At 01:58 AM 9/18/2002 +0900, you wrote: >me@myplace.to writes: >[snip] >> ..........felt the pain of >> a kidney stone as it moved into a new and interesting location in my right >> kidney. ... > >Aha! See http://www3.yomogi.or.jp/chandler/pics/14stn1.jpg It is amazing that something so small and fragile can cause so much pain, blood, and suffering... come to think on it, that pretty well describes my first wife! >............................. do you think that jiggling the zoom lens can allow >you to see around corners? I've not got much into .. jiggling. Does it involve any erectile tissue in any way? Maybe I've done it with out knowing the proper nomenclature. >> (the) ....................... formula for finding the >> focal length for a given pinhole is diameter of pinhole times itself times >> 750 so the FL of a .4mm pinhole is 120mm. > >It is? How would you calculate that? Sorry... thought I'd covered that. To calculate the focal length of a .4mm pin hole one would multiply .4mm times .4mm and get .16mm. Now multiply .16mm by 750 and arrive at 120mm. This is the distance from the pinhole to focal point or the point where the light beams form the sharpest image. >How would you account for the fact >that with a pinhole of "focal length" 3 ells, a film 7.4 attoparsecs >>from the film, and a subject ranging from 3 mm to 4 miles distant >everything is equally "in focus" modulo diffraction effects? This is a kind of mental masterb... uh... jiggling you are doing here... right? >> This shows just how sharp a pinhole shot can be if it is exposed at the >> proper focal length for the size of the pinhole. 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. >This does seem to be counter both to theory and practice... ??? The theory I'm familiar with says a pinhole has infinite DOF _IF_ it is infinitely small. That of course is impossible. Practice says for any focal length there is an optimal pinhole diameter for image sharpness. >> Every lens has a "normal" format and every format has a "normal" lens. > >It does? Yes and yes. >And how do you calculate this "normal" lens/format? Can it be >empirically determined? Or just looked up in an old book? Consider it an exercise for supercilious twits. >Sorry, too many questions? >Brian Chandler >---------------- Oh no, just a bit too much mental ... jiggling. Dave East Englewood --------------------------
