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Thread: Changing shutters?

  1. #11
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Changing shutters?

    Quote Originally Posted by Andrew View Post
    so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect
    Sorry... wrong.

    As I said above (#6), Flange Focal Length (FFL) has absolutely nothing to do with the aperture scale.
    That's because the FFL has nothing to do with the optical focal length. The f/setting depends on optical FL.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  2. #12
    IanG's Avatar
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    Re: Changing shutters?

    The flange focal distanc is slightly different depending on which shutter is used, the 210 Symmar S is 200.9 mm in a Compur and 201.0mm, not critical on a field camera/monorail etc but the Protor is only 199.5mm enough (1.5mm) to affect infinity focus on a camera with a helical mount (like some 617, 612 etc cameras) or where Infinity stops are used.

    Ian

  3. #13
    Andrew's Avatar
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    Re: Changing shutters?

    Leigh, so...
    by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?
    [we'll ignore cell seperation issues]

  4. #14

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    Re: Changing shutters?

    Quote Originally Posted by Andrew View Post
    Leigh, so...
    by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?
    With what impunity? Aperture scales will differ not quite as much as when switching focal lengths, but they may still change significantly when it comes to asymmetric lenses. And unless the shutter and cells have been independently shimmed (so that you own separate kits of shims to neutralize both the shutter and cell set) it is a matter of luck (and the spacing vulnerability of the lens design) whether the spacing is acceptably accurate or not...

  5. #15

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    Re: Changing shutters?

    Quote Originally Posted by Leigh View Post
    The proper depth of a Copal #1 shutter, measured from the front face to the rearmost surface, is 22mm.

    - Leigh
    20.00 mm. See http://www.skgrimes.com/products/new...standardcopals And although everyone says thickness, the distance is measured from the front of the front tube (front cell screws into it) to the rear of the rear tube (rear cell screws into it)

  6. #16
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Changing shutters?

    Quote Originally Posted by Dan Fromm View Post
    20.00 mm. See http://www.skgrimes.com/products/new...standardcopals And although everyone says thickness, the distance is measured from the front of the front tube (front cell screws into it) to the rear of the rear tube (rear cell screws into it)
    Dan,

    I took the 22mm dimension directly from the Copal drawing.

    Sorry, but SKG does not make these. Copal does.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  7. #17

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    Re: Changing shutters?

    Quote Originally Posted by Andrew View Post
    yeeees... so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect
    No.

    You're confusing flange focal distance (the distance from the back of the shutter or the barrel's rear flange to the film when the lens is focused at infinity) with focal length. Focal length is the distance from the lens' rear node to the film when the lens is focused at infinity. Where the rear node is located depends on the lens' design. Most modern more-or-less symmetrical lenses (this includes the Dagor in its many versions and clones) have rear nodal points near the diaphragm. For such lenses flange focal distance is usually not very different from focal length. But not always. Lightly asymmetrical double Gauss types, in particular, seem to be somewhat telephoto.

    Telephoto lenses have it in front, sometimes far in front, of the diaphragm. Retrofocus lenses have it behind, often far behind, the diaphragm.

  8. #18
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Changing shutters?

    Quote Originally Posted by Andrew View Post
    by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?
    Nope. Sorry.

    There are two parameters in the f/stop equation: 1) the optical focal length and 2) the diameter of the entrance pupil.

    The diameter of the entrance pupil is the physical diameter of the opening through the diaphragm blades multiplied by a constant that's a function of the lens design. Each of your lens types will have a different constant.

    With real shutters the problem is exacerbated by the fact that the diaphragm hole is not a perfect circle, but the f/stop equation assumes a perfect circle. So there's an additional correction factor applied to equate the physical area of the hole with that of a true circle.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  9. #19

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    Re: Changing shutters?

    Quote Originally Posted by Sevo View Post
    With what impunity? Aperture scales will differ not quite as much as when switching focal lengths, but they may still change significantly when it comes to asymmetric lenses. And unless the shutter and cells have been independently shimmed (so that you own separate kits of shims to neutralize both the shutter and cell set) it is a matter of luck (and the spacing vulnerability of the lens design) whether the spacing is acceptably accurate or not...
    Leigh, I agree completely with you about the risks that stuffing any old pair of cells in any old shutter entails. Also about the risks of swapping a pair of cells from one #00 shutter into another #00 shutter; #00s, especially ones used in folding 35 mm cameras, don't all conform to the #00 standard.

    But for post-WWII lenses mounted in post-WWII lenses that conform to the Compur/Prontor/Copal/Seiko #0, #1, and #3 standards, moving a pair of cells from one shutter to another seems fairly safe.

    On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?

  10. #20

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    Re: Changing shutters?

    Quote Originally Posted by Leigh View Post
    Dan,

    I took the 22mm dimension directly from the Copal drawing.

    Sorry, but SKG does not make these. Copal does.

    - Leigh
    Have you measured? I have. Pukka Copal and Compur #1s are 20 mm. The #1 Copals engraved Polaroid Copal are 22 mm. Which drawings did you consult?

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