On Tue, 29 Dec 1998 06:59:30 GMT, litefoot@my-dejanews.com wrote:

>I have noticed a very slight light fall off (vignetting) on the corners of the
>pictures taken with the AF Nikkor 20 mm. I suspect that this is caused by the
>protective Hoya UV filter (not the slim version) on it. I have yet to try the
>lens without any filter but I would like to have a filter on at all times.
>
>Is this a problem with the 20 mm? Will a slim filter from Hoya, Nikon or B+W
>solve this problem or do I have to live without a filter?

If there is a fairly sharp darkening only in the far
corners, this is vignetting, generally caused by a filter
and/or shade that cut into the angle of view of the lens.
If there is a slow roll-off of illumination only at wide
stops, this is normal and it generally is gone by f5.6
in good wide-angle lenses. BTW, much as I like the Nikkor
20mm f2.8 (and consider it one of the very best very-wide
lenses), I do not use it wider than f5.6 (where its
edge/corner performance "hops up" in quality) if at all
possible. (the lens can easily be hand-held at 1/15th, and
even 1/4 second is not difficult...). Lenses have optimum
stops for best performance, and that is one of several
consideration to be included in exposure decisions (which
is partly why I prefer manual exposure determination
to auto modes...).