The Heliopan 77mm Kaeseman Circular Polarizing Glass Filter is constructed from select polarizer foils and especially prepared optical glass. Kaeseman ("encased") filters are completely edge-sealed for maximum durability under extreme climatic conditions.
Polarizing filters are used to select which light rays enter your camera lens. They 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 varied by rotating the filter. The filter factor varies according to how the filter is rotated and its orientation to the sun.
Heliopan Lichtfilter-Technik of Munich, Germany, has changed their black anodized brass filter rings on most Heliopan non-rotating filters to their "slim" mounts. These slim mounts are made of black anodized brass stock and have so little rim in front of the lens (5.4mm) that they will not vignette with lenses as short as 21mm.
Heliopan offers a wide selection of sizes, screw-in, series, bayonet, square and rectangular filters including digital, video, center weighted, graduated, wide angle, Kaesmann polarizers, drop-in polarizers, etc.