TECHTALK: Popular Telescope Design Types Compared
The Refractor Design
Refractors are what the average person identifies with the word “telescope”, a long, thin tube where light passes in a straight line from the front objective lens directly to the eyepiece at the opposite end of the tube. Heavier, longer and bulkier than equivalent aperture Newtonian designs and catadioptrics such as the Cassegrain designs. They are easy to use and good for terrestrial and celestial viewing but the design is the most costly per inch of aperture and large aperture models suitable for deep sky viewing are bulky and costly. This design however tends to dominate in the small aperture telescope range.
diagram of refractor design
Newtonian Designs
The Newtonian design halfs the actual length of the traditional refractor by using a parabolic mirror inside the tube to double the actual focal length of the telescope. Compact up to 1000mm in focal length and lowest cost against other designs comparing tubes of the same aperture. Not good for terrestrial viewing but very good for celestial observation. Good but not ideal for astrophotography.
Schmidt-Cassegrain and Maksutov Cassegrain
A typical Cassegrain design
Both Cassegrain designs are catadioptric, using both mirrors and lenses in the design so that the light reflects up and down several time within the tube. This design can produce a tube that is a fraction of the actual length of the traditional refractor. This is the most compact design and usually employed on focal lengths greater than 1000mm.
Don’t worry too much about the difference between Cassegrains when purchasing. The Maksutov secondary mirror is usually smaller than the Schmidt-Cassegrain (SCT), giving it slightly better resolution for planetary observing. A Maksutov is heavier than a SCT of the same aperture and because of the thick correcting lens it takes a longer to reach thermal stability at night. Cassegrains are excellent for terrestrial and celestial viewing as well as astrophotgraphy
Diagram of a cassegrain design
Social Links
Please feel free to use the links below to share this post with others.