The Cassini 3x Barlow increases the focal length of a telescope 3 times. The result is 3 times the magnification with the eyepieces you already have. If you have 3 eyepieces, adding 1 Barlow will in effect expand your eyepiece collection to 6 without having to purchase an additional 3 eyepieces. The Cassini 3x Barlow Features and Benefits: Format: 1.25″ Focal Length: 3x Coated lens