Optics Myth 1:

Higher power binoculars will let me see more.

REALITY - Actually, with a higher power binocular you may end up seeing less!

One would think that the more magnification, the more you could see. But it's not necessarily so. The usable power of a binocular is limited by the steadiness of the hands that hold it.

And even a birder with normally steady hands won't be able to hold a binocular as still after running up a steep hill to see a bird as the same person sitting quietly on the back porch.

There is an inevitable wobble in any handheld binocular's image. The higher the magnification, the greater the wobble. At some point, the wobble negates the increased resolution that magnification provides.

It's generally agreed that 10 power is the upper limit of hand-held binoculars. That's why few binoculars with over ten power are marketed to birders.

Many experts believe that birders can see just as much or even more with 8 power binocular, or even 7 power.

This is particularly true when a birder's muscles are fatigued. While watching warblers in the treetops, for example, the longer a birder's arms are raised, the harder it gets to hold the binocular steady.

To get a sense of how much the shaking of your hands degrades a binocular image, try stabilizing your binocular on a tripod. You may be surprised how much more detail you can resolve than you can when holding the binocular in your hands.

The bottom line is that a binocular with higher magnification might not let you identify more birds. What you need may not be stronger binoculars, but better ones.

Optics Myth 2:

Bigger binoculars are more powerful

REALITY

The size of the binocular tells you absolutely nothing about the power. Some 10-power binoculars are smaller than some 7-power ones.

What determines a binocular's power, or magnification, is the design of its eyepiece. And eyepiece design has little or no effect on the size of the binocular.

Often a manufacturer makes the same binocular in more than one power.

For instance SVBONY make a 10x and an 8x both binoculars have the same casing.

The look the same, don't they? By the way, you wouldn't be able to tell by their appearance even in you were holding them in your hands not without reading the numbers printed on the outside. The two models have the same dimensions, shape, and weight, and the share the same sized objective lenses. The difference is in their eyepieces, one of which magnifies the image 8x and the other 10x.

Well, then, what does make a binocular bigger?

Mainly it's the size of the objective lenses. (The objective lenses are in the end of the binocular closer to the object you're looking at). In the formula printed on the binocular, the size of the objectives is the second number. Binoculars that are 7x42, 8x42, and 10x42 all have objective lenses that are 42mm in diameter. Binoculars in the same product line with the same sized objectives will usually be the same size.

Optics Myth 3:

Bigger binoculars are brighter.

REALITY - Bigger can be brighter, but only in dim light!

Many people buy 42mm or larger binoculars in hopes of getting the maximum brightness. But in ordinary light, a good-quality 32mm binocular delivers all the light a person can use, producing just as bright an image as does a 42mm or even a 50mm binocular. And since it's smaller, weighs less, and usually costs less, a 32mm binocular is certainly worth considering, at least for daytime birding.

In late dusk when you can hardly see to walk around, you might see a brighter image with a full-sized binocular than with a mid-sized or pocket binocular. But even in the dark, you get the benefit of the larger objective lenses only when your eyes are fully darkness adjusted and your pupils are fully dilated.

It's a matter of how much light gets into your eye.

Getting darkness adjusted takes most people's eyes at least half an hour. Furthermore, as we age, our pupils lose the ability to dilate as much as they did when we were young. Most middle-aged or older people's pupils don't widen enough in darkness to use the large exit pupil of 42mm or 50mm binoculars, and a 32mm binocular might be a better choice.

For brightness, the coatings on the lenses matter much more than the binocular's size. Some of the light that enters your binocular gets absorbed by the glass or is reflected back and never reaches your eye. Higher-quality binoculars use special coatings that allow for nearly complete light transmission, whereas binoculars without coatings may lose as much as 50% of the light. As a result, a top-quality 25mm binocular can actually yield a much brighter image than a lower-quality 50mm binocular.The bottom line is that you can't judge a binocular's brightness by its size.

Optics Myth 4:

Bigger binoculars have a wider field of view.

REALITY - Field of view is in the design of the eyepiece.

A person might expect a bigger binocular to have a wider field of view, but it's not necessarily so. In fact, a smaller binocular can have an even wider field of view than big one.

Although the field of view depends primarily on the binocular's eyepiece design, the magnification also has a bearing. If you're looking at two binoculars of the same model but different magnification, the lower powered one will have the wider field of view. That is one reason that many birders prefer 8-power binoculars rather than 10-power.

It's a manufacturing challenge to provide the wide field of view that birders appreciate. The laws of eyepiece design dictate that the wider the binocular's field of view, the shorter the eye relief. Unfortunately, people who wear glasses need long eye relief in order to see the full image. By adding extra glass elements in the eyepiece, some optics makers produce binoculars with both long eye relief and a wide field of view. Such binoculars usually come at a premium price.

