Polarisers for camera lenses

tony1941 | 23:39 Fri 10th Jun 2005 | How it Works

3 Answers

Can anyone explain the difference between a normal (linear) polariser - which is just like your polaroid sunglasses - and a "circular" polariser, which doesn't interfere with auto exposure/focus etc?

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kempie

Linear and circular polarisers have the same effect (at least insofar as any two polarisers are the same). A circular polariser is in fact a linear polariser (which does all the work as far as you and the ccds are concerned), followed by a 1/4 wave plate (which scrambles or depolarises the resulting light just to make the AF and metering system happy, but doesn't affect the way things "look").

tony1941

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Thanks, Kempie! I should have thought of the quarter wave plate, but Iv'e been away from the sharper end of physics for too long. What this implies, though, is that the circular filter won't work if reversed, since the image will look as expected, but the AF and AE won't work. Is this true?

kempie

Good point, and your reasoning appears sound since the last transformation upon the light would leave it linearly polarised, but I cannot give a definitive answer.

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