Lenses can be a very expensive investment. Good lenses can cost hundreds or even thousands of dollars. Such a investment is worth protecting. And it's easy to do. Simply by installing a ultra-violet filter (UV filter). A UV filter is a simple piece of glass that screws on to the front of your lens and protects it from scratches, dust, dirt, moisture and fingerprints while reducing unwanted ultra-violet light. Remember, it's far cheaper to replace a scratched filter than your $1000 lens.
When shopping for filters be sure and buy a high quality multi-coated glass. Be sure and stay away from cheap UV filters as cheap plastic filters will degrade your picture quality. One of the best UV filters is the B+W MRC UV , it's made from high quality glass and I consider this the best UV filter available.