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Buying a New Telescope

Every year we are asked what type of a telescope we recommend for a kids. The answer is always the same, start with binoculars. Binoculars are easy to use and when the child is ready for a bigger telescope, binoculars remain useful. Binoculars start at under $100. Binoculars are rated by two numbers, eyepiece magnification and objective size [large front lens measured in millimeters (mm)]. Eyepiece magnification should be 7 or 8. Objectives should be 35 to 50 mm. Binoculars with larger objectives with are too heavy for kids to use for more than a few minutes.

If you really want a telescope, you best value is a Newtonian telescope on a Dobsonian mount. These telescopes are simple, rugged and give excellent views of the heavens. Dobsonians cost $300 and $500 depending on features, the size of the mirror and the manufacturer. The bases and tubes each weigh about 25-40 pounds. If the child is too small to manage a standard Dobsonian, you may wish to consider a variation sometimes called the bowling ball design. This 4" telescope [base and tube] weighs about 10 pounds. Prices are in the $180 to $350 range depending on the manufacturer and the features. My bowling ball type telescope is very popular when kids use it themselves at Frosty Drew Observatory [FDO]. I'm not going to recommend a telescope by brand name, but I do suggest that anyone looking for comparisons should look at the advertisements and products reviews which appear in the two most popular magazines Astronomy and Sky&Telescope. Back issues of these magazines can be found in the library and at FDO.

Let me warn you about a common advertising practice among shoddy telescope makers. Poor quality telescopes are often advertised by stressing their magnification. Manufacturers get around truth in advertising by speaking only partial truths. Any telescope can magnify images to almost any power by using an oversized eyepiece but only at the cost of terribly blurred images. The maximum eyepiece power must not exceed 50 times the diameter of the objective measured in inches. [For objectives measured in millimeters the power should never exceed 2 times the size.] A 2" [50 mm] objective can support a 100 power eyepiece under ideal conditions. Under average conditions, a 40 to 60 power eyepiece will give better images in a 2" [50 mm] telescope. An 200 power eyepiece on a 2" [50 mm] telescope will always give a fuzzy foggy sky image.

Low and high power eyepieces of the same type cost about the same to manufacture. Main objectives costs rise rapidly with increasing sizes. Disreputable manufacturers have a great economic incentive to boost the eyepiece power rather than making a larger objective. Naive buyers may think they have a better telescope because of its high magnification, but they will be very disappointed in the image clarity.

The best telescope for a kid is the telescope [or binoculars] that get used. Don't buy something with meaningless controls, worthless optics, wobbly mounts, flimsy balancing mechanisms or a jerky focuser. At FDO, we collectively have centuries of experience, but some department store "telescopes" we have been asked to fix have defeated our best efforts. Think how much more frustrating this is to a budding young astronomer. Simple telescopes and binoculars that are used are far superior to telescopes that sit in closets because they are too hard to set up and use.

One final suggestion, come down to FDO, where we can show you a wide variety of telescopes owned by the Observatory and our visiting astronomers. We'll be glad to show you the good and bad points of various instruments.

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Dec 1, 1999
Published Under:
Leslie Coleman's Columns
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