Top 5 Types of Astronomy Telescopes

There are so many types of optical telescopes that it would be the work of an entire book to begin documenting the inner workings of each. Nevertheless, most of them have specialized applications and are only used by select customers, so we can restrict our discussion to those types that are most applicable to the average consumer. The three major types of optical telescopes are the refracting, reflecting, and catadioptric telescope.

Refractor-type telescopes are the simplest and oldest kinds. They use two lenses; the objective and the eye lens, in order to capture, focus and magnify light before letting it enter the eye. The most common kind of refractor microscope is the non-achromatic objective type, whose lenses are not corrected for chromatic aberration, which can distort the image. This is done because the amount of work put into correcting the aberration would exceed the amount of benefit derived from doing so, particularly for the common customer, so that step is often dispensed with in the interests of making the telescope affordable.

Reflector telescopes use curved mirrors to concentrate and focus light, before reflecting it into the eyepiece. There is typically a large concave mirror, called the primary mirror, which focuses light onto the secondary mirror, which in turn reflects it to the viewer. While the basic principle is the same throughout all reflector telescopes, the exact configuration varies depending on the sub-type. For instance, the Newtonian reflector telescope has its secondary mirror reflecting light at right angles to the primary mirror, so the viewer can see an image at ninety degrees to the path of the light’s travel. The Cassegrain reflector telescope instead has its secondary mirror reflect its light in the same direction at which it strikes the primary mirror. A hole is bored through the primary mirror so the user can see through the telescope as though it were a refractor telescope.

Finally, we come to the catadioptric telescopes – telescopes that combine elements of refractor (dioptric) and reflector (catoptric) telescopes. As one can see, the name of this hybrid telescope derives from those of its forebears. The two main types of catadioptric telescopes are the Schmidt and the Makutsov telescopes. In Schmidt telescopes, the light enters an aspheric lens and is then reflected off a primary mirror and onto a section of photographic film where the secondary mirror would have been in a Cassegrain telescope. The Makutsov functions similarly to the Schmidt, but instead, the back of the aspheric lens (which fills the aperture) serves as the secondary mirror, and it reflects light out through the back of the telescope, like a Cassegrain telescope.

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