In article
>Does anyone know why the 8/2.8 Nikkor is so expensive? Both the 16
>and the 8 provide a 180 degree angle of view, but the 16 actually >covers more (full frame) while the 8 is only partial frame (circular >image). I know that there are built in filters for the 8 but I can't >see that as the reason for it being almost twice the price. BTW, what >is orthogonal projection?
See Tom Davis' post above for most of answer. To restate a bit, your
question is a bit like asking why a 15mm lens is more expensive than
the longer and faster 35mm. The shorter you go with retrofocus lens
design, the more difficult and expensive it is to accomplish - not
only because of having to correct well over a greater angle (not true with the 8 and 16 fisheyes, since they both cover 180 degrees), but
also to provide the same back space necessary to clear the SLR mirror while shortening the focal length (lots more, and much larger glass
elements are required). IMO, Nikon would have been better off making
the 8mm slower than f2.8 to reduce the size and weight, as Sigma did
in its excellent 8mm f4. Even f5.6 is O.K., since hand-held speeds
down in the 1 second area are practical with 8mm lenses, and the
Nikkor is none too sharp at the widest apertures, anyway. BTW, the
16mm f3.5 Nikkor (If you want to see how good a super wide can be,
try this one!) also has built in filters, as do many of the other
early Nikkor super wides.
Concerning orthographic projection which the 10mm OP fisheye Nikkor
supposedly has, it appears to produce an image that has less fisheye
curve near the middle, and more extreme curve near the edge of
coverage. (Now, if only Nikon would make a 21mm f5.6 OP with the sharp
curved edges of coverage cropped out - like a normal w/a lens with
lots of barrel distortion, but short of full fisheye curvature.....
(I approximate such a lens with a 1.4X on a 16mm fisheye.)
Hope this helps.