Celestron Barlow lenses double the magnification of your eyepiece by doubling the effective focal length. With careful selection of eyepieces - perhaps 3 - plus a Barlow lens, the user has a very useful range of different magnifications to choose from. Of course, this is also more cost effective than purchasing 6 separate eyepieces. Barlow lenses can be used in both the focuser and the eyepiece.
This photo-visual Barlow lens can be used for all 1.25" connections and where there is a focus problem with adapters. When inserted, the Barlow lens moves the focus position further back, to resolve any focus problems as they may occur, especially with Newtonian telescopes with their shorter focus ranges.
