In article <4dukoc$gjv@agate.berkeley.edu>, beorn@alumni.EECS.Berkeley.EDU says... (.....)

>I just posted to anther photo group (in another thread?) that the
>fogging problem may be a result of the filter box (round plastic case)
>"outgassing" -- releasing minute plastic/polymer particles which then
>collect on the filter glass.

I find the Tiffen filters acquire the mysterious fogging even in
non-original filter boxes that cause no problems with other filters.

>Other than
>the potential 28mm vignetting, I would say the Tiffen "kit" is a fine
>deal (though my experience is a bit less than most). Even then, you
>may be able to live with the vignetting (either take off the filter or
>stop-down).

The darkest vignette (though smallest) will occur at the smallest
aperture - if a filter vignettes, it vignettes at all apertures
(though it may not be noticeable at wide apertures because it is
large and soft-edged - or at small apertures if it gets cut off
in printing). The Tiffen rims are too thick for use on many
wide-angles.
Hope This Helps