Gregory Fraser <Gregory.Fraser@pwgsc.gc.ca> writes: > I went to a web site that had a calculator for the image circle diameter of pinhole setups. I calculated that a focal length of 3 inches would give me an image circle that would cover 4x5 inch film. I forget the pinhole diameter. Then I remembered how drastic the falloff is at the edges of pinhole images so I thought perhaps by increasing the focal length, I would have more of the brighter central part of the image and that would reduce the effects of falloff. 'But wait,' I yelled, 'if this were the case wouldn't Guy have been able to find a hotel room long enough to prevent the falloff he experienced in Montreal? Certainly someone as intimate with pinholes as Guy would know about that.' > > So, does the light falloff of a pinhole camera image follow an inverse square rule? Will it always be an issue no matter how big your shoebox, cigar tube or Quaker Oats box is? Presumably. Light does, generally speaking. If the angle of view (diagonally, say) is p, then the ratio of the distance from the pinhole to the centre of the film to the distance to a corner is cos(p/2), isn't it? So the ratio of intensity is cos^2(p/2). With a 90-degree angle of view, the light level is just twice at the centre. But that's only 1 stop: scan the resulting image, and correct digitally? Brian Chandler ---------------- geo://Sano.Japan.Planet_3 Jigsaw puzzles from Japan at: http://imaginatorium.org/shop/
