Bird Watcher's Digest: Optics: Choosing Optics

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Weatherproof or Waterproof	Focusing Mechanisms
Pocket Optics	Lens Coatings
About Prisms	Magnification
For Beginners	Choosing Optics
Spotting Scopes	Glossary of Terms

Choosing Optics

Binoculars are the tools of the bird watching trade. You can watch birds without the magnifying power of binoculars, but you won't always get a satisfactory look at the birds. A myth about binoculars is that they're expensive. They can be, but they don't have to be. Recent advances in lens technology and the manufacturing process have resulted in affordable binoculars for bird watchers. In this article, I discuss what binoculars are, how they work, and how to choose them and use them most effectively for watching birds.

Types of binoculars

Two basic types of binoculars are used by modern bird watchers: Porro prism and roof prism. You can tell them apart by how they're constructed.

Porro-prism binoculars

Porro-prism binoculars were first designed in the mid-1800s by an Italian inventor named Porro. His concept of placing two right-angled prisms in each barrel of a set of binoculars is still used today. Porro-prism binoculars are the stereotypical angled-body binocular design. When standing on their barrels, or hanging from a strap around someone's neck, Porro-prism binoculars appear to form an M shape.

Porros focus by relying upon an external focuswheel which, when turned, causes the eyepieces for each side to slide forward or backward along an external tube. This type of focusing allows for sharp images of close birds and other objects, as well as precise focusing on objects as close as six feet.

The advantages of this binocular design are:

Brighter images due to greater transmission of light.
Fast focusing.
Close focusing.
Wider field of view (the amount of area you see when looking through the binoculars).

For low-to-mid-range priced binoculars, Porro-prisms offer the best value. The disadvantages are weight (the better transmission of light is due to large prisms, which are weighty) and bulkiness, which can make Porros hard to use for small-handed folks. In addition, the external focusing mechanisms of many Porros can make for less durable binoculars, that is, ones that can be more easily jarred out of alignment.

Roof-prism binoculars

Roof-prism binoculars were first developed by a German binocular manufacturer in the mid-1800s. This design features two straight barrels, giving it an H-shaped appearance.

The design reflects light through a series of five small prisms in each barrel. Roof-prism binoculars have grown in popularity among birders in the last few decades, primarily because many leading optics manufacturers are producing excellent optics in this format for the bird watching market. Because of the way roof-prisms are designed, most of the focusing hardware is enclosed inside the body of the binoculars. This hardware is adjusted with an external focusing knob or wheel.

The advantages to roof-prism binoculars are:

Ease of handling
Fewer external moving parts (which means increased durability)
A better ratio of power-to-weight; that is, in general, a 10x roof-prism weighs less than a 10x Porro.

At the mid-to-high price range for binoculars, roof-prisms dominate the market. The disadvantages are that roof-prisms tend to be more expensive than Porros, and they often don't focus as closely, making it hard to see nearby objects clearly. Because of the additional prisms required to reflect incoming light, roof prisms often do not offer as "bright" an image as Porros.

What Binoculars Do for the Bird Watcher

If you can see a bird well, you can see its identifying field marks. If you can see its field marks, you can identify the bird. And identifying birds is the central purpose of bird watching.

Besides giving you a close-up view of birds, your binoculars help you in other situations. I like to use my binoculars when I go to Pittsburgh Pirates games because I can get close-up views of the game. And when the baseball is bad (which it often is), I can watch the birds that fly over the stadium or spot the nearest guy shouting "Cold beer here!"

One seldom-used feature of binoculars is their excellent utility as a magnifying glass. If you turn your binoculars around and look in the big-lens end, you see that things appear farther away. Lean down close to look at a ladybug or flower and you see the incredible magnifying power of backwards binoculars.

Choosing Binoculars

You need to consider a number of factors when choosing binoculars, but the most important three are cost, power (or magnification), and comfort. When selecting binoculars for yourself, you'd be wise to bear these three factors in mind. Neglect any one of them, and you will almost certainly regret your decision later.

For example, if you decide to buy an inexpensive pair of binoculars even though you like a pricier pair better, you may find at a later date that you wished you'd made the additional investment. Or if you purchase a large pair that seem heavy when hanging around your neck in the store, imagine your agony months later when you're out on a long bird walk. Talk about a pain in the neck.

Before you buy, I suggest you gather all the information you can about binoculars. Tip: The best sources for information and advice on bird-watching optics are your fellow birders. Ask your friends and fellow birders about their binoculars. What brand and power do they have? What do they like about them? What do they dislike? How much did they pay? Where did they buy them? Would they do anything differently the next time they buy binoculars? If you can get answers to these questions, you'll begin to get a picture of what you would prefer in a pair of binoculars.

