Earlier today I tried using the 5D as a wildlife cam, and initially I got some odd exposures which at the moment I can't explain. As a sanity check, I was going to test it against the 7D at home under controlled conditions.
I set up a simple test - put the 50mm f/1.8 on the 5D. Pointed the combo at a random leaflet lit by mains powered continuous lights. Set aperture priority mode to f/5.6, manually vary ISO through range taking a shot at each. When I scrolled through the 1st set I noticed the apparent brightness wasn't consistent. I repeated this, and got a different set of variations. On the histogram, there was a variation of about 1/10th of the whole range between the extreme shots. This is visible on the image as a variation in brightness.
The exposure set by the camera was consistent, with the shutter speed varying shutter proportionately to ISO. It did not fluctuate even 1/3 stop from 1/25 at ISO100 or equivalent. Taking 3 shots at 1/400s, I got the bigger variation. Taking 3 shots at 1/25, there was insignificant variation.
Does that mean my "continuous" lights are flickering? I haven't looked at them on computer yet, to see if there is any banding from the shutter movement if this is the case. Otherwise, is there any other mechanism? Guess now to do part 2: repeating it on 7D and see if it still happens.
Edit: Done same on 7D, it metered exactly the same, and also exhibited the brightness variation. On average, it is about 1/10th of a histogram width brighter though, but I do have different picture style setting applied which may contribute to that.
_________________Canon DSLRs: 7D2, 7D1, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L, 100L, MP-E 65, EF-S 10-18, 15-85
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 50/1.4A, 150 macro, 120-300 f/2.8 OS
Compacts: Sony HX9V, Fuji X100.