Camera-back/film-holder interface lightproofing

Discussion in 'Large Format' started by ron_hughes, Feb 9, 1998.

  1. I would like to make a pinhole camera that uses 4x5 filmholders. Not ever having seen the inside of a large format camera, I'm not sure how to make the film-holder/camera-back interface light tight.

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    Presumably the film-holder should be pressed tightly up against the back of the camera. Is this pressure normally achieved by means of leaf springs?

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    Presumably the user slides the film-holder into and out of the back of the camera at right angles to the axis of the lens, rather than moving it along the axis towards the lens.

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    What methods are commonly used to prevent light from leaking around the four sides of the film-holder and fogging the film? Particularly from the top, where most ambient light will be coming from, and which must be open to allow access to the dark slide.

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    Any advice that you can offer would be very welcome. Thank you.
     
  2. That's somewhat difficult to explain in words, but become clear
    when you see a spring back. I suggest that you visit a local store,
    maybe buy a holder from them (since you'll need them anyway) then
    ask them to try it on one of the cameras they stock, preferably a
    wooden one.
     
  3. I already have some used Fidelity film holders. Unfortunately, there doesn't seem to be a supplier of LF cameras anywhere near where I am in the UK, which is why I posted the message :)

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    LF seems to be a lot more popular among "amateurs" in the US - here in the UK their use seems to be limited to professionals. Maybe I'm wrong ...

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    Meanwhile, someone has suggested using draught/draft excluder strip. I still need to devise a way of pressing the film-holder against the strip.
     
  4. If you can't look at an actual camera back, see if you can find an illustration of one in a book. The way the leaf springs provide the necessary pressure is difficult to explain, but will be quite apparent when you see it.

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    Most of the cameras that I've seen do not use weatherstripping or any similar soft material to provide a light trap; they rely instead on pressure and a smooth mating surface. My guess is that a soft material could cause problems in focussing accuracy for a regular camera, since the exact position of the film would depend on the degree of compression of the material. However, this shouldn't be a problem for a pinhole, which has virtually infinite depth of focus.
     

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