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Recognizing circular vs linear polarizer


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#1 Mike Medavoy

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Posted 20 March 2007 - 03:15 PM

Hello!

I want to buy a Tiffen 4-1/2 circular polarizer filter. The seller insists that it is CIRCULAR not linear. I want circular.

However, on the filter itself it only says Tiffen Professional 4-1/2 polarizer USA. it doesn't say circular nor linear.

Is there any way to make sure the filter is indeed circular? Can it be tested? How can one tell?

Thanks a lot for any advice.

All the best,
Mike
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#2 Dominic Case

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Posted 21 March 2007 - 02:10 AM

Is there any way to make sure the filter is indeed circular? Can it be tested? How can one tell?

A so-called circular polariser polarises light and then depolarises it on the way out. It's a one-way effect.

Take a second polarising filter (circular or linear) and place it behind the one you are interested in. Looking through them, rotate one relative to the other.

Assuming they are both genuine polarisers, the only way you won't see the pair of filters getting lighter and darker is if the first filter is a circular polariser facing the correct way. If it's linear, or if it's back to front, the filters will go through crossed and uncrossed phases as you rotate them.
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#3 Mike Medavoy

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Posted 21 March 2007 - 03:05 PM

Thanks so much for the tip Dominic.

As it happens, I do have another circular polarizer, a Cokin 77mm wide angle which I use on my video camera. I tried the trick you told me and - while the colors do change a bit looking through the two filters as you rotate - they do not fade in/out. So The 4 1/2 filter is indeed circular.

However, I tried it the other way (out of curiosity), looking through the 77mm to the 4 1/2 filter. As I rotate the 77mm, the 4 1/2 fades in completely and back again.

So the Cokin is not circular, even though it says clearly on the ring "circular"...

Thanks again for the advice,
Mike


A so-called circular polariser polarises light and then depolarises it on the way out. It's a one-way effect.

Take a second polarising filter (circular or linear) and place it behind the one you are interested in. Looking through them, rotate one relative to the other.

Assuming they are both genuine polarisers, the only way you won't see the pair of filters getting lighter and darker is if the first filter is a circular polariser facing the correct way. If it's linear, or if it's back to front, the filters will go through crossed and uncrossed phases as you rotate them.


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Aerial Filmworks

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Technodolly

CineTape

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