- A cylinder is not a plane, but you know what I mean. Alternately, we simply have to postulate a suitable geometry, and the two are equivalent anyway.
- About 0.24mm in diameter.
The simplest possible camera.
This is an anamorphic pinhole camera made out of a film canister, a piece from a can of root beer, some glue, and black paint. I used it to take this picture.
What the diagram above attempts to show is that the film rests against the wall of the canister, in a cylinder parallel to the optical axis (in a normal camera, it's flat and perpendicular). Where in a normal camera you have a field of view shaped essentially like a cone, in this arrangement the centre of the cone is invisible. I've tried to show what this looks like on a picture of the original scene.
There's also a significant amount of distortion, from a couple of different sources. First, the focal length varies with the height of the film; in this case it's around 19mm at the top of the film, and about 50mm at the bottom. Unwrapping the cylinder to view the picture certainly doesn't make it any simpler, either.
Because the f-number depends on the focal length, it varies over the height of the film as well; from around f/80 at the top of the film to f/210 at the bottom. That sounds like a dramatic difference when you're used to values around 2.8-16, but it's really only about 1.5 stops.