A professional put it to me this way. "Every filter you put in the way degrades your image, so it is extremely important to not be cheap in this area." B+W, aka Schneider Optics, aka Century Precision Optics, makes the best filters I have found. The Circular Polarizer will run you about $75-$120 for a good one, a UV will be about $40 or so, and most others fall in between. However, you will not be disappointed. The ring around the filter itself is made of a sturdy metal alloy, as opposed to plastic, giving a MUCH more reliable and sturdy product. And, in my experience, they definitely have the least distortion and aberration of any of the other manufacturers. B&H Photo, www.bhphoto.com, has a very nice spread of B+W filters.