----- Original Message ----- From: "Simon Cygielski" <si...@wbj.pl>
> I've uploaded a couple of my first efforts with my 6x17 cm panoramic > pinhole camera. They're up at > http://www.p at ???????/discussion/upload/images/path1.jpg and > http://www.p at ???????/discussion/upload/images/phones2.jpg Wow, I like them. That camera/format shows lots of potential, try some images of very close subjects/objects. > I built the camera out of a Holga using bookboard to expand it to its > present size. "Focal" length is 7.5 cm. Any comments would be > appreciated. There is nothing like either making your own camera or modifying a camera to make it a pinhole one. Congratulations on your industriousness. Having said that, I wish I had the expendable money to get a Finney!! :-( > I also have a question: is the loss of sharpness on the far edges > inevitable, or can it be corrected somehow? perhaps thinner stock? This > hole was made (fairly carefully) out of a Coke can and sized according > to some pinhole formula (though I forget which one), so it should be > somewhere in the ballpark size-wise. Most people would be asking about the fall off at the edges, which in most cases I really like, it adds favorable pinhole quality to many subjects. Here is an idea that may or may not be helpful in answering your questions, it is based on the loss of sharpness due to diffraction: Geometrically speaking, the edges of the film see an oval shaped pinhole, fact that is made worst if the stock is very thick compared to the diameter of the pinhole. At the farthest corner of the film, in your case, the pinhole would appear to be just about 64% as it actually is. Assuming your pinhole is about 0.0125" in diameter (optimum for 75mm focal length according to D= 0.0073 * SQRT(focal length) , the farthest edges see an oval 0.0125" tall and 0.008" wide. The "vertical" sharpness is not affected "as much", the film still sees a pinhole as big as the original. The "horizontal" sharpness" is affected diffraction wise as the film now "sees" a smaller hole (0.008") that is optimum for 30mm instead of 118mm (focal length) at the farthest corner of your film. If you make the pinhole bigger to fully compensate for its apparent "ovalness" when seen from the edges of the film, you will be affecting the sharpness at the center of the film. Sharpness is affected at the edges not only because the film sees no longer a round aperture, but also because the "focal length" or distance pinhole-film at the edges of the film is much bigger than at the center of the film, requiring a bigger pinhole. By making the film plane to conform to a cylindrical shape with the pinhole in the center, the edges will still see an oval instead of a round aperture, but at least the focal length will be the same, helping to decrease diffraction and hopefully improving edge sharpness satisfactorily. One thing for sure will be improved substantially and that is fall off at the edges. In resume, for very wide angle of view cameras with flat film planes: use a thinner stock, make sure the pinhole is clean of burrs and make your pinhole a bit bigger than the optimum for the center of the film plane. Guillermo
