TELESCOPE TYPES
There are several general categories of telescopes.
There are also several modern words used in conjunction with these types of telescopes.
With a long tube and objective lens up front, the refractor is what most people think of when someone mentions telescope. Quality refractors will generally never need alignment and usually produce fine images . Typical amateur sizes are from 2.5" to 7" of aperture. Before you purchase a telescope, PLEASE see my page on purchasing a telescope. You're generally better off with binoculars than a telescope below 2.5" of aperture, and .
Reflectors are often called "Newtonian" after the inventor, Isaac Newton. Reflector telescopes use a concave mirror at the bottom of a tube to focus the light. A small flat mirror called the diagonal at the top of the tube reflects the light sideways toward the eyepiece. The Mt. Palomar 200 inch mirror telescope is a Newtonian reflector. Before you purchase a telescope, PLEASE see my page on purchasing a telescope.
This classification is a more modern implementation of telescope. These scopes combine lenses and mirrors to make a very versatile, compact telescope. For equivalent aperture, this type of scope is more expensive than a reflector. There are two general types of Catadioptric scopes "Schmidt-Cassegrains", or "Maksutov", classified depending on the type of correcting lens. Before you purchase a telescope, PLEASE see my page on purchasing a telescope.
- Aberration -
- The imperfection of an optical device (like a lens). Aberrations include astigmatism and chromatic (prism like color separation).
- Achromat -
- A lens made with 2 or more elements which tends to prevent chromatic aberration.
- A lens made with two glass elements which lessens chromatic (color separation) aberrations.
- Aperture -
- The diameter of an optical system. In a telescope, it is usually designated as the diameter of the objective (first) lens of the telescope.
- Apochromatic -
- A highly color corrected lens system. Note that this is an over simplified definition.
- Baffling -
- Light stopping walls in a telescope installed to prevent off-axis light reaching the eyepiece.
- Chromatic aberration -
- The prismatic color separation of light as it passes through a lens. This is an imperfection in a lens.
- Coma Corrector -
- A negative lens which corrects "light smear" at the eyepiece edge of view.
- Diffraction Limit -
- The limit of optics which allows for pinpoint sharpness of star images.
- Dob or Dobsonian -
- John Dobson, a telescope maker, decided to make telescopes out of simple, readily available parts. This design idea has become popular for commercial visual telescopes. This telescope design is generally not usable in astrophotography.
- Eyepiece -
- The changeable section of the telescope that you look into to view the skys. Various types exist, the Plossl is currently very popular.
- Filter -
- A flat optical lens which promotes the passing of some colors while impeding other colors.
- Maginification -
- The process of enlarging the size of something with optics.
- OTA -
- Optical Tube Assembly. The telescope body with the lenses and focuser is what makes up an OTA.
- Power -
- The measure of magnification, often expressed with an "x". Example: 2 power ("2X") would be 2 times magnification in size.
- Resolution -
- The ability of an optical instrument to distinguish detail.
- SCT -
- Schmidt-Cassegrain Telescope. The SCT scopes use both mirror and lenses for the optical assembly. The first optic is a lens, which corrects the path of the light which then strikes the mirror and is directed to the eyepiece. The corrector lens (first lens) allows the mirror to be spherical. Other common reflector telescopes use parabolic mirrors.
Some information on this page was adapted from the book The Backyard Astronomer's Guide by Terence Dickinson and Alan Dyer
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