. We are using flash after all. Then group B messed it up, maybe related to Nikons default TTL BL balanced flash concept. But the indoor incandescent lights are orange, and Nikon started pushing the CTO filters for flash to let it be possible. Then group C fixed it again. Two stops to ISO 400 is very reasonable for bounce flash.

 

[cwgrizz]

I think I finally got it figured out for the D7100.
Auto ISO Max 3200 and shutter Minimum 1/50
First shot: A priority f4.5, Shutter 1/50, ISO 3200 No Flash

Second shot: Hot Shoe mounted flash set on i-TTL, A priority f4.5, Shutter 1/60 (minimum set for flash), ISO 250 after initially setting to ISO100 to start.

If I just went to flash from the first shot and did not move the ISO back to 100 the Auto ISO went to 2000 from 3200.

Hope that helps. I will try the D5300 in a little bit.

 

[cwgrizz]

D5300

A Priority No Flash ISO3200

With flash Set ISO to minimum, jumped to ISO 400 for i-TTL flash

 

[WayneF]

D5300

A Priority No Flash ISO3200

With flash Set ISO to minimum, jumped to ISO 400 for i-TTL flash

Thanks Walt. I do think both the D7100 and D5300 are indicating as being in the recent group C (since 2012), with 4x Minimum ISO as a limit with TTL flash.

But you have pointed out that there is a little mystery, for two new reasons actually, and this would be my fault, because I failed to specify the problem well enough. You did your job, but I think my part may be a bit shabby. But in my defense, certainly the fact that the flash did not use ISO 3200 like group B does seems like stand alone evidence of Group C.

To me, your D5300 situation does not cause attention, it sounds just like it ought to be, as expected, in a normal routine situation.

If I just went to flash from the first shot and did not move the ISO back to 100 the Auto ISO went to 2000 from 3200.

I am a little afraid to ask, but I did not understand that part about the D7100. What was the Minimum ISO before? Hopefully ISO 500? (4x500 = 2000).


The D7100 only going to ISO 250 would mean TTL did not need more (like if at a close distance) if it didn't need to. Do you remember an approximate distance then? Without the flash, it needed ISO 3200, so the room was properly dim, but if the TTL flash was pretty close to subject, then it may only need ISO 250 at f/4.5. Which was surely right, and I can duplicate that situation here if at a close distance. That is Effect #1 we discovered. It uses only enough ISO that the TTL flash actually needs, less than 4x Minimum. I had seen that before, but did not stop to think (it is sort of wondrous actually). But that does not show that ISO 400 is a limit.

And so as yet, I don't know what a clear specific complete test situation would be. (arguing with myself here, sane readers could stop here ). I think that it did not use ISO 3200 with flash is pretty strong evidence of Group C, but close range could override. However, it does seem clear that if we said camera A mode and say f/22 to be impossible, then any normal distance would need more than ISO 400, so then it would be meaningful if it stopped at a ISO 400 limit (and the picture would be dark too). But it doesn't happen that way.

I've had my D800 nearly 4 years, and I know it does limit at ISO 400 with TTL flash, and in any normal situation, it certainly does, ISO 400 is all I ever see if Auto ISO is used. But just playing with it now with f/22 at 20 feet in a dark room, which would be impossible for the flash power and ISO 400 (and the picture would be dark at ISO 400), I see that the ISO will go even higher with TTL flash, to ISO 1000 in my test (20 feet at f/22), to deliver a halfway reasonable picture anyway (power was still insufficient). That is Effect #2 that we just discovered. The viewfinder shows ISO 400 then, but the data shows it used ISO 1000. The old group A did that too, and I didn't realize they still did that. I suppose #1 and #2 are actually the same thing in different situations.

So IMO, it sounds like it should still be worded that Group C cameras do stop Auto ISO at ISO 400 if with a TTL flash. But if does not need ISO 400, it may stop sooner, your 250, and I saw it too, by playing with a close distance. And there is a detail or two, but stopping at ISO 400 still leaves a wide range of TTL flash power to handle different situations. But also, when the situation does need more that ISO 400 can provide (meaning the flash power level capacity was insufficient for ISO 400), then it will use whatever ISO it needs, like ISO 1000.

So you just caused a need for a rewrite about Group C.

I'm not sure what a complete test situation should be, but it still seems fair to say that in most normal routine situations, Group C does stop advancing at ISO 400. Certainly it does not still go to ISO 3200 like Group B did. But there are additional ifs and buts about it too.

