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.

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?

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.

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.

Any advice that you can offer would be very welcome. Thank you.

-- Ron Hughes (rhcc@compuserve.com), February 10, 1998

Answers

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.

-- Quang-Tuan Luong (luong@ai.sri.com), February 10, 1998.

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 :-)

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 ...

Meanwhile, someone has suggested using draught/draft excluder strip. I still need to devise a way of pressing the film-holder against the strip.

-- Ron Hughes (rhcc@compuserve.com), February 12, 1998.

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.

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.

-- Rob Rothman (rrothman@riag.com), February 17, 1998.