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 and the benefit of extra inward focus travel insert any 125 eyepiece into the chamber and youll enjoy double the magnification while retaining all the eye relief of the inserted eyepiece the celestron universal barlow and t adapter can also be used for prime focus photography which means you use the telesco