Question

Draw a ray diagram of an astronomical telescope for distant objects in normal adjustment. What is the expression for its magnifying power?

Answer 1

1. The objective is to a converging lens and creates an image at $f_o$.
2. In the normal adjustment, the final image is at infinity and the view of the field is small.
3. The magnifying power of a telescope is given by $m=\frac{f_o}{f_e}$ , where $f_o$ is the focal length of the objective and $f_e$ is the focal length of the eyepiece.
4. To have a high magnifying power we should keep $f_o$it as high as possible and $f_e$ as low as possible.

Given below is the ray diagram for an astronomical telescope -