The Celestron 2x Barlow lens with T-Adaptor can be used three ways: as a 2X Barlow for visual use, as a prime focus T-adapter, or as a "" Barlowed"" T-adapter for double the magnification & the benefit of extra inward focus travel. Insert any 1.25"" eyepiece into the chamber & you'll enjoy double the magnification, while retaining all the eye relief of the inserted eyepiece. The Celestron Universal Barlow & T-Adapter can also be used for prime focus photography, which means you use the telescope as a photographic lens.