A primary mirror of a reflecting telescope has a focal length of 4.0 m
PHYSICS · Subjective · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
A primary mirror of a reflecting telescope has a focal length of 4.0 m. It forms an image that is viewed with a plano-convex eyepiece of focal length 2.5 cm.
(a) Derive an expression for the magnifying power of a reflecting telescope when the final image is at infinity and state clearly the sign convention adopted for its value.
(b) Using the data given above, calculate:
(i) the separation between the focal point of the primary mirror and the eyepiece for normal adjustment,
(ii) the magnifying power of the telescope.
(c) List two optical defects present in a large refracting telescope that are either absent or greatly reduced in the reflecting telescope designed here, explaining the physical reason in each case.