An astronomical refractor has a thin objective of focal length mm and clear diameter mm
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Astrophysics & Cosmology · Geometrical optics and imaging
Optics and Photonics, Ch Stops, pupils and optical instruments
Problem
An astronomical refractor has a thin objective of focal length fo=900 mm and clear diameter D=90 mm, and a thin eyepiece of focal length fe=25 mm placed fo+fe behind it, so that the instrument is afocal. The objective rim is the aperture stop. A circular field ring of diameter 15 mm is mounted in the common focal plane of the two lenses. Rays are paraxial and light travels left to right.
((a)) How far behind the eyepiece is the exit pupil, and what is its diameter?
((b)) What full angular width of sky (in degrees) does the field ring admit?
((c)) Through what full angle (in degrees) does that sky appear to the eye at the exit pupil? Use the ratio fo/fe for the angular magnification.