A beginner's star-book; an easy guide to the stars and to the astronomical uses of the opera-glass, the field-glass and the telescope (1912)
Murphy, Edgar Gardner, 1869-1913 · New York, London, G.P. Putnam's Sons · leaf 118
lens has always a fixed focal length. The focal length of a lens represents the linear distance betweenthe centre of the lens and its focus. The magnifying power of a telescope is that of the eyepiece and the object lensin combination; and this power equals the focal length of the objective divided… … TELESCOPE—MODEL A Alt-Azimuth Mount Ins 104 a BcGinner0 Star*16ook ends of the instrument. The objective, however, is fixed; so we secure our changes inmagnifying power by changing the eyepieces. And as this is easily and quickly done wefall naturall} into the habit of speaking of 40-power…
Astronomy
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