The optimal size of the pinhole is found this way...Optimum pinhole diameter in inches = 0.0073 times the square of the focal length (in inches) . So for a 360mm (14") focal length, it is 0.0073 times 3.74 = 0.027" pinhole ...optimal for sharpness, I believe. So that is a type of compensation one does for extended bellows...the longer the focal length, the bigger the hole. Of course, one needs a way to measure/make a pinhole that is exactly, or close to 0.027"!!!

It is the very short focal lengths that can be problematical. I have several pinhole cameras made out of old 250 sheet boxes of 8x10 photo paper. The distance from the pinhole to the film directly across from the pinhole is 3". From the pinhole to the corner of the 8x10 film is 7". The old inverse square law says that I will have a little over two stops less light hitting the corner than the center. (works great if I point the camera at something that is dark in the center and brighter around the edges!). But at 14 inches, that will not be a problem!

Vaughn

PS...my avatar was taken with one of the photo paper box cameras (I have no idea what size the pinhole was).