difference between a CP and a Plain Polirizer?

[ak_powder_monkey]

So whats special about the CP as compared to a plain polorizer?

[PhotoJourno]

as far as I know, the circular polarizer allows you to move the filter for optimum view, while I do not think you can do much with a regular polarizer, except change your angle of light incidence into your lens until you reach the desired effect.

[neil_r]

They have the same effect and can both be rotated, some (most) auto focus/metering cameras have problems with linear polarizers and require the use of circular ones.

[SkipD]

A "circular" polarizer is the same as a "linear polarizer", but with an additional layer called a quarter-wave plate on the camera's side of the filter that changes the light's polarization inside the camera.

Here's a couple of links that describe it far better than I could: Polarization (http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html) Quarter-Wave Plate (http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/quarwv.html)

[ak_powder_monkey]

oh I see the quarter wave plate makes it so the polarized light is twisted off axis 45°

[islandtime]

Make sure you get the CP. Your EOS camera will not focus propery with the Linear type. I learned the hard way.