Stopping it down is more likely to make it worse.  Think of it this way.
The vignette is caused by the "image" of the filter mount.  Wide open it is
fuzzy because it is so close.  Stop down and you bring it into sharper focus
and you will notice it more.  In either case it will or will not be in the
image without regard to the aperture as the angle of view and the part of
the filter in the image path will remain the same.

   You can bring your camera and lens down to the camera shop and ask if
you can try it on.  You should be able to at least get a rough idea by just
looking through the lens assuming it is an SLR.

(Joseph Meehan) wrote:
Most of the time. To be sure, try it and see.
=================================

I would if I had one, but I don't have one yet and don't want to buy one
if it won't work on wide angle lenses. I think it might do ok stopped
down, but I think it would probably vignete at wider apertures.

Cody,

http://community-2.webtv.net/AnOvercomer02/PhotographyLinks

--
I'd never bother to use a step down, chances are you'll get vignetting at
any thing less than stopped down.  IMHO, this falls under the heading,
"False Economy."