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Telescopes from the Ground Up
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What makes a good telescope?
A telescope is judged on these qualities:

Its magnifying power

Except in the case of solar telescopes, magnification is the least important element of a research telescope.

Magnification depends on focal length. As the magnification increases, the telescope focuses on a smaller piece of the sky.

Most research telescopes are designed to operate at the smallest magnification possible, to examine a larger piece of sky. The distance and details they see depends more on their light-collecting ability and resolution than their magnification.

Solar telescopes, however, can rely on magnification because they don't have to look deep into space, see much of the sky, or gather much light to clearly view the Sun.

Instrument quality

A modern research telescope is only as good as the cameras and other instruments that record and analyze the light that it captures. Instruments are judged by many factors, such as the quality of their images, how effectively they spread out light, and how much light they capture.

Its light-collecting ability

Faint objects are hard to see. Objects appear faint because they’re far away, and/or because they glow dimly. The more light a telescope can collect, the better it can see faint objects. Large mirrors and lenses allow telescopes to collect more light.

Its resolution

Resolution is the ability to see detail in an object. A telescope with high (good) resolution will be able to see two points of light as being separate from one another. A telescope with low resolution will blur the two points together into a single point of light.

Diagram illustrating the effect of resolution on two separate, but barely separated, objects.

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