In article <310A9A0E.6E15@best.com>, kes@best.com says...
>Mark Brethen wrote:
>> I've read that you should use a UV or Skylight filter to protect the >> lens when you are shooting. Still, others have said that these
>> filters degrade picture quality. Who's right?

>Both are. Odds that your skylight filter is carefully designed and
>manufactured to work with a particular lens are... low. Even if it
>were, you are adding another glass element to the lens. It is safe to
>state that the ultimate performance of the lens is compromised.
>Whether this has any real world effect on the quality of the >photographs shot with a lens/filter combination is debatable. What
>is not debatable is that if you shoot without a filter, and get a huge >scratch across the front of your expensive camera lens, you won't be >able to unscrew the damaged piece and replace it for $15 in 15
>seconds; nor will you be able to resell the lens without a huge >depreciation.

The points above are well made - and I will add these experiences:
In careful checking with a 400mm f3.5 Nikkor (longer lenses, and
faster lenses, show filter optical defect effects more than shorter, slower lenses) to see whether (good) UV filters have any effect on
lens image quality, I came to the conclusion that there was no discernable degradation in the image caused by the use of good
filters (Nikkors, both front and rear on the lens - though I have
found no problems using the cheaper Hoya filters). And, someone
once grabbed my camera to get it away from me, and scratched the
filter on the front of the lens. I was sorry to lose the filter,
but happy it was only the filter. Unfortunately, several of my
lenses will not accept protective filters......
Hope This Helps