The prime focus cage of a telescope whose primary mirror is 3 m in diameter has a diameter of 0.5 m. What fraction of the incoming light is obstructed by this cage?

Question

Quizplus · Accepted Answer

The fraction of light obstructed is the area of the cage divided by the area of the primary mirror. The area of the cage is π(0.5/2)^2 and the area of the mirror is π(3/2)^2. The fraction is (0.5/3)^2 = 1/36, which is approximately 3%.

The Prime Focus Cage of a Telescope Whose Primary Mirror