Vixen's 2x Barlow Lens DX conveniently doubles the effective magnification of any eyepiece in use, and does so without reducing the eyepiece's eye relief so that you'll get the power of a lower-focal-length eyepiece without its normally corresponding small eye relief.
This Barlow lens fits directly into the visual back of telescopes, and if you do so with a diagonal mirror or prism behind the Barlow(closer to your eye in the optical path) you'll have an effective 4.0x magnification of the normal scope/eyepiece combo. This is the DX version of the Barlow, with full multicoatings on each air-to-glass surface.
