At 12:35 PM 9/17/2002 -0700, you wrote: >Dave...........2000 messages ....now that's >painful.........glad you're back........but I can't >buy this: > >"....... When you move a pinhole back and forth you >are NOT changing the focal length, you are just moving >it in and out of focus......." > >doug This may be because you are accustomed to seeing horrible results from badly out of focus pinholes. Light emitted from a pinhole is not refracted as with a lens because it does not pass from air to glass. Light rays are not focused to a point but bundled, in parallel, into beams. The size of the beam is dependant on the size of the pinhole and the focal length of the pinhole is the distance from the film plane to the pinhole which will produce the sharpest image. This is about all I remember from high school physics as taught before "high school education" became an oxymoron. Be that as it may, buy or no, that is your decision but before you make it you might consider looking at: http://www.stanford.edu/~cpatton/ip-ph.html You could also just search on <pinhole focal length> or <pinhole theory> in Google and spend a few moments perusing the results. I'm in the planning process for a pinhole of about "normal" focal length (a FL that will produce images approximating real world spacial relationships at usual viewing distances) for a Canon D60. Dave East Englewood ------------------------- "Art is not what you see, but what you make others see." - Degas
