Sometimes Binoculars are Best

I’ve always thought it’d be just a matter of time until I’d write an article in praise of using binoculars for amateur astronomy, something not immediately thought of by many who enjoy stargazing. The notion of trying binoculars on the night sky seems to be by no means an automatic consideration to a fair percentage of amateurs, unfortunately. Among this group are some of the very people, ironically, who stand to benefit the most from using “binos”—newcomers to our astronomy fraternity who may not be familiar with the night sky and who could really use all the help they can get in gradually easing into simple, straightforward star watching and constellation recognition. To some, binoculars just don’t seem, somehow, appropriate for looking up at night to the stars, something mistakenly considered to be properly reserved for astronomical telescopes. A bino is such a common item in many households that daytime use on traditional terrestrial scenes such as sporting events, bird and animal watching, ships at sea, distant mountains or hills, etc. registers on the mind of the user as the normal and “correct” way to use such an instrument. Perhaps the thinking is that a binocular is simply too small, basic and underpowered to meet astronomical viewing criteria, so why bother? I can’t overemphasize to those who hold this opinion just how much you’re missing! There are four basic points I should make before getting into specifics on reasons for using binoculars. I’ll do a follow-up piece explaining many of these reasons in next month’s issue, due to space limitations here. First, we recognize that telescopes have their obvious applications in astronomy and can show the observer a number of things not revealed at all in binoculars. (Separation of tight double stars, resolution of planetary details, highly magnified enhancement of tiny angular-size deep-sky objects so as to enable resolution, far greater light-gathering ability in medium-to-larger aperture scopes, and so on.) Second, no writer can write for everyone—there’ll be many among you who are already well aware of this subject and need no introduction. I chose this topic for those of you who might simply enjoy a piece on binocular viewing and perhaps could be encouraged to give it a try, if you’ve not done so already. Third, this article is concerned with hand-holdable binoculars of 50 to 60mm aperture or under and magnifications of approximately 10 power maximum. Fourth, so-called “giant” binos—owing to their size, weight, and the necessity of attaching them to some kind of mount—are not mentioned here because they’re deserved of a separate article all their own and are not as quick and easy to use as smaller, hand-held types. (The giant types, if of good quality and in proper collimation, can yield superb views that might be classed roughly midway as an observing experience between, say, a 7x35mm bino and a good 6 to 8-inch telescope. Should you have an opportunity to try one sometime, there’ll be a good chance you’ll be so impressed that you might end up reviewing your budget for new toys.)

Plenty of good information on the most important features that binoculars for astronomy should have is readily available in a number of books and magazine articles, and some publications have fine, comprehensive listings of recommended objects for observing. Phil Harrington’s Touring the Universe Through Binoculars is an absolute treasure trove in this respect. Phil has put together object listings for each of the 88 constellations that are so extensive that his book can easily serve as a good observing guide for telescope users, although his choices are things that can actually be seen in binoculars. If I were to compile a “short list” of a dozen or so of the best books for an amateur astronomer’s library, this splendid book would have to be included.

Although the information is available elsewhere, it won’t hurt to go over some recommendations here. Due to the nature of the images presented by stars and other celestial objects, the optical criteria for viewing them well is much higher than for, say, watching players on a football field or spotting a hawk in a distant tall tree. (Remember: stars themselves, other than our own Sun, are technically “point sources” of light because of their fantastic distances.) Should you happen to own a binocular now, I hope it’ll be in collimation, meaning that the two barrels are parallel and therefore give one clear image when using both eyes simultaneously, which is what a binocular is intended to do. (You’d be surprised at how often the “double image” problem comes up!) I also hope that your binocular has sufficiently long eye relief that you can see the entire width of field, even when wearing eyeglasses. Eye relief is simply the distance-expressed in millimeters- between your eye and the point at which the full field of view is rendered in an optical instrument. The more generous this important value is, the better. An eye relief of 20mm, for example, is vastly superior to one of only 12mm—it’s critical that you be able to comfortably and effectively see your binocular’s entire field without having to just about “glue” your eyeballs up against the ocular (eyepiece) lenses, particularly when wearing glasses.

