Circular Vs. Linear Polarizers

[RCGillespie]

Found this info on the web.
I am looking tp buy some filter.

Circular Vs. Linear Polarizers
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.

[directshooter]

In my exp circular is the way forward..
Si.

[sobhana]

I now have a circular and I love it. I think Coffee mentioned the vignetting you can sometimes see but other than that I really like it. I think I got my filter (72mm) for about $25 bucks..so it wasn't that expensive at all.

[pauld]

The 1M$ question is, of course:
how do you know which is which ?

Imagine you have a pola filter but it does not say what type it is?

:confused:

Imagine a test.

Paul.

[reval8r]

The only difference is that auto focus lenses will not auto focus with a linear polarizer. If you use auto focus lenses you'll need a circular polarizer, that's the reason circulars are higher in price. Other than that they do the exact same thing.

[pauld]

The 1M$ question is, of course:
how do you know which is which ?

Imagine you have a pola filter but it does not say what type it is?

Imagine a test.

Paul.

This is the test:
To distinguish a Circular Polarizer from a Linear Polarizer, turn the filter backwards and look through it into a mirror. If the filter image in the mirror is black, you have a circular polarizer. If the image is clear, you have a linear polarizer.

Paul.