Exposure Inconsistancies with High Frame Rates with D5, D6

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Warren D

Warren D

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This was brought up some time ago with respect to the 800mm lens and the D6 with a drop in FPS. I'm starting this as a broader look because I think it's a wider target than first thought.
This past weekend I found myself shooting old aircraft flying for the first time this year due to COVID closures. I was using the D6 and 500 PF. When I was looking at the shot sequences I noticed that after 6-9 shots the images got brighter by 1/2 to 1 stop while the exif data didn't change. That sent me looking into what might be going on.
First, my settings were: D6, manual exposure, 1/250 sec, f11, auto ISO with base at 100. 500PF: VR on sport. Previously, it was alleged that VR was the culprit for reduced frame rate, which I did experience several times, but I was also in sport mode which should not have caused that problem.

Yesterday, I set to testing various combinations of bodies and lenses. I used my D6, D5 and D850 with the 500PF, 200-500 and 70-200 EFL. I chose the 200-500 so I could use it wide open at f5.6 like the 500PF but also because it is a non-E lens. I used the 70-200 EFL as it is an E lens. All bodies were set the same, as the D6 was during the initial problem with the exception that I also did sequences with the apertures @ f5.6. All lenses were set the same and tests were done using VR in sport mode only as well as vr off. Bodies were all set for their max FPS, D6:14, D5:12 and D850: 9 (gripped).

I find the results both interesting and concerning. Both the D5 and D6 showed the same exposure increase several frames into each burst @ f11 but only with the E lenses. With VR on the E lenses turned off there was a minor shift in exposure @ f11 but nothing I would call troublesome. I did not see an exposure shift with the 200-500 with VR either on or off @ f11. When lenses were set to f5.6, there was no exposure shift seen in any of those tested.
The D850 did not exhibit any exposure shift @ f11 nor f5.6 with or without VR on any lens tested.

My preliminary conclusion is that with VR on in sport mode, variations of exposure may occur when using E series lenses stopped down at higher frame rates. I have further testing to do over time. I'll try backing off the frame rates on the D5, D6 as well as testing a couple of other E and non-E lenses I have. I also want to get better control of a few variables that might have had a slight influence yesterday. I don't see those as drastically affecting the outcome but you never know. The big surprize was that in all of yesterday's tests I never saw the drop in FPS that was the catalyst for this! YMMV.......
 
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Not logical, we got the electronic aperture for consistency and speed.
As I was told the old mechanical aperture would possibly get inconsistent at high speed.
According to your results the E-aperture closes to slow after a number of shots in a burst on high speed.

Don’t get me wrong but I think flying aircraft is not the best subject for this kind of testing and I wouldn’t use Auto-ISO neither for this kind of testing.
Interesting anyhow and I will test this myself too. (Allthough I selden/never shoot @F/11)
I suggest to conduct the tests with a static well-lit subject and the camera with fixed ISO in A-mode to rule out differences caused by metering.
Will let you know my findings.

Btw the drop in FPS with the 800mm stopped down is an issue but I’m still not sure what’s causing it as I’m still waiting for an answer from NPS.
The 180-400 was caused by the ‘wrong’ choice for normal VR in stead of Sport mode (as stated by Nikon, sometimes it helps to RTFM LOL)
 
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I already have plans to test in full manual, same settings but without auto ISO. The tests were not with the airplanes but on a static subject. I noticed the problem when shooting the old airplanes. I'm trying to think of as many variables as I can and eliminate as many as possible. I shot at f11 to keep my shutter speeds at 1/250 to keep from freezing the props. In reality i don't usually shoot action at any aperture other than wide open, I was just too lazy to use a CPOL as I usually do in this situation.
 
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That is really odd. I seldom stop down that far for my work, so I've not come across it, but I may take a look tomorrow. Also, note that the 200-500 is an "E" lens as well.

It really does sound like the cameras aren't getting the F/stop to drop fast enough, but I do agree with going full manual and eliminating that variable.
 
