wrong exposure when pressing shutter-release half way and recomposing

[thrillmetoo]

I'm using a D7200, but this issue may also concern other models. Let me explain the situation:
Auto ISO is on (max value 1600), camera is in Aperture prio. Also, in custom setting c1, shutter-release button AE-L is set to off.
When taking a picture of a somewhat dark subject, shutter speed and ISO is automatically set by the camera and this works fine.
When first focusing on another, much lighter subject, pressing the shutter-release half way and then recompose to the same subject in the first shot, the shutter speed is changed correctly by the camera, but the ISO stays at the value measured at the focusing subject. The picture of the subject is now underexposed.
In live view, this issue is not present and the ISO changes accordingly when changing to the subject.
This works the same way the other way around (a light subject, but focus locked first on a darker subject)
Is someone familiar with this behavior? And more importantly, is there someone who knows the solution?

I'm a regular reader of this very informative forum and never started a new topic because I could always find an answer. Until now that is...

[Erik Lund]

To lock the exposure and re-frame you need the function called AE-L Exposure-Lock, can be set up together with AF and custom buttons depending on camera.

[David H. Hartman]

I'm probably not grasping the question but I'll make a fool of myself (as I am want to do) and suggest that if I used a D7200 I'd set the AE-L/AF-L button to be my AF-ON button and I'd use the Function Button on the front, the button below the Preview Button to be my AE-L button. Why would I use the Function Button for AE-L? Well going way back to the Nikon FE2 and maybe the Nikon EL-2 pressing the self time lever towards the lens locked the exposure when in Aperture Preferred mode, a very old habit.

Dave Who is trying to be helpful though he is probably clueless. 

AE-L means Exposure Lock: press and hold to lock the exposure and recompose.
AF-L means Auto Focus Lock: press and hold to lock the focus.

These days I use the F1, Function Button on my D850 for a FV Lock (Flash Value Lock).

----

I'm wondering about the half press meter activation, auto ISO, AE-L and shutter release all in one control, that being the shutter release button. On my cameras the shutter release only activates the meter and releases the shutter and I only use release priority. If the camera is out of focus when it takes a photo that's my fault. It seems to me too much is controlled by the shutter release button.

[Matthew Currie]

Check custom setting C1, "shutter button AEL."  (e.t.a. it's C1 on both D7100 and D7200)

Because these cameras lack a separate AF-On button, if you activate back button focusing to use the AEL/AFL button, you lose AEL unless this option is activated.  Because I use BBF, I have this set to "on" so I can separate all functions.  In a complex situation, you can use spot metering, focus first on one thing, let go of the button and set exposure on another, then, keeping the shutter button half-compressed, recompose and shoot.  I got used to this on a D3200, which lacks assignable function buttons, though I don't often use spot metering.  David Hartman's solution of assigning AE to a function button would also work, but I prefer putting it on the shutter button to minimize the number of buttons I have to locate in a hurry.  Either read, hold, move and shoot, or just move and shoot.

But if you don't use BBF, the shutter button AEL can be, as you notice, a nuisance, since you cannot hold focus to recompose without also holding AE.

[David H. Hartman]

But if you don't use BBF, the shutter button AEL can be, as you notice, a nuisance, since you cannot hold focus to recompose without also holding AE.

On my D800 I designated the AE-L/AF-L button as my FV Lock. FV Lock is dear to my heart as a former PR events shooter. I probably designated the F1 (function button) as my AE-L. I would release the AF-ON button to lock the focus.

At first the use of all these buttons is a bit fiddly. In a short period of use it all becomes reflex and you don't think about any of it. The fingers know what to do and they just do it.

Dave

The thing I like about the FV Lock is the flash fires and people think you've take a photograph. At first they pose with a say cheese smile. The flash goes off and they smile naturally and you take your actual shot. Then you can follow up with a second and third shot. You press the FV Lock to release the lock and move to the next group of subjects.

All typographical error are expressly intended. 

[Matthew Currie]

Unfortunately the D7100 and 7200 don't have enough spare buttons to do everything one might like.  If you back button focus, there are only two other assignable buttons.  My current two are DOF preview on Fn, and virtual horizon on Pv.  I would happily be rid of that latter, but cranial nerve damage results in too many tilted verticals.  I don't often use flash for portraits, but if I did, I'd likely put Fv in its place.  It's a neat feature.

[David H. Hartman]

I would loose the virtual horizon. I understand the issue as I have to straiten most photographs I shoot hand held.

Dave

[Bent Hjarbo]

I have not been able to recreate the problem on my D500.
Could be a software error, have you the latest update installed?

[Matthew Currie]

I would like to lose the horizon, as I do all right on horizontals, but on verticals I tend to tilt rather consistently by about 5 degrees, which is enough to induce more crop on fixing than  I can sometimes afford, and knowing that this occurs it also slows me way down when shooting, since I am trying to figure out how to avoid the tilt.  The artificial horizon fixes both these issues fairly well, and when I turn it off I find myself wanting it back.

[thrillmetoo]

Thank you all for replying so quickly and excuse me for waiting too long for my answer.
All your answers make sense. But I don't use back button focus and I have the latest firmware. I use the Fn button for the artificial horizon and the preview button to toggle the grid.
The problem is, with AEL off on the shutter button (c1 in the custom setting menu), I expect the exposure including the auto ISO to change according to the scene, even when engaging the shutter button half way. I don't want the exposure to lock. I want the shutter button to only lock the focus.

[Matthew Currie]

I just tried this on both a D7100 and a D7200, and with C1 set to "off" and shutter button focusing, it does indeed change the exposure as expected, when you recompose. 

