PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging
Optics and Photonics, Ch Radiometry and photometry
Problem
A pair of 10×50 binoculars (angular magnification MA=10, objective diameter D=50 mm) is used in bright daylight, when the observer's pupil has contracted to a diameter of 3.0 mm. Chapter 2 gives the exit pupil diameter of a telescope as Dep=D/∣MA∣. The beam leaving the eyepiece may be treated as uniform in irradiance across its circular cross-section, so the fraction of the light that enters the eye is the ratio of the eye's pupil area to the exit pupil's area, whichever is the smaller aperture.
((a)) Find the exit pupil diameter of these binoculars.
((b)) Find the fraction of the light gathered by the objective that actually enters the observer's eye in daylight.
((c)) Explain, in terms of etendue, why the light that does not enter the eye is not lost inside the binoculars but is simply blocked at the iris.