These filters are used to reduce or eliminate reflections. They are ideal for photographing through glass or water as the glare from water tends to be white. Polarizing filters can also reduce the effects of haze and darken the blue sky image in black and white and color photography. There are various polarizing filters available to increase color saturation in a photo without altering the hues of image colors, but there are only two principal styles. One style fits over your camera lens, while the other is made to be used over the source of light. They don't affect color, that's why polarizing filters and screens are used in both black and white and color photography. There are two pieces to a polarizer. The front part rotates so you can change the angle of polarization. If you look at the blue sky through a polarizer and rotate it, the sky appears to get darker and then lighter. These filters range in price from about $15 to $800. They come in various sizes.