Circular polarizer

[Crashoran]

I've never understood clearly, when using a CP, you lose 1-2 stops of light?

If shooting in AV mode I should have +1-2EV set?

[Madweasel]

Light is lost because the filter is selectively letting through light of a given polarisation. Your light meter in the camera is seeing the lower light level and therefore gives the correct exposure without adjustment.

[Crashoran]

thanks!

[JackProton]

Yep, as far as the camera is concerned, you're just shooting in dimmer light.