A Beginner’s Guide to Binoculars for Birding

In this article, we discuss some background information that will help a beginner select a first pair of binoculars for birding.  We also cover uses to which you may put binoculars and some of the terminology associated with them.  We do not include any brand name or model recommendations.  But armed with the information here, you can use check out stores and Web retailers to select the model that’s right for you!

Background

The range of binoculars available for sale is enormous.  Some easily fit into a pocket, others are huge.  Prices range from under a hundred 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 or contacts? 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, more weatherproof, and usually more expensive than those using porro prisms.

The issue of weatherproofing is worth a special note.  Water on the outside surfaces of binoculars is no more than a mild annoyance.  But if moisture gets inside binoculars, it can wreak havoc: lenses may fog up internally and, in some cases, mold may grow inside the binoculars (yuck!).  So when we talk about weatherproofing, we’re talking about the ability to keep water out.  For technical reasons, it is very difficult to completely seal porro prism binoculars, but roof prism models easily can be made water resistant or even waterproof.  This is especially important for birders, who often find themselves outdoors in the rain or even snow.

In the past, only a few roof prism models were available, and they mostly were high-end (meaning expensive) models.  But in the past few years, advances in technology have lowered the cost of roof prisms while still offering all of their advantages, especially weather resistance.  As a result, roof prisms have become much more popular in all prices ranges except the very low cost range.  In fact, roof prism models now dominate binocular product lines at most price levels. Still, porro prism models may be worth considering, especially if you are looking for the greatest “bang for the buck.”

Specifications

The first thing you encounter when looking at binoculars is a set of numbers like “7×35”, “10×50”, 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.  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 “7×35” 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 another 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.  (Oddly enough, it also can be difficult to hold steady binoculars that are too light! There’s a “just right” weight for most people.)

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 7×35 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 more light than your eye can 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-around 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 7×35, 8×30, 7×42, or 8×42, with the latter two tending toward the heavy side.  Some birders (with steady hands) prefer 10x magnification helpful, especially when looking at distant subjects such as 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 (7×50, 10×50) 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, as well as 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.

Do not consider fixed-focus (“focus-free”) or “zoom” binoculars.  These may do for sporting events, but will quickly result in eyestrain and headaches when birding.  Also, consider only center-focus binoculars, which allow you to focus both eyes at once.

The weights (and prices!) of binoculars with the same specifications vary widely. 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 the past, greater weight was a sign of stronger construction, which meant more resistance to damage.  But technological and manufacturing improvements again save the day: advanced materials such as high-quality plastics, lighter metals such as magnesium or even titanium, and carbon fiber composites all allow binocular makers to reduce weight while maintaining durability.  However, keep in mind that some of these advanced materials also may increase the cost dramatically.

Any pair of binoculars you consider should have “coated optics”.  The coatings reduce glare and provide a much sharper view. All but the cheapest optics these days are coated, but keep in mind that not all coatings are created equal.  Optics manufacturers constantly compete to improve lens coatings, and more expensive models probably have higher quality coatings than their less expensive counterparts.

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 identical images to your eyes, this can cause severe eyestrain.  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 about 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 the same position in the lenses.

Keep in mind that, while cheap binoculars are the most subject to being out of alignment, individual variation can occur in the most expensive models.

An especially critical point for eyeglass wearers (but not contact lens 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 view.  Most binoculars you will consider will have some form of eyecups that 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.

If you have the specifications on the binoculars, look for eye relief of 15 – 16 mm or more.  (Some eyeglass wearers with deep-set eyes need may need more like 18 – 19 mm.) However, your eyes are the real test here.  Eye relief specifications vary from manufacturer to manufacturer, and one line’s 16 mm may seem more like another’s 14. 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 (intraocular 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.  Many retailers allow you to return binoculars if they don’t meet your expectations, provided that the binoculars are not damaged and are returned in the original packaging.  Try to 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.

You may be surprised to learn that your eyes almost certainly are not quite identical. The brain compensates for this under normal conditions, but when you use binoculars, different between the eyes are magnified.  Therefore, any pair of binoculars you consider should have what is called a diopter adjustment to compensate.

Here’s how to adjust your binoculars.  Assuming that the diopter adjustment is on the right side (it usually is), look through the left eye only and, using the center- focus mechanism, carefully focus the binoculars on an object which has some fine detail.  Now, without moving the center focus mechanism, and using the right eye only, adjust the diopter for the 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 diopter setting from time to time.  It’s easy for it to get out of adjustment.

Binocular Straps

It might seem odd to talk about straps in an article about binoculars, but the strap holding the binoculars around your neck can make quite a difference.  Most binoculars come with some kind of strap, commonly a narrow piece of nylon webbing or something similar.  While such straps certainly will hold up the binoculars, many birders find them uncomfortable and prefer wider straps, often with softer materials to cushion pressure on the back of the neck.  An option that has grown in popularity over the past few years is a binocular “harness,” which has straps that pass over the shoulders and under the arms.  These move the weight of the binoculars to the shoulders, thus relieving strain both on the neck and the lower back.

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, and many will offer to let you look through their binoculars.  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.

Internet and mail order sellers may offer substantial discounts over retail stores. However, testing binoculars obviously is a lot more difficult when you are not at the store! If you consider buying over the internet, 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).

If you are at a store specializing in optics, the salespeople probably will be knowledgeable enough to help.  But if you are shopping at a more general merchandise store, don’t be surprised if the salespeople have little or no knowledge of anything technical relating to the binoculars they are selling.

Finally, 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.)

Some people advise always buying the best binoculars that you can afford. One reason for this approach is that you may well keep the same binoculars for years, and higher quality ones will give you far more pleasure than those costing a little less.  But when you buying your first pair of binoculars, it may be wise simply to buy a pair that is reasonable for you at this time.  If you decide to upgrade later, it still will be handy to have a spare pair around.