[toni-a]

This is simple logic, when you are using a device to capture the photo, another one to focus electronically and a third one for manual focusing you have to align/calibrate all three, when one device does everything all three you don't have to. Canon does a great job having all three factory aligned most of the time, when it's not the case, or when changing focus screen you do it manually, Canon did their best so that if you use their focusing screens it is already calibrated most of the time.

The thing I didn't understand, how by using an f1.4 lens I can see a DOF of 2.8 in the viewfinder while the lens aperture baldes are wide open?