Anthony Farr wrote: >You could be assuming (excuse me if you're not) that because 24mm x 36mm >and larger chips are in service on medium format and bigger cameras then the >doubts about WA use are dispelled.
No, I'm assuming it won't be a problem because the difference in angle of incidence is only about 5 degrees. Here's a really informative Bill Peifer post on the subject I dug out of the archives: I'm curious where this whole idea of CCD sensors requiring (or preferring) perpendicular rays originated. I'm pretty convinced that it must have originated because somewhere along the line, something got taken out of context, and a fundamentally incorrect idea grew from there. From the standpoint of the underlying physics, Tom is absolutely right -- the purpose of a lens is to bring an image to critical focus at the focal plane, and the nature of the sensor (film, CCD, CMOS, or other) isn't particularly relevant. After all, if all the light rays strike the sensor perpendicularly, then they are necessarily parallel and thus cannot form an image at the focal plane! I suspect that this perpendicular-ray story -- dare I say "legend"? -- may have originated from a misinterpretation of the characteristic behavior of CCD sensors. We all know that in single-chip color CCD sensors, some of the pixels are sensitive to red, others to green, and still others to blue. For the case of color cameras with single CCD sensors, color sensitivity is imparted to a particular pixel by incorporating a microscopic optic -- a lenslet and filter -- in front of that pixel, which I believe is accomplished as part of the manufacturing process for the sensor chip. I can imagine that the numerical aperture of this microscopic optic may not be terribly large, and it might very well constrain the field of view of its corresponding pixel. Maybe someone that knows more about chip fab can comment on this. Anyway, although each individual pixel may very well be "looking" through an optic with small numerical aperture, it's only "looking" a very short distance (microns? tenths of microns?) to the illuminated spot on the focal plane directly in front of it. In fact, this is precisely what you want. If each pixel had a more "wide-angle" view, it would not only register the intensity of light directly in front of it, but it would also register the intensity of light from a immediately adjacent pixels (perhaps pixels intended to sense a different color), resulting in a spatially and chromatically degraded image. The characteristics of the macroscopic, "analog" lens mounted onto the front of the camera -- focal length, f-number, etc. -- isn't particularly relevant, except that a faster "analog" lens will make each pixel-size spot of light at the focal plane correspondingly brighter. Bill Peifer Rochester, NY -- 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 .
