In article <4d4r86$3poe@argo.unm.edu>, ttkk@unm.edu says...

> Last weekend I rented this lens to do some interior shots
>of a computer training facility. I was working under cool white
>fl blubs so I put the requisite CC30M filter behind the lens.
> I had a big problem with lens flare - I used f8 on all the
>shots and about 1/3 of the shots had some degree of flaring. Some were
>slightly magenta. The fluorescents were 4*40 watts with a diffuser on >them. How could I minimize the flare in the future? Different aperture? >Flash? Better positioning?

My guess is that either the lens had some smudges on it (check the
rear element especially, since you were mounting a gel there [how?]),
or (more likely) the gel had some smudges on it. Was the gel large enough to more than cover the skylight filter that is normally at the
rear? If not, having the edge of the gel in the photo may have caused
problems. Try some identical photos to the ones that flared, but
with a clean lens and without the gel - they should be fine, except
for the putrid color (color negative material, especially Reala, can
save the day here, though a clean, sufficiently large, reasonably
flat cc30M gel taped to the rear of the lens should work fine).
BTW, unlike most lenses, there is enough DOF with this one (and the
front element is sufficiently far from the optical center of the lens)
to almost bring into focus anything on the front element.
Hope This Helps