The Heliopan Bay 104 #15 Dark Yellow Glass Filter for Black and White Film is commonly used for a more than noticeable increase in contrast with black and white films.
When a #8 or #12 Yellow isn't enough, the #15 is the next stop. This filter adds a significant amount of contrast to black and white film. And, should this filter not be sufficient, an orange filter is recommended, followed by red, which will provide maximum contrast with black and white film.
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.