Brief history of the Telescopes

 Yeah guys do you know the story of the telescopes?
 It all started with........, galileo? Oh he was not the inventor as many of us know.
But it all started with Hans Lippershey,he was a spectacle maker from germany here in short about them

Hans Lippershey
Born	1570 Wesel, Duchy of Cleves, Germany
Died	September 1619 (aged 48–49) Middelburg, Netherlands
Nationality	German, Dutch
Occupation	spectacle-maker
Known for	Inventor of the telescope(earliest known patent application) ,via wikipedia.org

know more

Okay then let us get back to the story of the telescopes though it is unclear if lippershey was the inventor, it was a great thing to be invented , it started with refracting telescopes then came galileo the problem of the then existing telescopes is that the astronomical telescope was that the magnified images though clear was inverted, so galileo  improved the version the astronomical and it was called the galilean telescope, the speciality of this was that instead of only using convex  mirror, galileo built one which had a concave mirror which made the images erect . but still there was a disadvantage in the telescopes was the chromatic aberration (a rainbow seen around some objects viewed with a refractor telescope).

Optical diagram of Galilean telescope

Then it was The Keplerian telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design.It uses a convex lens as the eyepiece instead of Galileo's concave one. The advantage of this arrangement is that the rays of light emerging from the eyepiece are converging.

 Optical diagram of Keplerian telescope

The Gregorian telescope, described by Scottish astronomer and mathematician James Gregory in his 1663 book Optica Promota, employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image, useful for terrestrial observations. Some small spotting scopes are still built this way.

Light path in a Gregorian telescope.

 Then it was Isaac Newton who came up with the reflecting telescope model which did not suffer from chromatic aberration. 

  newtonian reflector telescopes use two mirrors instead of two lenses, one of them is a paraboloidal mirror.

But then even the reflector had  a problem-coma. it is an inherent property of telescopes using parabolic mirrors. Unlike a spherical mirror, a bundle of parallel rays parallel to the optical axis will be perfectly focused to a point (the mirror is free of spherical aberration), no matter where they strike the mirror.

Light path in a Newtonian telescope

But in the recent times there has been a combined use of both the types lately that is 

Schmidt Cassegrain telescopes it did not suffer from the chromatic aberration or  

 comatic aberration. But you know every telescopes has its own pros and cons the Cassegrain telescopes are a bit costly. 

The Cassegrain telescope (sometimes called the "Classic Cassegrain") was first published in an 1672 design attributed to Laurent Cassegrain. It has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. Folding and diverging effect of the secondary creates a telescope with a long focal length while having a short tube length

there are ways to correct both the aberrations. in refractor it is the achromatic lenses and for reflector's it is rowe-coma-corrector

  After this there was n number of telescopes invented to know more about the comos x-ray telescopes and others.

Light path in a Cassegrain telescope

Light path in a Cassegrain reflecting telescope

   

images via wikipedia.org , brunelleschi.imss.fi.it

know more about optical aberration

 about the whole history of the telescopes, here

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