Originally posted by mee
However, are you saying an adapter is calculated to match the distance to the sensor and resolve this issue? I thought this was a physical property more than one of electronics.. but if they can counter that then ok. Still I don't see why they wouldn't offer a lens mount that had the K and new mount electronics since the supposedly new 'A' mount would be FF anyways. Plus having to route the screw drive through the adapter or potentially losing screwdrive support.
Yes, an adapter has to mount the lens at its designed register distance/flange focal distance for the lens to work as designed (e.g., macro tubes may get you closer focus, but the lens can no longer focus to infinity). The adapter has to be as long as the K-mount register distance (45.46mm) minus the new mount register distance, unless it has some internal optics like a speed booster.
In addition, most of the K
AF pins are there to communicate the smallest and largest apertures of the lens (NOT the current aperture setting, mind you- just the largest and smallest it is capable of). A mechanical linkage opens and closes the aperture, based on how far the camera thinks it should move the arm. That's a 1980s way of doing things - most new mounts communicate digitally between the camera and lens, and the lens does the work. So do you force the new A mount to still use an 'old' linkage method, or do you put the servo motor and mechanical bits in the adapter? Do you keep the screwdrive motor in the camera body, or put that in the adapter, too? (Sony did just that for the non-motored-lens-Alpha-to-E-mount adapter.)
Backward compatibility is a great selling point, but how much size/weight/cost/complexity can you afford to add to a camera body that might not ever mount a K-mount lens (especially if the whole point is to make it smaller/cheaper)?