Astronomical telescopes produce inverted images. Why are the images not corrected to look normal as in the case of terrestrial telescopes?
All Telescopes first produce an inverted image. In a terrestrial telescope, an erecting prism is used to make the make the image look normal. However, such a prism causes a slight loss of brightness undesirable in observing the faint light from the stars. Hence, astronomical telescopes tolerate inverted images.
How do astronomers observe the Sun without damage to their eyes?
Instead of observing the Sun directly through dark glasses, astronomers view the image of the Sun projected on a screen by a telescope.
What is the magnification of a telescope? Focal length of the objective
Magnification of the Telescope = ——————————–?
Focal length of the eyepiece
For example, with an objective of focal length 1 meter and an eye piece of focal length 10 mm a telescope will give a magnification of:
1000/10 = 100
Since the focal length of the eyepiece does not very much in actual practice, the focal length of the objective is of paramount importance in determining the magnification of the telescope.