China (Mainland) Circular Polarizer Glass Filter

Specifications: This filter is specially designed to be used with auto-exposure and auto-focus slr and video cameras. It does not influence the metering systems of these cameras. Filter factor is 2.3 to 2.8. Linear and circular polarizers both consist of a linear polarizer foil but differ in their construction in the following way. Modern slr cameras have a beam-splitting prism that sends part of the incoming light to the meter and part to the viewfinder. The effect is that the light entering the meter is partially polarized by the beam- splitter. A linear polarizer placed on the lens of such a system will act as a second polarizer and block light to the meter to a degree dependent on the angle between the prism and the polarizer on the lens. The result is incorrect exposure/aperture values from the meter. The circular polarizer circumvents this problem through the addition of a 1/4-wave retarder, or delay, foil. This ensures that the linearly polarized light is changed into a rotation that appears unpolarized to the meter, resulting in proper exposure/aperture readings. Remarks: OEM welcome