Thanks ath [QUOTE][The sonnar needs the additional elements for correcting the errors coming with the bigger aperture and they interfere with the mirror.
While there is no direct link aperture - mirror clearance there is an indirect one.
As for the symmetrical lenses (gauss lenses): they need additional elements as well. A 50mm/1,4 has typically 7 elememts, a 50mm/2 has 5 or 6. The lens block gets physically longer and has to be moved slightly more outside for mirror clearance./QUOTE] This is what I was getting at.
OK you could make a simple 3 element non retrofocus f1.4 50mm - but the the opticla errors would make it a grim lens to use (compared to a more complicated design). so if some one wants to manufacture a high quality say f1.2 50mm lens - due to the length of the optical train, when would the 15mm rear lens /fim plane distane become a concern for the lens designer. I thick the 50mm f1.2 would not cause them concern but a 24mm f1.4 etc. OK with modern computing they can try diferrent optical lay outs which would have a slight effect on the rear lens element so it won't be a hard and fast rule.
TomThanks for that, so a 35 f1.2 does not have to be a retrofocus design - this is what I am trying to get at. People say its a lump of a lens ...but its not as big or heavy as the ZF F2 35mm (but I love the handling of this lens).My 35mm f1.2 CV Nokton is my fastest M mount lens, it is an Aspheric non-retrofocus wide angle design. The front-most lens element diameter is about 52mm. The rear-most lens element diameter is about 29mm.