Karthik Subramanian, karthik !remove spaces! 301176 !+! bas !AT! gmail !DOT! com
Binoculars are a relatively inexpensive and often overlooked piece of equipment that can be used to explore the night sky. This article tries to provide a quick overview of binoculars for beginning stargazers. Note that this is not a comprehensive review, and many details have been left out for the sake of brevity and accessibility.
No originality of content is claimed, except perhaps for the presentation.
Why use binoculars for stargazing? There are a few good reasons.
Owing to their their wide field of view, it is much easier to locate objects through binoculars than in a telescope. This makes it easier for a beginner to learn their way around the night sky, which is a useful skill for any observer.
Two eyes are better than one, as the adage goes. This is true of binoculars as well. The presence of two light paths as opposed to one results in a brighter image. This is partly due to how the brain processes images that are being looked at by both eyes. The author is not knowledgeable enough to say anything more about the biological processes at work; but can instead recommend the following simple experiment: look at your favourite object in the sky through a pair of binoculars, with both eyes open. Next, look at the same object with one eye shut. Look at the object through both eyes again (this time, you might have to wait for a few seconds for your eyes to reach focus.). The difference between the single-eye image and the two-eye image should speak for itself.
Lastly, if you’re a beginner, binoculars are a relatively inexpensive way to get started in the hobby. They are also multipurpose, and can be used in pursuits other than stargazing. Should you ever decide that stargazing is not for you, you can still use your binoculars otherwise, and they will not be a dead investment. The author does recommend that you not point them at your neighbour’s windows, however.
A lot; but here’s a small list (courtesy Akarsh Simha). The “M” stands for Messier. You can look these objects up in a sky chart like Stellarium, or SkEye.
Most of these objects should be visible from Bangalore rooftops, as long as your skies in that direction don’t look orange. This, of course, depends upon your location in the city.
If you want more objects to look at, then Ed Zarenski’s list of 100 Binocular Deep-Sky Objects and the Binocular Sky’s Object Search should help.
If you would like a taste of what you can see through binoculars, Rony de Laet’s Binocular Sketches are illuminating, to say the least. Please do note that these observations were mostly done under dark skies, and with mounted binoculars. That said, the sketches give you an idea of what can be achieved with binoculars.
Binoculars are primarily specified in terms of their Magnification and Aperture. A pair of 10x50 binoculars refers to binoculars with 10x Magnification and 50mm of aperture. Typically, more aperture gathers more light - but be aware that with increasing aperture, the weight of the binoculars also goes up (not to mention the expense).
Another important parameter is the Exit Pupil. This is the (minimum) diameter of the tunnel of light that exits the binocular eyepiece. The exit pupil diameter can be calculated by dividing the aperture by the magnification. The exit pupil should ideally match the size of your eye’s pupil.
The Eye Relief is the maximum distance from the eyepiece that you can position your eyes, and still view the entire field. This is of particular importance to observers who wear glasses.
Most (if not all) binoculars use prisms internally to provide the correct focal length within the small frame of the binoculars. The kind of glass used for the prisms is usually either BAK-4 (Barium Crown Glass) or BK-7 (Borosilicate Glass). BK-7 is considered inferior to BAK-4, but for most practical purposes, this should not matter. If you hold your binoculars up to the light, and look at the eyepieces from a foot or so away, the shape you see can tell you what kind of glass has been used for the prisms. BAK-4 prisms show a nice circular shape in the eyepiece. BK-7 prisms show a diamond shape in the eyepiece.
Mention must also be made of ED glass - this is Extra-low Dispersion glass, with virtually no chromatic aberration. It’s very good to have in a pair of binoculars, and also comes at a price.
In order to avoid stray reflections and scattering of light within the light path, binocular glass surfaces are usually protected by anti-reflective coatings. You might come across the terms Multi-Coated and Fully Multi-Coated in this context. Multi-coated binoculars usually have their objectives and oculars coated. The Fully Multi-Coated kind have anti-reflective coatings on all glass-to-air surfaces. FMC binoculars are preferable to the other kind, but are also more expensive.
Avoid binoculars with Ruby (or similar visibly red) coatings. These coatings work by filtering out the red parts of the spectrum, rendering them pretty much useless for astronomical use.
Binoculars come in two broad constructions - Porro-Prism and Roof-Prism. Porro-Prism binoculars are the most common kind. Roof-Prism constructions are supposed to have lower light losses. Between the two, Porro-Prism binoculars are definitely more cost-effective.
Stay away from zoom binoculars. Good zoom binoculars probably do exist - like the Nikon XL series. They are however, very expensive, and not easily available. Cheap zoom binoculars are bad. Stay away from them.
