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Thread: supplementary lenses

  1. #1

    Join Date
    Sep 2003
    Location
    Kalamazoo
    Posts
    648

    supplementary lenses

    I have an old Polaroid Miniportrait model 454 camera that takes 4 images on a single sheet of film. As near as I can figure, it has 4 lenses of focal length ~68.5mm set to focus at a subject distance of 120mm. The focal plane appears to be about 160mm back. The camera body is rigid.

    I want to focus on a subject to produce a full length portrait so the object size would be approximately 1,800mm for an image size of about 60mm.

    Can anyone tell me what diopter I need to add to the camera lenses to achieve this? I think I'd need to end up with a focal length of ~147mm.

    I thought it would be a neat way to create a modern multiplying camera to shoot tintypes with.

    Joe

  2. #2

    Join Date
    Jul 1998
    Location
    Lund, Sweden
    Posts
    2,209

    Re: supplementary lenses

    You're looking to approximately double the focal length, which means you need a diverging lens, not a normal close-up diopter. Some optical supply houses have them (for optical tinkering or for binocular microscopes) but your best bet would be an eyeglass blank from an optician.

    That means (if I remember rightly) you need about a -4 diopter, or a diverging lens with a focal length of -250 mm.

    I've been looking at afocal converters on eBay. You can get a 2x add-on converter for digicams and the like very cheaply. That would probably be the easiest route, as they come mounted in a cell, with a thread for attachment.

    If you find it works for you, you might want to track down a Polaroid/Cambo miniportrait 451. This model had a short bellows and a focussing gear which allowed some focus adjustments. There was even a coupled rangefinder included.

  3. #3

    Join Date
    Sep 2003
    Location
    Kalamazoo
    Posts
    648

    Re: supplementary lenses

    Thanks for the info Struan. I just picked up a Cambo Passportrait camera that appears to have a focusing adjustment for the 4 lenses. It should arrive in a couple days.

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