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  1. #1

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    Lens Coverage on homemade polaroid/20's plate camera

    As some of you may have seen I recently mounted a polaroid back on an old plate camera http://www.apug.org/forums/forum147/...te-camera.html, the contraption works fine, but I've since added a new lens mount so I have tilt/swing movement.

    The mechanism works great, but I've encountered a new problem (one I'm sure most here will have already guessed) - just as I start to get some worthwhile blur there starts to be some vignetting and swung further I lose image area.

    so, the problem seems to be one of coverage. The lens is an old IBSOR DRB 105mm shooting on 7.5cm x 9.5cm instant film. the lens covers fine straight on and covers the rise and shift fine.

    my question is, how do I best solve this problem - do I need a wider lens or just a lens with a bigger diameter?

    thanks for any suggestions

  2. #2

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    You need a lens that projects a larger diameter image circle.

    That means a longer focal length lens of the same projection angle—provided that the camera has a long enough bellows to accommodate it, a lens of a similar focal length to the one you have now but that projects a wider angle to give you a larger image circle, or a combination of both of theses characteristics.

  3. #3

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    Quote Originally Posted by Ian C View Post
    You need a lens that projects a larger diameter image circle.

    That means a longer focal length lens of the same projection angle.
    thanks Ian, but how much are we talking?

    the bellows length should be ok, it's a double extending bellows and because the film plane has been moved back so much with the current lens it barely comes out of the box anyway.

  4. #4

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    I looked at the photos of your camera in the link. The lens appears to be a Rodenstock 105/4.5 Doppel Anastigmat.

    I don’t know the exact dimensions of the image rectangle on the film. If we assume it is the same dimensions as the stated film size of 75mm x 95mm, then the diagonal is 121mm. So apparently the 105mm lens you have produces an image circle at least that large in diameter. You can measure the diagonal of the image on film for an accurate size that the lens must cover.

    From your comments I think that you’re able to pivot the lens board horizontally. With a marginal coverage it wouldn’t take much swing for the image circle to fall off of the film at one side.

    Just guessing, I’d estimate that you’d need a lens of at least 150mm or longer, if it has about the same projection angle, to give you a reasonable amount of movement. For an old camera of this type you won’t have as many options as you would with a larger camera. The shutter and lens must still fit the board and its size is limited by the relatively small lens board.

    Hopefully someone with experience with cameras of this type and size might have a specific recommendation that will fit and give you the coverage you need to swing the lens as you choose.

  5. #5
    michaelbsc's Avatar
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    Quote Originally Posted by Ian C View Post
    I looked at the photos of your camera in the link. The lens appears to be a Rodenstock 105/4.5 Doppel Anastigmat.
    You won't get too much coverage with that, or most, 105mm lenses.

    Look for a lens designed for use with 4x5. The older Angulons should do well for you. Or if you want a little longer focal length try to find an old Polaroid 110 and rob the lens from it (127mm that covers 4x5 well).

    Or perhaps an old Wollensak 90mm WA lens.

    But Ian is right. The focal length of the lens isn't what you need to concern yourself with first. You're first issue is the image circle the lens produces. If you want to tilt and swing the lens, the image circle has to be large enough to give you the movements or you get the vignetting.
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  6. #6

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    thanks Ian

    Quote Originally Posted by michaelbsc View Post
    Look for a lens designed for use with 4x5.
    I was afraid some one woud say that, 4x5 lenses are out of my price range and probably wouldn't fit the camera.

    thanks tho'

  7. #7
    holmburgers's Avatar
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    By the way, awesome looking camera.

    What about the Kodak rectilinear lenses from the old 2A/3A variety folders I heard that if you unscrew one of the elements they cover 8x10". Could be a drop in replacement, or perhaps you can unscrew one element on this lens? I know just enough to be dangerous, but some food for thought perhaps.
    If you are the big tree, we are the small axe

  8. #8

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    Quote Originally Posted by holmburgers View Post
    Could be a drop in replacement, or perhaps you can unscrew one element on this lens?.
    thanks, it was born out of the need to replace a broken polaroid reporter and being fed up with relying on "the magic eye" but being too poor to go full LF.

    I have the camera at hand and with a quick flick of the wrist discovered that unscrewing one of the filters doesn't help with coverage and makes it impossible to focus on anything closer than about 3m, so not very practical.

    great suggestion tho' and I'll keep an eye out for the lenses you suggested

  9. #9
    michaelbsc's Avatar
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    Quote Originally Posted by himself View Post
    thanks Ian



    I was afraid some one woud say that, 4x5 lenses are out of my price range and probably wouldn't fit the camera.

    thanks tho'
    Some of the older lenses are very compact. An old Wollensak from a dead Graphics would work.
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

  10. #10

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    Quote Originally Posted by michaelbsc View Post
    Some of the older lenses are very compact. An old Wollensak from a dead Graphics would work.
    good good, I'll keep an eye out for them.

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