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angular magnification

(a magnification measure for a magnifier with an eyepiece)

The term angular magnification is used for magnifying instruments (telescopes, microscopes) that include an eyepiece. The more general term magnification is used for the ratio of the size of an image with the size of the object it is an image of. When viewing through an eyepiece, the apparent size is because light from two points a certain angle apart (without the telescope) appear to be coming from a greater angle apart when viewed through the telescope. This ratio of angles is the telescope's angular magnification.