Telescopes

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Refractor telescopes, which use glass lenses

Reflector telescopes, which use mirrors instead of lenses.

Both types accomplish exactly the same thing, but in completely different ways.

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Refractor Telescopes

Refractors are the type of telescope that most of us are familiar with. They have the following parts:

a long tube, made of metal, plastic, or wood

a glass combination lens at the front end (objective lens)

a second glass combination lens (eyepiece)

Refracting telescopes focus light rays by bending them with glass.

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This is the simplest telescope design you could have. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.

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Refracting telescopes are

not used for astronomical

research (anymore)

because they are large

and have heavy lenses

(i.e. expensive).

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Reflecting Telescopes

History:

Isaac Newton developed the reflector about 1680, in response to the chromatic aberration (rainbow halo) problem that plagued refractors during his time. Instead of using a lens to gather light, Newton used a curved, metal mirror (primary mirror) to collect the light and reflect it to a focus. Because the mirror reflected light back into the tube, he had to use a small, flat mirror (secondary mirror) in the focal path of the primary mirror to deflect the image out through the side of the tube, to the eyepiece; otherwise, his head would get in the way of incoming light.

In 1722, John Hadley developed a design that used parabolic mirrors, and there were various improvements in mirror-making. The Newtonian reflector was a highly successful design, and remains one of the most popular telescope designs in use today.

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Reflecting telescopes focus light by bending them with mirrors

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Not everything is visible…

Many modern day telescopes do not use visible light to collect images.

Radio telescopes, x-ray telescopes and infrared (IR) telescopes have become a staple of modern day astronomy, producing some amazing images.

www.yorku.ca/eye/spectrum.gif

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Famous Telescopes

Keck Telescope

Kitt Peak Observatory

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