The B+W 67MM 81-B SC (81B) Conversion Filter is also similar in effect to a Kodak Wratten filter and its strength of 27 Mired makes it comparable to the KR 3 conversion filter. Like the 81A it is recommended for color films that have an inherent reddish tone. This filter is popular as it leads to very pleasing skin tones in portraits. In addition, the 81B conversion filter is ideal for compact flash units with color temperatures higher than 6000 K. Its filter factor is approximately 1.2.
This filter uses a 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.
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%.