Choosing binoculars: The Details
You can spend anywhere from $30 to $3000 on a pair of binoculars. At the high end you get superb optical performance, extreme durability and meaningful lifetime warranties. Drive you car over your binoculars and they will replace them. The low end is useless junk. For a decent pair of lightweight waterproof backpacking binoculars that will last many years expect to pay from $200 to $400. More expensive binoculars would likely provide better durability, a better warranty, and incrementally improved optics.
Binoculars are identified with two numbers that will read 8×32 or something similar. The first number is the magnification; backpacking binoculars should have a magnification between 7 and 10. Smaller and they become pointless to carry; larger and they become too heavy and are difficult to hold still enough to be useful.
The second number is the diameter of the objective lens in millimeters. The larger the lens diameter, the brighter the image, however the weight of binoculars goes up quickly with increased lens diameter. The most significant trade-off is between weight and clarity in low light conditions. You never need more than a 1:5 ratio (7×35, 8×40, 9×45, 10×50) between magnification and lens diameter as anything greater provides more light than the eye can use. If optimizing for low light conditions, 1:5 is ideal; if optimizing for weight 1:3 is acceptable. A good compromise for backpacking is 1:4, i.e. 8×32. Anything over 35 millimeters is going to be too heavy for most backpackers. Anything less than 25 millimeters is going to have poor light gathering ability and possibly a poor field of view.
Any decent pair of binoculars will have coated lenses. These coatings, often multiple layers of them, vastly improve optical performance. You don’t need to worry about the specifics. Be aware that these coatings can be a bit fragile, so clean your lenses with a soft clean cloth or lens tissue. Do not use hot water.
Particularly for backpackers, the binoculars must be warranted to be waterproof. If you carry binoculars outdoors, they will get wet: count on it. Any water inside a binocular and the internal surfaces of the lenses will fog, most likely permanently. The glasses should also be factory filled with an inert gas like nitrogen or argon. These gases displace the air inside the instrument. That air contains some moisture. Take warm binoculars outside into the cold and that moisture will condense, again on the inside surfaces of the lenses. Moisture on external surfaces of waterproof binoculars is not a problem can be easily wiped away with no damage done.
Close focus is very nice to have. Many binoculars can now focus down to a few feet. This is handy when looking at bugs, reptiles, flowers, or in lucky Jim’s case, an echidna curled up between his feet.
Many brands offer a very lightweight binocular model, often described as pocket or compact, which folds into itself along two sets of hinges. These are notoriously slow and fiddly to deploy, and although the weight and size are attractive, we recommend avoiding any model that folds along two junctions instead of a single center-line hinge.
Binoculars are made with plastic, aluminum and magnesium frames. With metal frames the binoculars are much less likely to get knocked out of alignment. Magnesium frames are lighter but usually more expensive than aluminum frames.
You will need a shoulder strap that you can use comfortably when wearing your pack. If you don’t carry your binoculars in a handy place, you won’t use them. Many models come with fancy padded straps or shoulder harnesses which are unnecessarily complicated or too heavy for backpackers. Straps can be replaced with a simple piece of nylon webbing, as shown in the photograph.
Eyepiece cover caps are essential to keep crap ranging from raindrops to pine needles to blowing sand from falling into the eye cups. The caps protect the lenses and also protect your eyes, since that crap lands in your eyes in your hurry to catch a glimpse of the mountain lion that just crossed your path. Many binoculars come with caps that are already attached to the strap, however some of the caps are fiddly to use and not easily deployed and replaced. After market replacement caps are available if the ones on your pair are bad.
There are many brands and models on the market. For backpackers’ purposes, the better brands have functionally equivalent optical quality. Companies make claims why their model is better, but ignore the marketing noise. The best way to choose a pair is to visit stores and try the various models. Some will fit your face and feel better in your hands than others. If shopping online be sure you can return them if they don’t feel comfortable. Take them outside and try focusing on a far horizon or the moon and make sure they work with your eyes. Also try focusing them at something four to six feet away.