American-made shutter dimensions?

Discussion in 'Large Format' started by Fiddlefye, Jun 11, 2021.

  1. I suppose this is technically a medium-format question, but it seems the answer to it can only lie in this forum.

    I have a Rolleiflex SL66 and have been adding various boards to my lens arsenal. One board that came into my hands recently is a bit of a mystery. It was listed as being L39 (I was planning on mounting enlarging lenses on it), but is in fact slightly larger. My digital calipers put the diameter of the inside ot the threads at 39.6mm (1.56in). I've tried a Copal No.1 and it drops in without contacting the threads. That is the only metric-dimensioned shutter I can think of that comes close. I've been through listings of every lens mount known to man and nothing matches. Given that someone once bothered to get a blank board and have it machined to these dimensions I can only presume they must have had something good and suitable to mount on it.

    Any ideas? Anyone know of a listing of US shutter thread dimensions?
    _DSC3048.jpg
     
  2. Your ID would make it an M40.5, depending on the pitch. I think that's a standard filter size but not sure what else.
     
    Fiddlefye likes this.
  3. A 40.5mm filter won't thread in, but the 40mm off my 50 f1.8 Serenar catches nicely, though the thread pitch of the filter is far too fine. The only threaded lens mount I can find in the listings at 40mm is the Practiflex and cannot imagine why anyone would machine a board for a lens for that!
     
  4. Try a 39mm Leica thread lens.
     
    Fiddlefye likes this.
  5. What the board was presented as when I bought it, but 39mm Leica thread just drops in without even contacting the threads. I keep wondering if thinking "metric" is the right approach given where the board was sourced and if perhaps one of the American-made shutters just happens to approximate 40mm.
     
  6. But when you use the Leica Thread jam nut it should fit fine.
     
    Fiddlefye likes this.
  7. Yes, I can certainly make something work, what exactly was the board actually machined for? Therein lies the question.
     
  8. Leica thread mount lenses and 0 shutters.
     
    Fiddlefye likes this.
  9. Yes, the hole size will serve the purpose just fine with a retaining ring on the inside, but someone went to the bother of cutting threads rather than just a hole. What would possibly use a 40mm opening with relatively coarse-pitch threads? That is what I am trying to determine. None of the European shutter types have the identical diameter and thread pattern, but what of American types? I'm still looking for specific data on the possible candidates.
     
  10. There's also the possibility that somebody just f'ed up. It's not easy cutting internal threads without a gage or the mating part and, depending on the lathe, it's not that hard to just accidently go oversize. It might never have fit anything! Don't ask me how I know this.
     
    ajkocu likes this.
  11. There are threads?
    You'd never know it from that picture.

    Maybe what look like threads are just machining marks from someone quickly boring a hole in the plate.

    Then there's the possibilty that someone cut a custom thread for something like an old Schneider 105mm Componon enlarging lens.

    I sometimes wonder if Jos. Schneider and Co. had ever heard of the word 'standardisation'. They certainly didn't believe in using the industry standard 39mm Leica thread for their enlarging lenses until quite recently.
     

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