Curving the film plane

[yeknom02]

Hi all,

I was thinking I'd like to start designing and building a pinhole camera. Something for 120 roll film, to give me either a 6x6, 6x9 or even 6x12 negative. (Maybe I could build one camera to handle all three? Don't know if this is feasible... anyway...)

I've come across some different designs, the most notable being the panoramic Holga pinhole camera, which is along the lines of what I'd like to make: simple, but with seemingly little distortion - I'd hate anything that would give me that "fisheye" look. Another design, located at the link below, actually curves the film plane to reduce vignetting.

Dead Link Removed

It's hard to judge hoe distorted the edges are, but I know from the classic "Oatmeal Box" camera that curvature can lead to some ugly things. Is there a tradeoff between distortion and vignetting that I'm going to have to make? Or are there any ways around distortion that will also let me achieve a decent exposure around the whole image?

 

[Mike Wilde]

Well the basic Agfa Clack box camera from 50 or so years ago did the same thing to counter the deficiencies in its basic lens.

I have also seen a 50 or more year old folder camera that took a mask insert to shoot 12 - 6x6cm frame images on what was otherwise normally an 8- 6x9cm frame images per roll camera.

 

[Ian Grant]

So did the highly sophisticated Purma cameras made in the 1930's to the 50's, with their unique Focal plane shutters and stunning Beck lenses

Ian

 

[yeknom02]

Yes, I've actually had an Agfa Clack. My question is, should I somehow incorporate this curved design or stick with a linear film plane? Am I correct in assuming it's a tradeoff between vignetting and distortion or can I reduce vignetting using some other method?

 

[Rich Ullsmith]

This is an interesting question!

Even with sheet film, bending the plane is tough. I tried it. In the end, I said to hell with it, as an f250 gives really close to a 90 degree view, and a little distortion on the edges is okay. It's pinhole.

Never had an issue with vignetting.

4X5 I think is the way to go. If you are making your own cameras, may I suggest those 50 cal. ammo cans, as they are impermeable to air, water and light. You can drop them from heights. They can fall off the side of the boat, no problem. They won't let you bring them on an airplane, though.