"This is a high quality 2x Barlow that doubles the magnification of all 1.25"" eyepieces. This economically priced Barlow has great features like, low profile, 2-element fully-multicoated optical design and blacked lens edges.Barlow lenses offer an easy, economical way to increase the magnification range of your eyepieces, and Celestron carries two of these highly useful lenses. A Barlow lens doubles the magnifying power of your eyepiece by doubling its effective focal length. For example, an 18mm eyepiece used with a 2x Barlow lens would have the magnifying power of a 9mm eyepiece. It's like having two eyepieces in one! If you're looking for an affordable way to achieve high-power viewing of the moon and planets, double stars and even close-up views of terrestrial subjects, a Barlow lens is the answer. Barlow lenses mount into either your telescope's focuser or visual back."