5d mark 3 viewfinder light leak question
David Franklin wrote:
The answer is simple. As I suspect you are already aware, especially on a sunny day, light travels through an un-blocked viewfinder eyepiece into the viewfinder and biases the exposure meter reading of all the DSLR's that I know of. This is almost certainly going to happen if the proper conditions for it are in place. To avoid this on the Mark III, if you must shoot with your eye no longer covering the eyepiece, and if you are shooting in some auto-exposure mode (manual exposure, if already set, will, of course, not vary) simply put the supplied rubber eyepiece cover in place, and your exposures will no longer be affected.
As to why similar exposure variations did not happen on another camera in the same relative time and place, there are many possible explanations. If one meters the scene with cameras just seconds apart, light entering the viewfinder can change dramatically from cloud coverage. etc. If the location of the second camera is just a foot away from the first, light entering the viewfinder can change dramatically from the direction and shape of the light source. If the metering pattern or metering sensitivity of the second camera differs from the 5D3's, then the light entering the viewfinder can affect exposure quite differently as well. there are probably other explanations as well, but I thought I'd mention a few that came to mind.
Bottom line: don't worry, but use the eyepiece cover if you're in a situation where eyepiece light may affect your exposure. If your metering manually with your eye to the camera, then stepping away to shoot, whatever the changes to the indicated proper exposure that occur are irrelevant in any case.
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thanks a lot
but this troublesome behavior doesn't happen with 5d mark II and 7D
i did a test with a tripod in a day without change of light