Identifying Cir-Polarizer stops


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mobby

New Member
Mar 5, 2005
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Ysh ,SGP
www.pbase.com
#1
Hi guys,

How do you identify how many stops down does a Cir-polarizer produce?
Is there a marking or something? or there is only one kind of polarizer ?

Sorry if the question sounds stupid... new to polarizers ... hehe

Thanks.
 

Drudkh

Senior Member
Mar 2, 2004
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lulu island
#2
not sure how many or how much.
given a contant lighting environment, you meter a spot without the filter and another with the filter, then the difference will be the answer. :)
hope i'm right.
 

grantyale

Senior Member
Oct 4, 2004
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Bedok
#3
OOPS... I thought I answered it but somehow the post didn't came up...

It should be slightly more than 1 stop of light loss, if the incident light is circularly polarized(isotropic). (Ideally it is 1 stop but there's always extra losses here and there. )
However, light reflected off non-metalic surfaces are ovally polarized, meaning the intensity of EM wave is different in different directions. And how 'oval' the light is depends on the incident angle of that reflected light beam - and the ovality and direction of your PL front plate determines how many stops are lost.

Drudkh - good point :cool: it's tested to be slightly over 1 stop with a Hoya 67mm CPL, against a blank wall.
 

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