Select Your First Telescope (Episode IV: Catadioptrics)

Finally, this article has entered the last episode! I myself love the catadioptrics the most because it’s considered lighter than most of the others. One of the reason is they are always mounted on altazimuth mount instead of equatorial mount which is heavy since it has to be equipped with counter-weight.

Catadioptrics use a combination of mirrors and lenses to fold the light and form an image. Catadioptrics are the most popular type of instrument, with the most modern design, marketed throughout the world in apertures of 3.5 inches and larger. There are two popular designs of these mirror/lens â€œhybrids,â€ the Schmidt-Cassegrain(right top) and the Maksutov-Cassegrain(left down). I myself own a Schmidt-Cassegrain.

Let’s start the introduction of both types of telescopes!

Schmidt-Cassegrain

In the Schmidt-Cassegrain, the light enters through a thin, aspheric Schmidt correcting plate, then strikes the spherical primary mirror and is reflected back up the tube, where it is intercepted by a small, secondary mirror. This reflects the light out an opening in the rear of the instrument to form an image at the eyepiece.

Advantages

Best all-purpose telescope design, combining the optical advantages of both lenses and mirrors, while canceling their disadvantages

Amazingly optics with razor-sharp images over a wide field

Superb for deep-sky observing or astrophotography

Very good for lunar, planetary and binary star observing

Great for terrestrial viewing

Closed-tube design reduces image-degrading air currents

Compact and portable

Ease of use

Durable and virtually maintenance-free

Offer large apertures at reasonable prices(less expensive than equivalent-aperture refractor designs)

Greater accessories availability

Best near-focus capability of all designs

Disadvantages

More expensive than reflectors at equal aperture

Slight light loss due to obstruction by the secondary mirror

Maksutov-Cassegrain

The Maksutov design is a catadioptric (using both mirrors and lenses) with basically the same advantages and disadvantages as the Schmidt. It uses a thick meniscus-correcting lens with a strong curvature and a secondary mirror that is usually an aluminized spot on the corrector.

The Maksutov secondary mirror is typically smaller than the Schmidt’s giving it slightly better resolution for planetary observing. The Maksutov is heavier than the Schmidt and, because of the thick correcting lens, takes a long time to reach thermal stability at night in larger apertures.

Conclusions: Before I start my conclusions, I would like to thanks www.telescopes.com for allowing me to use their information such as the advantages and disadvantages of all the telescopes and the technical informations for references.

I shall start the conclusions now. If you haven’t made up your mind that what types of the objects you are interesting in, I suggest you to get a catadioptric as it’s the combination of refractor and reflector so it does well in terrestial viewing and celestial observing including deep-sky, lunar & planetary, galaxy as well as others. It’s really amazing! I personally don’t like neither reflector nor refractor because of their limitation of applications. That’s why I have a Schmidt-Cassegrain at the moment. Please let me know if you have any further question.