A x2 Barlow Lens (unless already supplied) is a very useful accessory. It effectively doubles the focal length and hence the magnifying power of the objective lens. Therefore, when used in conjunction with an eyepiece, it has the effect of increasing each standard eyepiece magnification by a factor of 2, giving twice the range of standard magnifications than available before. (e.g. if your telescope offers magnifications of x20 and x50 without a Barlow lens, with a Barlow lens magnifications of x40 and x100 are also now possible.) Using a Barlow lens to increase magnification also has other benefits: Improved eye relief and reduced spherical aberration in the eyepiece.