Originally posted by drougge Blue, you keep saying registration distance while meaning the distance from the real element to the sensor. The registration distance is from the mount surface, it's unrelated to where the rear element is positioned. (Except of course that if the registration distance is larger than the distance to the rear element, it will protrude from the back of the lens.)
yes, I know this. That is why it doesn't make a lot of sense to design a lens that protrudes so deeply into the body.
Originally posted by drougge You also seem to think retrofocus means something fairly close to opposite what it actually means. (It's used to put the rear element further away from the image plane, and as a side effect makes the light rays more parallell, which is good for digital. All SLR wide angles that don't require mirror lockup are retrofocus.)
Nowhere have I said how a retro-focus lens operates. All I said is Pentax has designed them a long time, in fact one of the first for slr 135. Therefore, what you seem to think I think, is wrong.