Polarizers are used to eliminate reflections from smooth, nonmetallic, polished surfaces, such as glass, tile, tabletops, and water, and they can improve the color saturation by screening out the polarized part of the glare. This can make a clear blue sky appear deeper and richer and have more contrast without altering the overall color balance of the scene. The increase in saturation results from a decrease in surface glare. Since most semi-smooth objects, such as flowers, leaves, rocks, and water, have a surface sheen, they reflect light, thus masking some of the color beneath the sheen. By reducing these reflections, the polarizer intensifies the colors.
A quality circular polarizing filter should work on any SLR camera, including auto-focus, but check the camera manual to be certain. The traditional linear model will produce underexposed and out-of-focus pictures with an auto-focus camera.
When using a polarizing filter, focus first; turn the filter mount until the glare decreases and the colors look richer; then make the exposure. The filter factor will remain the same, regardless of how much the filter is rotated. The filter factor varies, from about 2X to 3X, depending on the type of polarizer used.
The amount of the effect is determined by how much polarized light is present in the scene and the viewing angle of the scene. At an angle of about 35 degrees from the surface, the maximum reduction in reflections can be achieved when the polarizer is rotated to the correct position.