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Old Jul 20, 2009, 3:28 PM   #1
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Default Filter / Circular Polarizing

How often do you use a Circular Polarizing Filter and under what circumstances do you use it?
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Old Jul 20, 2009, 4:18 PM   #2
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A CP has two primary purposes:
1) cuts down on reflections (shooting through glass, shooting cars, etc)

2) Deepens blue of the sky, add's punch/contrast to clouds. If you have polarized sunglasses you can see the effect. The 'circular' part allows you to control the degree of the effect. But the effect also depends on the angle of the sun/time of day. At highest sun on many days you wouldn't see the effect.

It really is like putting sunglasses on your lens - you lose a couple stops of light so it can be used for those purposes too (i.e. overly bright and you still want to use wide apertures).
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Old Jul 23, 2009, 9:24 PM   #3
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The “circular” part has nothing to do with the effect. A circular polarizer has a quarter wave plate (another filter layer) behind the polarizing layer to keep from confusing beam-splitter focus and metering systems. Non-DSLR cameras work just as well with a cheaper linear polarizer, as do some DSLRs that don’t use beam-splitters.

I think John is thinking in terms of a “rotating” polarizer which does control the effect.
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Old Jul 24, 2009, 5:51 AM   #4
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Every circular polarizer I've seen rotates. I've never seen marketing for a 'rotating' polarizer. For example, here is the description for a b+W circular polarizer:
http://www.bhphotovideo.com/c/produc....html#features

Note - the name doesn't say "rotating polarizer" - it says "circular polarizer"

And a quick look at Hoya's website lists 2 types of filters: Linear and Circular. Again, no third category of "rotating".

But I do see your point about 'circular' - the circular itself doesn't control the affect.

Last edited by JohnG; Jul 24, 2009 at 8:13 AM.
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Old Jul 24, 2009, 8:54 PM   #5
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All polarizing filters, AFAIK, are made to rotate, in order to control the polarity of the light entering the camera. Stacking two of them and adjusting the rotation of one, will give you a variable density filter up to nearly black, if you want reallllllly long shutter times. (this works with two linear, or two circular polarizers, but I'm not sure of the effect if you mix types)

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Old Jul 28, 2009, 1:37 PM   #6
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Quote:
Originally Posted by JohnG View Post
Every circular polarizer I've seen rotates. I've never seen marketing for a 'rotating' polarizer. For example, here is the description for a b+W circular polarizer:
http://www.bhphotovideo.com/c/produc....html#features

Note - the name doesn't say "rotating polarizer" - it says "circular polarizer"

And a quick look at Hoya's website lists 2 types of filters: Linear and Circular. Again, no third category of "rotating".

But I do see your point about 'circular' - the circular itself doesn't control the affect.
I was just trying to be nice and blunt the obvious criticism that the statement “The 'circular' part allows you to control the degree of the effect” is in error. I obviously know that polarizers rotate and don’t appreciate your deflecting the ignorance of your statement my way. I never said there was such a thing as a rotating polarizer as opposed to a non-rotating one. I said I thought maybe you confused "circular" with "rotating" as a means of effect control.


Brian Believe it on not, way back in film days I ordered a polarizer from Spiratone (remember them) that was a simple filter with no way to rotate it other than unscrew it. The useless thing is probably still with my antique camera gear somewhere. I never looked in the ad to see that it rotated as I assumed as you do that all polarizers must rotate.
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