The prime reason for the use of aspheric glass surfaces has to do with simplifying and reducing costs in manufacture where using multiple spherical section elements would either more costly or produce lower quality, given today's manufacturing processes. Same reason as using ED glasses.
Projection onto a flat sensor or film surface has been an embedded assumption in the design of camera lenses for many many years, with few exceptions. Some history on the exception that I know of: The Minox ultraminiature cameras obtained an extra measure of resolution and quality by incorporating a matched-curvature pressure plate which clamped the film into position when the shutter was cocked, until such time as lens design, materials and manufacture made it unnecessary. The original Complan lens introduced in the late 1940s had a five element design, the rear element was in contact with the film to enforce the curvature but problems with scratching and tolerances were such that a revised, four element design replaced it with the introduction of the Minox III in 1951, and the revised four element Complan was retrofitted to the majority of the Minox II cameras as well. Around 1973, the Complan lens was replaced by the Minox lens in the Minox C model run, which was designed for a flat pressure plate/film plane. It's much more expensive and much more difficult to manufacture a sensor/film gate with a matched curvature, particularly if you are talking about an interchangeable lens system camera. Godfrey On Oct 20, 2006, at 11:34 AM, Jack Davis wrote: > That's the prime reason for aspheric glass? > > Jack > > --- John Francis <[EMAIL PROTECTED]> wrote: > >> On Fri, Oct 20, 2006 at 10:32:46AM -0700, Jack Davis wrote: >>> Would it make sense to develop a concave sensor? Finest possible >> focus >>> would then be possible due to a constant light path distance across >> the >>> sensor. >>> Varying focal lengths a problem? Somewhat accommodated by a sensor >> that >>> moves in and out? >>> >>> Jack >> >> It only makes sense if you don't expect to use it with any lenses >> currently in use, all of which are designed for a flat sensor. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
