Ostara Achromatic 2x Barlow Lens RRP £36.99 Save with Buy It Now + Free UK Postage   Doubles Eyepiece Magnification - Standard 1.25" (31.77mm) Fitting - Achromatic Lens 2x Achromatic Barlow lens that doubles the eyepiece magnification Achromatic lens reduces the effect of chromatic and spherical aberration Metal body construction with fully coated glass lens Size: 1.25 in (31.75 mm) Barlow lenses mount into either your telescope's focuser or visual back. What Magnification is this Eyepiece? The magnification produced by an eyepiece depends on the optical system it is used in. In a standard astronomical telescope the magnification is found by dividing the focal length of the main tube by that of the eyepiece. For example, a 1000mm scope tube used with a 10mm eyepiece gives 1000/10 = 100x magnification. Used with a 5mm eyepiece gives 1000/5 = 200x. Check out my other items! Sign up for my email newsletters by adding my eBay Shop to your Favorites