The circular polarizer filter produces the same effect as a linear polarizer filter, but is used in cameras where polarizing elements are used in the beam-splitters of the camera. If using a linear polarizer with such cameras, the light can become cross polarized (giving the same effect as using two polarizers together). Circular polarizers are made from a different polarizing material than linear & will usually prevent the cross polarization. Note that circular polarizers may only be used one way in front of the lens & are marked accordingly.