Why are most research telescopes reflectors instead of refractors?

Answer 1

Reflectors started becoming the preferred research telescope in the second half of the 19th century when processes for silvering glass were developed. (Modern mirrors are mostly coated with aluminum.) Prior to that, reflector mirrors were made of polished metal and the shape had to be re-done every time the mirror was re-polished. Glass mirrors can simply be re-coated.

Research telescopes are mostly large - over 2 meters in aperture. Single mirrors are now being made in sizes up to 8.4 meters, and larger telescopes can be built using segmented mirrors. The largest refractor lens ever made was 1 meter in diameter. Mirrors can be supported all across the back, but lenses can only be supported around their edges. Larger refractor lenses would have to be made impractically thick or they would sag under their own weight.

Also, making large blanks of optical quality glass is difficult. Mirrors can be made or ordinary annealed pyrex (some have even been made of bottle glass), and the quality requirements are much lower than lenses because light does not pass through the glass. A refractor requires two or more different types of precisely matched glass of very high quality. As a result, refractors are much more expensive than the same size reflector.

There's also the problem of chromatic aberration in lenses. A large refractor would need a very long focal length to correct for it. Reflectors have no chromatic aberration because the light does not pass through any glass.

Answer 2

Refractors use an objective lens at the front of the telescope. Reflectors use a curved mirror at the back (bottom) of the telescope. For a given size (aperture) a refractor will usually give a sharper image. However, there are practical limits to the size of a refractor. Reflectors can be made to much larger sizes and are much less expensive to manufacture at any size. Both types of telescope do a fine job at gathering and magnifying the light of distant objects. There is no "better" when talking about the two types.

Answer 3

The largest refractor ever built, the Yerkes telescope in Chicago, stretches the limits of what you can do with a suspended lens. Any larger, and the lens will sag, distorting the view.

Reflecting telescopes also have the advantage of needing only one side of the glass. That's one less side to grind, and that saves a lot of money.

Answer 4

The mere fact that light has to travel through a lens means that there are transmission losses, also lenses are subject to chromatic aberration because different coloured light refracts at slightly different angles.
The quality of glass and the difficulties of accurate grinding,combined with the weight of really big lenses is a no win situation, too expensive for mediocre results.
The only worth in refracting telescopes is in terrestrial use like binoculars (which are only two telescopes mounted together.)

Answer 5

Reflecting telescopes offer 'the most bang for the buck' as far as aperture is concerned.
Refracting telescopes have a large piece of glass at the objective end of the instrument. The larger a piece of glass is, the more subject to sagging from its own weight it becomes.
Large mirrors are much easier to control, because they don't have to be made as a solid piece. The Keck telescopes in Hawaii have huge mirrors in them (11 meters), but they are segmented into much smaller, more managable sizes.

Answer 6

the refractor or also telescope Galileano is less brightness of the telescope reflector it has inside one mirror that overcome the bright on ocular and you can see better the immages.

Answer 7

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Answer 8

That's not wrong

Answer 9

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