The 81C Filter from Heliopan controls the bluish coloration that affects daylight film. This is a strong salmon colored filter that can bring skin tones back to a respectable tone when the light changes during the day. It is especially useful under cloudy or open shade conditions since as the light changes, so does the color temperature. An 81C will decrease the color temperature by approximately 100 degrees Kelvin more than an 81B.
It's Autumn. The clouds are low hanging and the sky is "patchy blue". You've gone for a ride upstate to the mountains and the light in open shade is bluish. A photo taken of your girlfriend with daylight balanced film leaning against the side of a barn will yield bluish tones that she might not find particularly flattering. If the sky is significantly cloudy, an 81C filter will bring her skin tones back to a more appealing level than, perhaps, an 81B. The cloudier the day, the warmer the filter you require to eliminate the blue tint often found on such days. An 81C can also be used with electronic flash to reduce the amount of "blue" generated by the flash. An 81C is a strong filter that can also be used to make a warm scene even warmer such as a beach shot where you wish to enhance the overall sense of temperature.
The filter ring is made from brass yielding a stronger product. Brass filter rings are also less prone to jamming. In addition, the seal between the glass and filter ring is exceptionally strong giving the filter added strength and durability.
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.