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Don’t Buy A Department Store Telescope for Christmas

by Tom Minahan, Door Peninsula Astronomical Society

Let’s assume you have a budding astronomer in the family or as a friend. If you are thinking about getting them a telescope for a holiday gift, please heed this sound advice from experienced amateur astronomers:  Don’t buy a cheap department store telescope! They typically have inferior optics (plastic lenses?) and shaky mounts. Some makers of inferior telescopes promote large magnifications that are beyond the limits of its stability and light-gathering and focusing ability, which can frustrate. Much better to spend a little more for a quality telescope that will give satisfying views of the heavens for years.

Two decisions are to be made when choosing a new telescope: Refracting vs. reflecting optics and GoTo vs. point-yourself mount.

Refracting telescopes have a convex glass called the objective lens that refracts the light coming in, reducing the image to eye-size. The image is collected by a smaller concave lens called the eyepiece, which straightens out the light to produce a magnified view. Because the eyepiece is positioned behind the focal point of objective, the image is upside-down and flipped left-to-right.

Refractors are known to provide more contrast and a blacker background than reflectors of equal size. Refracting telescopes are generally good for viewing the moon and the planets, but only small apertures are practical and affordable. Reflecting telescopes have a concave mirror at the base of a tube and a slanted flat mirror that bounces the reduced image out the side of the tube into an eyepiece. Although they are splendid for viewing the moon and planets, reflecting telescopes come in practical, larger apertures needed to bring in dimmer galaxies and nebulae.

A GoTo telescope has a computer-controlled mount that aims the instrument at targets in the sky automatically – one need only pick from a database of objects on the controller. GoTos are great for beginners unfamiliar with the night sky and for more experienced stargazers who like efficiency. They would also be the choice if one has a disability like a bad back because they eliminate the need for awkward positions to sight through the finder. The downside of GoTos:  they are more expensive than basic mounts – the cheapest I found on the internet is $250 – and they require an initial learning period and a nightly, sometimes tricky alignment process.

Many amateur astronomers prefer to learn their own way around the constellations and star hop to targets. For this, a manual altitude-azimuth or an equatorial mount are the choices. Either on a tripod or tabletop, an altitude-azimuth mount allows the telescope to be aimed anywhere above the horizon – the altitude is measured in degrees of angle above the true horizon (the zenith is at 90°) and azimuth is measured in degrees of the circle with North at 0° and East at 90°. One need only rotate and tilt the telescope. An equatorial mount has a rotational axis parallel with the Earth’s axis of rotation. The mount must be aligned with the north star (not real hard) but it allows easy compensation of the Earth’s rotation to keep the telescope on target. One need only turn a knob incrementally to keep an object in the field of field. They frequently have an electric clock-drive that does this automatically. Another advantage of manual targeting:  Some amateur astronomers spend much of their viewing time just randomly exploring magnified areas of the night sky. No GoTo control needed and personal discoveries can be made!

What is the most effortless way to get magnified views of the night sky? Buy a good pair of binoculars. Think of them as a giant pair of bug-eyes that can increase your “depth of view” by imaging astronomical targets several times dimmer than what can be seen with the naked eye. Because ours brains are better able to filter out visible noise when using binocular vision, binoculars generally give a 40 percent increase in contrast over viewing throughout a single lens of equal size and magnification. Therefore fainter objects can be seen. The most preferable size for stargazing is in the vicinity of 7 x 50, i.e. a magnification of seven (a 6° field of view) and objectives lenses that are each 50 mm in diameter. Magnifications 10x or higher make it difficult to keep the image steady when held in your hands. Objective lenses larger than 60 mm start to get heavy and are tiresome to hold. Feel free to get a pair of larger, more powerful binoculars, but you will need a sturdy mount. Most quality binoculars are compatible with an inexpensive tripod-binocular connector to lock down the binoculars. Also: Binoculars provide a view that is right-side-up, not flipped like in a telescope, and they are great for lounge chairs!

Here are some buying options for products less than $200 that should provide quality views of the night sky. When shopping in store or online, look for major astronomy brands like Orion, Celestron, Meade, etc. [I do not work for any of these companies and shall not accept any money for these recommendations.]

  • Binoculars. Quality binoculars will have optics that are coated. Look for Porro-Prism BAK4 glass. They provide sharper imaging, brighter edges in the field of view and a nice circular exit pupil. Here are just a few binocular choices:  Orion Scenix 7 x 50, $130; Celestron SkyMaster DX 8 x 56, $200; Vixen 10 x 50 Ascot Super-Wide, $200; Bushnell 7 x 50 PermaFocus, $70.
  • Small telescopes. Inexpensive refracting telescopes from a major astronomy brand start at $80 (like the Celestron PowerSeeker 70AZ) and go up from there. These will come with either a ground or tabletop tripod and one or two eyepieces. Be sure the telescope has high-transmission coated optical glass.

A great choice for a beginner or novice is a tabletop altitude-azimuth reflector such as the Meade Lightbridge Mini 82 at $59 (see figure) – they provide quality imaging, are easy to use, lightweight, portable and not expensive. A stable, relatively level surface is required, but the tripod shakes are eliminated. They come with two eyepieces and a 2x Barlow lens, so four different magnifications are provided out-of-the-box.

  • Larger telescopes. A Dobsonian telescope is a reflector at the bottom of a long tube, which is mounted on a base allowing the telescope to be swiveled and tilted. The eyepiece is conveniently located near the top of the tube. Easy to set up and easy to use. Comes in sizes with larger mirrors and is a good choice for pulling in dim deep sky objects. $285 and up.
  • Accessories. An excellent accessory for beginners is a green laser pointer, about $50. The ability to accurately point out targets in the night sky makes teaching others much easier. These lasers are powerful enough to damage the retina, so never point them at people or airplanes. A few other ideas:  a red flashlight which preserves night vision, a planisphere or book of star maps, lens defogger, wide-angle eyepieces – there are too many choices to list here.

 

“Eye On the Night Sky” is a monthly column by the Door Peninsula Astronomical Society. For more information on the organization, visit DoorAstronomy.org.

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