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.