Astronomical telescopes all use interchangeable eyepieces. These are available in a variety of powers and optical quality. To calculate the magnification an eyepiece will give you take the focal length of your telescope and divide it by the focal length of the eyepiece. For example a 6.3mm eyepiece used on a telescope with a 1000mm focal length would give a magnification of 158x. A 32mm eyepiece used on the same telescope would give a magnification of 32x.