Nikon CLS camera Auto ISO behavior with flash

Nikon iTTL DSLR have used three methods of camera Auto ISO behavior with flash:

1. All those camera models in the D70 to D300 era (2004 to 2009), all left Auto ISO at Minimum value if any TTL flash was present (because we were using flash after all). These would only increase ISO if the TTL flash metered as insufficient power for the situation (Commander did not even do that, but on-camera TTL flash would).

2. But then the D300S (2009) until ... (not sure which was the last one, but up until about D800 time, 2012) ... got the notion to always set Auto ISO very high for the indoor ambient, regardless of any TTL flash. Indoor flash always saw very high ISO, even though flash was being used.

3. And the D800 and D600 (and possibly others since 2012?) changed Auto ISO with flash again. The internal flash remained the previous way (flash presence does not affect high ISO indoors), but a speedlight on the hot shoe now will only allow Minimum ISO to increase two stops (like from ISO 100 to 400, but no higher, if hot shoe flash is present. 400 is about right for bounce flash).

The camera manuals never mention this aspect.

This is about TTL flash... a flash in manual flash mode will always leave Auto ISO at Minimum, unchanged.
And is about hot shoe speedlights, the internal flash since 2009 probably leaves Auto ISO near Maximum indoors.


One problem in discussing Auto ISO, we don't know which models do what. We know D800 and D600. D7100 being the new method seems reasonable, but that is pure speculation. The time change was about the D3100, D3200, D5100, D5200, D7000, D7100 models, and I think we simply do not know which does what?

I would invite those with these recent camera models (and a hot shoe TTL speedlight) to do this most simple test, and post results here, in this thread (camera and speedlight model, and result).

Method:

Set Auto ISO, with a Minimum and Maximum ISO.

Put the speedlight on the hot shoe, TTL mode, but leave its power off at first.

Aim camera at anything not bright indoors (but not hard either, maybe f/4), half press shutter, and see the ISO in the viewfinder. Indoors, we would expect a fairly high ISO value, probably near maximum.

Reach up and turn on the flash (TTL mode), and then half press shutter again.

On the same scene (very carefully the same, to not introduce other variables), did the viewfinder ISO change, or is it still the same high value? Same high value would be the previous Auto ISO method.

If it changed, to what? Is the new value two stops higher than Minimum? For example, it was ISO 1600, but now it is 400, which is two stops above 100 Minimum. This would be the newest Auto ISO method.

My guess, based only on introduction dates, is that the D3200, D5200, D7100, may be the new way, like the D800 and D600.
And the D3100, D5100, D7000 probably are the previous way (maximum ISO not affected by hot shoe flash).
But we really do not know this dividing line.

We know the TTL internal flash (since 2009) will leave ISO high when its door is opened.
And we know if the flash (internal or hot shoe) is in Manual flash mode, ISO will stay at Minimum (when flash is enabled). Auto ISO cannot possibly work with manual flash mode.

So, this is about a hot shoe TTL flash.

Thanks for posting your camera model and results.

I have 2 of the cameras that you are looking for these numbers from.
Will try it after work & post what i see

Got a chance to try this.
Quite interesting-

On the D5100, with 18-55mm lens
set max ISO to 6400, min shutter speed to 1/40s
Shot at f/4, Aperture Mode, Auto ISO.
With Flash OFF - ISO was 3200
With Flash on TTL - ISO was 400

On the D7000, with 35mm lens
set max ISO to 6400, min shutter speed to 1/40s
Shot at f/4, Aperture Mode, Auto ISO.
With Flash OFF - ISO was 2500
With Flash on TTL - ISO was 400

WhiteLight said:

Got a chance to try this.
Quite interesting-

On the D5100, with 18-55mm lens
set max ISO to 6400, min shutter speed to 1/40s
Shot at f/4, Aperture Mode, Auto ISO.
With Flash OFF - ISO was 3200
With Flash on TTL - ISO was 400

On the D7000, with 35mm lens
set max ISO to 6400, min shutter speed to 1/40s
Shot at f/4, Aperture Mode, Auto ISO.
With Flash OFF - ISO was 2500
With Flash on TTL - ISO was 400

Click to expand...

Thanks, that is a real surprise to me. D5100 dates to April 2011, and D7000 to Sept 2010, both relatively older than the current models. But your results show they are of the current class of Auto ISO behavior.

1. Old CLS DSLR (D300, D90, etc): Your flash ISO would have remained at minimum, ISO 200 in those days for almost all.

2. Intermediate date models (starting with D300S, July 2009) Flash ISO would have remained at the high value metered with no flash, regardless of flash.

3. Current models (D800, D600, D7100). Flash ISO would increase only two stops, to ISO 400. And ISO 400 is about right for bounce flash.


Clearly your two are the latter current version, which obviously goes back farther than I was aware. I guess that may be reasonable, we heard many complaints about indoor ISO being absurdly high when we were using flash, but I guess no one complains when it was fixed.

Thanks much.


FWIW... different subject, but "Minimum Shutter Speed" in the Auto ISO menu is NOT a minimum shutter speed, not exactly. It is the threshold shutter speed that must be reached before Auto ISO will be increased. Then it does hang at that minimum, (insuring it will use that specified shutter speed, so to speak), but when Auto ISO hits its Maximum, then shutter speed must go lower, as necessary for the exposure.