Lens filters alter the way light reaches the camera's sensor.
Single-lens reflex cameras allow you to change the lens attached to the body to help you get the shot. Most single-lens reflex camera lenses also allow you to attach lens filters. These filters alter the light that enters the camera and hits the camera sensor. Good lens filters do not negatively affect the sharpness of a photo.
Polarizing Filters
Polarizing filters reduce the amount of reflected light that enters your lens, which increases the color saturation. They are particularly useful for landscape photography because the filter makes the skies appear a richer blue and the colors of flowers and trees deeper greens. The intensity of the polarizing filter can be adjusted by rotating the filter.
Neutral Density Filters
Neutral density filters reduce the amount of light that reaches the camera's sensor. Photographers use neutral density filters when the scene is particularly bright or when they want to slow the shutter speed. For example, if you wanted to take a picture of a stream and wanted to blur the water, you might attach a neutral density filter to reduce the light entering the camera so you can use a longer shutter speed. Neutral density filters come in different strengths, ranging from one f-stop to six f-stops. The more f-stops the neutral density filter, the less light the lens lets in.
Graduated Neutral Density Filters
Graduated neutral density filters are similar to neutral density filters except the entire filter does not block light. You can adjust the filter so more or less of the lens is covered by the filtered part. This filter is particularly useful for landscapes that have a bright sky and a darker ground, such as sunset photos. The filtered top part decreases the light from the sky so the ground also can be properly exposed. Like neutral density filters, graduated neutral density filters come in a variety of strengths.
Ultraviolet Light Filters
Ultraviolet light (UV) filters are most effective on film cameras because digital camera sensors are not affected by UV light as much as film. On a film camera, the UV filter increases the contrast of the photos. On a digital camera, a UV filter is used primarily to protect the lens. A filter is much less expensive to replace in the event the glass becomes scratched rather than the entire lens.
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