Quote Originally Posted by jrw View Post
even though Canon doesn't support the focus screen as being replaceable. It was inserted for assembly, so it can come out... maybe? Time will tell.
I'm presuming that the 5D3 screen can be replaced just as easily as the 7D screen. I put my KatzEye split-prism screen in my 7D a few weeks ago, and it's definitely worth it. Installation was nowhere near as hard as they make it out to be with all their warning as such (which are all basically "you can do it yourself, but if you stuff up your camera, we take no responsibility").

I've tried it with a lot of lenses already, mostly FL 55 f/1.2, Zeiss MC Biometar 120/2.8, and 70-300L + Kenko1.4x.

The FL 55 was the first I tried after installing, and I found that at a focus distance of maybe 50cm at f/1.2, the photo and live-view (and AF chip) were focussed maybe 1-2cm closer than the prism was telling me. I haven't had time to investigate fully, firstly tried changing the Diopter which helped a bit but not enough. There's nothing wrong with the screen itself, and i kept all the shims from the original screen. But the original screen just wasn't accurate enough so whether it was calibrated properly or not didn't make any difference.
So it's either that I need thicker or thinner shims for the focussing screen, or maybe the mirror isn't exactly in the right spot. Not sure how I could go about fixing either of these to be honest, so i'm going to have to do more testing with more lenses at more apertures to see how bad a problem it's going to turn out to be.

But with the 70-300L and 1.4x Kenko t/c, it was pretty damn accurate because it was down to f/8 and deeper DOF masked any calibration problems, i'll have to post some samples when i get time to process them.