Reflectors (Newtonians)

Learning About Newtonian Reflectors

Newtonian reflectors are a popular choice in astronomical telescopes that use curved mirrors to reflect light onto smaller angled mirrors and into side-mounted eyepieces. Newton developed this telescope to overcome chromatic aberration problems with the lenses used in early refractor telescopes. You can use this simple, yet effective design with a large aperture that's ideal for looking at faint objects in the sky.

What Are Newtonian Reflectors?

Newton telescopes, such as Bushnell reflector telescopes, have a cylindrical shape that's open at the top. A large diameter parabolic primary mirror is at the bottom, and a small flat mirror sits at 45 degrees near the top of the tube. This second mirror reflects light onto an eyepiece mounted on the side of the telescope. Some reflector telescopes have coma corrector lenses to reduce aberrations at the edge of your viewing field. Because the eyepiece is on the side of the telescope, viewing is more comfortable than with comparable lens-based refractor telescopes.

The focal length of the primary mirror in a Newtonian telescope determines its overall length. Compound telescopes, also known as catadioptric (Cassegrain) telescopes, use a combination of two curved mirrors and an end-mounted eyepiece that reduces the overall length of the telescope, while permitting an increase in focal length.

Dobsonian Telescopes

Dobsonian telescopes, such as Tasco reflector telescopes, are Newtonian reflector telescopes mounted on an altazimuth mount. This type of mount has two degrees of movement, one vertical and the other horizontal, and is similar in concept to a photographic tripod. Although the original Dobsonian telescope concept was that it was lighter than comparative Newtonian telescopes, the main attribute of current Dobsonian telescope kits is a mount that's simple and easy to use.

Celestial Tracking Capabilities

While an altazimuth mount is easy to use, it doesn't follow the path taken by stars, so constant horizontal and vertical adjustments are necessary when tracking celestial bodies. An equatorial mount overcomes this problem by tilting the angle of rotation to match the earth's axis of rotation. This satisfies any astrophotographer's need for a long-time exposure. However, you can overcome the disadvantages of the altazimuth mount by using GoTo Dobsonians. These are Dobsonian telescopes with digital axis control that automatically tracks the movement of the stars.

Telescope Aperture and Magnification

A telescope's aperture is the diameter of its primary mirror. Larger mirrors collect more light and are brighter and sharper. The focal ratio is the focal length of the lens divided by its aperture, and as with camera lenses, smaller values are brighter. Determine magnification by dividing the focal length of the lens by the focal length of the telescope eyepiece. As a rule of thumb, it's best to avoid magnifications greater than 50 times per inch of aperture. If you're an amateur photographer, you may want to use a lower magnification, especially when using solar telescopes to view large objects like the sun or moon.

You can find the best Newtonian reflector telescope for your celestial viewing at B&H Photo and Video.