In article <322BDFA8.1896@lulu.acns.nwu.edu>, cbl638@lulu.acns.nwu.edu says...
[most deleted...]
>I was all set to get it [15mm f3.5 Nikkor] until I met a pro
>photojournalist who has one but claims he really didn't like it.
>Apparently it is not at all rectilinear and light drop-off occurs
>too quickly in the corners. [...]

The above may be true of the 14mm Sigma, but not the Nikkor 15's
The 15mm Nikkor f3.5 is very even in illumination, contrasty, fine
in sharpness to the corners in color (but not B & W) by f11 or so,
and has a reasonably small amount of linear distortion. The 15mm
f5.6 Nikkor is very even in illumination, contrasty, fine in
sharpness to the corners in both color and B & W by f11 or so,
and has virtually no linear distortion (which is unusual for
ANY SLR lens shorter than 50mm) - though it is about 1/2 stop
slower than rated, and requires meter compensation of about 1/2
stop. (Very slow shutter speeds can be used with these, so the
slow lens speed is not a problem.) The 15mm f5.6 is my favorite
of the super-wide rectangular lenses for Nikon.
Hope This Helps