Don’t Buy a Toy Telescope

Last week I carried on about telescopes vs toys and the dilemma a parent faces in making choices. This week I will spell out two basic qualities to look for when buying a telescope. Because there are different types of telescopes, it will seem more complicated than it is.

First – The Mount and Tripod – It’s not the telescope, but it provides the telescope with its home support. A good telescope on a rickety mount will be no fun to use.

I do not recommend getting Pier type support, a tripod will be more stable.

The best mount for beginners is the Altitude-Azimuth (Alt-Az, or A-Z) mount. They simply move from left to right and up to down and do not have to be expensive to be sturdy. It should attach solidly to the tripod and have tight controls with little or no play when going from one direction to another. It should not wiggle loosely.

For a beginner, avoid Equatorial Mounts. They look cooler and are intended for more advanced users but will be frustrating to use.

For a beginner, I do not recommend computerized mounts. A manual A-Z mount is the best place to start.

A common A-Z mount is  the Fork Mount  and are generally sturdy and easy to use. Some are offered with slow motion controls. They are not required and can make moving the telescope in a chosen direction more tricky or difficult. Another A-Z mount is called the Dobsonian (Dob) mount, used most often with reflector telescope optical tubes. See picture below.

Next – The Telescope, also known as the Optical Tube

The good news, there are way more well-made telescopes today than back in the 70s. The bad news, there are way more options, which can be daunting. I’ll try to simplify your choices.

There are three basic types of telescope Optical Tube, Reflector, Refractor, and Catadioptric/Compound.

A Reflector uses specially shaped mirrors to capture an image and send it to the eyepiece.

A Refractor uses specially shaped lenses (objective lens) to capture an image and send it to the eyepiece.

A Catadioptric/Compound is a hybrid, using mirrors and lenses. It folds the light path in half, so this type of telescope Optical Tube is much shorter than either equivalent Reflector or Refractor Optical Tube. Catadioptric telescopes come in two common designs, Schmidt-Cassegrain (SCT), or Maksutov-Cassegrain (MCT). SCTs are good all-around telescopes, while MCTs are better for the Moon, planets, and double stars.

Start Small-ish:  In terms of the mirror for a reflector or catadioptric  5 or 6” (127-152mm) is the practical maximum size for a beginner. For a refractor, 4” (102mm) is the practical maximum size for a beginner.

Mind that f-number: Optical tubes will be labeled with their size, focal length and/or focal ratio (f-number). Make sure the f-number is between 5 and 13. Why? Making mirrors or lenses with smaller f-numbers is more difficult and they are subject to more imperfections and misalignment issues.

What’s in the Sky?

November 25; after sunset; east: A nearly full Moon and Jupiter rise together.

November 27; 3:16 am CST; Full Moon – aka Beaver Moon