I am looking at getting a 135/2 lens for use with the Canon, but it has a finder screen optimized for lenses no faster than 2.8. With the older 5Dmk2, I could get a higher contrast focusing screen for use with fast lenses. 5Dmk3 omitted that option, and 5DS R seems to lack it as well.
My options seem to be live view with a magnifier (clumsy) or just using the Sony A7R. I am not at all sure that Canon AF (or electronic focus confirmation with manual focus) is accurate enough for focusing a 135/2 lens wide open consistently. Does anyone have experience either way?
Based on a recent test, Samyang 135/2 seems to provide sharper, cleaner images with less stray color in out of focus areas. How realistic is that comparison?