Question

A simple telescope used to view distant objects has eyepiece and objective lens of focal lengths $f_e$ and $f_0$, respectively. Then

Answer 1

Most cameras are equipped with adjustable diameter for aperture to control the intensity of light entering the lens.

Angular magnification depends on focal lengths of objective and eyepiece.

$m=-\frac{f_o}{f_e}$

Length of telescope also depends on focal length.

Sharpness of image depends on the aperture which controls brightness and detail.

It also depends on dispersion of lens and spherical aberration.

Spherical aberration is a loss of definition in the image arising from the surface geometry of a spherical mirror or lens.

Dispersion of lens is considered because of their ability to reduce levels of chromatic aberration, or color fringing, an optical phenomenon in which the colors that make up the image come into focus at slightly differing planes as they strike the surface of your camera’s imaging sensor. The net effect is a loss of contrast, color tonality and a perceptual loss of image sharpness.