With approximately twice the strength of the KR1.5, the Heliopan Bay 3 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.
Note: Whereas the 81 Series of filters creates a feeling of warmth, the 82 Series creates a feeling of coolness. This filter is specific to lenses with Rollei's exclusive B3 (Bay 3) filter size;
Heliopan cuts, grinds, polishes and coats their filters with the same techniques and equipment as used for the finest German camera lenses
All Heliopan screw-in type and series size filters are mounted in precision black anodized brass rings to eliminate binding or cross threading and to ensure optimal alignment
Filters still retain front threads for a lens cap, a lens hood or even stacking a second filter
The portion of the Heliopan slim filters that are in front of the lens have been reduced in thickness by 37% over the former mount
81 Series Conversion Factors
81 decreases color temperature from 3300 - 3200 Kelvin
81A decreases color temperature from 3400 - 3200 Kelvin
81B decreases color temperature from 3500 - 3200 Kelvin
81C decreases color temperature from 3600 - 3200 Kelvin
81D decreases color temperature from 3700 - 3200 Kelvin
81EF decreases color temperature from 3900 - 3200 Kelvin
The 81 series adds warmth to the image
Good for general scenics when the photographer wishes to remove the bluish cast from open shade or just add warmth to the photograph, with an 81EF having the greatest effect
Decreases color temperature from 3600 - 3200 Kelvin