@timtam has very good points, but I just thought I might bring some balance in regards to clear/uv filters. While adding a cheap piece of glass in front of your lens is less than optically ideal, scratching the front element of your lens (by cleaning or by use) is not a way to get sharper images. Always use high-quality filters such as b&w (why go cheap on what’s already not that expensive?) It is actually unlikely you’ll be able to distinguish any difference with a filter on, unless you start stacking nd’s cpl’s etc, then take your clear/uv filter off to avoid vignetting, naturally. Here’s Bryan Carnathan on filters: http://www.the-digital-picture.com/Reviews/UV-and-Clear-Lens-Protection-Filters.aspx The effects of a *high quality* filter are negligible, and most of us would rather chuck a 100$ filter, than send our lens into CPS to get a front lens element replaced. It’s also worth mentioning that most “weather sealed” lenses (such as the 70-200 2.8 is II) require a front filter to complete weather sealing.
