Question

The Moon was photographed with a telescope that has a primary mirror with diame- ter - 20 cm and focal length - 150 cm. To get a good photograph (neither over- nor a) What should the exposure time be for a good exposure, using a telescope with (b) What is the size of the image of the Moon in both cases? If you take the photos under-exposed) required an exposure time of 0.1 s mirror diameter 15 cm and focal length 200 cm? using a CCD detector which is 2 cm on a side (typical for the detectors in most regular digital SLR cameras) will the entire moon fit in the images?

Answer 1

(a) As focal length increases exposure time increases.

Exposure time for good exposure will be approximately =0.2 seconds