The B+W 39mm 81B MRC Filter is a color conversion filter that helps to slightly decrease color temperatures and provide a warming effect. The 81B filter adds more warmth to the image for use with tungsten films in natural lighting. It provides a decrease of 300K, helping to render the scene more similarly to incandescent illumination.
The Multi-Resistant Coating (MRC) is both an anti-reflection coating as well as a protective surface. It helps to increase light transmission by reducing reflections, scattered light, and ghosting. Additionally, it offers greater protection to the filter substrate and stays cleaner for longer than uncoated filters.
There is a 1.5x filter factor with this filter, requiring an increase of 0.6 stop for normal exposure. B+W filters are constructed from high quality Schott glass for increased optical clarity and color fidelity. They feature a brass filter ring for durability as well as jamming prevention.