Quote Originally Posted by Ed Sukach View Post
Trying before buying might not be easy, or possible.

In reading this, my "carved-in-stone" belief that ALL autofocusing systems REQUIRE the use of a circular polarizer was shaken. So - I went to my latest acquisition, and my only autofocusing camera, a Canon EOS Elan IIe.
In scouring the Instruction book .. not one word about polarizing filters. Nada.

Then to the B&W web site and their .pdf Filter Catalog, page 15:

"B&W Circular Polarizing Filter - Highly efficient standard circular polarizing filter for all cameras with beam splitters in the light paths of their TTL exposure meters and with autofocus lenses. Circular polarizers have the same pictorial effect as linear polarization, but allow for proper exposure metering and distance settings."

The question then is whether or not the camera in question has a "beam splitter". If so, proper operation would be suspect, at least, with the use of a "linear polarizer"; while a circular polarizer would be appropriate in either case.

It might be wise to opt for the "circular", given the possibility of its use in a future system, with "beam splitter".

B+W are in the know, ditto Hoya.
It is the meter that is going to be most affected by the type of polariser, much less the autofocus. Particularly evaluative / matrix meters. Most cameras using evaluative (Canon) or matrix (Nikon) et al systems have one or more beam splitters and thus a Circular Polariser (C-POL) is requisite.