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 364
enses are turned into contrary directions inthis eye-piece—-one facing the object-glass, andthe other the eye of the observer; and as the imageformed at the focus of the object-glass, lies paral-lel to the flat face of the contiguous lens, everypart of the field of view is distinct at the… … vex lenses, with their convex sides inwards. Theyhave nearly the same focal length, and are placedat a distance from each other, equal to about twothirds of the focal length of either. The focallength of an equivalent single lens is equal to threefourths the focal length of either lens,…
Astronomy · Astronomical instruments · Telescopes
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