Contax Rangefinder Lens on Sony A7R Body

Discussion in 'Adapted Lenses' started by biogon44, Aug 14, 2014.

  1. biogon44

    biogon44 New to TalkEmount

    Aug 14, 2014
    I am able to fit my Carl Zeiss Contax Rangefinder lens Biogon 21mm f4.5 on my Sony A7R body using two adapters, namely Contax (outside mount) to Leica M adapter and Leica M to Sony E Mount adapter. My Sony Leica M Mount adapter has a helicoid component; hence It becomes the focussing unit for my Zeiss lens (designed originally to use the built-in focussing component of the Contax Rangefinder camera body). However, at 'infinity' setting with the two adapters, it is slightly unsharp. I feel tha the two adapters are correctly specified and made and that the unsharpness lies with the lens. I wonder whether my lens has been collimated accurately. Any comment about my difficulty would be appreciated.
  2. Bugleone

    Bugleone TalkEmount Veteran

    Aug 21, 2011
    Some points in no particular order;......

    Does the Biogon not have it's own focussing ring?....and attach to the 'outside' mount on Contax? As I remember (a long time ago!) only the standard 50mm lenses use the internal focussing mount via the small focus wheel under the right index finger........

    I think I remember that Zeiss lenses of this era have shims to adjust true focus point.
  3. davect01

    davect01 Super Moderator Subscribing Member

    Aug 20, 2011
    Fountain Hills, AZ
    One thing to remember is that often adapters don't quite line up with infinity. I have three adapters, two line up at infinity, and one does not. With the one that does not, I simply have to back it up a touch.
  4. biogon44

    biogon44 New to TalkEmount

    Aug 14, 2014
    Thanks for the replies. The Contax Biogon lens that I have does not have a focussing component. The Contax-to-Leica M Mount Adapter does not have a focussing helicoid either.

    The Voigtlander-made Leica M-to-Sony E Mount adapter is extremely well made and I am sure does not have any specification error. I think that I will send my lens with the Contax-to-Leica M adapter to Don Goldberg, a very well known camera equipment repairer, and have him collimate lens alone and lens with Leica M adapter attached. I think that this procedure will give me the answer as to why this lens is unsharp at infinity presently. I suspect that the lens only needs to be collimated correctly.
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