Maybe you don’t have a bino but might consider buying one? The following points can help greatly in guiding you; for brevity’s sake I’ll skip a few lengthy technical explanations and hope you can accept what I say as a given.

1. Coatings: Avoid any bino having red (so-called “ruby”) lens coatings; same goes for gold-colored coatings— these can be cheap gimmicks intended to impress the uninitiated and optical performance will be poor on stars. Buy a bino with the highest grade of coatings you can afford, multicoated (MC) or, better still, fully multicoated (FMC). The best coatings will show a deep greenish-violet color when examining the lenses at an angle under light.

2. Collimation: We covered this but I’m repeating it here for emphasis. A bino has to be in proper collimation to be of any use to you, so be fussy when checking one out. 3. Eye relief: Same story—eyeglass wearers should be able to leave glasses on and still make easy use of a binocular. Get the longest eye relief rating possible.

4. Variable (“zoom”) power binoculars: Don’t buy one of these for astronomy purposes! Stick with a fixed-power instrument. I’ll forego explaining why; just trust me.

5. Tapped hole: Any binocular purchased for astronomy should have a tapped hole in its central pivot brace at the front end—standard size is 1/4x20 thread. The hole enables you to easily attach the bino to a bracket which, in turn, goes on a mount head. Even small, lightweight binos can benefit by the ability to be used on a mount of some kind, although one of their primary advantages over telescopes is hand-holdability.

6 “BAK-4” or “BK-7” prisms? These code designations refer to special kinds of optical glass used in the internal prisms. Always choose a bino having BAK-4 prisms; various optical qualities inherent in BAK-4 make them superior for astronomy viewing to BK-7. You can usually check this feature by just holding a bino up to light at about one foot away from your eyes and studying the appearance of the light dots emitted through the ocular (eyepiece) lenses. If they’re nice and round, the prisms probably are BAK-4. If, however, they’re slightly squared-off and appear a bit diamond-shaped instead of truly round, then the prisms are the inferior BK-7 type.

7. “Roof” or “Porro” prism type? Some might argue this point, but in general, you’ll be better off with a Porro prism binocular, the basic type having 90-degree offsets in the barrels. Because of this design feature the distance between the centerlines of the barrels will always be greater than your eyes are apart. This enhances stereoscopic depth perception, even if only by a slight margin. Porro prism binos are simpler and easier to assemble and test by a manufacturer, meaning they’re less expensive than a roof prism type of comparable quality. They’re often a bit shorter in overall length, too. Roof prism binos employ a more complicated arrangement of their internal prisms, a design making it possible for the barrels to be straight all the way though with no side displacement. This makes them more compact, on average, than the Porro type, a good reason for their recent increase in popularity. Quality roof prism binos tend to be appreciably higher in price than a Porro instrument of the same quality level. Also, there tends to be greater loss of light in the image due to the complexity of the prism arrangement, a condition minimized in very high quality models of extreme price.

8. Power (magnification) and aperture (diameter of main lens) selection: A binocular will always be defined by two very important numbers, power being first and aperture being second in the description of any given model. Examples are 7x35, 8x42, 10x50, and so on. You might find the variety available to be confusing, especially if you’re surfing the websites or looking through, say, Orion’s catalog. We’ll narrow things down rather quickly, though. Many experienced bino users would say that the ideal “one size fits all” astronomy model is 10x50mm, followed closely by 8x42mm or 8x40mm. Ten power is the best compromise in magnification between higher powers with images that are hard to hold steady by hand and lower powers that often don’t magnify quite enough for pleasing resolution. Fifty millimeter aperture seems about ideal between the size and weight concerns you’d have with a model larger than 60mm, and the reduced light-gathering ability that a 35mm gives. A good bino of 10x50mm type should yield an apparent width of field of about 5 degrees; some models will do even better. An 8x42mm should, because of the lower power, yield 5.5 degree to 6.5 degree fields. By the way, you can easily figure a binocular’s “exit pupil” rating by simply dividing the aperture (in millimeters) by the power number, as in this example: 10x50 works out to a 5mm diameter exit pupil, which is ideal for most people. The exit pupil is simply the diameter of the light beam emitted though the eyepiece into your eye, always expressed in millimeters. This value should approximate the diameter of your dark-adapted pupils at their full dilation, and not be substantially larger or smaller. (I’ll skip a detailed reason.)

