B+W Basic Circular Polarizer is vacuum coated with one layer of anti-reflection coating, which helps to prevent internal ghosting and reflections. This filter has a filter factor between 2.3 and 2.8 (approximately 1-1.5 stops of light loss) The filter ring is made from brass with a female thread, enabling more filters to be stacked. Note that vignetting may appear with any lens less than 20mm on a full frame camera body.
This filter incorporates the MRC (multi resistant coating) by B+W, an effective multiple layer coating which is harder than glass so it protects filters from scratches, and it is also water and dirt repellent. The coatings help keep the filter clean from smudges, reducing the need to clean as often as un-coated filters.