- 1DX has a built in shutter for the eye piece (the 5D III does not). I have a tendency to set up and compose a shot on the tripod, and then I do not look through the view finder any more... I just look at the back panel to look at exposure readings and setting because I am usually shooting when the light is changing rapidly. In shooting this way, my eye does not block the view finder and I find the exposure reading changes by about a stop and a half to 2 stops from the light entering the eye piece

. I keep loosing the little black rubber eye piece cover so I have to hold my thumb over the eye piece to expose properly. So I would find this feature useful.