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  1. #11
    kram's Avatar
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    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.

    Tom
    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.
    Thanks 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).

  2. #12

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    [QUOTE=kram;647044]Thanks ath
    [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.

    Tom Thanks 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).
    You are welcome! Of course, the Zeiss ZF F2 35mm is not an M mount lens (it's an SLR lens and IT IS a retrofocus design).


    The Zeiss Biogon T* 2/35 ZM is an M mount lens and IS NOT a retrofocus design.

    I also have the ZM 50mm f2 Planar and the ZM 50mm f1.5 Sonnar.
    Tom Hoskinson
    ______________________________

    Everything is analog - even digital :D

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