Quote Originally Posted by Rich Ullsmith View Post
The only optics instruction I got was phys101 about a million years ago, but it seems advantageous to have the rear element of the lens right up to the film plane, like on a RF, instead of a few cm away to accomodate a mirror assembly.

Ahh, but isn't it the inverse cosine rule that states that the closer you get to the film, the more vignetting you'll have? Light falls of at the square of the distance, there's no free lunch. Every thing that might optimize one aspect of performance usually will screw up something else... Lens design, and more importantly lens construction, has come a long way over the years. The newer lenses with retro-focus designs can be amazing. That said, I still do want to own biogon one day... :-)