Why concave mirror is used in telescope?

Question

Why concave mirror is used in telescope?Give answer with explaination.

Answer 1

From my studies, i knew that there r two types of telescopes:
1) Refracting telescope (doesn't need concave mirror)
2) Reflecting telescope ( need concave mirror, & its has 2 types)

Refracting telescope:
----------------------------
Construction:
- Objective lens
- The eyepiece

How it works:
- The objective lens forms a real, inverted, (diminished) small image of the object, which lies at the focus becouse the incident rays r parallel
- The eyepiece forms a virtual, erect, magnified image of the object, inverted (with respect to the original object), this image lies at a distance from the eye = 25 cm in normal person

Reflecting telescope:
---------------------------
1st type:
-----------
Construction:
- Concave mirror
- Plane mirror
- converging lens

How it works:
- The concave mirror recieves the parallel rays emitted from the object to be observed & reflected them towards the focus
- The path of the reflected rays is changed before reaching the focus of the plane mirror to fall on the eyepiece (lens)
- The eyepiece recieves the rays reflected from the plane mirror & the final image is seen through it (or mirror recorded on a sensitive film)

2nd type:
------------
Construction:
- Concave mirror
- Convex mirror
- Converging lens

How it works:
- The concave mirror recieves the parallel rays emitted from the object to be observed & reflected them towards its focus
- The path of the reflectedrays is changed before reaching the focus by the convex mirror, which reflect them once again towards a hole in the concave mirror to fall on the eyepiece (lens)
- The eyepiece recieves the rays reflected from the convex mirror & the final image is seen through it (or recorded on a sensitive film)

Also the real reasons behind using concave mirrors in reflecting telescope:
1) Decrease its mass
2) Get rid of defects of lens
3) recieve parallel rays & reflect them to a plane mirror or convex mirror, which also reflect them to the eyepiece

i hope u got ur point from my explanation

Answer 2

Uses Of Reflecting Telescope

Answer 3

A concave mirror will focus light, whereas a convex mirror will make the light rays diverge (spread out).

Focusing is required for a telescope to magnify objects, so concave mirrors are used.

Answer 4

The idea is too kind of take a huge cylinder of light that is coming into the mirror and focus it on a point.

"paraboloids do this"

This magnifies it kind of like a magnifying glass, which brings up the point "why not use a giant lense" I think the answer to that is cost, not to mention that they are now computer controlling the shape of the mirror which is hard to do with a lense.

To picture the idea, think of the reverse of a flashlight. a tube of light comes in and focuses on a point in the center.

Answer 5

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usually, glass mirrors are polished to achived a very precise final shape. I don't believe that technology exists for plexiglass. It probably could be done but is likely to be much more expensive than the traditional glass.