Next month in this space look for part 2 of this article, which will take you through reasons why binoculars are sometimes a better choice for certain kinds of observing than telescopes.

In line with that thought, here’s a brief preview of my main reason—it’ll dramatize beautifully why no telescope is the equal of a suitable binocular for viewing large celestial objects (or rich starfields) that can truly only be seen in their entirety and appreciated fully in a binocular. If you’ve got a bino, train it on the Pleaides, M45. Never seen this cluster in a bino? You’ll be a believer! Also, sweep the central Cygnus Milky Way just below Gamma Cygni (Sadr)—only a binocular can show this spectacle the way it should be seen. Part 1 of this article appeared in the November issue. I had intended this follow-up segment to be printed in the December issue; things didn’t work out. Reading a continuation of a two-part article after a lapse of two months could be a bit problematic, so I suggest, for those interested, that you retrieve (if possible) Part 1 from November and reread it now. Sorry about any confusion.

I wrote about my notions regarding why many amateurs seem disinclined to use binoculars on the night sky and urged those who don’t to give bino observing a try. Most of Part 1 dealt with features that binoculars for astronomy should have and why celestial objects generally are more demanding of optics than typically-viewed terrestrial scenes like sporting events, bird watching, etc. Very little of importance was omitted from a listing of guidelines to use when choosing binoculars as a first-time purchase, although I didn’t mention a recommended price range, “image-stabilized” models (very expensive, heavy, low battery life, usually available only in medium-to-smaller apertures), or inexpensive models touted as having ultra-wide fields. (Some of these have inferior optics with very poor star images near the edge of the field!) Binocular viewing devices for telescopes also were not mentioned, although their popularity keeps rising as ever more models become available. Many telescope owners love these bino-viewers as an adjunct to conventional single-eyepiece observing, but they don’t function as true binoculars—they are “beam splitting” devices which divide the light coming from one optical tube assembly so that two images are formed. Standard hand-holdable binoculars are the subject of this article.

