At 12:09 PM -0800 12/20/00, Winsor Crosby wrote:
The one weakness of SLR design, I have heard it said, is the
requirement of the lens to be a retrofocus design in order have room
for the mirror/light box. Supposedly it is difficult to design such
a lens and to manufacture it to the same high standard as a lens for
a camera with an auxiliary viewing system such as a rangefinder. A
secondary result is the comparatively large size of the retrofocus
design. Since, apparently, an SLR design is not retrofocus enough
for a digital sensor, won't the problems of the design become even
more exaggerated as the the steepness of the angle is decreased? If
so, it is understandable why a complete redesign of the camera is
needed for digital, ie., small sensor=small field=offset of lens
size increase due to more extreme retrofocus.
This is a sort of scary thought, because it means that a digital camera
with resolution close to that of a 35mm camera might end up being bigger
than an SLR, with heavier glass. If we assume that today's pixel sizes of
3-4 microns are a likely minimum (due to the wavelength of light and such
things) that would mean a 4k by 6K array would be between 12x18 and 16x24mm.
SLR's typical have a film-to-flange distance of 40mm or more, which means
that the maximum angle of the light hitting the film is about 30 degrees
(figure 20mm offset into the corner). If the maximum angle allowed for
silicon sensors is, say, 10 degrees (I think I've seen articles that said
7 or even less) that would mean a sensor-to-flange-equivalent distance more
like 60-80mm. All of this is just back of the envelope, and maybe the
extra 20-40 mm of thickness needed can be taken up somewhere else in the
design, but I would bet on people figuring out how to build pixels with a
wider FOV...
paul
--
Paul Wallich pw@xxxxxxxxx
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