This is the Heliopan Bay 6 Circular Polarizing Filter. Light rays which are reflected become polarized. 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 changed by rotating the filter. The filter factor varies according to how the filter is rotated and its orientation to the sun.
One of the "wow" factors of this filter are the index markings on the edge of the filter ring. This allows you to hold the filter up to your eye, choose a point that you like for polarization, replace the filter on the camera and simply rotate the ring to the chosen mark.
If you're out walking on a lovely day - in the mountains or at the beach - and you want to get a fabulous shot of a cloud-filled sky or make the water seem more saturated, then a polarizer is the way to go. This filter is the best way to make the clouds stand out, increase or decrease the saturation of the ocean or increase or decrease the reflection off the water. You can also use this filter when shooting into glass or windows since it will, again, either increase or decrease reflections.
If you're shooting black and white and want to simulate a threatening storm, try throwing on a #25 Red filter. The vista will take on the appearance of an imminent, ominous storm.
Along with a UV or Skylight Filter, a polarizing filter should be a part of everyone's gear bag. It can turn a run-of-the-mill image into a stunning, creative photo by increasing color saturation.
Heliopan has been a leader in the filter industry since 1949. They are known for their high quality and production standards. Their slim mounts facilitate using them with wider angle lenses. Heliopan offers most of their filters with either their standard hard coating or with their industry leading SH-PMC 16 layer multi-coating that transmits over 99.5% of the light striking it on to the image plane for the lowest flare and greatest color saturation.
The reputation of Schott glass is world renowned. The high production standards combined with a sturdy brass filter ring make this filter hard to beat. It has a "heft" that is impressive. It may feel heavier but the benefit is in the construction and results. Not only is the glass exceptional but so is the seal between the ring and glass. Schott Glass used in the manufacture of this filter is legendary and synonymous with the highest standards of filter production.