Question

A telescope works by taking a distant object, creating an image at the focal point with the objective lens, and then having the eyepiece lens use that image as its object to create a second image at infinity. Why infinity? So that you don’t need to put your eye in any particular place to see it, and it looks like any other distant object.

Q0.1. If both lenses are converging, what should the theoretical magnification be, positive or negative? If you want an upright image, what combination of lenses do you need?

Answer 1

Generally incase of an aastronomical telescope which is mentioned in the problem here ,final image formed for eye piece is inverted since the final image is formed at infinity. Hence theoretical magnification formed is Negative .

To have an upright image a convex lens or converging lens of magnification -1 should be placed in between objective and eyepiece.So that final image formed is Errect or Upright. This tyype of telescope where errecting lens are used is called Terrestrial telescope.