Originally posted by morfic You assume AF dslr screens are calibrated the way screens were when they were the only way of reaching focus. now a viewfinder mostly just serves composition, else we would get calibrated screens that are siutable for manual focusing.
That may be true but, I've talked with the friendly and experienced service techs at the Pentax authorised agent where I am (who happen to service Hasselblad and previously Nikon too) and I can assure you the stock screens are accurate for manual focusing and AF.
There are any number of reason why we don't focus very well manually:
Diopter not set correctly
Differences in magnification and size in DSLR viewfinders compared to film cameras.
No focus aids like split image rangefinder/microprism that film cameras had.
Focusing with lenses that do not have a fast aperture, especially wide angles where everything appears sharp
As we age, our eyesight deteriorates.
The lenses we use could have been opened up at some point and not collimated for proper focus. I have seen this plenty of times with old lenses that have been serviced by people without proper equipment.