Different types of telescopes
While all telescopes, in principle, work on similar methods, they are all rather different, and offer different advantages.
Here we help remove some of the confusion, and highlight the differences between all currently used types of optical, amateur telescopes.
Refractor
Refractor telescopes were the first telescopes built, and are probably the most recognizable. The telescope consists of a long, thin tube with a lens at the front which focused directly to the eyepiece at the opposite end of the tube.
Advantages
Newtonian Reflector
Newtonian reflectors usually use a concave parabolic primary mirror to focus incoming light onto a flat secondary mirror that in turn reflects the image into the eyepiece, mounted on the side of the barrel. This increases the path length of the light within the telescope, which provides for a greater magnification.
Advantages
Schmidt-Cassegrain
Schmidt-Cassegrains are one of the most popular forms of Catadioptric telescopes. Catadioptrics use a combination of mirrors and lenses to fold the optics and form a much larger path length, and increased magnification for size. In the Schmidt-Cassegrain the light enters through a thin aspheric Schmidt correcting lens, then strikes the spherical primary mirror and is reflected back up the tube and intercepted by a small secondary mirror which reflects the light out an opening in the rear of the instrument, where the image is formed at the eyepiece.
Catadioptrics are the most popular type of instrument, with the most modern design, and are commercially marketed throughout the world in apertures ranging from 3 ½ to 20 inches.
Other Catadioptric telescopes include: Maksutov-Cassegrain and Ritchey-Chrétien.
Advantages
Here we help remove some of the confusion, and highlight the differences between all currently used types of optical, amateur telescopes.
Refractor
Refractor telescopes were the first telescopes built, and are probably the most recognizable. The telescope consists of a long, thin tube with a lens at the front which focused directly to the eyepiece at the opposite end of the tube.
Advantages
- Easy to use and reliable because of the simplicity of design.
- Little or no maintenance required
- Excellent for lunar, planetary and binary star observing especially in larger apertures
- Good for distant terrestrial viewing
- High contrast images with no secondary mirror or diagonal obstruction
- Sealed optical tube reduces image degrading air currents and protects optics
- Lenses are permanently mounted and aligned
- More expensive per inch of aperture than Reflectors or Schmidt-Cassegrains
- Heavier, longer and bulkier than equivalent aperture Reflectors and Schmidt-Cassegrains
- Cost and size factors limit the practical useful maximum aperture
- Less suited for viewing small and faint objects, such as distant galaxies and nebulae because smaller apertures
Newtonian Reflector
Newtonian reflectors usually use a concave parabolic primary mirror to focus incoming light onto a flat secondary mirror that in turn reflects the image into the eyepiece, mounted on the side of the barrel. This increases the path length of the light within the telescope, which provides for a greater magnification.
Advantages
- Lowest cost per inch of aperture as mirrors can be produced cheaper than the lenses used in refractors and Schmidt-Cassegrains.
- Reasonably compact and portable
- Larger available apertures provides for excellent viewing of faint objects, such as remote galaxies, nebulae and star clusters.
- Low in optical aberrations and deliver very bright images
- Generally not suited for terrestrial applications
- Slight light loss due to secondary obstruction when compared with refractors
Schmidt-Cassegrain
Schmidt-Cassegrains are one of the most popular forms of Catadioptric telescopes. Catadioptrics use a combination of mirrors and lenses to fold the optics and form a much larger path length, and increased magnification for size. In the Schmidt-Cassegrain the light enters through a thin aspheric Schmidt correcting lens, then strikes the spherical primary mirror and is reflected back up the tube and intercepted by a small secondary mirror which reflects the light out an opening in the rear of the instrument, where the image is formed at the eyepiece.
Catadioptrics are the most popular type of instrument, with the most modern design, and are commercially marketed throughout the world in apertures ranging from 3 ½ to 20 inches.
Other Catadioptric telescopes include: Maksutov-Cassegrain and Ritchey-Chrétien.
Advantages
- Best all around, all purpose telescope design. Combines the optical advantages of both lenses and mirror while canceling their disadvantages.
- Excellent optics with razor sharp images over a wide field
- Excellent for deep sky observing or astrophotography
- Very good for lunar, planetary and binary star observing or photography
- Excellent for terrestrial viewing or photography
- Closed tube design reduces image degrading air currents
- Extremely compact and portable
- Durable and virtually maintenance free
- Large apertures at reasonable prices and less expensive than equivalent aperture refractors
- Best near focus capability of any type telescope
- More expensive than Reflectors of equal aperture
- Slight light loss due to secondary mirror obstruction compared to refractors.