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Buying a Telescope

As Christmas approaches, people want to know what type of telescope to buy for an aspiring young astronomer. Take it from an old hand, what you buy must have good optics, a sturdy mount and simple controls. Time and again I have watched kids frustrated by poor lenses on a wobbly tripod as they fool with strange levers and knobs. With some of these department store telescopes it is hard for an experienced viewer to see the Moon, much less a planet or a galaxy. Kids don't have a chance with these pieces of glitzy junk.

I strongly recommend binoculars as a first "telescope". Just a few twists of a knob or an eyepiece brings everything into focus. Add a solid tripod to support the binoculars and you have an excellent wide angle telescope. When your young astronomer is ready for more equipment, the binoculars will not be left behind. I use my binoculars whenever my telescope is out. Binoculars are measured by a pair of numbers n•mm. The value of mm (size of the lens) must be at least 35 mm, but 50 to 80 mm binoculars will allow you to see dimmer objects. The value of n (magnification) should be 7 or 8 for 35 to 50 mm binoculars but can be as much as 10, 15 or 20 for 70 mm or more binoculars. Wide angle fields of view are a plus for binoculars.

If you have your heart set on a telescope for your child, ask yourself a few questions:

What is the best child's telescope, a reflector, a refractor or a catadioptric? Reflectors have mirrors in back. Refractors have lenses up front. Catadioptrics are stubby tubes with both lenses and mirrors. Catadioptrics are best left for older viewers. Either reflectors or refractors can be fine for kids. The merits of one over the other are largely a matter of personal preference. For a given diameter, a reflector is cheapest. Refractors tend to withstand hard use better.

What type of a mount do you want for a telescope? For a kid's telescope I recommend a "dobsonian" mount for reflectors and alti-azimuth yokes for refractors. Stay away from counterweighted mounts and any mount which requires alignment with the north celestial pole. These advanced mounts are for astrophotography and serious users.

Is your kid a technical wizard? If he or she is a true technical whiz kid, perhaps a telescope with setting circles, fine tuning adjustments, a clock drive and PC controller is reasonable. Otherwise the fewer controls the better. Many excellent small telescopes have only a focusing knob. In the dark, simple telescopes are easy to point, focus and view. Complex telescopes befuddle kids looking for missing pieces or reading arcane instructions by a hand held flashlight.

If the telescope is to be used during the day you want one which does not invert images. Many astronomical telescopes flip images side to side or top to bottom. Watching a boat sail upside down is odd to say the least.

You can buy books or software for your young astronomer. A lot of quality books and software are available in college books stores. Astronomy books challenge kids without overwhelming them. Kids love to make their own sky charts with easy to use software.

One final warning, beware the high magnification sales gimmick. Any telescope can be given any magnification by simply using too powerful an eyepiece. Under the best possible conditions a telescope magnification cannot exceed 50 times the diameter of the objective (the biggest mirror or lens) measured in inches. Generally, 10 to 30 times the diameter works best. A refractor with a 2 inch lens can never be successfully magnified above 100. Most of the time a 20 to 60 power eyepiece is best. If the objective is measured in millimeters, convert to inches by dividing by 25.

If you have questions, I would be happy to discuss telescopes with you at Frosty Drew Observatory any clear Friday evening. Afterwards we can look at the early Winter constellations. Saturn and Jupiter are visible all night. Taurus [the Bull] is up in the East in the early evening. By 11 PM the greatest of the constellations, Orion [the Hunter] will be well up in the eastern sky. I never miss a chance to look at the Great Nebula in the sword of Orion. It is awe inspiring to see a stellar nursery when new stars are just beginning to shine. The Fall and early Winter are wonderful times to view the Sky. At least, they are wonderful if you remember to add an extra layer or two of clothing and foot protection.

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Nov 1, 1998
Published Under:
Leslie Coleman's Columns
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