After you get answers to these questions (and if you feel you can pester them a bit more without endangering your friendship), ask to try their binoculars for a few minutes. Try to avoid asking just as a peregrine falcon flies overhead--your friend may get cranky. While trying your friend's binoculars, ask yourself a few questions: How do they feel in your hands? Are they easy to focus? Are they too heavy for you to hold steady?

Cost

It may seem hard to believe, but binoculars are one of those few items for which a higher price means higher quality. Another way to say this is: You get what you pay for. So the guiding rule for binocular-buying birders has been: "Buy the best optics you can afford."

But what's the price range for good binoculars? I'm glad you asked that question. The answer depends on you and how you use the binoculars.

The low end of the price range for a new pair of adequate birding binoculars is $100. You can get some compact (small and lightweight) binoculars for slightly less than that, but not all of these are ideal for in-the-field bird watching. The high end of the price range is in the thousands of dollars. But you need not spend this much to get good optics.

Why not shoot for the mid-range of $150 to $350? In this price range, you can get a pair of binoculars that will be well-suited to you and your mode of watching birds. Dozens and dozens of binocular brands and models are available to choose from in this mid-price-range. If you choose to get mid-priced binoculars, you can always invest in a better (more expensive) pair at a later date.

But isn't a $100 pair of 7x35s the same as a pair of $350 7x35s? Probably not. A lot of competition exists among binocular manufacturers, and the not-worth-the-money brands and models are quickly taken off the market or greatly reduced in price. Perhaps the more expensive 7x35s have better lens coatings, thick rubber armoring, and come with a manufacturer's warranty of several years.

If you think of your binoculars as an investment that will last you years, you'll feel better. Sure, it may sting a bit to fork over several hundred or even a thousand dollars for something that you hang around your neck. But think of it in terms of all the birds you'll see and enjoy. Your new binoculars will always be there, ready to serve you.

Here's an interesting thought: A new pair of fairly expensive binoculars, costing, say, $750 would, over the course of a year, average out to only about $2.05 per day. Over five years, the figure becomes $0.41 per day. Not much to pay for what you get in return.

If you find a store that's willing to let you pay off your binoculars over five years at 41 cents per day, be sure to call and let me know where it is.

Don't, under any circumstances, buy any binoculars that are marketed without a recognizable brand name or that are marketed at unbelievably low prices. These optics stink! Believe me, you'll be sorry. One warning sign of El Cheapo binoculars is a prism like halo of colors around any object you view. This effect is caused by inferior optics inside the binoculars.

Power

The best binoculars for bird watching come in the 7x to 10x range (that's 7-power to 10-power). Optics in this range provide enough magnification to make distant birds look bigger without being too heavy to hold steady or to have hanging around your neck. Three of the most common powers are 7x35, 8x42, and 10x40.

Power is as much a matter of personal preference as anything. You may like the high magnification of 10x binoculars, but their increased weight may make your arms tired after holding them to your eyes for only a few minutes. Try several different binoculars, either at a camera/optics store or at a gathering of bird watchers. You'll notice a difference in weight between binoculars of different powers. Any binoculars above 10 power are likely to be too heavy to hold still, but can be used successfully when mounted on a tripod.

Recent advances in binocular design have helped make binoculars lighter and better balanced in the hand. For many bird watchers, a new well-designed 10x binocular is now as easy to hold steady as an older pair of 7xs. The mantra is "Try before you buy!"

The first number in a binocular description such as 7x35 refers to the power or magnification of the binocular. The higher the number, the more powerful the binoculars (which means a 10x binoc makes a distant bird appear much closer than a 7x one does). The second number in the description refers to the diameter (in millimeters) of the objective lens. The larger this number is, the more light is allowed into the optics. Lots of light means a bright, clear image is presented to your eyes.

Using the logic that more is better, wouldn't a 12x50 binocular be great? Lots of magnification and lots of light? The answer is an emphatic no! Such powerful binoculars require large lenses and internal prisms, which make them almost impossibly heavy to use without mounting them on a tripod.

Comfort

"The best binoculars" an optics expert once wrote, "will disappear from your awareness while you are using them."

When you try binoculars, ask yourself if they feel comfortable to use. Comfort is a combination of factors: Are they easy to raise to your eyes? Does your forefinger automatically rest on the focus wheel? Can you easily adjust the settings to fit your needs? Do the binoculars feel very heavy around your neck? Do they feel good in your hands?

You can have the best optics money can buy, but if you're not comfortable using them, they may as well be a lead doorstop. If you have trouble holding a pair of binoculars steady (if the image is constantly moving and jiggling), the binoculars may be too heavy for you to use. Try using a friend's lighter or smaller binoculars and see if you have a more stable image.

Field of View

Make sure the binoculars you choose have a reasonable field of view (the amount of area you can see at one time when looking through the binoculars). Binoculars with narrow fields of view make it hard to find the bird when you raise the optics to your eyes.

