B+W 40.5mm MASTER High Transmission MRC Kaesemann Circular Polarizer Filter, with a rotating mount to control the polarization effect. The Circular Polarizer will work with all auto-focus lenses, and reduces reflections from a non-metallic surfaces such as water, glass, and glossy paint and increases color saturation and contrast. Objects behind shop windows or car windshields can become visible again. The multiplying factor with the HTC Filter is 2 to 3, which is equivalent to 1 to 1.5 f-stops, compared to other polarizers up to 3 stops, giving you better light transmission.