Which telescope is best?
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You’ve enjoyed the stars, just looking at them when you step outside. Curiosity has led you to dig out the binoculars for a closer look. Sooner or later, you may decide to buy a telescope. Which one?
Longtime star watchers—often called “amateur astronomers”—differ in their opinions, perhaps in part because of the varied experiences they have had. Some say it is better to buy a larger telescope offering better views to keep the beginner interested. Others, like myself, find value in starting small and working up.
If there is enough passion just from enjoying the night sky with eyes alone, it should keep you going. A small instrument will still show wonders you may never have dreamed of seeing; eventually you might wish to upgrade.
Part of it depends on your budget. Good quality, small telescopes meant for those starting out are available for somewhere near $100, at least the last time I noticed.
“Big Box” or department store telescopes have a bad reputation of being priced low to sell but “giving you what you paid for,” as the saying goes.
You need a telescope with a steady mount; any wobble will make it almost useless to point and keep on a sky object. There are two main types of telescopes, the refractor and the reflector.
Astronomical telescope observations began with Galileo’s humble refractor in 1609. They consist basically of a large, front convex lens, called the objective, and smaller back lens or lenses within the eyepiece.
Because of the high quality required of the objective lens, which must allow light to properly pass, refractors are more expensive than most reflectors, unless you keep to a small version. You need to have a dew hood affixed to the front to ward off moisture on the lens.
A big disadvantage of a refractor is that you would need to bend your neck at a painfully awkward angle to look through it when pointing up if you didn’t have a “diagonal.” This is a small device containing a slanted mirror in which the eyepiece is inserted. You then can look down at a 90 degree angle into the image being reflected off the mirror.
Unfortunately, this makes everything you see a “mirror image.” The good news is that you can purchase a special “correct-image prism” diagonal that flips the image back.
The reflector has a large concave mirror objective in the bottom of the tube. Light reflects back up the tube to a small angled mirror, which both flips the mirror-image and sends it to the eyepiece on the side of the tube. This is by far the most common design for amateurs.
There are variations to both refractors and reflectors. Cassegrain reflectors have a hole in the center of the main mirror. The small mirror in the front is convex, which sends the light beam back down through that hole, to the eyepiece in back of the mirror. Again, a diagonal is required to save your neck.
Some will have pedestal mounts; others use tripods. A very common design for reflectors is known as the Dobsonian Mount, which has a box attached to what resembles a lazy Susan. The box cradles the tube and allows up and down motion. Invented by amateur telescope maker John Dobson, this mount revolutionized amateur astronomy, allowing for relatively inexpensive, large backyard telescopes.
Here’s some popular telescope company Web sites: http://www.telescope.com (Orion Telescopes), http://www.meade.com (Meade Telescopes) and http://www.celestron.com (Celestron Telescopes). See also ads in popular monthly astronomy magazines found on news stands, such as Astronomy, and Sky & Telescope.
New Moon is on April 14. Be sure to see brilliant Venus in the west after sunset, with less bright Mercury, to the lower right.
Thank you to Glen, a reader of this column in California, who inspired this week’s topic with a question he sent.