 

[Blacktop]

@WayneF.

D750. Flash off
ISO 3200 1/6th SS F/4

Flash on TTL

ISO 400 1/60th SS F4

D7100 Identical to D750.

Both cameras were shot with the same lens, set at Min 100 Iso-Max 3200 ISO in Aperture priority.

 

[WayneF]

@WayneF.

D750. Flash off
ISO 3200 1/6th SS F/4

Flash on TTL

ISO 400 1/60th SS F4

D7100 Identical to D750.

Both cameras were shot with the same lens, set at Min 100 Iso-Max 3200 ISO in Aperture priority.

Thanks much, I think the evidence about D7100 is in.

The D750 I didn't think was really in much doubt, but I appreciate knowing for sure.

 

[WayneF]

Thoughts on Auto ISO action with the current Group C camera models

These group C camera models will limit Auto ISO with TTL hot shoe flash to 2 stops maximum ISO increase, or to 4x Minimum ISO, presumably usually to ISO 400.

A fully powered speedlight (Nikon SB-800 or Yongnuo YN565 class) has 24mm guide numbers of about
Full power GN 98 x2 for ISO 400 is GN 196
1/128 power GN 8.5 x2 for ISO 400 is GN 17

So these TTL flash can operate over a seven stop range of power level, which at 24mm and this ISO 400 situation is from GN 17 to GN 196. Which describes very many common situations, and TTL at these extremes might range from f/16 at 1 foot (at 1/128 power to stop motion in water drop splashes), to f/2.8 at 70 feet (a ball game?). There are charts in the Nikon flash manuals describing these ranges. Longer zooms could approach up to 2x this 24mm GN, which both the water drops and the ball game would surely use.

But exceptions exist, due to limitations of maximum and minimum flash power level capability.
Suppose we try f/4 at 24mm at ISO 400 (and I did try it).
If at 6 feet, this is GN 24, and it uses the ISO 400, at very low power.
If at 3 feet, this is GN 12, which the flash at 24mm cannot do, even at 1/128 power. So it used ISO 200, out of necessity.

Suppose we try f/11 at 22 feet. This is GN 242 at ISO 400, but the flash at 24 mm can only do GN 196. So it used ISO 1400, out of necessity.

Both the Nikon and the Yongnuo flashes see this same action (deviating from ISO 400 when necessary). The camera controls TTL, but I am unaware how the camera determines maximum power capability of the specific flash. It must be part of CLS communication?

Top camera models also show the current Auto ISO value in the viewfinder right beside where it says Auto ISO. But in this situation (Group C TTL flash), it always continues to say ISO 400, even if conditions do switch it to ISO 200 or ISO 1400. It cannot meter and switch until the TTL preflash, so there is no time to affect the viewfinder. But the rear LCD result does show Auto ISO in red.

Group A cameras (TTL flash at Minimum ISO) also do this too, always have.

And Group B (TTL flash at high ISO) also must do it. I don't have a Group B camera, but obviously Group B cannot do much flash at ISO 3200. Because ISO 3200 GN is 5.67 times IS0 100 GN, or GN 98 x 5.67 = GN 555 at ISO 3200, therefore 10 feet would require f/55.5. This does not happen. I assume the same algorithm is used in all models.

So ISO 3200 is obviously reduced at last instant. Which then ISO also obviously affects the metered ambient exposure, underexposing it. However, it is lighted by flash, we might not notice much. So, there are unknown things happening, but my guess is in much less degree at ISO 400, with a more reasonable seven stop range.

 

[litrattonijuan]

I tried this experiment 2 times today using D7000 with SB700 as instructed.
A mode f4 base ISO 100 auto ISO 3200 max.
First shot as expected auto ISO 3200


2nd shot auto ISO become 400(4x the base ISO), should be in group C. Also take note that shutter speed with flash became 1/100

 

[WayneF]

I tried this experiment 2 times today using D7000 with SB700 as instructed.
A mode f4 base ISO 100 auto ISO 3200 max.
First shot as expected auto ISO 3200


2nd shot auto ISO become 400(4x the base ISO), should be in group C. Also take note that shutter speed with flash became 1/100

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.

 

[singlerosa_RIP]

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.

 

[Horoscope Fish]

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.

Count me confused as well...

What exactly is the advantage of using Auto-ISO when using flash?