The practical astronomer : comprising illustrations of light and colours, practical descriptions of all kinds of telescopes, the use of the equatorial-transit, circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy (1845)
Dick, Thomas, 1774-1857 · London : Seeley, Burnside, and Seeley · leaf 259
focal distanceof the lens to that of the eye ; and when the lensis very broad—such as the 26 feet lens mentionedabove—two or three persons may look through itat once, though they will not all see the sameobject. I have alluded above to a lens made byM. Azout of 600 feet focal distance. Were… … F THE ACHROMATIC TELESCOPE. 235 nify objects above 100 times, which is abouthalf the magnifying power it produced with itseye-piece. Suppose Azouts lens had been fittedup as a telescope, it would not have magnifiedabove 480 times, as it would have required an eye-glass of 14 or 15 inches focal…
Astronomy · Astronomical instruments · Telescopes
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