Avoiding the “Trash Scope” Trap

Here we go with another article that experienced amateurs can ignore—this is intended for readers who might not feel knowledgeable enough to make a wise purchase of a first-time telescope, or who are considering buying a scope as a gift for another person, particularly a child. We give gifts at other times of the year, of course, but Christmas is probably the biggest occasion for astronomy-related gift purchases. This is also the season when you’ll see the most ads or merchandise displayed in stores that carry optical equipment. Stores that cater mainly to amateur astronomers are rare in these parts and usually involve a lengthy drive to reach. This means that if you’re not doing catalog or online shopping, you might be inclined to patronize one of the big camera “superstores” or discount “box” stores. If so, here’s one of the best pieces of advice that you are likely to get regarding buying a telescope or binocular, assuming you’re not sure how to make a good choice on your own: Beware the low-priced “trash” scope or binocular that so many end up buying! Such things only serve to discourage budding observers and are, in effect, worse than useless.

How do I define one of these? 1) PLASTIC lenses! Believe it or not, there are items out there that may not seem to be just toys but actually have plastic lenses, so make sure your choice does not. 2) Inferior grade coatings on lenses, or—amazingly—NO coatings at all. Don’t choose any instruments to be used for astronomy with anything less than MC as a rating; this means multicoated. (FMC, meaning fully multicoated, is another step higher in light transmission and antireflectivity, but will cost more.) MC coatings are adequate but never buy anything rated simply as C. Coatings on lenses have distinct shades of color when a scope or bino is held beneath a light and viewed from a side angle. Absence of color indicates no coating at all, pale steel-blue might indicate a “C” rating only, distinct greenish-blue means better quality (MC), and deep greenish-violet usually indicates a higher level of coating, FMC. In general, the deeper the color, the better. Regarding binoculars, never buy anything having red (so-called “ruby”) coatings or amber/gold-tinted coatings—this is a certain indication of inferior, unsuitable instruments that don’t satisfy the viewing requirements of astronomy. (Be sure to read item #9 thoroughly for more references to binoculars.) You’d do well to choose a fixed-power (not “zoom”) model of at least 35mm aperture up to 50mm, with a magnification of anywhere from 7x up to 10x. Also, the “eye relief” distance rating is critical and should be at least 15mm; anything longer is better still.

3) Plastic drawtube, focuser, or star diagonal components. These parts should be made of metal, ideally, although certain high-impact plastics are adequate for the part of the focuser or star diagonal into which the eyepiece is inserted. If in doubt as to quality of the plastic used on this specific part, insist on metal. (Plastic adjustment, locking, or control knobs elsewhere on a scope are fine, generally. Many manufacturers use them to keep costs down, although I’d be more comfortable with metal on any LOCKING knobs.)

4) Flimsy, shaky, spindly, jittery, etc. mounts and tripods. Cheap, inadequate scopes almost invariably are furnished with such mountings, making the scope unusable—I repeat, unusable—for astronomy purposes. If a mount head doesn’t have smooth motions, but operates in a “rattling” excess play fashion, it’s no good. If a tripod is so weak and unstable that 15 or 20-power magnification is your limit for seeing anything with a reasonably steady image, then it’s inadequate.

5) Small aperture refractors or Newtonians with focal lengths sufficiently long so as to make the optical tube considerably longer than it is wide. What’s the problem here? Simple: Quite often, such scopes lack an altitude-adjustment/locking bar and you might as well be playing with a tripod-mounted see-saw! (Reflectors on Dobsonian mounts don’t need this part.) I’ve been exasperated for years upon coming into contact with outrageously bad excuses for telescopes that have utterly no provision for holding the tube firmly in altitude. On a tripod-mounted scope of a certain general range in length, you’ve absolutely got to have the capability of keeping the tube pointed steadily in altitude, as well as make convenient and positive slight adjustments up-and-down. This is why the altitude bar (or shaft) I’m mentioning here is so critical for long-focus small scopes, such as an f/11 60 or 70mm aperture refractor. Over-tightening the main attachment knobs never works reliably and can easily damage the optical tube itself; besides, how can you possibly make small changes to the altitude alignment quickly and easily? Answer is, you can’t!