Close Focus

An ideal pair of binoculars focuses on objects as close as 10 feet away or even closer. Some compact models focus on closer objects, but you may sacrifice power and field of view. High-powered binoculars, such as my own 10x40 wonders, may only focus to about 20 feet. This limited focus is a drag when a warbler perches 10 feet away and I have to naked-eye it while my wife oohs and ahhs at the close look she can get through her 8-powers. For butterfly watching (a natural spin-off of birding), close focusing is a must. It seems ridiculous to back up to get a good look at a resting butterfly!

Brightness

The level of image brightness produced by your binoculars is a factor of how large the objective lenses are (35, 40, 42, and so on) and the quality and coatings of the optical elements (lenses and prisms). Larger objective lenses produce brighter images.

Lens coatings

Coated lenses and high-quality prisms reduce the amount of light lost and thus transmit more light, which makes a brighter image. Test several models with coated and uncoated optics and you can see the difference. But remember, the better the coatings, the more expensive the binoculars are likely to be.

Armoring/waterproofing

If my binoculars weren't armored, I'd have smashed and dented them at least 400 times since I got them 10 years ago. Armoring is a rubberized coating that encases the binocular body, providing protection from bumps and knocks, as well as providing some protection from moisture. Rubber armoring can also keep your binoculars from sliding off of the car roof until you notice that they aren't around your neck. Most binoculars are not waterproof, but they are water resistant. So if you drop them in the pool, call your insurance agent. Armoring is a very good thing, and I recommend that you buy rubber-armored binoculars.

Tip: Avoid zoom binoculars, which may have optics inferior to regular non-zoom models. Avoid fixed-focus field glasses, which are simply impractical for watching birds. Avoid binoculars that have individual-focus eyepieces. These binoculars are too hard to use.

Using Binoculars

For several years after I started watching birds, I didn't know how to focus my binoculars properly. I'm going to save you from a fate such as mine (and from some painful headaches). When a friend finally showed me how to focus binoculars properly, I couldn't believe how three dimensional the birds looked. And I had no moment of dizziness after lowering my binoculars.

Using binoculars isn't as simple as raising them up to your eyes. But the process is pretty simple nonetheless. Because not all eyes are created equal, binoculars are designed to be adjusted to accommodate your needs.

Setting the eyespace

All good binoculars are made in a way that allows the two optical barrels to pivot so that the space between them can be adjusted. When using binoculars, it's key that you get the two halves of the binoculars the right distance apart to get the two images aligned. This spacing should match the amount of space between your eyes.

That statement may seem overly obvious to you, but you'd be surprised how many bird watchers use binoculars for years without getting the eyespace aligned properly for their eyes. To set the eyespace of your binoculars correctly, push the two barrels together so that they're adjusted to their minimum spacing. Raise the optics to your eyes and slowly expand the space between the barrels until you have the maximum amount of view or image space. If the barrels are too close together, the image area you see is circular, and you may be able to see your hands or lots of black space out of the corners of your eyes. If the barrels are too far apart, you see two separate image circles with a black area in between.

If you have the proper eyespace for your eyes, your image area appears oval-shaped and you notice the large, clear image space.

Tip: If you wear glasses, beware of older-model binoculars that have metal or hard plastic eyecups. These eyecups not only scratch your glasses, they also greatly reduce your field of view because your eye is farther away from the eyepiece than is ideal. Think of it this way: Isn't it easier to see more through a keyhole if your eye is right up next to the hole?

Using the diopter: The eye equalizer

Almost everyone has one eye that is stronger than the other. This means that when the eyes focus on a distant object, the images transmitted to your brain from each eye are different. To test this, stick out your thumb as though you are about to be fingerprinted. Raise your arm and cover up a distant object, such as the light switch across the room, with your thumb; that is, block it from view. Now close your eyes alternately. See how the image jumps around? In addition, many people suffer from near-sightedness or far-sightedness. If your eyes aren't a perfectly matched 20-20, you may have a difficult time using binoculars because you can't focus clearly.

The word diopter is used by optometrists to measure the amount of correction needed for eyeglasses prescriptions. The diopter (sometimes spelled dioptre) adjustment on binoculars compensates for these differences between eyes, as well as for any near-sightedness or far-sightedness. Adjusted properly, the diopter helps you to focus clearly on your target image.

You can use two basic configurations for adjusting a diopter. One is controlling the diopter adjustment with a second focus wheel, mounted in front of the primary focus wheel. Many roof prism binoculars use this method. The other configuration has the diopter adjustment in the right eyepiece of the binoculars. In either case, the diopter scale appears on the focus mechanism. Once set, these markings, with 0 as a center point, allow you to remember the best setting for your eyes.

But how do you use a diopter? Using it is an intrinsic part of focusing your binoculars.