The maximum fall off will always be an issue of the ratio of the diameter of the image coverage circle to the distance from the film to the pinhole. If the film is flat and centered on the normal to the pinhole, then the fall off at the edge of an image circle whose diameter is equal to the distance from the film to the pinhole will be approximately 1/3 stop from center image. Where the image circle diameter is twice the distance from the film to the pinhole, the fall off will be 1 stop. Geometry. Regards, Bob... -------------------------------------------- "Do not suppose that abuses are eliminated by destroying the object which is abused. Men can go wrong with wine and women. Shall we then prohibit and abolish women?" -Martin Luther From: "Gregory Fraser" <Gregory.Fraser@pwgsc.gc.ca> > 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?
