I have not experimented to find the optimum pinhole size. Chris Patton has, and his conclusion was that the Prober-Wellman Formula is a practical values to use for f/stop to pinhole size for reasonable Circles of Confusion. See http://www.stanford.edu/~cpatton/phcalc3.htm which uses the Prober-Wellman Formula. or http://www.huecandela.com/hue-x/pin-pdf/Prober-%20Wellman.pdf for the white paper study. Also the formula can correct for pinhole to subject distances, for Close-up and Micro pinhole pictures. see http://www.huecandela.com/hue-x/Pin-html/PinPlus.html Bottom center for examples of close-up and macro pinhole with pinhole size correction. The pictures are full size on 4 1/2 by 3 1/2 Polaroid prints that have been reduced to fit the page. The train is a "N" gauge in size or about 3/4" at maximum height.
Paul Prober