Most “beginner’s” binoculars come with centre-focus. In other words, both the optical tubes are focussed by a single knob which lies between them. If not centre-focus, the optical tubes can be focussed individually (Individual Focus). We will not worry about Individual Focus further in this article, since most beginner’s binoculars are centre-focussed.
When you look through a pair of binoculars, you should see one image, preferably crisp. You should also not feel any strain in your eyes whatsoever. In order to achieve this, it is good to try out the binoculars in daylight against a distant target, preferably something like a telephone pole or power line, that has both vertical and horizontal lines.
If you look through the binoculars and see two disjoint images, or if you can only see one eyepiece, you need to adjust the Inter-Pupillary Distance. Simply put, the distance between the eyepieces needs to match the distance between your eyes.
Binoculars usually have a central “hinge” about which you can “push” or “pull” the two optical tubes. Doing this will reduce or increase the distance between them. The idea is to adjust this distance (the binoculars’ IPD) until it matches your IPD.
How will you know if you’ve adjusted it properly? It’ll feel a lot more comfortable than when not. Ideally, you should also see a single image instead of two disjoint images.
One of the downsides of wearing glasses is that it is impossible to look through most binoculars and see the full field while wearing your glasses. Some binoculars provide sufficient eye relief for eyeglass wearers, but most do not.
If this is the case, then the only option is to divest yourself of your glasses, and adjust the binoculars for your eyesight. Most binoculars have an adjustable right ocular for this purpose.
The procedure (best done at night) is as follows:
Look through the binoculars with only your left eye open. Preferably cover your right eye with a patch. If this is not possible, just hold the right eye shut. This is not ideal, but will suffice. Then, adjust the focus until you get a crisp image and pinpoint stars.
Patch/shut your left eye, and look through the binoculars with your right eye open. Twist the right eyepiece and achieve pinpoint stars. Do not turn the eyepiece through a large angle, make small adjustments.
Look through the binoculars with both eyes. If need be, adjust the focus. Do make a note of the position of the right eyepiece.
If you’ve adjusted the IPD correctly, and have made the dioptre adjustments, but still feel some kind of eye strain, or see a “cross-eyed” image, then perform the following test, in daylight.
Look at a target that has both vertical and horizontal lines. Check that the horizontal lines are at the same level in both the eyepieces. In other words, you should only see one horizontal line. If you see a broken horizontal line, then your binoculars are out of collimation, and are best returned to the manufacturer. If you’re feeling adventurous and don’t mind voiding your binoculars’ warranty, read References 1 and 2 and proceed further.
The “intuitive” way of holding binoculars is usually not the right way, in the sense that it becomes hard to hold them steady for more than a few seconds.
Holding the binoculars by placing your hands as close to the objectives as possible (without your fingers hanging over them) will provide more stability.
The author’s personal favourite is the “A-Brace” hold, described under a different name in 3.
Hand-Holding binoculars for more than a few seconds can be cumbersome. It is not much fun to look at stars dancing to form elliptical shapes. The solution lies in mounting the binoculars, so as to hold them steady.
Using a regular camera tripod to hold binoculars is not a good idea; this will result in much strain on the observer’s neck. A better solution is to instead use a monopod, preferably with a trigger-grip ball head.
One of the best binocular-mounting solutions is a Parallelogram Mount. This is probably the best way to mount heavier binoculars. One of the nice things about a parallelogram mount is that it can be hacked out of some plywood by someone with very little carpentry experience.
Reference 4 deals with binocular mounts in some detail.
Looking up through binoculars can be a pain in the neck, no matter the mount. To prevent strain on the back and neck, a (preferably reclining) chair is highly recommended. A chair and a monopod make for good binocular observing companions.
If you’re set on binoculars, but prefer hand-holding over mounting them, but do not want shaky images - despair not, there is a solution for you! It’s called Image-Stabilized Binoculars.
The author has no experience with Image-Stabilized binoculars, so what follows is gleaned from other sources - take it with a pinch of salt. This disclaimer will hold true until someone who’s experienced rewrites this section, which should happen sometime soon.
The idea is to internally move the binocular prisms to compensate for the motion of the holder’s arms. The mechanism to do so might be electro-mechanical, or completely mechanical.
Happy owners of Image Stabilized binoculars report that they are life-alteringly good. A small minority of users who are sensitive to motion-sickness, or suffer from borderline vertigo, claim that they are unable to use Image-Stabilized binoculars comfortably. As always, try it before you buy it.
There seem to be a few major vendors selling Image-Stabilized binoculars - among them, Canon, Fujinon, Zeiss, and Nikon. The Zeiss binoculars are mechanically stabilized, and don’t need power. The rest of them are battery powered.
