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Telescopes 101

Telescopes 101
Telescopes 101 Backyard astronomy is a challenging and rewarding hobby that can entertain you and your family for a lifetime. Purchasing a new telescope can be an overwhelming task if you know little about the product. Our "Telescope School" will help inform you on the different types of telescopes and their features. Spend some time reading these articles and you will dramatically improve your knowledge of telescopes to help you choose the one best for you.
Fighting Dew

Fighting Dew

You've waited weeks for a perfectly clear night and you're all geared up for a night of backyard observing. You've spent half an hour setting up your telescope and working out the perfect alignment. You begin your night with friends and fellow astronomers looking at favorite planets and deep sky objects - the night could not get any better. The conversations get more penetrating and before you know it you're asking whether the human race could possibly be alone in the universe.

New Planet

New Planet

Astronomers have discovered what many are saying is our Solar System's 10th planet. It's reportedly to be named Xena, and its discovery is the first of a planet since Pluto was found 75 years ago.

Telescope Glossary

Telescope Glossary

You're going to need this little to-learn list - trust us. The world of telescopes is deep and wide, and it helps to know the difference between your altitude and alzimuth. This is beginner's guide to telescope terms. We want you to feel comfortable as you peruse our many, many products, so familiarize yourself with some basic terms, and before long you'll know that an "exit pupil" isn't a kid kicked out of class, and that you don't order anything from an NGC catalog.

Deep Impact

Deep Impact

After a journey measured in the hundreds of millions of miles, Deep Impact's copper-loaded "smart bullet" slammed into comet 9P/Tempe1 1, penetrating deep beneath the comet's surface before vaporizing and blasting out a cone of debris. The flash from the 23,000-mile-per-hour impact was visible from Earth-based telescopes, and light reflecting off the spreading debris cone was improving the comet's visibility.

Refractor Telescope

A refractor telescope is a dioptric telescope that uses a long, narrow tube that permits light to pass in a straight line between the front objective lens and a rear-mounted eyepiece. Originally designed for use in spy glasses and astronomical telescopes, refractor telescopes are also used in binoculars and long or telephoto camera lenses.

Advantages of a Refractor Telescope

  • A simple design contributes to reliability and ease of use
  • Little or no maintenance is required
  • Good for distant terrestrial viewing, along with lunar, planetary, and binary star observing

Disadvantages of a Refractor Telescope

  • Cost per inch of aperture is more expensive than reflector or catadioptrics designs
  • Heavier, longer, and bulkier compared to equivalent-aperture reflectors and catadioptrics
  • Practical aperture limitations make it less suited for viewing faint and small deep-sky objects

For more information on selecting your first refractor telescope, see this article.

Reflecting Telescope

A reflecting telescope is an optical telescope that uses a single curved mirror or a combination of curved mirrors that reflect light to form an image. Invented in the 17th century as an alternative to a refracting telescope, it's designed for very large diameter objects. Nearly all major telescopes used in astronomy research are reflectors.

Advantages of a Reflecting Telescope

  • Brighter images are delivered with few optical aberrations
  • Ideal for viewing faint, deep-sky objects such as nebulae, galaxies, and star clusters
  • Compact and portable

Disadvantages of a Reflecting Telescope

  • Ultraviolet light doesn't pass through the lens at all
  • It's difficult to make a glass lens with no imperfections inside the lens
  • The glass lens sags under its own weight

For more information on selecting your first reflector telescope, see this article.

Schmidt-Cassegrain Catadioptric Telescopes

A Schmidt-Cassegrain Catadioptric Telescope combines a folded optical path with a corrector plate to create a compact astronomical instrument. The telescope design uses a spherical primary mirror and a Schmidt corrector plate for spherical aberration correction. From the Cassegrain, it inherits the convex secondary mirror, perforated primary mirror, and a final focal plane behind the primary.

Advantages of a Schmidt-Cassegrain Catadioptric Telescope

  • Optics provide razor-sharp images over a wide field
  • Ideal for observing deep-sky objects or for astrophotography
  • Very little maintenance needed

Disadvantages of a Schmidt-Cassegrain Catadioptric Telescope

  • Unusual look surprises some people
  • Higher in cost compared to reflectors of equal aperture
  • Obstruction by the secondary mirror causes a slight light loss

For more information on selecting your first Schmidt-Cassegrain Catadioptric telescope, see this article.

Maksutov-Cassegrain Catadioptric Telescopes

A Maksutov-Cassegrain Catadioptric Telescope employs a full diameter corrector plate (also called meniscus lens) to resolve problems of off-axis aberrations such as coma found in reflecting telescopes while avoiding chromatic aberration. The telescope's Cassegrain smaller secondary mirror provides slightly better resolution for celestial observing.

Advantages of a Maksutov-Cassegrain Catadioptric Telescope

  • Can focus on a nearby object
  • Fixing the alignment of the secondary mirror eliminates the need for a spider
  • Closed tube design eliminates image-degrading air currents

Disadvantages of a Maksutov-Cassegrain Catadioptric Telescope

  • Thick correcting lens takes longer to reach thermal stability at night
  • Corrector lens requires more material than that of a Schmidt Cassegrain
  • A slight light loss occurs due to the secondary mirror

For more information on selecting your first Maksutov-Cassegrain Catadioptric telescope, see this article.

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