I have a Nikon D7100. I fired off a burst of shots at 6 fps at a static outdoor scene, all shots using the same settings: 1/125 s, f/7.1, ISO 100. Some of the shots are clearly darker, some are clearly brighter. While variation is not extreme, it is also apparent in the histogram. Why did this happen? Does it indicate that something is failing?
The temperature was about -5 C and sunny. I don't think the camera actually cooled to below 0 C, but the only thing I can think of is that the cold made the aperture actuation unreliable.
I tried again later at home, 1/30 s, f/7.1, and all the exposures were identical this time.
Update: Here's a test I did with the exact same settings at room temperature: Dropbox link. Please click a thumbnail and use the left or right arrows to go through the pictures and observe the brightness variation.
Note: I know the exposure is not good on these but this was a test and I intentionally used the precise same settings: 1/125 s, f/7.1, ISO 100. EXIF data is left intact.
Note 2: I tried with a different lens, the other lens doesn't show the variation.
Request: At this point I am getting quite worried and I would appreciate it very much if someone could do the same test with the same lens. It is the Nikkor 12-24mm f/4G.
Update 2 I did more tests with the problem lens. All these tests are at room temperature:
- f/4 (max aperture) 1/125 s -- no problem
- f/10, 1/125 s -- no problem
- f/7.1, each of 1/30, 1/60, 1/125 and 1/500 all show the problem. Last night 1/30 was fine, today it's not.