A circular polarizing filter is for use with all cameras with beam splitters in the light paths of their TTL exposure meter and with autofocus lenses.
A Linear polarization filter is for SLRs and rangefinder cameras without beam splitters in their light paths.
Circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings.
Polarizers are multi-talented
Experienced photographers consider po-larizing filters to be the most important filters. Their ability to reduce or eliminate reflections is probably their best-known feature, but it is not the only one. They enhance the color purity of the subject (increased color saturation) by blocking the blue veil of light from the sky, They increase the contrast in black-and-white photographs, reduce haze, and make white clouds stand out dramatically from an intensely blue sky. When the filter is rotated by 90º from its normal reflection-reducing position, it can even appear to increase the relative intensity of reflec-tions on water, glass, lacquer and plastic materials up to a factor of 2. B&W Filter Handbook
With polarizing filters, reflections on glass, lacquer, on nearly all plastic materials and other electrically non-conducting surfaces can often be reduced or even eliminated. Polarizing Filters provide you the control over how much reflection you wish to remain because the light reflected at an angle of about 40° to 70° by these surfaces is strongly polarized. Its transmission can be reduced, blocked or even enhanced! In relation to the re-maining unpolarized light, depending on the rota-tion of the filter. Thus a clear view is made possible through plates of glass, of goldfish below the sur-face of the water, or of writing or pictures behind a glossy layer of lacquer.
Every object outdoors reflects light from the sky more or less diffusely and largely polarized, some objects, such as green plants and red roof tiles are covered by a bluish-gray veil that can make them appear pale and dirty. Polarizing Filters can remove this polarized veil and thus increase the saturation of the true color. Because the blue light from the sky, especially at an angle approximately perpendicular to the sun is strongly polarized, a polarizing filter can be used to render the sky with a more saturated color, so that white clouds will stand out more dramatically. B&W Filter Handbook