I could devote an entire article to my item #5, but let me impress upon you just two final points about the importance of an altitude-adjustment bar. First, it’s an outright shame that even big-name scope companies actually market these unusable telescopes; you’d think experienced outfits would recognize such problems and be willing to raise prices a bit so that necessary features like this are not omitted from their offerings. Second, you can verify presence of an altitude bar by seeing if a metal shaft about 1/4” in diameter and roughly a foot long is attached on a pivot stud at the rear end of the optical tube, at the side. (The bar’s front end simply slides through a hole in another pivot stud mounted alongside the mount head.) The pivot stud on the mount head should have a locking screw or knob which, when snugged up, will hold the bar in place firmly and thus also the optical tube in altitude. There should be a threaded knob or screw at the rear end of the bar which, when turned, either lengthens or shortens the bar’s length slightly. This, in turn, has the effect of raising or lowering the scope’s altitude in a controlled, slow-motion manner, provided the locking knob on the mount head is tight. (You loosen that knob to permit the bar to slide freely through the hole when manually moving the scope in altitude. Azimuth motions are not affected by gravity and therefore can be made without a locking provision, although decent mounts will have azimuth-locking knobs included.) German equatorial mounts do not involve an altitude-adjustment bar.

6) Refractors smaller than 60mm aperture are suspect—such small size usually indicates cheap overall quality, although there do exist some expensive, high-end scopes of 50mm size. Make your lower aperture limit 60mm, for refractors. If you can afford 70mm or larger, better still. 7) Don’t buy a scope having its basic eyepiece/focuser size less than 1¼” in diameter—this is now standard. (Many scopes now come with 2” focusers, actually.) If a scope has, for example, 0.965” eyepieces, it’s a problem! Insist on 1¼” diameter and you’ll save yourself some grief. We’ll skip lengthy explanations. 8) Avoid telescopes or binoculars priced way low, under $100 or so for scopes or $60 for binoculars. There are very few exceptions to this rule.

9) I have not fully covered binoculars in this piece, important as they can be. Many people would be better off using a binocular as a starter instrument for stargazing. I refer you to the two-part article on binoculars for astronomy that appeared in the November 2008 and January 2009 issues of this newsletter, entitled “Sometimes Binoculars are Best.” I wrote about many distinguishing features by which a binocular can be judged, as well as why binoculars are sometimes superior to telescopes for certain kinds of amateur astronomy. Regarding a dead giveaway characteristic by which you’d know immediately that a particular binocular is not one you should buy (in addition to aforementioned plastic lenses), steer clear of any bino having its body/shell or any other major components made of plastic. The popular rubber coatings so common these days are fine—the metal body is simply encased by the coating. Imitation grained “leatherette” wrappings around a metal body are equally acceptable, but a binocular which appears to be made primarily of plastic is definitely not. Cheap toys are one thing, but reasonable quality optical instruments are quite another.

10) Watch out for splashy, garish blurbs marked on telescope boxes or packaging, the ones that claim you’ll be able to see things at “500x power.” This is nonsense; figure about 150x as a maximum realistic magnification in most small instruments. If you get a “fast” scope having a very short focal length (400-500mm), the highest you can generally go is around 50x. Believe it or not, even in longer focal length scopes you’ll have much better luck sticking with eyepieces that yield 25x to 35x. (Divide the scope’s focal length by the number marked on an eyepiece to obtain the magnifying factor. Example: A scope has a focal length of 700mm and comes furnished with two eyepieces, one being 26mm and the other 10mm. 700 divided by 26 = 27 power, 700 divided by 10 = 70 power.) This is all you need to enjoy most of what stargazing in a telescope can offer you. In a future article I’ll explain in depth why, in many (but not all) cases, extreme magnification is a tremendous detriment to an inexperienced amateur astronomer’s efforts to locate and satisfactorily observe celestial objects.

By the way, if a scope you buy comes with a Barlow lens, forego attempting to use it until such time as you feel capable of attaining adequately steady images when doubling the power yielded by any given eyepiece. Believe me, you’ll quickly see what I mean when you experiment on your own. Unfortunately, some telescope companies understand all too well that the uninitiated customer likely believes that ultra-high magnification is the be-all and end-all of astronomical observing. To that end, they want to “hook” you into buying cheap stuff that’s advertised so as to highlight a much-overrated feature that just won’t work realistically; such companies figure many folks will simply be unaware of true aspects of quality when looking over their products and will buy scopes just because an item is touted as magnifying things seen by hundreds of times. Whatever you do, don’t fall for this trap!

I can’t say as I’d blame readers who might think that they’d never be able to spot all the potential poor quality indicators I’ve described thus far. After all, products sold in many larger stores come packaged (naturally) in boxes, so how will you be able to thoroughly check them out in the store? If at all possible, try to enlist the help of a friend or fellow club member who genuinely understands astronomy equipment, even if it takes a little effort to make this happen. I have not unnecessarily stressed nor exaggerated any points made in this article, and I’ll sincerely hope that none of you end up being disappointed by buying one of these “trash” scopes or binoculars that are out there waiting for the ill-informed, unwary shopper. Catalog or online browsing? Get that knowledgeable astronomy buddy to look over the information with you before taking the plunge and you’ll be far better off. This is important and should not be taken lightly, so best of luck to all concerned.