Quote Originally Posted by 0llym
i know that people recommend a circular polariser as it works with auto focus cameras, but i have just accidentally purchased a linear one on ebay
I'm assuming that i can still use it, but i will have to use the camera in manual focus mode.
Is this correct ?
Yes. The "autofocusing" depends on the difference in phase of two beams of polarized light. In a "linear' filter light is polarized ... once, and that is it... It removes a certain part of the light (filters can only remove) and the passed light stays polarized - and confused as to phase. In a "circular" polarizer there is another element... a "scrambler" plate to again "depolarize" the remaining light after the unwanted part is removed ... and the focusing sensors again have something closely related to light with the original polarization. Manual focusing does not depend on phase shifting - so everything should work OK.

Now - exposure. Hmm ... I *don't* think exposure itself should be affected. I've metered a LOT with the built-in OM-4 Olympus using both circular (I picked one up in a "Dump Them" bin -wrong size - but wonderful with an adapter) and the Cokin and Tiffen "Linear Polarizers", and I've never noticed an exposure problem.