Picking an astro binocular

Copyright (c) 1998 Jay Reynolds

The most important advice is to seek out a local astronomy club -- perhaps from the annual directory in Sky & Telescope or Astronomy, or via their web sites, www.skypub.com and www.kalmbach.com. Go to their star parties to try out other folks' telescopes, binoculars, and so on. Sometimes people will be so eager to show you things, that you can put off buying your own equipment for years and years.

The frequently-asked questions list (FAQ) for telescope purchasing, that appears on usenet newsgroup, "sci.astro.amateur", has information about binoculars. It includes a section on how to hold them steady. Wade through it and look for the sections you need.

Any binocular you find lying around will provide better views than the naked eye. Possibly you should not buy one at all, just mooch from friends or family for a while, till you know what you are doing.

Binoculars are low-power instruments that show little planetary detail. The moon will look wonderful, and you will be able to see moons of Jupiter and phases of Venus, but probably no other planetary stuff. Yet many deep-sky objects lie within range of a small binocular -- I have seen all the Messier objects with a 7x50 (some were very difficult), and lots more. The Great Spiral Galaxy in Andromeda, the Orion Nebula, and the summer Milky Way, will be wonderful.

The "right" binocular for most people is about a 7x50 (that is, it magnifies seven times and has front lenses 50 millimeters in diameter). Big front lenses gather more light and show fainter objects, but with lenses much larger, or magnifications much greater, the whole instrument may get too big and heavy to hold steady. Some people like more magnification -- 10x50s are common. I have a 10x70 I like, but it weighs twice as much as a 7x50; not everyone can keep it steady. If you are older than forty or fifty, the pupils of your eyes may be too small to take in the big beams of light emerging from a 7x50 binocular; a 10x50 might be best.

You can pay $1000 for a 7x50 binocular, but cheap and sleazy imports sell new for as little as $50, and sometimes real bargains show up at garage sales and such. If you are on a budget, do not worry if you must buy the cheapest and sleaziest binocular you can find -- it will be lots better than the naked eye -- but expect friends and fellow net-posters to be critical and condescending. Ignore us: We believe that fancy gadgets make us morally superior, we are dumb enough to think that more money always makes things better, and we are too cowardly ever to admit wasting money on something that wasn't worth the high price.

On the other hand, if you like high-tech gadgets, or if you are willing to pay a lot for the best binocular possible, and if you are certain you know exactly what you want, then go ahead and buy a more expensive one -- it will give noticeably better performance -- but expect friends and fellow net-posters to be critical and condescending. Ignore us: We believe that inexpensive technology makes us morally superior, we are dumb enough to think that more money never makes things better, and we are too cowardly ever to admit that our needs and desires have outstripped our budgets.

Seriously, a lot of what you pay for in a costly binocular is mechanical robustness and resistance to hostile environments. Those used by biologists get trampled by rhinos; those used by geologists fall into volcanos. Nautical units are exposed to yucky salt air, engine vibration, and attack by marauding submarines. Astronomical binoculars lead more sheltered lives, so there is no need to spend extra money and put up with the extra weight of a binocular built for harsh conditions.

Take care of your binocular. Things that will hurt it include heat (don't leave it in the sun, even in the case, especially inside a car), moisture, dust and dirt (do use the lens caps and case), vibration (don't toss it on the bed of your pickup for the drive up the mountain), and raccoons. Only the latter take protection payments.

When you are about to buy a binocular, try a few simple tests:

  • 1) If it rattles when you shake it, you are about to make a mistake. Put it back and try another. Don't laugh, a bad unit from even a reputable manufacturer may slip through quality control now and then, and who knows how many times the one in your hands has been dropped, and how far, in shipping and setting up for display.
  • 2) Move everything that is supposed to move. Does anything feel loose or sloppy? Does anything feel like the only reason it is tight is that some unscrupulous manufacturer tightened it down too much, to cover up looseness and slop? These are all no-nos.
  • 3) Can you get good images out of it? Take it to a door or window, preferably an open one, and focus it on something far away. If you had to take off glasses to use the binocular, are the images still clear? If you are using glasses, can you get your eyes close enough to the eyepieces to see the whole field? Is there any hint that the two sides are not perfectly parallel, so that only a chameleon can look through it without eyestrain? These are more no-nos.
  • 4) Is it too heavy for you to hold steady? (Be sure you have read the FAQ section on how to do so.) Will you still feel that way after observing for an hour? Even when you are cold and tired?
  • 5) Look into the binocular, through the lenses. Do you see any signs of scratches, dust, mold, deteriorating lens cement or damaged coatings? Some such defects will be cosmetic only, but be wary of large ones.
  • 6) Now a virtual test: Don't really do this, it's for experts only. Hold the binocular at arm's length and drop it on the floor. I say again, don't really do it, just pretend you are going to. If you have a virtual heart attack, or experience virtual financial ruin, perhaps you should consider a less expensive model. The theory is that if you worry too much about loss or damage, you may end up babying the instrument so much you don't use it, in which case you are a collector of scientific instruments -- a fine hobby in its own right -- but not an astronomer.

Have fun, keep your dark adaptation, and remember -- raccoons like Oreos.