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Polarizer Uses


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#1 Jonathan Bryant

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Posted 01 August 2005 - 08:03 PM

I have used polarizers some to help cut down glare and help get more detail in skys but I still have a few questions. What is the difference between circular polarizers and regular polarizers? Also what are the most common conditions to use a polarizer? What are some conditions where you wouldn't want to use a polarizer?
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#2 Dominic Case

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Posted 02 August 2005 - 12:02 AM

What is the difference between circular polarizers and regular polarizers?

A polariser only transmits those light waves that are polarised in line with the polariser. Reflected light is mostly polarised in one direction, so by rotating the polariser to be at right angles to that direction, the reflected waves are filtered out.

With a normal polariser, it follows that all light getting through is then polarised in one direction. So a second polariser at right angles to the first will filter it all out, while if it is rotated to match the first filter, it will have no further effect at all. A pair of polarisers can therefore be used as a variable ND pack, going from about a stop and a half (.50ND) to black as you rotate one filter against the other.

Because some prisms also have polarising proerties, using a regular polariser can present problems in the camera (ie you can't see through the viewfinder - or if you can, the light doesn't reach the film gate).

A circular polariser filters out one orientation of light the same as a regulaar polariser, but then re-scrambles the light, so that what comes out is filtered, but UNpolarised again. In other words, it has the desired effect, but won't interfere with the camera optics.

Of course you can't use two circular polarisers together as a crossed pair.
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#3 Jonathan Bryant

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Posted 02 August 2005 - 05:15 PM

DO you have to use a circular polarizer for a betacam with manual focus? Or can you use just a regular polarizer?
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#4 Greg Gross

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Posted 03 August 2005 - 12:13 PM

Hello johnhollywood,

I believe you will find that you need a circular polarizer where "auto focus" is
in use. I believe you can get a way with a polarizer in manual focus. My camera
is not set up right now here in my studio,or I would give it a try. I use a circu-
lar polarizer on my PD-170 exclusively in manual mode with out any problems.
I rarely shoot in auto focus but sometimes I will for a quick take. I am not a vid-
eo expert and of course I prefer film. If Phil Rhodes is around on the forum he
might make a comment on this subject.


Greg Gross
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#5 Greg Gross

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Posted 03 August 2005 - 01:15 PM

Mr. Case of course has given an excellent explaination of the theory behind
the polarizers. It appears to me from past experience that I get the same re-
sults when using polarizer or circular polarizer in manual mode. I'm referring
to the use of my PD-170 with these filters. I am not familiar with betacam.


Greg Gross
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#6 Bob Hayes

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Posted 03 August 2005 - 03:27 PM

A circular polariser filters out one orientation of light the same as a regulaar polariser, but then re-scrambles the light, so that what comes out is filtered, but UNpolarised again.  In other words, it has the desired effect, but won't interfere with the camera optics.



No poop!
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