A moon filter reduces irradiation, glare, and excess image brightness in lunar observing. It also improves the contrast between lunar albedo features. This green moon filter will screw directly into the barrel of most 1.25" eyepieces. Its green color cuts the glare of the brightly-lighted Moon and improves the contrast so it is easier for you to see faint details that might otherwise be washed out by the brightness of the lunar surface.