A pair of Galilean opera glasses is examined alongside a prescription for a mildly…
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging
Optics and Photonics, Ch Stops, pupils and optical instruments
Problem
A pair of Galilean opera glasses is examined alongside a prescription for a mildly myopic user.
((a)) The objective is the aperture stop: a converging thin lens of focal length fo=200 mm and diameter D=30 mm. The eyepiece is a diverging thin lens of focal length fe=−40 mm (negative, since f>0 is reserved for a converging element), placed so the pair is afocal (separation fo+fe). Using the thin lens equation 1/so+1/si=1/f under CV1, treat the objective rim as the object for the eyepiece and find the position of the exit pupil (distance from the eyepiece, real or virtual) and its diameter.
((b)) The user's far point is 1.25 m. Find the dioptric power of the spectacle lens that images a distant object at her far point. The lens is crown glass, refractive index 1.50, with front-surface radius R1=+25 cm. Use D=(n−1)(1/R1−1/R2) to find R2.