I’d like to preface my list of reasons as to why binos have a number of advantages over telescopes with a separate listing of many of the reasons that amateurs can have for what might be called “astronomy burn-out.” This happens to many of us from time to time; sometimes people end up thinking that it just isn’t a pleasant or worthwhile experience any longer and they give up on observing altogether. Some of you will know exactly what I mean. Here are my ideas regarding some thoughts that might occur to a typical amateur astronomer undergoing this burn-out: 1) I’m sick of freezing in the winter and having to dress like a grizzly bear just to go outside for observing. Bad enough if the air is calm, but any wind at all makes it unbearable! 2) I can’t handle mosquitoes any more during summer and it’s too much work having to mess with sprays, lotions, etc. The warmer and more humid it is, the more torture insects inflict on me. 3) Speaking of summer, it doesn’t get adequately dark for observing until at least 10:00pm around the June solstice and I have to get up for work by 5:30, which is too late to catch certain morning objects. Daylight saving time is a killer in summer! 4) There’s a bright Moon tonight—why bother? 5) Wasn’t it supposed to be clear? I’m not gonna bother setting up just to try snatching glimpses of stuff through “sucker holes” in clouds. Why can’t we ever seem to get a decent night with no clouds when it‘s not close to a full Moon? 6) The local skyglow keeps getting worse and there’s yet another big box store due to be put in near my house—you can’t win! 7) My neighbor just put up one of those killer security lights that beams out over his yard directly into my face when I’m trying to spot stuff in the only good direction I’ve got left for viewing from my yard. (Naturally, it’s on all night. I give up!) 8) My observing buddy moved to Arizona last month and it’s no fun doing astronomy alone, particularly where I used to like going. 9) I can’t do any observing from my porch or yard and I’m tired of always having to drive to places for astronomy. 10) Just lost my favorite observing site to development—what’s the use? 11) I just can’t seem to learn the sky and can’t find things to look at, other than the Moon, a couple of bright planets (when they’re up), parts of Orion, and the Pleiades. (Don’t have a go to scope that initializes itself.) It’s frustrating! 12) I’ve seen nearly all the worthwhile objects that my scope can show. How many times can you keep looking at the same things?
All of this was bad enough, but here’s possibly the single biggest reason for burn-out. Your scope and mount seem to somehow keep getting heavier, more time-consuming to set up, and more of a nuisance than it’s all worth, particularly if you don’t have a handy “grab-n-go” instrument with a simple alt-az type mount that would take only five minutes or less to get set up. Remember the winter cold and summer mosquito situations? If you’re tired of lugging stuff around and fussing with equipment just to begin an observing session, factor in the cold or bugs that seem to bother you all the more while you’re wrestling with gear and you’ll have to admit that your exasperation and impatience get even worse during these times of the year. Come to think of it, I didn’t even mention the huge hassles of ice and snow that winter can bring to the northeast, in addition to the cold! Anyway, one potential remedy for burn-out is a binocular, which is the first and best reason to use as a beginning to our list as to why a bino can be a great idea as an alternative to telescopes. Here we go:

1) Binoculars can be a fine burn-out remedy.

2) Low power, wide field views you’ll get with a bino will reveal wonderfully rich and expansive sections of the night sky that can’t possibly be compared to what would be seen in a “rich field” short focal length telescope. Rich star clouds along the Milky Way (or clustered masses of stars anywhere else) become beautiful, glistening scenes in a good bino, with a brightness and sharpness that can literally be dazzling. Your naked-eye view along can’t show you the magnified and enhanced detail; telescopes can only yield a much-constricted, tiny section of the sky in an eyepiece.

3) For the same reason, large, scattered star clusters or stellar associations (like the Pleiades or the Perseus OB association highlighted by Alpha Persei, Mirphak) can only truly be viewed in their entirety and fully enjoyed in the generous field given by a binocular. Such objects need to be seen surrounded by plenty of sky to be appreciated—only a bino will show such a view. The second and third nearest star clusters to our Sun—the Hyades in Taurus and Melotte 111, the Coma Cluster, in Coma Berenices—are the classic examples of objects much too large, extended, and straggling to be seen in even an Edmund Astroscan scope. True, you’d see parts of these clusters in such in instrument, but you’d have to sweep it around in order to take in the whole thing, section by section. The Coma Cluster spans about 5˚ but a 7-power bino should enable you to enjoy a view showing the entire group all at once! The closest cluster to our system is way too big to be viewed in a binocular. Five of its members are the five middle stars within the seven-star Big Dipper asterism. This is such a scattered and dispersed cluster that it is termed a “moving group”: the Ursa Major Moving Group, with its five Big Dipper members at an average distance from us of only 78 light years. (Alkaid, the star marking the outer end of the handle, and Dubhe, the lead “pointer” star at the upper, end corner of the Dipper’s bowl, are not involved.)

