Question about LTM to M adapters mount points

Discussion in 'Rangefinder Forum' started by chrism, Aug 21, 2008.

  1. chrism

    chrism Member

    Jul 5, 2008
    Santa Clara,
    Medium Format
    I have been using various FSU lenses on my Leica M3 via an LTM to M adapter.

    I have 2 different adapters (1 chinese, 1 voigtlander). When I mount my Jupiter-8 I notice that it does not line up with Infinity at 12 O'Clock on either adapter (both adapters mount the lens at slightly different points). Does this make any difference in usage? It seems like all of my lenses focus at slightly different distances for the same target. Infinity seems to be fine with the Jupiter-8 though.

    I also have a Voigtlander 15mm that mounts crooked as well. I bought an LTM to M adapter from voigtlander that is designed for this lens so I am hoping it fixes the problem. Any experiences with this combo? I am concerned right now that the lens shade is misaligned to the body.

    PHOTOTONE Member

    Oct 30, 2006
    Van Buren, A
    Large Format
    It really doesn't make any difference where the lens infinity mark lines up in relation to the top of the camera. There is a wide variance in FSU lenses. The 15mm Voigtlander, with a Voigtlander (brand) adaptor should be closer, but it won't be precisely at 12 O'clock. The FSU lenses and cameras are not calibrated exactly like the Leica's are, but are considered "close enough" for most situations.
  3. nemo999

    nemo999 Member

    Jul 20, 2008
    For any lens to focus properly, the critical factor is the register (lens flange to film plane distance). The relevant values are:
    Leica screw 28.8 mm
    Leica M 27.95 mm
    It therefore follows that an adapter for a LTM lens on a Leica M body must be 0.85 mm thick. If you have a micrometer and can check your adapters, you should find they are OK in this respect. From an optical point of view, it does not matter at all where the witness mark for the lens focus is positioned - cosmetically it looks neatest if it is in the 12 o'clock position, but the lens will work fine even if this is not the case. Of course rectangular lens hoods need to be positioned squarely and will have to be adjusted if the lens position is off. In general, you should find that Voigtländer adapters are better made.