Question

Telescopes either apply the principles of (via a lens) or (via a concave mirror) to form magnified images of astronomical objects.

Answer 1

Telescopes that uses Lens

The telescopes which uses a lens for seeing distant objects are called the Refracting Telescope.

In Refracting type of telescope we have Astronomical Telescope which is used to see the heavenly objecys like stars planets, satellite etc.  

• It consist of two covering lens (convex lens) which are mounted co axially at the outer ends of two sliding tube.
• One of the lens is called objective which is pointed towards object to which we want to observe. Light from distant planet enters through the objective. It is the convex lens of large focal length and large aperture. For getting bright image of the distant object aperture of objective is taken large so that it can gather sufficient light from the distant object.
• Another lens is called Eye piece which is held at eyes, on which the image of the distant object is formed. Eye piece is the convex lens of small focal length and small aperture. Aperture of eye piece is kept small so that whole of light may enter eye for distinct vision.

In Refracting type of telescope we have another telescope so called Terrestrial Telescope  

It is a Refracting type of telescope which works on the basic principle of refraction of light . It is used to see the erect images of the distant earthly objects.

It uses an additional convex lens between objective lens and eye piece getting the erect image of the earthly objects.

Telescopes that uses Mirror

These telescopes are called as Reflecting Type Telescopes which uses the Principle of Reflection of light to form the image of the distant object.

It uses the mirrors for viewing distant object. ie in the objective part of the telescope it has the mirrors.

They use combination of the mirrors to reflect the light and form the image of the distant object, image from the objective of lens was focussed to eye piece of the lens from where we can see the distant object using our eye.

​​​​​​The first reflecting telescope was developed by Newton which was called as the Newtonian Reflecting Telescope.

Newtonian Reflecting telescope uses Concave mirror and a plane mirror and eye piece to see the object. Eye piece is installed in side.

Plane mirror is inclined at 45 degree so that incoming light can be bent towards the objective.

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