Alexander Krohe wrote: >I may be wrong here, but I don't think for any wide >retrofocus angle lens, the light rays will hit the >film plane at an acute angle.
Not even *close* to an acute angle. Here's a cute (pun intended) story: When I was a a kid and my mother was working on her PhD in Medieval Literature she told me this great story: One day some medieval philosophers were having an argument. The subject was the number of teeth in a horse's mouth. One maintained that it couldn't be a multiple of 12 because that was the number of Jesus' apostles. Another claimed it couldn't be a multiple of 6 because god created the world in 6 days. A third claimed it *ought* to be a multiple of one of these numbers, for precisely the reasons mentioned! A loud debate ensued until one of their students, clearly too young and ignorant to appreciate the finer points of the dialectic, did something which totally shocked them all. He went outside, found a horse and counted its teeth. In that great spirit, I decided to conduct my own "tooth counting" exercise. The newest hot digital SLR is the Canon EOS-1D. Although it has the "disadvantage" of one of the largest CCDs currently evailable, it is clearly a high end product intended to satisfy the most discriminating photographers. Its CCD image area is 27.0mm x 17.8mm, which gives an image circle of 32.3mm. The film-plane-to-lens-flange distance for Canon EOS lenses is 44mm. Simple trigonometry reveals that the angle subtended by a line from the edge of the image circle to the center of the lens axis at the flange is 69.7 degrees. The image circle for full-frame 35mm is 43.3mm. Although this will make the angle a little farther from 90 degrees, this is slightly offset in the case of Pentax by a film-plane-to-lens-flange distance of 45.5mm. The net result is an angle of 64.6 degrees at the edge of the image circle. Clearly not as good as the Canon, but the difference of 5.1 degrees is far from earthshaking. Incidentally, carrying out these calculations for the "made for digital" Contax N1 yields an angle of 67.4 degrees. *Ever* so slightly better (by 2.8 degrees) than the Pentax, but 2.4 degrees *worse* than the "designed for film" Canon lens mount (at least with the CCD in the EOS-1D). To sum: Canon EOS-1D angle = 69.7 degrees Contax N1-D angle = 67.4 degrees Pentax full-frame = 64.6 degrees The largest difference between these three is an insignificant 5.1 degrees and the hypothetical Pentax full-frame camera would only be 2.8 degrees worse than the "made for digital" Contax. -- Mark Roberts www.robertstech.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
