A Barlow Lens can multiply the power of the eyepiece by a specified magnification factor. For example a 2x Barlow lens will double the magnification and a 3x Barlow will increase the magnification by 3 times. A Barlow lens is placed between the objective lens and the eyepiece.
The magnification/amplification factor of a Barlow is a function of its position in relation to the eyepiece and the objective lens. This factor can be increased by increasing its separation from the eyepiece using an extension tube. There are compact shorter tube Barlow lenses and longer tube Barlow lenses, both can achieve the marked magnification results.