Abstract said:
Circular polarisers........I can't remember how they work from taking optics at Uni, but I would have thought that they would block out pretty much all light.....
Wikipedia has some useful information. In short: light travels in a given direction, and has wave-like "vibrations" in the plane perpendicular to that same direction. (Perpendicular meaning that the angle between the direction of travel and that plane is 90 degrees, no matter how you measure it.) If those vibrations are strictly in one direction (so it traces a line from one end to the other), the light is linearly polarised.
If the vibrations are circular, on the other hand -- so the vibrations are such that they would form a circle on a sheet of paper if you could see them -- they are polarised as by a circular polariser. It's a different form of polarisation, but it is polarisation nonetheless. You're confusing circular polarisation with putting two linear polarisers together, at 90 degrees to each other -- which would block most of the light, as you say.
I don't pretend to understand what happens to light when it bounces off a given surface, so I'm not about to try to deal with the rest of your query.
None of this is really necessary to understand for the purpose of photography, but it's interesting nonetheless (at least to me
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