Ever wonder how the photographer got those big white puffy clouds to really pop out aginst a deep blue sky in a picture? She probably used a polarizing filter. Of all the filters, the polarizer is the most versatile and produces an effect you CANNOT DUPLICATE IN PHOTOSHOP. Yup, you heard me.

The function of this filter is to control reflected light and in doing so it is great for capturing the drama of the sky during a thunderstorm in Yosemite, saturating the Plum Crazy Purple paint job on a '71 Dodge Challenger, or minimizing the glare on shiny surfaces such as wine bottles, eyeglasses, oil paintings, etc.

For auto-focus cameras get the Circular Polarizer (not the more common linear one). This ensures proper functioning of the focussing function (say that 10 times really fast). For manual focus cameras, either a circular or linear one will work.