How does a telescope work?


Quick Answer

Refracting telescopes use objective lenses to collect light from distant images and bring those images into focus. Reflecting telescopes use primary mirrors. Both refractors and reflectors utilize an eyepiece lens that magnifies the image.

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Full Answer

Refractors are the most common type of telescope. They consist of a long tube made of metal, plastic or wood, a glass objective lens at the front end and a glass eyepiece lens at the rear. Both lenses are in a convex shape, which bends light inward and makes the image look smaller. In refractors, the size of the image produced is proportional to the focal length of the lens. The brightness of the image is proportional to the area of the objective lens.

Reflecting telescopes use mirrors to bend light and make parallel light rays converge to a focus. Reflectors have several ways of making images from the mirror visible. The Newtonian reflector uses a flat mirror to point the light out towards the eyepiece. The Cassegrain reflector uses a convex secondary mirror and a hole in the middle of the primary mirror. The Coude telescope combines the convex secondary mirror of the Cassegrain with the flat mirror of the Newtonian to move light rays to a focal point.

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