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FAQ-How to Choose
Binoculars Questions & Answers
In order to choose a pair of binoculars that are right for you, we have listed below information that is of a more general nature, but is important to know in choosing ANY binocular. WHAT DO THE NUMBERS MEAN? Every binocular on the market today is referred to by a set of numbers that look like this: "7 x 35" or "10 x 50" or "12 x 80", etc. The first number in this set is the Magnification. In other words, the examples listed above will bring things 7, 10, or 12 times closer, respectively. The second number is the diameter of the main lenses, listed in millimeters (there are 25.4mm in one inch). Also usually listed somewhere on the binocular body is the Field or Angle of View. This number is either listed in degrees (an angle, like 5 or 7 degrees), or as a width at a distance, usually a certain number of feet at 1000 yards. To convert one to the other, just remember that one degree equals a view of 52 feet wide at 1000 yards. TOP WHY ARE THOSE NUMBERS IMPORTANT? MAGNIFICATION:Most people believe that a higher magnification instrument, whether it be a binocular, a spotting scope, or a telescope, will automatically give them a "better" view. This is not the case, in fact high magnification will actually decrease the quality of your view. Binoculars are most commonly made at 7, 8, or 10 magnification. A lower magnification will give you a brighter image, a more steady view (less shake), and a wider field of view if you compare binoculars of the same size objective lens (the second number). As you go higher in magnification, you will find that the image is larger, but the field of view is more narrow. Higher magnification binoculars are also harder to hold still, and the image through them is dimmer than the same size binoculars set at a lower power. This is important to remember if you will be using your binoculars in lower light conditions. Generally, most people have a hard time holding anything over 10 magnification steady. If you insist upon higher power binoculars (above 10) because of a specific application, make sure they have a socket built into the body so that you can mount them on a tripod if you wish. DIAMETER OF MAIN LENS:In a nutshell, the larger the objective lens the more light it gathers, but the larger and heavier the binocular is. If you are going to be using your binoculars mostly in brightly lit situations, it is not as important to have a larger-apertured lens. But, if you want to use your binoculars for lower-light activities such as astronomy, bird-watching, or hunting, you will find a pair with optimum light-gathering more pleasing. In general, try to pick something that is reasonable to you as far as size and weight are concerned but that still gathers enough light to assist you in the bulk of your observational activities. FIELD OF VIEW: The field of view (or angle of view), simply stated, is the size of the "window" you are looking through (stated like the previous example, in either degrees or in width-at-a-distance). This is determined by the design of the prisms and eyepieces of a particular binocular. TOP WHAT ELSE AFFECTS BRIGHTNESS? EXIT PUPIL:If you divide the magnification of the binocular into the diameter of the lens, i.e. "35 divided by 7" or "50 divided by 10", you come up with the diameter in millimeters of the beam of light that is hitting your eye (35 divided by 7 = 5mm). The larger the number, the more light (or information) your eyes are receiving. Why is this important? Let's say you are looking for a pair of binoculars for bird-watching, you know that you typically are out at dawn or dusk doing your observations, and you find that many times, the birds you are observing are sitting in bushes, hidden in the shadows. Well, if you buy a small pair of binoculars, say a 10X25 compact, you will have an exit pupil of 2.5mm. The pupils of our eyes dilate anywhere from 2mm to 7mm, depending on the lighting conditions. The lower the light, the larger our pupils dilate (maximum dilation decreases as we get older, about 1mm for every 10-15 years beyond the age of 30). So, at age 40, under lower light conditions (not dark) your eyes would be dilated to about 4mm +/-. That means that your eyes would be receiving a lot less light through the 10x25's than they could if you had a pair of binoculars whose "eyes" were dilated closer to your own. So, if you are going to participate in activities that find you in lower light conditions, make sure to buy a pair of binoculars that will assist you in seeing better instead of hindering you. How about a pair of 7 x 50's, for instance? This gives you an exit pupil of 7.14mm... just about maximum for most people's eyes, no matter what your age. A pair with an exit pupil like this will bring as much light to your eye as possible... a high priority in poor light. TOP OPTICAL COATINGS: All reputable binocular manufacturers coat their optics to some degree with light-enhancing chemical formulas, but it is important to choose binoculars that are fully-multi-coated for optimum light transmission. If light is allowed to go through totally uncoated optics, up to 50% of that light scatters and never reaches your eye! There are terms generally used by manufacturers to let the consumer know just how coated their optics are:
WHAT IF I WEAR GLASSES? If you wear glasses, eye relief is especially important to you. The term "eye relief" means the distance between the binoculars and your eyes to see the entire field of view or achieve a good image. This number is also represented in millimeters, and generally ranges from 5-20mm. Rubber eye cups help to place your eyes at the correct distance for comfortable viewing. If you wear glasses when using your binoculars, either because you are correcting for astigmatism or because it is your preference, eye relief becomes critical. The longer the eye relief, the easier it will be to get a good image with your glasses on without dealing with the "tunnel vision" effect, since they are forcing your eyes away from the eyepieces. The best way to use your binoculars with glasses is to roll the eye cups back and place your glasses right on the padded surface that is revealed. Try for at least ten millimeters of eye relief for the best results... fifteen is better! TOP WHAT ABOUT THE DESIGN OF THE BODY ITSELF? There are a few things left to consider when it comes to choosing a binocular: ROOF OR PORRO PRISM? Porro Prisms are the most common type of binocular found today. You can distinguish them from their counterparts by the fact that the main lenses are normally spaced further apart than the spacing of their eyepieces. This design gives a better dimensional effect when viewing objects close by. Because they are easier to manufacture than roof prisms, they generally cost less. Roof Prisms are smaller in design because the main lenses are in line with the eyepieces, so this is a common ultra-compact design. These are harder to make than porro prisms, but when done correctly can produce images of equal quality. TOP WHAT'S THE BIG DEAL WITH BAK-4 PRISMS? Optical glass quality varies widely between models, this is one of the many reasons for the wide range in price that you will find in the stores ($30 - $2000+). The less expensive binoculars generally are manufactured with BK-7 prisms. If you turn your binoculars around and look down the front lens towards the inside, you can see the difference between BK-7 and BAK-4 (much better prism quality). If the binoculars have BK-7 prisms, you can see a squared off side to the general roundness of the image. BAK-4 prisms show a truer round, which translates to better light transmission and edge-to-edge sharpness. STABILIZING BINOCULARS: These are fairly new to the market....especially the Canon 12 x 36 model. These have a button on the top, that, when pushed, engages a mechanical gyroscope which "stabilizes" the image, so that you have a shake-free picture at higher-than-normal magnification. These are fairly expensive (about $1000) but are really fun! TOP HOW DO BINOCULARS FOCUS? CENTER FOCUS:Most binoculars have a center-post focusing mechanism which adjusts the focus of both eyepieces at the same time. In order to compensate for having a stronger or weaker eye, a diopter corrector is included (located either as part of the right eyepiece or on top of the binocular itself) to allow one eyepiece to adjust separately from the central focus. Once this adjustment is made to your stronger or weaker eye, the central focus will work perfectly, adjusting both eyepieces correctly. INDIVIDUAL FOCUS: Individual-Eye Focus is found most commonly in waterproof, marine binoculars. You adjust focus to each individual eye by turning the eyepiece. This is less convenient than center-focus styles, but is more rugged because of less mechanical parts. This is the reason you find them so often on armoured, waterproofed binoculars. FOCUS FREE: These binoculars have had their focus pre-set at the factory. The manufacturers assume that you have perfect vision, and so if you do not, the focus will be off. These are also difficult to use (and can give you a headache through eye strain) if you wish to focus closer than the binoculars are pre-set. This is more of a gimmick than anything else, and we strongly recommend you purchase a pair of binoculars you can adjust to your own, unique eyes. It only takes a second! TOP |
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