References 5, 6, 7, and 8 cover Image-Stabilized Binoculars.
Binocular owners are not immune to aperture fever. Most are content with 10x50s, but some go on to own big(ger) binoculars. The biggest that can be hand-held, with some effort, (in the author’s experience) are 20x80s.
Bigger models, like 25x100s are also available. These need to be mounted, and cannot be hand-held. As the size increases, it also becomes difficult to synchronize the focusing motion of the two optical tubes. Hence, big binoculars are more likely to be Individual-Focus (IF) as opposed to Centre-Focus (CF). In other words, each optical tube has its own focusing mechanism, independent of the other - not unlike two telescopes mounted next to each other.
Reference 9 shows a few (representative) models of Big Binoculars, with pricing information.
What prevents us from getting hold of two identical telescopes, and making a binocular telescope? Nothing. Reference 10 shows several successful BTs made from pairs of regular telescopes.
Firstly, fix your budget. As on this date (circa Oct 25, 2015 in Bangalore), the binocular budget buckets are roughly Rs. 5K, 11K, 15K, Motorbike-class, and Hatchback-class. There is some amount of overlap between the buckets, especially in the last two.
Secondly, decide how big you want your binoculars to be. The best binoculars for hand-holding are probably 8x40s. The biggest binoculars that you can hand-hold for short periods of time are 10x50s. Bigger binoculars, like 20x80s, give you better views (though some would disagree), but are also much heavier, and ideally need mounting. Most amateurs tend to start out with 10x50s.
Thirdly, please avoid ruby coatings and zoom binoculars.
Please note: the recommendations that follow are entirely personal opinions of the author, and may please be taken with a pinch of salt. They are not the gospel truth. If you find a better deal, and judge it to be a good buy, please go for it.
The pricing information below is merely representative, and is not accurate.
The Olympus 8x40 is the easiest to hold, and can double as a good pair of birding binoculars. Ditto the Olympus 10x50, except that it’s a little heavier.
The Pentax is probably the best 10x50 for its price.
A word of warning about the 15x70s - please don’t buy them unless you can return them easily. Many people have complained that the binoculars were miscollimated out of the box. It earns mention here because the views through a well-collimated pair are truly amazing, and it’s the most affordable 70mm binocular here.
There are definitely other models available at around the same price points, which are not mentioned here. (Like the Nikon AE series). It was the author’s decision to mention only models which he has personally looked through. It’s not that the others are bad, just that yours truly has no experience with them. The situation is similar with the bigger and IS binoculars.
If your budget is bigger, or you are undecided, please post on the B-A-S list. We’re all too happy to help you spend your money :) All of these binoculars are available locally, except perhaps for the last 3 buckets. If you’re willing to import, or have a friend visiting from elsewhere, then your list of available choices increases dramatically.
As far as possible, buy your binoculars at a place that lets you try them before you put down your money. Sadly, the author is unaware of such a place in Bangalore as on the date of writing. The next option is to buy them at a place with a well-defined return policy, so that you can buy them, unbox and check, and return them if necessary.
Check the binoculars for collimation. If they are miscollimated, return them.
If the binoculars say they are BAK-4, but they have BK-7 instead, return them. It’s not that BK-7 is bad - but you didn’t get what you paid for.
If you look at bright objects (like Jupiter or Venus) and see a purple hue around them, don’t worry. This is perfectly normal - unless you plonked down a lot of cash for a pair of ED binoculars. If that is the case, return them.
Look down the objectives (preferably with some lighting below), and check for dust inside the binoculars. If there is dust inside, or you see anything cloudy, return them.
DO NOT breathe on the objectives, or spit on them. A small amount of dust on the objectives is OK, and will not hurt. Keep human fingers (yours and others’) away from glass surfaces. DO NOT rub them with your shirt, undervest, or handkerchief.
Disclaimer Please read the manufacturer’s note before attempting to clean your binoculars. The recommendations below are given in good faith, but might not be the best way of cleaning binoculars. BAS and the author are not liable for anything that might go wrong by following this process - proceed at your own risk.
If you go birding with your binoculars, and you get pollen or tree-dust on the objectives, blow it away with a small air blower. A mechanical foot-pump (of the kind used to inflate bicycle or car tyres) works well for this purpose, as long as the nozzle is clean, and free of dust and grease.
To get fingerprints off the objectives, wipe them off very gently using a white soft tissue that has been made damp with distilled water. Do not use pressure. Discard the tissue after using it for two or three wiping motions. Use a sprayer to wet the tissue; if need be, squeeze off excess water so that the tissue is just damp. The process should not leave streaks on your glass. Do not use coloured or perfumed tissues, or tissue that is too stiff.