magnification (magnifying power)

The factor by which the angular size of an object is apparently increased when it is imaged by a particular combination of telescope and eyepiece. The magnification of an image made by a telescope is given by the focal length of the telescope divided by the focal length of the eyepiece. A high magnification is not always an advantage. It results in a small field of view in which the effects of bad seeing and any optical shortcomings are emphasized. The contrast between markings on planets and the Moon may also be reduced. Eyepieces should therefore be selected to be appropriate to the type of observations being made.