Every pair of binoculars has two numbers printed somewhere on the instrument (usually on the face of the focus wheel, but sometimes on the body of the binocular) — for example 10×42 (pronounced ten by forty two) or 8×32. The first of these numbers is the binocular’s magnification, the second is the diameter of the objective lens (we’ll get to that in a moment).
The focus adjustment is pretty easy and accurate. You will also find there’s an on-board compass. If you calibrate it properly, it’s accurate as well, and during something like a sailboat trip, you’ll love the fact that it’s there. The distance measurement is another great addition, and even at this price point, it is fairly accurate. You will undoubtedly find it useful for things such as birdwatching or wildlife exploration and, both the rangefinder scale and compass have an illumination switch, which is useful in darker and overcast situations.
The Athlon Talos 8 x 32, Minox BV 8 x 33, and Vortex Diamondback Classic 8 x 32 are “tweener” or “large compact” binoculars—not particularly compact, but a size down from full-size. They feature the largest focusing wheel, wide/heavy bodies, and weigh as much as some full-size models. Though I wouldn’t trade them in for my go-to 8 x 42 pair (due to the narrower field of view), I actually found them to be a comfortable size for birding/nature-study, and didn’t find serious drawbacks during testing (though the Vortex Diamondback gave me minor eyestrain).
The “42” in our 10x42 binocular refers to the diameter of the objective (front) lens in millimeters. Since the objectives will often be the largest portion of the optic, it will affect the overall size and weight of the binocular, and how much light it can gather. In basic terms: larger objectives allow more light to pass through them than smaller lenses, which means images will appear brighter, sharper, and clearer. However, the larger objectives will also add bulk and weight, and that is where certain tradeoffs and compromises need to be considered when deciding if certain models will be convenient to carry, pack, hold, and use comfortably.
You may also find more numbers below the magnification-x-aperture rating. These give the field of view, which is how wide a scene you'll see. It's expressed in feet at a distance of 1,000 yards, or, more commonly these days, in degrees. (The conversion is simple: 1° is 52 feet at 1,000 yards.) Binoculars' fields of view vary from about 10° (the size of the Big Dipper's bowl, or the size of your fist held at arm's length) for wide-angle models, to a mere 2° (the width of your thumb at arm's length) for high-power models. Most of the time, though, the field of view is about 5° to 8° wide: about as much sky as is covered by a golf ball or squash ball held at arm's length.
Eric Lind, Center Director of the Audubon Constitution Marsh Center & Sanctuary, in Garrison, New York, prefers 8x binoculars and says, “8-power gives you a little bit more than 7-power. I’ve tried 10x, but they were difficult to hold steady.” Eric uses an older pair of Zeiss 8x42 binoculars. “10x,” he says, “might be more appropriate for shore bird viewing from the beach.”
The coating on a lens has almost as much to do with clarity and brightness as the lenses themselves. A good coating can reduce the amount of scattered light down to a quarter of a percent per a surface. Scattered light is lost or misaligned information. You can have the best lens and coatings, but if all the elements aren't lined up and centered your image will come out distorted. With a minimum of 6 elements and some models having up to 20 elements, plus the two barrels, getting everything aligned can be very difficult. Fortunately, our brains are good at compensating for small misalignments. However, misalignments can add to eye strain.
3. First, view the moon with binoculars. When you start to stargaze, you’ll want to watch the phase of the moon carefully. If you want to see deep-sky objects inside our Milky Way galaxy – or outside the galaxy – you’ll want to avoid the moon. But the moon itself is a perfect target for beginning astronomers, armed with binoculars. Hint: the best time to observe the moon is in twilight. Then the glare of the moon is not so great, and you’ll see more detail.
High Reflectivity Coatings on the Prisms - If you plan on choosing a roof prism binocular then you need to look out for what (if any) coatings are on prism to increase light reflectivity. Roof prisms have a number of advantages over porro prisms, but it does have one surface that does not have total internal reflection. It is therefore very important for binoculars' optical performance to raise the reflectivity of this surface. Typically an aluminum mirror coating is used that has a reflectivity of 87% to 93% or a silver mirror coating (reflectivity of 95% to 98%) is used. This light transmission of the prism can be improved by using a dielectric coating rather than a metallic mirror coating. A well-designed dielectric coating can provide a reflectivity of more than 99% across the visible light spectrum. So firstly make sure at least aluminum mirror coatings are used and then depending on your budget you could choose to get higher quality silver or dielectric coatings. Roof prism binocular without high reflectivity coatings on the prisms should be avoided.
Modern binoculars all come with an adjustable eyecups around both eyepieces. This is either a foldable rubber cup or one that adjusts in and out using screwing motion. The simple rule of thumb is that if you wear glasses make the eyecup as small as possible, i.e. you need to get your glasses as close to the glass eyepiece in your binocular as you can.
We chose to limit our tests to 8×42 binoculars for a number of reasons, one being that we found 10x binoculars to be too shaky, like walking around with a fully zoomed telephoto camera lens. Plus, the 42 objective-lens size is perfect for balancing brightness and clarity with weight. Compact binoculars, which have smaller objective lenses, are often much dimmer. They’re not great if you want to truly spot and identify something in the field, though good reasons to use smaller binoculars do exist, as many backpackers and travel-light types will attest. We plan to test compact binoculars soon.
The UpClose G2 8x21 Roof Binocular from Celestron is a light weight 8 ounces with a closed hinged bridge design. At less than 4 inches they are a prime candidate for an easily mobile binocular that leaves no excuse to be caught without some magnification for that surprise situation. The water resistant, rubber covered, aluminum body adds an added level of worry free use from too much rough handling and never too much use. The sure grip furnished by thumb indents and finger ridges are a welcome feature allowing a firm non-slip hold. Just another reason to make sure that this binocular gets taken along.
I’ve peered through binoculars of different types and made by dozens of different brands over the years, and had settled on my current pair of $2,500 Leica Ultravids. After eight weeks of testing over 30 pairs of binoculars in the $150 to $350 price range (and a few that were cheaper or more expensive), I can honestly say that if my Leicas got lost tomorrow, I wouldn’t hesitate to replace them with one of our top picks.
Looking at the basics, you’ll find that all binoculars come with a set of two numbers. They can be 7×42, 7×50, 8×42, 10×52 etc. This is a pretty important number with rangefinder binoculars, and any binoculars in general. The first number will tell you the magnification. For example, a 7×42 will show you objects 7 times closer than the naked eye. The second number tells you how big the objective lens is in mm. A larger objective lens lets in more light, and you’ll be able to see a brighter image. This could be especially beneficial in darker conditions. What you should know is that higher magnification will reduce the amount of light that’s available, and a large objective lens will make the binoculars large and heavy.
Glass wise these are quite a step up from the Bushnell’s but not yet at the level of the Leica’s and Swaros. Ranging wise, they smoke the Bushnells and nudge just above Swarovski El’s. In fair weather (sun, overcast, light rain, etc) the Leica Geovid HD-B is going to outrange it most of the time. If weather turns to crap or there is heavy fog the Steiner will be unbeaten.
Meteor showers offer a practical example. You never know exactly where the next bright streak will appear. Yes, you're pretty sure it will come from the "radiant." That’s the name of a constellation (usually) whose location on the sky roughly corresponds to the cloud of cosmic crap into which Earth is plowing to create the shower. [Example: The Leonid meteor shower in November appears to come from the direction of Leo.]