Chapter 27, Problem 15PCE

The Hale Telescope The 200-in. (5.08-m) diameter mirror of the Hale telescope on Mount Palomar has a focal length f = 16 9 m (a) When the detector is placed at the focal point of the mirror (the “prime focus”), what is the f -number for this telescope? (b) The coudé focus arrangement uses additional mirrors to bend the light path and increase the effective focal length to 155.4 m. What is the f -number of the telescope when the coudé focus is being used? (Coudé is French for “elbow,” since the light path is “bent like an elbow.” This arrangement is useful when the light needs to be focused onto a distant instrument)