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Thread: How are the aperture scales on shutters determined?

  1. #11

    Join Date
    Feb 2009
    Posts
    310

    Re: How are the aperture scales on shutters determined?

    Yes mine had that, too. The damned thing was also restricting the maximum aperture. Yes I head to disassemble such shutters and make the opening larger (that thing was part of the aperture assembly and could not be thrown away completely). The shorter the Polaroid lens was in focal length, the narrower the opening was and the more often disassembling was mandatory but some Copal Press shutters of the type had that ring thin so it did not get in the way of the glass elements, and in this case it was possible to leave it in its place - unless a really large lens like a 210 Symmar that needed a larger aperture opening was to be fitted into the shutter.

  2. #12

    Join Date
    Dec 2001
    Location
    NJ
    Posts
    8,470

    Re: How are the aperture scales on shutters determined?

    About the diaphragm's position in Compur/Copal standard cock-and-shoot and press shutters, see http://www.skgrimes.com/products/new-copal-shutters for the standard dimensions.

    Short version, press shutters' diaphragms are closer to the rear of the rear tube than cock-and-shoot shutters' diaphragms. This makes mounting lenses whose rear cells' go deep into the rear tube on press shutters impossible. Two little toes that I have stubbed, neither a large format lens: 60/5.6 Konica Hexanon (for Koni-Omega) and 80/2.8 CZ (BRD) Planar.

    Earlier posts alluded to what the late Steve Grimes called "the shoulder problem." Shutters with correct tube lengths, lenses whose cells won't seat properly on the tubes. This is a problem with #00 shutters, especially ones extracted from 35 mm folding cameras. Steve didn't shorten the tubes, which ruins the shutter for general use. He cut the threads back as needed.

    About those infernal Copal Polaroid press shutters with incorrect tube lengths. The version for the CU-5 127/4.7 Tominon's tube length is 20.5 mm, 0.5 mm longer than the standard. I discovered this when I put 150/5.6 Saphir BX cells that had arrived in barrel in one. I mentioned this to my friend Eric Beltrando, who's written a ray-tracing/lens evaluation program (visit his site www.dioptrique.info) and has the Saphir BX/Zircon prescription. He did some calculations, reported that 6/4 plasmat types' performance isn't very sensitive to cell spacing, that 0.5 mm was less than half a percent of the lens' focal length, and that I should use the lens and be happy. He also warned me not to use dagor type cells in off-specification shutters.

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