Field of view in degrees The field of view is usually printed on the binocular, often expressed as an angle.

Another way to describe the field of view is the width in feet at 1000 yards. One degree equals about 52.5 feet at 1000 yards, so a 7 degree field of view could also be described as 367.5 feet at 1000 yards).

Optics Myth 5:

I can share my binocular with others.

REALITY - No you can't. Somebody's going to end up missing the bird, and they're going to be crabby. Many a marriage has been saved just by buying a second pair of binoculars.

Every birder needs his or her own binoculars.

Unlike scopes, which birders commonly share, binoculars are strictly monogamous. You need your binocular ready to grab when you glimpse leaf movement that could be a cuckoo or a warbler. What you don't need is to have to hand over your binocular to the person next to you before you get a satisfactory look at a bird.

Chances are the second person will take just long enough to find the bird and focus on it so that he or she won't get a good look either.

And you don't want to have to borrow your friend's, either. You need your own.

Also, the comfortable way to carry binoculars is with a harness. Now try to get out of the harness before the bird flies away! Especially if your harness is under your vest or jacket. It's even worse if you try to share the binocular without taking the harness off! Let's just say it gives passersby a fine story to tell when they get home.

Optics Myth 6:

A really good pair of binoculars is outside my price range.

REALITY - There's some good stuff now in mid-priced binoculars .

Although the top end of binocular prices has gone stratospheric, mid-priced binoculars have been rapidly closing the quality gap.

When coating technology was new, a few manufacturers guarded secret techniques and formulas.

A few years ago, only the highest-priced binoculars were waterproof.

It was a rare binocular that focused close enough to be useful at a feeder.

Eyecups had to be folded down, a process that took several seconds and often required both hands.

And a person who wore glasses could hardly find a binocular with enough eye relief to reveal the whole image.

Now the secrets of coatings are out, and a wide range of optics, including relatively inexpensive instruments, offer fully multi-coated lenses. The marketplace is full of waterproof, nitrogen-filled binoculars of good optical quality at moderate prices.

Many of this new generation of binoculars work well for people who wear glasses, have the ability to focus closer than ten feet, and offer twist-out, click-stop eyecups. And, thanks to new materials used in construction, they weigh noticeably less than binoculars of ten or fifteen years ago.

While it's still generally true that the more you pay, the better optics you will get, the quality curve is not the same at both ends of the price scale. There's much more difference in optical quality between a $120 and a $400 binocular than there is between a $400 and a $1000-and-up binocular.

Optics Myth 7:

I don't need waterproof binoculars. I don't go out in the rain.

Waterproof wet binocular

REALITY - You do need waterproof binoculars. Even if you never go out in the rain.

When warm, moist air contacts a cool surface, water condenses. That's why your car's windshield fogs up when you breathe inside your car on a wintry day and your bathroom mirror fogs up when you take a shower.

It's also why your binoculars may fog up inside when they go from a cool environment, such as an air conditioned car or house, into a warm or moist environment, such as outdoors in summer, or near the ocean, not to mention a trip to the tropics. Even if they eventually dry out and clear up again, the trip or the day's birding may be ruined.

A waterproof binocular is prepared for changing climate. Its insides are isolated from salt spray and dust, and if it gets dusty on the outside, you can rinse if off under the tap. Waterproof binoculars are sealed and filled with a dry, inert gas that contains no water vapor to condense inside.

Since waterproof binoculars are no longer expensive, it makes sense to ensure that you're getting this feature in any binocular costing over $100. Look for the expression "nitrogen purged" or "nitrogen filled.

Optics Myth 8:

I can just buy what my friend has. He's an expert birder.

REALITY - Binoculars need to fit the individual, just like shoes. Everyone is different, and what works well for your friend may not work at all for you. Here are a few issues to consider in choosing your own binocular.

You can immediately eliminate any binocular that does not accommodate your glasses, because a binocular with insufficient eye relief only gives you tunnel vision, shows you only the center part of the full image. Binoculars with long eye relief, let you see the whole picture while wearing your glasses.

Consider the steadiness of your hands. Everyone's hands introduce a certain amount of motion. If your hands aren't as steady as they once were, you will see more with an 8-power or even a 7-power binocular than you will with a 10.

Some people feel comfortable with a large binocular that gives them something solid to hold on to. If that is you, by all means, get a full-sized binocular. Others want something as small and lightweight as possible. These are the folks that compact and pocket binoculars are made for.

There's something tangible but hard to define in the way a binocular fits a person's hands. It's a good idea to try a binocular personally before buying. Make sure the binocular will spread wide enough or close in narrow enough for your eyes. Notice the way the eyecups fit against your eyes or glasses. See whether you like the way the focus knob turns. Feel how your thumbs fit the shape of the binocular's body. Do you like the texture of the binocular's covering? In short, does this binocular fit? Does it feel right for you?

