Originally posted by wallyb Buy crummy UV filters. Seriously, for 95%+ of all photographic situations, the cheapest multicoated glass UV filter will be perfect and will not degrade the image at all.
Although it's highly unlikely a filter will have any impact on sharpness, it
will induce extra flare.
The first two shots were from a D80 borrowed from a friend, since I was away from home without my camera. He had a UV filter on the 50mm f/1.8 and no lens cap, and it not being my equipment I didn't want to take the filter off. The third shot is from the 16-45 with a Tiffen circular polarizer. Although the hood was blocking the angle of the sun, the reflection off the car was enough to cause flare. Now, if I were shooting in a sandstorm I would definitely want a filter protecting the front element. But, I would probably also want to wrap the rest of the setup in a bag of some sort, as I'd be more worried about sand getting into the focus rings and wreaking havoc there.
As for causing damage when you clean your lenses, cleaning is something that should only be done when there is some major smudge covering the lens. I've seen enough fungus ridden lenses that produced great shots to know that specs of dust and dirt on the front element aren't going to impact the image in any way. When I do clean I always start with compressed air or a rocket blower, followed by a light touch with a lens brush, and finished off with a microfiber towel. Even if you do scratch the lens, though, you'll be impacting resale value more than you will be affecting image quality in any way.
Bottom line: if you bought your lens as an investment that would return money, use a filter. However, if you bought your lens as an investment that would yield images, don't. For the types that buy and sell lenses constantly, filter usage makes sense. How clean the glass is on a lens usually determines its value. This is especially true for pricier examples where lenses become a collector's item as much as a tool (FA*s, limited, etc). But, for those who believe the worth of a lens is the images it produces, then using a filter makes little sense. I'd rather live with the slight chance that I might scratch my lens a little, rather than the slight chance filter-induced flare would ruin a good image. In the end, that scratch won't affect my pictures, but the flare will.