Leica screw mount and other screw mount lenses

Discussion in 'Projects/Repair' started by Country Parson, Apr 7, 2012.

  1. Country Parson

    Country Parson SC Top Veteran

    Apr 5, 2011
    North Carolina
    I am confused by the designations for screw mount lenses. I bought by mistake an adapter that says M42. But when I put my calipers into the threads it reads just shy of 39mm. Is that not the size for Leica screw mounts? If so why does it say M42 and is being sold as a Leica adapter? Anybody understand this? I thought Leica screw mount adapters said M39.
  2. greyelm

    greyelm SC Top Veteran

    Oct 1, 2011
    London, England
    M42 is the 42mm screw mount for early SLRs, often called Pentax screw when in truth it should be called Praktica screw. Because the film plane on these cameras is different to the Leica the adapters are much deeper than the M39. So in a nutshell the Leica RF screw mount is 39mm usually called LTM but sometimes M39. Some old SLRs such as the Russian Zenit also use a 39mm thread but the lenses are different to LTM.

    Here is a LTM adapter

    View attachment 51983

    Here is an M42 adapter

    View attachment 51984

    On my m4/3 camera I have both adapters and have successfully used Leica & Soviet M39 (LTM) lenses and Pentacon M42 lens with great results
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  3. grebeman

    grebeman Old Codgers Group

    I'm assuming that since you have an adapter you are measuring the inside diameter of the thread. The 42mm size would be the outside diameter of the thread. My Leica screw thread adapters have an inside diameter of 37.9mm

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