The Sky Watcher 2" Anti Light Pollution (ALP) filter features special coatings to improve contrast and makes emission nebulas and other faint targets easier to see by reducing the effects of light pollution. The filter rejects specific wavelengths of light, typically the wavelengths emitted by mercury and sodium vapor lighting (the two main types of urban lighting) while allowing the important wavelengths for the viewing of nebulas like Hydrogen-Alpha, Hydrogen-Beta, Oxygen III, as well as wavelengths of the visible light spectrum to pass through. This premium filter compares very well to more expensive light pollution filters many times the cost.

The nebula filter (often called a light pollution filter or LPR) is a must when viewing faint objects anywhere near town lighting. The filter will greatly enhance your views of emission nebulae and it will even improve views of galaxies.