I was doing a timelapse recording of sunrise with my Canon 1100D. I set manual mode of exposure (M on the disk), exposure time to 1/4000 s (smallest), aperture to f/3.5 (maximally open), ISO to 100 (minimum). These aperture&shutter settings are meant to maximally avoid starburst effect while also avoiding overexposure. Then I just took photos with maximum frequency the camera was able to when connected via USB. Namely, I just simulated very frequent clicks on "Capture an image" in Entangle using
xdotool, which effectively resulted in about 5 seconds between frames.
After having done the photo set, I opened the photos in Geeqie and started going next,next and so on. Looking at this "slide show", I noticed that brightness of the images randomly varies between shots, despite the weather was completely cloudless and couldn't be the reason.
Following advice in comment to a related question, I checked bracketing mode — it appeared off. I then tried setting smallest aperture (f/22) and much longer exposure time (1/80 s) — and the result didn't have any variation of brightness. So I conclude that my camera isn't able to precisely move its shutter to achieve prescribed fast timing.
Thus my question: is it normal for a photo camera like Canon 1100D to have visible variation in exposure times when they are at/near their lowest settings? Or is it a sign of wearing?