Query to Larry Bullis:
I have experimented with a set of 12 pinholes obtained fromCalumet, ranging from 0.0059 to 0.032 inches in diameter, on a 4x5 view camera. It quickly became apparent that angle of view is dependent only only on lens to film plane distance. Any of the 12 varying pinhole sizes give the same angle of view at a given bellows extension. The difference is in the amount of light admitted by the pinhole aperture. Thus it makes sense that, as the pinhole aperture becomes smaller , admitting less light, the bellows extension must decrease, to maintain the same amount of light, which means the focal length gets smaller. You've given a formula to calculate the optimum pinhole size for a given focal length to give the "sharpest image." The formula is pinhole(in) = square root FL x 0.0073 or pinhole(mm)= square root FL x 0.03679. My question is; does this formula really give the sharpest image? First, you've said that depth of field is essentially uniform from near to far and somewhat soft because of diffraction. Since, for a given focal length, aperture(pinhole) varies inversly with f-stop, the formula must be designed to balance pinhole against f-stop, one admitting more light and the other admitting less light. The constant (.oo73 or .03679) is what determines the answer. So, now the question is; How is the constant determined? Does it give the "sharpest" image or is it just a trade off between exposure time and pinhole size? Do smaller pinholes give more diffraction and thus less sharp images? Using a different constant will gives different answers; what is unique about the given constants?
