Quote Originally Posted by jochen View Post
Sorry, off course I ment the former used 4-lens types Tessar and Xenar. If you increase the distance between the front lens group and the rear lens group by inserting a washer, I think besides poorer image quality and increased aberrations you will get a change in the reproduction scale. It is something like a front lens focussing.
That's correct. More importantly that's introduces distortion when a lens is then used at or near infinity.

One of the long CZJ Tessars has quite a large spacer like a small extension tube for close up work where its used as a process lens, this needs to be removed for normal work. G-clarons are also optimised this way.

Ian