The Celestron Omni 1.25\" 2x Barlow Lens is the astronomy accessory that keeps on giving!. Insert it between your eyepiece and your telescope to get double the magnification instantly. Say you have two eyepieces in your accessory case, a 10 mm and a 25 mm if you add a Celestron Omni 2X Barlow Lens to the mix, you now have four magnifications to choose from. Combining this lens with the 25 mm provides double the magnification, or the equivalent of a 12.5 mm eyepiece, while the 10 mm gives you the power of a 5 mm eyepiece. Eye relief is the distance your eye has to be from the first lens in the eyepiece in order to see the full field of view. When you use a Barlow lens with an eyepiece, you get double the magnification, but the eye relief is not affected. This is a good thing, because normally the shorter the focal length of the eyepiece, the less eye relief you have. The Celestron Omni 2x Barlow comes in a sleek, silver package. The two-element optics are fully multi-coated, and the edges of the lenses are blackened to cut down on internal reflections. The 1.25\" barrel will fit in standard 1.25\" focusers and diagonals, and the Barlow will accept 1.25\" eyepieces. A metal thumbscrew locks the eyepiece firmly in place.Features- Double the magnification of each eyepiece you own with the Omni 2X Barlow Lens- Keep the eye relief of your eyepieces while getting 2X the power- Slides into 1.25\" focusers and diagonals and accepts 1.25\" eyepieces- Fully multi-coated optics with blackened edges for good light transmission and minimal reflection