Columbus Audubon (Columbus, Ohio)

Learning Aids

A Beginner's Guide to Binoculars for Birding

This note is intended to provide some background information which will help a beginner select a first pair of binoculars for birding. It discusses the uses to which you may put binoculars and some of the terminology associated with them. It does not include any brand-name or model recommendations.

Background

The range of binoculars available for sale is enormous. Some easily fit into a pocket, others are huge. Prices range from a few tens of dollars to well over a thousand dollars. If you go birding with true birding enthusiasts, you will likely find that they have fairly high quality binoculars - in part because they use them extensively, in part because there are real advantages to good binoculars, and (for some) for the prestige involved. If you ask, you will likely find that these birders didn't start out with their current equipment. The big question for you is what's right for you at this time.

Your Birding Needs

Before looking at binoculars, you need to think about your birding needs. Will you just use the binoculars to look at a few birds in the yard? Will you take them on hikes and occasionally look through them at birds or scenery? Are you likely to spend hours on end in the field looking through the binoculars? How good is your vision? Do you wear glasses? Contacts or frames? How steady are your hands? What kind of birds will you be looking at? What else do you wish to do with the binoculars? Under what weather conditions will you use them? Last, but not least, how much can you afford? Keep these questions in mind through the discussion below.

Binocular Basics

There are two basic designs of binoculars - "roof prism" and "porro prism". The latter are the most common and "look like binoculars" in that the objective lenses are offset from the eyepieces. Roof-prism binoculars give the external appearance that one is looking straight through the lenses, but, in fact, there is a complex light path inside true roof-prism binoculars. (Never consider cheap "field glasses" which are shaped like porros but have a simple straight-through viewing path.) In general, roof prism binoculars are lighter, more compact, and more expensive than those using porro prisms. For your purposes, there is little difference between the two types. You should be far more concerned with how well the binoculars are made and how well they perform.

The first thing you encounter when looking at binoculars is a set of numbers like "7x35", "10x50", etc. The first number is the "power" or magnification of the binoculars. Thus, a 7-power (or 7x) set of binoculars makes things look 7 times closer, etc. While increased power does bring things closer, it does have disadvantages. It magnifies any motion of your hands - an especially important consideration for some older and very young birders. All other things being equal, an increase in power also is associated with a reduction in the field of view - that's how wide a scene you see through the binoculars. In general, the wider the scene, the easier it is to locate a bird or follow one in flight. (More on this below.)

The second number, say "35" in the "7x35" specification is the size, in millimeters, of the "objective" lenses - the big lenses on the front of the binoculars. The bigger these lenses, the more light they gather, and the better they are for looking at birds in shadows or poor light. With the bigger lenses, however, comes a real disadvantage - weight. Spending all day with a heavy pair of binoculars hanging around your neck can be a tiring experience. A heavy pair of binoculars can also be more difficult to hold steady.

Getting more technical, the two specification numbers above are combined to calculate what is called the "exit pupil". This is simply the size of the objective lens divided by the magnification. Thus, for 7x35 binoculars, the exit pupil is 35/7 = 5 millimeters. The exit pupil is essentially the size of the light beam coming out of the binoculars. If the exit pupil is too small, it restricts the amount of light entering your eye. If it's larger than the pupil of your eye, it's providing light your eye can't use. Exit pupils should be roughly in the 3-1/2 mm to 6 mm range for birding binoculars. Older person's eyes usually can't get additional benefit from exit pupils larger than about 4 mm.

For most all-round field birding uses, a magnification of around 7x or 8x, combined with objective lens size of around 30-42 mm, is a good compromise among magnification, light-gathering ability, and weight. Typical binoculars might have specifications such as 7x35, 8x30, 7x42, or 8x42, with the latter two tending toward the heavy side. Some experienced birders (with steady hands) find 10x magnification helpful when looking at shorebirds or waterfowl. Pocket-size binoculars, with objective lenses in the range of 20-25 mm, are handy for vacation travel and looking at an occasional bird, but are not likely to be satisfactory for serious birding. At the other extreme, binoculars with 50 mm objectives (7x50, 10x50) are heavy and bulky, and there is little benefit to be gained from the additional size and weight.

The field of view of a pair of binoculars is expressed in either the width of the field in feet at 1000 yards or in degrees. If the field of view is stated in degrees, you can convert it to feet at 1,000 yards by multiplying by 52.5. All other things being equal, a wider field of view makes it easier to find and follow birds - and sports activities such as football. Increasing field width is often associated with significant increases in weight and size, sometimes with price as well. Typical fields of view for 7x - 8x binoculars fall in the range of 350 - 450 ft at 1,000 yards, with the larger values being associated with "wide-field" binoculars. Look at the actual specifications, inasmuch as any pair of binoculars may be labeled as "wide-field".

Close focusing ability is an important characteristic of good birding binoculars, and is often overlooked by manufacturers. The ability to focus down to 10-12 ft or less is highly desirable, and a close-focusing distance of more than 15 ft is to be avoided if possible. By no means consider fixed-focus ("focus-free") or "zoom" binoculars. Also, consider only center-focus binoculars, which allow you to focus both eyes at once.

