With approximately twice the strength of the KR1.5, the Heliopan 40.5mm KR3 (81C) Warming Color Conversion Glass Filter reduces blue and green. Even the strong blue cast of a high standing sun in a cloudless azure-blue sky, in regions with especially clear air, or the haze in distant views is removed very effectively. This filter also blocks disturbing UV radiation completely.
An 81C can also be used with electronic flash to reduce the amount of "blue" generated by the flash. The 81 series (81A, B, C, D and EF) allows you to choose how much warmth you wish to replace in the image.
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.