Circular Polarizer

[GenJerDan]

Got one. 72mm screw on.

It rotates.

Why?

Have I misunderstood what "circular" means in this case? Doesn't make sense to me to rotate it...should be the same no matter what.

I hope I'm right... I'd like to superglue the damn thing so it doesn't rotate. A real bear to screw on/off with my fingers reaching down the throat of the sunshade.

So, should I go ahead and glue?

Dan

 

[Stas_Tagios]

Rotating the filter allows you to adjust the degree to which the polarizer affects your image.

 

[Shaw]

Indeed. Rotating is very useful!

 

[GenJerDan]

Then what do they mean by "circular"? I thought it was concentric rings.

Dan

 

[thisiswells]

There are two types of polarizing filters available — linear or circular. Linear polarizers are more effective and less expensive than circular ones. But circular polarizers are needed with just about any camera that has a through-the-lens metering system, or autofocus.

The reason for this is that both of these systems use semi-silvered mirrors to siphon off some of the light coming though the lens. If that light is linearly polarized it renders either the metering or the autofocus ineffective. This means that you're going to have to buy circular polarizers unless you're shooting with a pre-1970's camera, or a view camera.

from here:
http://www.luminous-landscape.com/tutorials/polarizers.shtml

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Generally speaking, use a linear pola on film and a circular pola on video, or or on film if the camera has polarized optical elements in the viewfinder system.. Just use the circular and don't worry about it.