A Barlow lens is an additional lens that multiplies the total magnification of a telescope. Typically, Barlow lenses are usually 2x or 3x in power, therefore, doubling or tripling the overall power. They can be handy to get a closer view of an object, but a regular eyepiece without a Barlow should be used first. Once you have found and focused on the object, then insert the Barlow lens before the eyepiece and view again to get that extra close image.