There is a wide variation in weights (and prices!) of binoculars with the same specifications. Binocular weights are affected by objective lens size, design, ruggedness, and quality. Typical birding binoculars weigh from 22 to 30 oz. That's quite a difference when the binoculars hang around your neck all day. Weights in the 25 oz. range are not uncommon. In general, heavier binoculars are more resistant to damage from being knocked around.

Any pair of binoculars you consider should have "coated optics". The coatings reduce glare and provide a much sharper view.

Some higher quality binoculars are waterproof or "showerproof". While such features are desirable, they are not critical unless you plan to use the binoculars in extreme conditions.

Testing Binoculars

One of the most important features of binoculars is the hardest to assess - optical quality. Look through each barrel of the binoculars to see if the full field of the binocular is in focus and relatively free from distortion. Good alignment is probably the most important optical characteristic. The two halves of the binoculars are essentially two telescopes. If they don't present essentially identical images to your eyes, this can cause severe eye strain. Here are a few things you can try to get a rough measure of alignment.

Rest the binoculars on a level table in a way such that they are focused on a distant horizontal line. From a few inches behind the binoculars, look through each lens in turn. The horizontal line in each lens should be seen as horizontal, and should be in approximately the same position (vertically) in both lenses.
Repeat the above, but look at a vertical line. Again both lines should be vertical and should be in essentially the same position in the lenses.

An especially critical point for eyeglass (frames, not contacts) wearers is the "eye relief" of the binoculars. Eye relief is a measure of how far away from the binocular lenses your eyes can be and still see the full field of the binoculars. Most binoculars you will consider will have some form of eye cups which are extended for people who don't wear glasses and retracted for those who do. You can check the adequacy of the eye relief in a couple of ways. If you have to move the binoculars from side to side to see the full field, the eye relief is inadequate. Similarly, if you can see a larger field when looking through the binoculars without your glasses than you can with your glasses on, there is inadequate eye relief. Your eye is the real test here. However, if you have the specifications on the binoculars, look for eye relief of 15 mm or more. If you do wear glasses or contacts, wear them when you test and use binoculars. If your correction is for myopia only (no astigmatism), you can use binoculars without glasses and not develop eyestrain.

If your eyes happen to be closely spaced, or if a child will use the binoculars, be sure the distance between the eyepieces (interocular distance) can be adjusted to match.

Don't look through store windows when testing binoculars. Windows introduce a great deal of distortion. As part of your test, look at a dimly lighted area to see how bright the image is. This is comparable to looking at birds in shadows.

The ultimate test of comfort is how the binoculars work for you. If possible, buy binoculars on approval and spend several hours in the field using them.

In field testing (or using) binoculars, be aware that atmospheric shimmer (over a hot road, a warm lake on a cold day, a warm lake on a hot day) can make the field appear blurry. To avoid this, try to look at objects well above the surface, preferably over a relatively uniform field.

Adjusting Binoculars

Contrary to what you see in the movies and on TV, you should not see two overlapping circles when looking through binoculars. The distance between the lenses should be adjusted such that you see a single circle when looking through the binoculars.

Any pair of binoculars you consider should have adjustments to compensate for differences between the left and right eye (and the binocular optics). To adjust the binoculars, look through the left eye only and, using the center- focus mechanism, carefully focus the binoculars on an object which has some fine detail on it. Now, without moving the center focus mechanism, and using the right eye only, adjust the right eyepiece for sharpest focus on the same object. Repeat the process a time or two to ensure best adjustment. Now, both eyes will be in focus when the center focus wheel is moved. Remember to check the right-eye setting from time to time. It's easy for it to get out of adjustment.

Buying Binoculars

Always try out a pair of binoculars before buying, at least a pair of the same make and model you are considering. Unless you are really knowledgeable about binoculars, giving binoculars as a "surprise" gift is usually not recommended if the recipient hasn't tried out the binoculars.

Ask for advice from experienced birders. Most are quite willing to share their knowledge with you. At the same time, keep in mind that your needs may be quite different from theirs.

Shop around. You may be surprised at the differences in price and quality you encounter.

Mail-order houses usually offer substantial discounts over retail stores. If you consider buying from a mail-order house, be sure to choose a reputable firm and get a clear understanding of exactly what you are getting. In addition to price, inquire about return policies and U.S. warranties by the manufacturer (as opposed to the seller's warranty).

Don't be surprised to find that salespeople have little or no knowledge of anything technical relating to the binoculars they are selling, especially in a general merchandise store. Camera dealers are usually more knowledgeable (and list their binoculars at a higher price).

Be prepared to compromise. You likely will not find your "ideal" set of binoculars at a price you are willing to pay. (Some would say the ideal set of binoculars hasn't been made yet.)

Unless you are absolutely certain you will be using the binoculars intensively for a long time, don't listen to the advice to "buy the best binoculars you can afford". Buy a pair that is reasonable for you at this time. If you decide to upgrade later, it will still be handy to have a spare pair around.

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Page updated 06/11/03