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 455
f the object is formed most distinctly;which is to be nicely measured from the objectlens, and compared with the solar focus of thelens or telescope, so as to ascertain their difference.And the rule for finding the distance is,—c Asthe difference between the focal distance of theobject, and the… … Let AB (fig. 84.) be the object lens, EY theeye-glass, FC the radius, or focus of the lens AB,and C/the focal distance of the object OB, whosedistance is to be measured. Now suppose CF =48 inches, or 4 feet, and that we find by theabove method that C/is 50 inches, then F/ is 2inches ; and the…
Astronomy · Astronomical instruments · Telescopes
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