Quote:The basic error is: The focus screen could be well placed for all lenses.

 

If every lens needs a different AFMA value, you would also need for every lens a different shimmed focus screen. No matter, if it's the AF module which is focusing indirectly or the matte-screen, which is also at the end of a mirror.

 

On Nikon, I have or had AFMA ranges between -15 ... +10. So, if they cannot manufacture there lenses to tighter tolerances, what is the point of a focus screen? Estimating or guessing sharpness? And if they cannot manufacture lenses without focus drift, there's only a very specific distance being exactly right.