4) Binoculars are so small and light in weight that they can be transported (easily when flying) or stored in a car or home almost effortlessly. The compact size and ease of use of a bino, particularly a hand-holdable model, means zero set up time, unless you include a few seconds to withdraw from a case and pull the lens covers off. In other words, no muss, no fuss! If you’re mingling with friends at a star party, you can just carry a bino around the site with you, something not so readily done with most telescope/mount combinations. Want to spot something in the sky? Take just five seconds or so to raise the bino to your eyes and point towards whatever catches your interest. You can even track apparently slow-moving objects like the space station or shuttle, and those rarely-seen big meteors that take many seconds to move across the sky as they “skip” across the atmosphere. Such sights are a real treat and don’t have to be missed by the observer armed with a binocular. Remember my point about compactness and ease of carrying: An amateur taking a plane flight to anywhere having enticing night skies might not want to pack along a scope with mount if it’s inconvenient and more expensive to do so, but your bino can be popped into a carry-on bag with ease.

5) Unless a telescope is equipped with what’s called an “Amici” prism diagonal (these don’t yield images of the quality expected by most amateurs), the image seen will be inverted and/or a “mirror” image showing something having its natural orientation reversed. Generally, astronomers don’t really mind this effect, but it can get tedious and very confusing at times, especially when doing low-power star-hopping while trying to locate a specific star or other object. It’s also tricky when you’re trying to identify features on the Moon, as many of you know. Here’s where binoculars really shine: The internal prisms are designed so as to yield a “correct image” to the user, meaning you see things as they naturally appear. Up and down, left and right, the view matches the object’s true orientation with no confusion.
6) A binocular is really a paired assembly of two short-focus telescopes, one for each eye. Since both of your eyes are used simultaneously when viewing, the net effect is better color perception for most people, meaning more attractive starfields. Also, the image your brain forms is a combination of two optical receptors that are separated by a small distance from each other—the center-to-center spacing of your eyes, enhanced even more by Porro prism binoculars, those having the 90˚ offset in each barrel. This is stereoscopic in effect, rendering a view that actually can seem almost three-dimensional on certain sky objects. It’s as if you begin to sense depth perception in astronomy, an experience nearly impossible to achieve when using a telescope with a single eyepiece. (The Pleiades cluster, M45, and the Moon are perhaps the best two examples.)

7) A good binocular for astronomy can be bought for roughly $100 to $250. The lower end of that price range will get you a better quality instrument than a comparably-priced telescope. Many inexpensive telescope/mount combinations are so poor in quality as to be nearly unusable.
8) The light weight and hand-holdability of most binos make them ideal for “sweeping” around the sky, something you’ll especially enjoy when viewing those richer sections of the Milky Way. Low power, wide-field images contribute to this ease of use when contrasted with a telescope. Here’s another related advantage that just occurred to me. When you look into the eyepiece of a scope, you’re generally not looking up at the sky, but somewhere downwards or angled-off sideways, etc. With a binocular, you end up looking in the exact same direction that you would with your naked eyes. In other words, binoculars are much more easily “pointable,” even while viewing through them. A bino can seem to be a natural extension of your eyes.

9) Low surface brightness objects like the galaxy M33 in Triangulum are tough to make out in many telescopes, even in a dark area on a good night. Using both eyes simultaneously in a wide-field bino, such difficult targets can become more readily seen. In fact, some deep-sky objects will actually reveal themselves far better in a bino than in a telescope—two eyes are better than one!

10) If you’re tired of optics on your scope becoming dewed-up in fifteen minutes or so on humid summer nights, consider this: used with a little common sense, a bino can escape dewing altogether. (Just keep lens caps on between views—they’re quick to detach.) Plus, the heat from your own hands gripping the barrels can serve to work as natural “dew heaters” for the lenses.

Perhaps I’ll add a bit more to this binocular astronomy subject in a future article. Observing or object lists might be included, along with brief descriptions of more good books on bino viewing. (Remember my praise for Phil Harrington’s Touring the Universe through Binoculars? I mentioned Phil’s book in Part 1.) In closing, I hope at least a few readers will be able to see binoculars for amateur astronomy in a new light, and then go out and use them.