Hello Thom, Is that you want to get a circlar image with dark corner or dark edge? What film format are you going to use. I try to make pinhole camera to avoid dard corner, my 1 inch focal legnth cameras can cover the whole 4" x 5" film!
If you want to control the circular image to 2' or 3" (the range is quite big!), the main factor is the thickness of the front panel of your camera that hold the pinhole and where you mount the pinhole, and also the size of the opening of the front panel. Focal length is also a factor. Try to draw a section view (1:1) of your camera with the pinhole, front panel(with opening) and the film plan, then draw a projection line starting from the pinhole, through the upper and lower edge of the opening of the front panel, then you can get the image circle (you can get the diameter from the drawing). Adjust the thickness of the front panel or the distance between the pinhole and the front panel, or the focal length will change the size of the image circle. You can also control the sharpness of the circular image by adjust the distance between the pinhole and the front panel. ***We don't take in consideration of the thickness of the pinhole material, the one I use is 0.001 inch. Hope this may help. Zernike > ----- Original Message ----- > From: "Thom Mitchell" <tjmi...@ix.netcom.com> > To: <pinhole-discussion@p at ???????> > Sent: Monday, March 25, 2002 5:44 PM > Subject: [pinhole-discussion] image circle relative to focal > length/fstop > > > How can I quickly determine the size of the image circle for a given > focal length and f/stop. I want to be able to keep an image circle > from getting too big, i.e. I want it to be 2' or 3''. Any quick help > would be appreciated as would simple rules of thumb as opposed to some > of the derivative calculus I sometimes