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Yesterday was the first day I had clear skies, so I attempted to repeat the previous tests with the intention of adding total manual exposure to the criteria. First test was to replicate the original issue. I'm at a loss to explain, but I was not able to replicate the original issue with the D6 and 500 pf. I tried a clear blue sky (consistent lighting) as well as the same shot I used for the previous test, a branch sticking out into an otherwise blank sky. While I did note a couple of minor variations in the histogram, they were well within acceptable error. There was more light yesterday than when I saw the issues so don't know if that is a factor.
I'm not sure why I saw what I did. I thought the first test was supportive of the initial issue but it appears there may be more going on or maybe nothing but some circumstancial perfect storm. As I rarely shoot action at f11, going forward I'll make a mental note to avoid situations that require it. I think auto ISO may have a role even though yesterday's tests didn't point to it. I'll be doing some more tests over time to see if I can first replicate the problem and if so, then proceed to narrow it down.
 
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Warren D said:
Yesterday was the first day I had clear skies, so I attempted to repeat the previous tests with the intention of adding total manual exposure to the criteria. First test was to replicate the original issue. I'm at a loss to explain, but I was not able to replicate the original issue with the D6 and 500 pf. I tried a clear blue sky (consistent lighting) as well as the same shot I used for the previous test, a branch sticking out into an otherwise blank sky. While I did note a couple of minor variations in the histogram, they were well within acceptable error. There was more light yesterday than when I saw the issues so don't know if that is a factor.
I'm not sure why I saw what I did. I thought the first test was supportive of the initial issue but it appears there may be more going on or maybe nothing but some circumstancial perfect storm. As I rarely shoot action at f11, going forward I'll make a mental note to avoid situations that require it. I think auto ISO may have a role even though yesterday's tests didn't point to it. I'll be doing some more tests over time to see if I can first replicate the problem and if so, then proceed to narrow it down.
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It wound't be Auto ISO in particular, just how the camera was metering. I'd bet it would have done the same thing on the first test with normal ISO and aperture priority. Auto ISO has nothing to do with metering (I need to make a video about this), so I think what you may have experienced the first time was a variation in the camera's interpretation of the scene by the meter.
 
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Steve said:
It wound't be Auto ISO in particular, just how the camera was metering. I'd bet it would have done the same thing on the first test with normal ISO and aperture priority. Auto ISO has nothing to do with metering (I need to make a video about this), so I think what you may have experienced the first time was a variation in the camera's interpretation of the scene by the meter.
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Yes, that is the correct interpretation. It's the metering of the scene that drives the ISO changes. The only variable in my original settings was ISO which I chose because I needed a given shutter speed above all else. In the past I have used Shutter priority and kept the ISO fixed, letting the aperture move for this type of shooting but I'll blame it on the migraine; I was already set up for my usual BIF settings so I got lazy and rolled the shutter speed down and the aperture up. A burst I shot of a redtail hawk flying by did fine. I'd also normally shoot full manual at that location but the day called for some automation due to the variable cloud cover/density and the aforementioned headache.
 
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A cloudy day overhere today, meaning not much variance in available light.

D6 plus 180-400
Distance camera to subject 12 meters
ISO100, Aperture F/4, VR Sport on, rig on monopod.
Burst 20 images (restricted in camera)
Matrixmetering no variance
Centerweighted average a very slight variance (that little I’m not really sure)
Spotmetering same result, MAYBE a bit more variance but again it’s that slight it’s only noticeable when you’re very hard looking.

Then same ‘story’, only difference F/11 and ISO800
Same results.

Same test with the D5 plus 800mm at F/5.6 and F/11 same results

I did also run the test from a tripod and ballhead with the 180-400 and VR off
No difference!

Note that the inconsistencies were never an increasing ‘overexposure’ like you witnessed Warren.
The so-called inconsistencies I experienced were explained by me as ‘user error’ due to little movement.
 
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