If you hang around photography forums for long enough, you will inevitably come across the debate of whether or not to use a UV filter at all times on each of your lenses. I even accidentally initiated this argument once when I offhandedly mentioned filters in a forum post.
Some people claim they degrade image quality and thus passionately detest them. (However, why is it that when you look at their sample images, you often discover that image quality is the least of their photographic issues?). Others, like myself, recommend them for protecting lenses and offering a surface that one can quickly clean without worrying about creating a scratch across an actual lens element. You know what degrades image quality? A scratch or crack across the front element of your lens!
My opinion is that one should always use a high quality, multi-coated UV filter at all times on each lens, for protection against scratches and impact dents and dings (plus a lens hood to assist with both flare and bumps of the front of your lens against hard objects). No one intends to drop or bang their lens, but it can happen – when traveling, working in a hurry, falling from a not-fully-zipped bag, or an accidental loss of grip at anytime. When I worked in a camera store, people came in weekly with busted filters from dropped lenses, but the lenses themselves were nearly always fine. And in fact, it recently happened to me. As I was picking up my camera with a big heavy lens, the strap got caught on a low table corner and the camera was yanked from my hand. It crashed to the floor with a thud. I quickly inspected it and found the filter glass had broken but the ring was not dented (it was a pretty high quality filter). The filter apparently took the brunt of the impact and thus saved the front of the lens from damage, denting, and glass breakage. It stinks to have to replace an expensive filter, but that is cheaper and quicker than having a lens repaired or replaced.
The higher-quality the lens, the better the filter should be. A $50-60 coated or multi-coated filter may be sufficient for $300-$400 lens, but the highest quality B+W MRC filter should be used on a professional quality lens, like a Canon L lens. Some lenses, such as the Canon 16-35 f/2.8L II, even require a filter to complete their weather-proofing.
Anyway, I bring this up because there is a funny article about UV filters, cheap filters, good filters, stacking 50 filters, and the benefits of using high quality UV filters – here at lensrentals.com