Types of Telescopes

Telescopes are precision instruments that gather light to form an image. As such, an important feature of telescopes is the “aperture” which is the size of the openning at the end of the telescope that points ot the sky. It is measured in millimeters or inches and the bigger the aperture, the more light you can capture. In other words, bigger aperture is better but more expensive. There are many types of telescopes, but the most common types are listed below. Keep in mind that buying a telescope is just one piece of the puzzle. Some accessories, particularly telescope eyepieces, will greatly enhance the overall experience and allow you to get the most out of your telescope.

Refractor Telescopes

A refractor telescope has a lens at the end which captures lights and focuses it to a smaller point at the other end. There are two types of refractor telescopes: Achromatic and Apochromatic.

Learn more about the refractor telescope design.

Achromatic

Orion AstroView 120ST EQ Refractor Telescope

Rugged, reliable, portable and virtually maintenance free, these telescopes are often a first buy for backyard astronomers. They are excellent for observing the moon and the planets, star clusters and double stars. They are poor on nebulas, faint clusters and galaxies because of their small telescope apertures. They work well in city and suburban sky viewing. Aperture on these telescopes usually ranges from 60mm to 4 inches.

Apochromatic

Orion SkyView Pro ED100 EQ Apo Refractor Telescope

These telescopes have an excellent optical system that produces sharp and crisp images. Portable in 4 inch and smaller designs. They are fantastic for observing the moon and planets, stars and good deep sky. They are the ideal choice for astrophotography. They are limited by the aperture size compared to Newtonian telescopes. They can be very expensive. Aperture on these telescopes usually ranges from 60mm to 7 inches.

Newtonian Reflectors

Orion SkyQuest XT8i Computerized IntelliScope Dobsonian Telescope with Object Locator

A Newtonian telescope does not have a lens at it’s end. Rather, it lets the light into its tube and bounces it back up from a large mirror at the bottom of the tube. As the light goes back upwards it hits a secondary mirro angled at 45 degrees which redirects the light to the telescope eyepiece area. the end which captures lights and focuses it to a smaller point at the other end.Newtonian telescopes are by far the most popular telescopes in use by backyard astronomers. This is because they offer large apertures at a reasonable price. They are definitely the “best bang for your buck” and are great “all around” performers. They work well for all types of celestial observation. These types of telescopes are often referred to as “Dobsonian” telescopes. This is because of the mount they typically use, which was invented by an amateur astronomer (John Dobson). In other words, they are Newtonian Reflectors that use a Dobsonian mount, and this is pretty much the standard nowadays. Photographic application is excellent but it requires additional accessories and a special “equatorial mount”. These mounts are essentially a motorized stand that counters the movement caused by the earth’s rotation. Portability can be an issue for larger apertures (12″ and up). There is a bit of easy maintenance as these require regular telescope collimation. Aperture on these telescopes usually ranges from 4 inches to 16 inches for most users, although there are some gigantic ones (up to the 40 inches range). The telescope we recommend for new users is a 6″ or 8″ Newtonian Reflectors.

Learn more about the Newtonian reflector telescope design.

Compound Telescopes

Compound telescopes are essentially a combination of the two types above. They have a glass end which focuses light as it enteres the tub, and a series of mirrors within the tube bounces the light back and forth until it reaches the eyepiece area. On of the benefit of compound telescopes is that their tube lenghts can be shorter because the light travels back and forth. This means that they are generally more portable. Below are the two most popular types of compound telescopes.

Schmidt-Cassegrain

Celestron NexStar 6SE GoTo Schmidt-Cassegrain Telescope

The optical performance of these telescopes is very good. The shorter tube makes it easy to transport and provides more stability. They can be equiped with a vast range of telescope accessories for all applications and is the telescope of choice for astrophotography. Aperture on these telescopes usually ranges from 5 inches to 16 inches.

Learn more about the Schmidt-Cassegrain telescope design.

Maksutov-Cassegrain

Orion SkyView Pro 127 GoTo Maksutov-Cassegrain Telescope

Excellent all around telescope. Good overall performance and compact format. However it is not the best choice for wide field viewing and low-power viewing. Small “travel” models make these a great little telescope for those who travel regularly. This particular type of telescope has not been really popular with backyard astronomers and it’s not really due to performance issues, but rather the cost as compared to other options. Aperture on these telescopes usually ranges from 90mm to 7 inches.

Learn more about the Maksutov-Cassegrain telescope design.

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