The 52mm Drop-in Circular Polarizing Filter from Canon is used with long Canon lenses that accept rear-mounted drop-in filters. The filter is rotated from a ring on the outside of the filter mount. You do not have to remove the filter to use it. The glass is secured within a strong metal frame that slips in and out of the rear mount with ease. The degree of polarization can be seen through the viewfinder of your camera as you rotate the filter.
Light rays which are reflected become polarized. A Polarizing filter is used to select which light rays enter your camera lens. It can remove unwanted reflections from non-metallic surfaces such as water or glass and also saturate colors providing better contrast. The effect can be seen through the viewfinder and changed by rotating the filter. The filter factor varies according to how the filter is rotated and its orientation to the sun.