Choosing Birding Binoculars Part II

Here is our continuing discussion of choosing birding binoculars:

You want to be able to use your birding binoculars without having to constantly remove your eyeglasses to look. That can cost valuable time when trying to spot a bird. Some bins will have rubber eyecups that fold down to get your eyes/eyeglasses closer to the lenses, while other more expensive models will have adjustable eyecups.

As a general guideline, for those who wear thinner, closer fitting glasses choose an eye relief between 14-15mm. For those who wear thicker, farther fitting glasses, choose 16-18mm. Of course, your best bet would be to try out several bins & see what works best with your particular eyeglasses. It is still a good idea for non-eyeglass wearers to also try out binoculars for eye relief as well, to find the distance that works best for them.

The field of view is measured as the width of area visible at 1,000 yards (or meters) from the observer. It is sometimes expressed as degrees near the eyepiece (i.e. "Field 6.5 degrees"). The eyepiece design mainly determines the the field of view.  If the angular field of view in degrees is provided, you can calculate the FOV by multiplying the number by 52.5 (the # of feet in 1 degree at 1,000 yards). So the field of view for a 6.5 degree binocular would by 6.5 x 52.5 = 341.25 feet. This means that the width of the view you are looking at is 341.25 feet at a distance of 1000 yards.

Generally, the higher the magnification, the narrower the field of view (10x40s have a narrower FOV than 8x40s). A wider FOV will enable beginners to find birds easier and track them as they move about. However, a wider field of view on a cheap pair of binoculars is not always a better choice. Inexpensive wide-angle models nearly always obtain a wide angle at the expense of image sharpness. It's better to have a sharp, clear smaller field of view than a larger fuzzy one.

Again, decide what's most important to you. Do you want a larger field of view or more magnification? Test drive as many as you can. Just remember, field of view decreases as magnification increases. Verify this by checking the FOV on the manufacture's specifications for the model of binoculars you are interested in. 

Lens Coatings

In terms of light-gathering power, objective diameter and exit pupil size are not the only important parameters. Lens coatings are just as important in increasing light transmission and improving image brightness. Each time light enters or leaves a piece of glass, about 5% is reflected back. Binoculars may have 16 air-to-glass surfaces, with light lost at every surface. This lost light bounces around inside the binoculars, making the image hazy and hard to see. Lens coatings effectively lower reflection losses which finally results in a brighter and sharper image. For example, a 8x40 binocular with good optical coatings will yield a brighter image than an uncoated 8x50 binocular.

A classic lens coating material is magnesium fluoride which reduces reflections from 5% to 1%. Modern lens coatings consist of complex multi-layers and reflect only 0.25% or less to yield an image with maximum brightness and natural colors. For roof-prisms, anti-phase shifting coatings (p-coatings) are sometimes used which significantly enhance resolution and contrast. The presence of a coating is typically denoted on a binocular by the following terms:

• Coated (C) ? A single layer on at least one lens surface.
• Fully Coated (FC) ? A single layer on all air-to-glass surfaces.
• Multi-Coated ( MC) ? Multiple layers on at least one lens surface.
• Fully Multi-Coated (FMC) ? Multiple layers on all air-to-glass surfaces.

So as with everything else, more coatings, more cost, but better images through your birding binoculars. You'll have to shop & compare to see what's the best you can get for your $ and without compromising image quality and brightness. Test drive if you can!

Binocular Weight

Thanks to technology, we don't have to lug around 4 pound binoculars. But weight is still a factor. When you start looking around at the various bins available today, you will see that they can range in weight from 10 ozs (compact 8x25s) to 44ozs (large 10x50s). Although you can find compacts of the same size that weigh more as well as 10x50s that weigh less.

If you are deciding on a pair of bins and one weighs 26 ounces, the other 30, don't chose the lighter one based on that factor alone. Most people won't notice that kind of weight difference, even after using them all day. As a general guideline, for long days of birding, choose a binocular that weighs less than 30 oz.

Weight distribution, or balance of the binoculars, may be more of an important factor than weight alone. A poorly balanced 25 oz binocular may cause more fatigue than a well-balanced 32 oz pair. The balance affects the feel in your hands, and over a long day of birding, this may be a fatiguing factor. Your hands, wrists and/or arms may notice the difference. So again, test driving is always a good way to determine what's best for you. If not, it's safe to assume the higher quality, more expensive bins will have better weight distribution & balance.

Also, to help with weight fatigue, today's harnesses are a good option over the standard neck straps to relieve neck and shoulder strain when using your birding binoculars.

Binocular Waterproofing

Waterproof optics provide protection against not only water, but also dust, dirt, cracker crumbs, etc. as well as internal fogging. It is certainly a nice option, especially for active birders. Waterproof seals are made with rubber O-rings and and nitrogen gas purging.

If you take your warm binoculars to go birding on a chilly morning without nitrogen gas-filled optics, they will most likely fog-up on the interior because of the quick temperature change from warm to cold. You'll be bummin' when you can't see anything through the fog! And you never know...you just may slip when crossing that creek. It would be nice to know your bins are waterproof. It is also a plus if you live in humid climates.

Rubber Armoring

Just so there is no misunderstanding, rubber armoring does not provide waterproofing.

Rubber armoring is a nice option (at the cost of a little extra weight & $) that protects your birding binoculars from bumps, scratches, and corrosion. It also provides a comfortable,

cushioned gripping surface. It certainly will be more comfortable to hold a rubber-coated pair of binoculars on very cold or hot days. Just another option for you to consider.

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