A light leak? Really?
A light leak issue in the 5D Mark III has been reported over the last couple of days. It seems the top side LCD may be to blame. I can confirm this is happening on at least one of the 5D Mark III's I own (the rest are out for rent), I will look into the issue with more bodies in the coming days.
Simple Test Procedure
- Put your body cap on the camera body.
- Put the viewfinder cover that came with the camera over the viewfinder.
- Set the camera ISO to 800 and put the camera in “P” mode.
- Turn on the backlight for the LCD panel and watch the exposure change
Below is a video showing the issue.
Other light sources cause the issue?
Yes, shining a flashlight on the top LCD causes the exposure to change, as does sunlight and bright overhead lights. All of which happen with the body cap on.
Does this matter in the real world?
For the moment, I'm not sure. I haven't noticed any issues with metering on the 2000 or so shots I've put through the 5D Mark III. I'm sure we'll know more in the coming days.