Newtonian Reflectors

 

The Newtonian reflector (named after Sir Isaac Newton, its inventor) is a popular and economical astronomical telescope.  Its simple, high-performance design provides tremendous light grasp at the lowest cost per unit of aperture of any telescope type.

A reflector focuses light with mirrors, instead of with lenses, as refractors do.  Incoming light is reflected off a concave "primary" mirror at the base of the optical tube up to a smaller, flat "secondary" mirror near the front end.  The light is deflected out of the optical tube into the eyepiece.

Size is a Factor

Newtonian reflectors of 6" aperture or less are quite portable.  Bigger than that and the size and weight of the scope and mount must be considered carefully, so you don't end up with something you can't easily handle.  The bulkiness of large Newtonians is one reason that more compact scope designs such as the Schmidt-Cassegrain have gained in popularity.

 

reflector.gif (11831 bytes)Reflectors are Versatile

Optically, reflectors can provide outstanding performance.  Their large apertures make them ideal for observing faint deep-space objects.  Those with focal ratios of f/7 or higher also provide good, high-contrast views of the planets and Moon.   Short-focal-length reflectors (f/6 or lower), while not as desirable for planetary observation, provide a wide viewing field and allow a shorter, more manageable tube length at large apertures.

The mirrors in a reflector require frequent alignment (collimation), but are easily adjusted.  Dew does not readily form on the mirrors because the open tube acts as a passive dew shield.  The tube can admit dust, though, so it should be capped when not in use. 

Newtonian tubes can be supported on a variety of different mounts; the standard altazimuth mount, a cabinet-style "Dobsonian" altazimuth mount, or an equatorial "tracking" mount.

Reflectors are not well suited for terrestrial observing, because the image is often rotated upside-down or sideways.

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