Astronomical telescope: Using objective and eyepiece lenses.

Astronomical telescope: Using objective and eyepiece lenses. The astronomical telescope is used to view objects that are far away. This simple telescope consists of an Eyepiece which is a converging lens with a short focal length (fe = +5"), and an Objective which is a converging lens with a longer focal length (fo = +28"). The lenses are mounted on an optical bench to insure alignment. The object to be viewed is an Arrow Object Card mounted on a distant wall, 25 feet or so away. The Objective (the lens nearest the viewed object) forms a real inverted image at fo, which is a focal length fe away from the Eyepiece. Thus, the distance between the lenses to have the arrow in focus for viewing is the sum of the focal lengths (fo+fe = 5"+28" = 33"). Placing an eye (or a TV camera) close to the eyepiece will see the distant arrow magnified by the ratio of the focal lengths (fo/fe = 28"/5"_6). That is, the arrow is 6 times larger than what would be seen by the unaided naked eye.