The neutral gray half of this filter transmits 50% of the incoming light, so that it darkens the respective portion of the subject by one f-stop without altering its colors. For example, when the sky is too bright in relation to the landscape, this is an ideal amount for good detail rendition in the clouds and for preventing the sky from being "washed out" by over-exposure.Multi-Resistant Coating (MRC): MRC by B+W is not only an extraordinarily effective multiple layer coating, it is also harder than glass, so that it protects filters from scratches (for instance when cleaning the filters), and it is also water and dirt repellent, thus facilitating filter maintenance.his filter uses our standard B+W rotating 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.