B+W's 37mm Neutral Density 0.9 Filter reduces the light intensity by three f-stops (log density 0.9). It still features very good color neutrality. This ND filter is especially appropriate for use on video cameras when the lens cannot be stopped down sufficiently in great brightness or when a deliberately low depth of field is desired.
Each glass surface is vacuum coated with one layer of Anti-Reflection coating. This single layer helps to prevent internal ghosting and reflections. It also improves light transmission from approximately 92% (uncoated glass) to over 98%.
This filter uses the standard B+W F-Pro filter mount, which has a front accessory thread and is made of brass. Compared to the earlier standard mount introduced in 2001, the F-Pro mount has become thinner. Now it can be used with wide angle lenses, including most 24mm focal lengths on a full frame body, without vignetting. Another advantage of the F-Pro mount is it's modified retaining ring, which is no longer threaded in from the front, but holds the filter glass in place from the back. When removing a filter or lens hood that has been screwed on too tight to the filter, the retaining ring is not at risk of loosening.