The Heliopan 39mm Deep Blue KB12 Glass Filter blocks so much red, orange and yellow that it increases the color temperature of very bright halogen and special photoflood lamps (of around 3400K) to that of daylight. With that kind of illumination, and with daylight color reversal film, the subjects will be reproduced in their original colors.
With weaker halogen bulbs or stronger incandescent bulbs in conjunction with this filter and with daylight reversal film, a residue of "warmth" will be retained for an optimal mood in interior photographs.
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.