I don't want to discuss it. But of course I'll going to explain points which I may not have expressed in a way easy enough to understand. So, here we go ...
Originally posted by konraDarnok 1. I don't understand this reply.
2. Again I'm losing you.
3. I did, and I don't see as how the sensor assemble would weight more.
1. The Contax AX only moved the entire lens (the mirror box actually) by a certain amount. Almost exactly like the Pentax 1.7x AF TC does. The lens needs to be prefocussed, using manual focus.
While this is doable, it is not an acceptable approach to AF for a modern camera. Manual prefocus is not generally accepted anymore. And if you ever worked with the 1.7x AF, then you know that it requires its own kind of skill to work satisfactorily. Moreover, the solution added substantial and unavoidable bulge to the camera.
And this is for any kind of lens (except wide angles), not just a macro lens.
2. A
fully functional sensor shift would have to span 400,000µm with 30µm precision, or a relative precision of ~10,000:1. This is actually easier to achieve with a focus wheel and a gear box than a linear shift motor. As I said, I don't see a problem with tiny movements as required for AF fine tuning for the last steps of a CDAF. But I consider it to be impractical if it is to replace a full focus system, be it manual or automatic.
3. I wrote "AF performance would be affected negatively because larger masses need be accelerated as soon as the lens rather than the sensor needs to be shifted due to the limited space in the body".
So, why did you reply that the sensor is lighter than the lenses? I said that the lenses need to move as soon as the sensor reaches its maximum travel. The weight of the sensor doesn't matter then.
The entire point I am making is that the sensor cannot shift enough (to make your idea work satisfactorily) and that it isn't generally good enough to only alter the distance to the focal plane. Moreover, such a solution certainly is much more expensive than adding a simple screw to a lens mount.