A refracting astronomical telescope has an objective lens of focal length 700.0

Question

A refracting astronomical telescope has an objective lens of focal length 700.0 mm and eyepiece of focal length 35.0 mm. (a) Calculate the angular magnification of this telescope for most relaxed viewing. (b) Determine the distance between the lenses. (c) Describe the nature of the image formed by this telescope. To convert this telescope to a terrestrial telescope an "erecting" lens of focal length 40.0 mm is inserted between the objective and the eyepiece. (d) Calculate the new distance between the objective and the eyepiece. (e) Describe another method which can be used to construct a telescope which produces an upright image.

Explanation / Answer

(a) angular magnificancation =-fo/fe

fo is the focal length of objective and fe is the focal length of eyepiece

given fo=700mm and fe=35mm

so angular magnificancation =-700/35=-20 answer is( minus 20)

(b) distance between the lenses =fo+fe = 735mm

(c) nature of image is inverted

(d) if erectiting lenses of focal length 40mm is inserted then the distances between the lenses= fo+fe+4f=735+4*40=735+160=895mm

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