What is a polarizing filter?A polarizing filter is most commonly used to increase the color saturation of a blue sky for more dramatic images of clouds. It can also be used to increase the color saturation of green foliage such as grass and leaves or to reduce the reflections from glass windows or water surfaces under some conditions.
The type of polarizer used is determined by the camera, not the lens. Autofocus cameras such as the F5, F100, N80, etc. use a beam-splitter design in their focus detection systems that is incompatible with older polarizing filters (now called "linear" polarizers) because the combination of the filter and the beam-splitter can block light from reaching the focus detector in some circumstances. "Circular" polarizers use a different type of polarizing material in their construction that filters the incoming light in a way that does not interfere with the operation of the detector.
Since circular polarizers are compatible with non-autofocus cameras (such as the FM3A, FM2N, and F3HP) as well as autofocus models, we now manufacture only the circular type. Customers who have the older (linear) type can use them with non-autofocus cameras, but an autofocus camera must be focused manually if a linear polarizer is mounted on the lens.