A backyard reflector has an objective (primary mirror) of diameter and is used at an…

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Astrophysics & Cosmology · Geometrical optics and imaging

Optics and Photonics, Ch Stops, pupils and optical instruments

Problem

A backyard reflector has an objective (primary mirror) of diameter

150\ \text{mm}

and is used at an angular magnification of

60\times

. A quick-view refractor has an objective of diameter

100\ \text{mm}

and is also used at

60\times

. A friend argues: "since they magnify by exactly the same amount, they must show stars of the same faintness." ((a)) Say whether the friend is right, and why. ((b)) If one telescope shows fainter stars than the other, find by what factor more light it gathers from a given star.

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