| A Catadioptric Telescope uses both mirrors and
lenses. The lens is sometimes a thin corrector plate, as in a Schmidt-Cassegrain.
Maksutov-Cassegrains have a thick, strongly curved correcting lens.
Schmidt-Cassegrain 
Schmidt-Cassegrain telescopes use a combination of mirrors and
lenses to fold the optical path and form an image. Incoming light
enters through a thin aspheric Schmidt correcting plate, then strikes
the spherical primary mirror and is reflected back up the tube.
The light is then intercepted by a small secondary mirror which
reflects the light through an opening in the rear of the instrument,
where the image is formed at the eyepiece. The tubular light-baffling
system, which includes anti-reflection threads inside the primary
mirror baffle, preserves high-contrast astronomical imagery at the
focal plane.
Some of the advantages of the Schmidt-Cassegrain design are:
- Excellent all-around, multifunction telescope design; it combines
all the optical advantages of mirrors and lenses while canceling
their disadvantages.
- Focal ratio usually f/10, which is useful for most types of
photography.
- Astrophotography with fast film; CCD imaging.
- Compact, portable, easy to use and has a closed tube.
- Capable of focusing on nearby objects.
- Large apertures at reasonable prices.
- Accepts many accessories
Design of the Schmidt-Cassegrain Telescope:
 
Schmidt-Cassegrain telescopes are designed to meet many needs,
and these compact, portable, user-friendly telescopes have a strong
following.
Maksutov-Cassegrain
The Maksutov design is similar to the Schmidt with the same basic
advantages. It uses a thick meniscus correcting lens with an aluminized
spot on the convex side. The Maksutov has excellent optics with
razor sharp images. It is excellent for deep-sky observing or for
astrophotography with fast films or CCDs. It is very good for lunar,
planetary and binary star observing. The focal ratio is usually
about f/15.
Design of the Maksutov-Cassegrain Telescope:
Advantages of the Maksutov-Cassegrain Telescope:
- Compact and portable design.
- Easy to use.
- Rugged and virtually maintenance-free.
- Closed tube design eliminates image-degrading air currents.
- Accepts many accessories.
- Capable of focusing on nearby object
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