Here's a quick explanation of why some film SLR lenses may have problems when used with digital SLR's. Basically, it comes down to that angle at which light impacts the sensing medium. Film is sensitive to light hitting it at an angle as well as straight on. Rumor has it that digital imaging arrays are less sensitive than film to light hitting at an oblique angle.
What does this mean? If you look at a ray-tracing diagram for a telephoto lens, the light hits the film (or imaging array) pretty close to perpendicular all across the whole image region. The light coming through a wide-angle lens, however, may hit the imaging array at quite an angle near the edge of the array. Depending on the lens design, this can lead to significant vignetting. The severity of such an effect will naturally depend on the focal length and optical formula of the lens as well as the imaging array. I've seen some pretty darn good images that came from Nikon D1x and Canon EOS-1D cameras and "standard" SLR wide-angle lenses, so I don't think a blanket "throw out your lenses" statement is warranted. --Mark - 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 .