I did not check whether auto ISO is included here, but remember that auto ISO follows in A,S and P modes only when other priorities run out.  It should be the first thing to change in M, but the last in others.  If your D7200 is not doing what it should, I would double check the metering mode (it may not occur right, or be visible, in auto area mode, but I don't know not having tried it), check that the menu option was OK'ed correctly, and recheck exposure value.  If you expose at a bright window and pan into a dark room, for example, the change is pretty clear.

If it still, after all this is not doing what it should, I'd wonder if there's something wrong with it.  Both the samples I tried worked correctly and quite obviously so.

e.t.a.  I did also try it just now with auto ISO in manual mode.  It also works correctly there on the D7100.

Don't forget that this is one of the settings you can set in U modes, so if you shift into a U mode, your current C1 setting will not be carried over to it, and the C1 setting will not be carried back.

[thrillmetoo]

I could narrow the issue down a bit. All works well with focus on AF-C (continuous focus) and measuring on matrix. All other settings the issue remains, that is, auto-ISO doesn't follow.
I use U1 for stills and highest possible picture quality (with amongst other things AF-S as focus and auto-ISO max. 1600 ISO) and U2 for moving subjects and challenging light (AF-C and auto-ISO max. 6400 ISO).
If you use AF-C and/or spot or center-weighted metering, you would not have experienced the issue.
I appreciate the effort you took to help me find the solution.

[Matthew Currie]

I just tried it on the D7100 in every combination I could think of.  AFS and AFC with shutter or focus priority both, A mode, and M mode with Auto ISO. Spot and matrix metering both.  I cannot duplicate your problem.  In A mode the exposure always visibly changes, and in Auto ISO, the ISO changes, though one must review to see what it is.

All I can suggest at this point is that you make very sure that all the settings you think are set are actually set in both normal and U modes, and that something has not accidentally been overlooked.  Among other things, don't forget to check that the ISO max in each mode has not somehow been lowered, and that you do this test with a starting ISO lower than your max. 

If you manually set ISO higher than the minimum when using Auto ISO, it will not go lower than your setting. So if your max is set to, say, 1600, and you set it at 1600, it will shoot at that speed alone and will not float. 

Some models (the D3200 is one) will also not allow you to override the max setting manually, so if you have set your Max to, say, 800, and try to take a shot with a setting of 3200, it will stay at 800 without telling you.  The D7100 does allow you to override, so if, for example, you have set your Max to 800 and manually set 1000, it will shoot at 1000, but since you're out of the Auto range, it will not float.

Of course there's always the possibility that something has gone amiss with your camera but I suspect that somewhere in there is a setting that escaped notice.

[Matthew Currie]

thrillmetoo, it occurs to me that since I have a D7100, and can borrow my wife's D7200 as long as I promise to restore all the settings, I think it would be worthwhile to do a  comparison here, and get a final answer on whether there is a setting gone off, or a camera malfunction.  No point in going on and on if it turns out the camera has a glitch in the firmware or something.

I suggest the following.  You put your camera in whatever situation it is under which it consistently misbehaves, and then post back to me the following information (as well as anything else you can think of)

1:  The AF mode and area setting (e.g. S and single);

2:  The settings for that setting's priority (custom A1 and A2) should not be relevant but who knows?

3:  The manual ISO at which you begin;

4:  The high ISO limit set (shooting menu "ISO sensitivity);

5:  The Auto ISO shutter speed set. (as above);

6:  The exposure mode you're using (A,S,P,or M) ---remember that in picture modes Auto ISO works completely differently;

7:  The metering mode being used;

8:  Whether shutter button or back button focus is used - remember on D7200 this is two settings, A4 and F4.

While you're at it please note what firmware version you're using, and consider doing a reset of the camera. The version on this D7200 is C1.04 and L 2.018 (though that latter should not matter).

Also do remember that when in Auto ISO it does not always show just what ISO has been chosen.  On the D7100, at least,  it notes that Auto ISO is set in the lower right corner, and when it changes, it flashes.  I presume you are looking for it to flash when you recompose.

And please forgive if you are already very experienced and know all this stuff.  It's hard sometimes to tell what people do and don't know, and I'd rather sound like a fool talking down than miss something.

Those are the only variables I can think of off the top of my head.  If you think of any more, add them.  Tell me what you're using and I'll duplicate it here, and can tell you if the problem occurs here or not.

[thrillmetoo]

Your help is very much appreciated.
To keep things manageable, I'll keep my reply according to your last reply.
1. AF mode S, area single point;
2. custom a1: AF-C prio release, AF-S focus;
3. manual ISO: 200;
4. ISO limit 1600;
5. auto ISO speed setting: auto;
6. exposure mode: A;
7. matrix;
8. AF activation: Shutter/AF-on, back button is AE lock only;

firmware version: C 1.04 and L 2.009. The last one is different from yours, but as you stated, most likely not relevant.
After locking focus on a bright subject and recomposing, a blinking auto ISO will tell auto ISO is working. But it is also confirmed afterwards in the picture details.
I am a long time Nikon analog and digital shooter and (I think) I know most of this stuff, but that doesn't mean I can't make mistakes. Nothing you said so far made you sound foolish. And of course I went through all possible causes I could think of before posting in this forum. So if anything comes out of this, the fool will most likely proof to be me. But I don't care; I rather learn what I want to know and look foolish, than touting my knowledge and be wrong.
So if you would be so kind as to try this at your end I would be grateful.
Focus on something bright, lock focus by pushing the shutter button half way, turn to a dark subject to force auto ISO to engage. In my case, shutter speed drops but auto ISO doesn't blink and checking the picture after exposure the ISO is 200 (the default ISO).
I don't think it will change anything, but I'll update my firmware anyway.

Edit: Updated the firmware. Didn't change anything.