When people buy astronomical telescopes, they have an option to buy a set of eyepieces to go with it. If Fred bought a telescope with an objective with a focal length of 2000 mm, and eyepieces with focal lengths of 40 mm, 16 mm, and 8 mm, then what magnifications will Fred expect from his telescope?
The power of the telescope is the ratio of objective to eyepiece focal lengths.
The power of a telescope is the factor by which the subtended angle of an object is increased, when the eye is focused at infinity.
The powers available in this case are
2000/40, 2000/16 and 2000/8. That converts to 50, 125 and 250.