These are the two filters I own that fit two of my four lenses. One is a UV filter that is meant to stay in the front of the lens just in case something hits the front while travelling with the camera. It’s literally an extra piece of glass. It doesn’t change the image that one creates very much.
However, the other is a polarizing filter. What it does is that it makes light entering the lens orient itself so that reflections from surfaces are minimized. It can also make the sky have a deeper blue look. This is done by rotating the filter itself. It’s designed so that it’s free to rotate while safely screwed in tight to the front of the lens. Pretty neat stuff.
Taken with Canon EOS Digital Rebel XTi.
Canon EF-S 18-55mm f/3.5-5.6 at 51mm.
Shutter Speed: 1/10s.
Edited with Adobe Photoshop CS5.