An amateur 150 mm (6-inch) Newtonian reflector has focal ratio
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging
What an Instrument Can See, Ch Pupils: the aperture of a linear system
Problem
An amateur 150 mm (6-inch) Newtonian reflector has focal ratio f/5, so its focal length is f=750mm. It is fitted with a 40 mm focal-length eyepiece sold as a 'low-power, wide-field' ocular. The observer's fully dark-adapted eye has an entrance pupil of diameter 6 mm.
((a)) State the pupil-matching condition a visual instrument imposes on the eye, and find the exit-pupil diameter this telescope-eyepiece combination produces.
((b)) Decide whether the combination is matched, underfilled or overfilled with respect to the observer's eye, and find the fraction of the light gathered by the 150 mm objective that actually enters the eye.
((c)) Find the longest eyepiece focal length, at this same focal ratio, whose exit pupil just matches the 6 mm eye pupil.