B+W's 37mm IR Dark Red #092 Filter has become a popular filter for IR photography with digital SLR cameras. This nearly opaque filter looks dark purplish when held in front of a light source and blocks the visible spectrum up to 650 nm. It passes only 50% of the radiation just below 700 nm and from 730 nm to 2000 nm, transmission is greater than 90%. As the sensitization of IR films barely extends beyond 1000 nm, the red portion that is transmitted still makes a relevant contribution to the exposure. Effectiveness and filter factor are largely film and light dependent and individual testing is recommended.
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.