Optics Myth 9:

"Twilight factor" is key to performance in dim light.

Dusk

REALITY - The quality of the coatings is much more important.

You sometimes see "twilight factor" listed in a binocular description, as a measure of the resolving power in dim light. This term was more important years ago, before modern optical coatings were invented, than it is today.

Twilight factor is a mathematical formula that shows how both the size of the objective lens and the magnifying power contribute to a binocular's ability to show detail in dim light.

Twilight Factor MathThe twilight factor is the square root of the product of the diameter of the objective lens and the magnifying power of the binocular. [For example, an 8x32 binocular would have a twilight factor of 16, and a 10x42 would have a twilight factor of 20.5.]

However, in a modern binocular, performance in dim light depends more on the quality of the optical coatings than on the twilight factor formula. Good coatings can double the amount of light that gets through the binocular.

If you pick up an old binocular from the 40s, or a cheap, low-quality binocular, you'll see very poor performance in dim light. Then look through a modern, top-quality binocular with the same magnification and lens size, and see how much brighter and clearer the image is, despite the fact that both binoculars have the same twilight factor rating.

So if you're looking for good image quality in twilight conditions, you shouldn't just rely on the twilight factor number. You have to take the quality of the coatings into account.

Optics Myth 10:

Straight-through spotting scopes are easier to aim and use

REALITY - Not really!

An angled-eyepiece scope is just as easy. It might take you five minutes to get used to it, if you're switching from a straight-through scope.

You aim a scope by using the sighting marks on the scope body. The angle of the eyepiece doesn't matter in aiming. But it matters when you try to use the scope! Here are some of the ways the angled scope is better for birding.

Birds have wings and live in trees (well, lots of them, anyway). Often you'll find yourself looking up. The angled scope will literally save your neck. And have you ever tried to get a straight-through scope mounted high enough on a tripod that you could look up with it? Most tripods won't even reach that high. If you had an angled scope, you'd be viewing comfortably.

You can share an angled scope. After you sight in and focus on a bird, people of various heights can easily view it, without having to disturb the aim of the scope. With a straight scope, you have to adjust the height for each individual, with the result that fewer people may get to see the bird. With an angled scope, you can set it at a height that will work for young and old, tall and short, rotating the scope so that the eyepiece angles to the side or even down to accommodate children.

Lots of birders use their scope on a car window mount. Here's where the angled scope really shines. You get the maximum range of viewing angle. You can easily see forward or back, up or down, without having to assume extreme acrobatic positions.

The resolution of a scope at high magnification depends upon the steadiness of its tripod. Just as with binoculars, the details disappear if the image jiggles. The shorter the tripod legs are extended, the steadier the image. Angled scopes always allow a lower, inherently more stable tripod height. Mount your scope on a tripod a foot higher, and you lose that high-priced image you paid extra for. It really matters at 60 power.

How Much Light

Gets in Your Eyes

The Exit Pupil

Light into the eye

by Michael and Diane Porter

What does exit pupil mean?

If you hold your binocular away from your eyes, toward the sky, you see a little bright circle in the middle each eyepiece. That's the column of light coming through the binocular to your eye. The diameter of that circle of light is called the exit pupil of the binocular.

Exit PupilYou can calculate the exit pupil by dividing the magnification of the binocular into the diameter of the objective lenses.

So a 10x32 binocular has an exit pupil of 3.2 millimeters.

An 8.5x42 binocular has an exit pupil of nearly 5 millimeters. (42 divided by 8.5 = 4.94)

Exit Pupil Formula The larger a binocular's objective lenses, the larger the exit pupil; but the greater the magnification, the smaller the exit pupil.

You often hear that a larger exit pupil makes a binocular brighter. It's true, but only within limits. We can see only the light that enters through our pupils.

How big an exit pupil do you need?

In daylight, when the pupils are perhaps as small as 2 millimeters, part of the column of light coming through the binocular will fall on the iris (pigmented part) of the eye instead of the pupil. That part of the light does not contribute to the brightness of the image. In the photo below, only the center portion of the light is actually entering the pupil of the eye.

Light to the Eye This is the reason that a binocular such as an 8x32, with an exit pupil of 4mm, usually gives just as bright an image as an 8x42 binocular of equal quality.

The older a person is, the less the pupil dilates in dark conditions. That's why compact binoculars, such as an 8x32, seem to be just made for an older person. For pupils that remain relatively small even in dim conditions, the smaller objective lens and smaller exit pupil provide just as bright an image as a larger, heavier, more expensive binocular.

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Enjoy your Bird Watching