Cokin 77mm Circular Polarizer
Great simple tool for eliminating reflections in windows, reducing glare on shiny surfaces, increasing reflections in glass and producing a deeper blue in sky. For 72mm lens threads such as XL1, XL1s, XL2 and DVX100a. This filter uses a circular pattern so that you can use the autofocus of your camera. Highly recommended for use with car-mounted cameras to reduce the glare of the windshield.
Works great for glare from shiny surfaces, you can reduce the amount of glare to produce a deeper color saturation. You can also use it to either reduce reflections in windows or increase the reflection, depending on which you want (eliminate the reflection or enhance the reflection). For the sky, it deepens the blue but works only if the sun is to your left or right — when the sun is in front or behind you, it does nothing.