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Numbers and specifications can be overwhelming at first. This rough guide to choosing binoculars is our attempt to give you the knowledge you'll need to choose the right binocular for your application.

What do the numbers in a binoculars name mean?

Binoculars are often referred to by two numbers separated with an "x", for example: 8x32.
magnification (power)
The first number is the power or magnification of the binocular. With an 8x32 binocular, the object being viewed appears to be eight times closer than you would see it with the unaided eye.
objective lens size
The second number in the formula (8x32) is the diameter of the objective or front lens. The larger the objective lens, the more light that enters the binocular, and the brighter the image.
Note: The diameter of the objective lens is directly related to the size of the binocular -- the larger the objective lens, the larger (and often brighter) the binocular.

How much magnification do I need?

You will want a binocular with appropriate magnification. Think about the demands of your hobby before you select a pair of binoculars. How much detail do you need, will you use your binoculars to view things close up or far away, do you want a small binocular that you can take anywhere?

The most popular binoculars are those with lower magnifications. These magnifications offer wider fields of view and are easier to hold steady than the binoculars with higher magnifications. A wider field of view is important when trying to follow fast-moving objects such as warblers or athletes in sporting event.

Higher magnifications may offer greater detail, but can also be difficult to hold steady because they have narrower fields of view. People might choose to use high magnification binoculars when viewing in open terrain, or if the desired targets are often stationary.

Note:The diameter of the objective lens is directly related to the size of the binocular -- the larger the objective lens, the larger (and often brighter) the binocular.

What are the different prism types?

porro prism
Porro Prism models are offset in design, deliver great optics for the dollar, but lack the durability and compact styling of roof prism models.
reversed porro prism
Mostly used in compact binoculars, a reverse porro prism allows for a binocular that easily fits in a fanny pack or coat pocket.
roof prism
The prism system in a binocular typified by a straight barrel design. Roof prism binoculars are generally lighter and more compact than porro prism binoculars.

BaK-4 prism
The BaK-4 prism transmits more light at the edges to enhance illumination for easy viewing in dim light.

What size binocular do I need?

Binoculars can be classified as either full-size or compact binoculars. The size of the objective lens affect how large or small a binocular is.

Full-Size Binoculars:
Full-size binoculars have at least 30mm of aperture or greater. They offer the light gathering ability needed to identify objects in low light conditions, however are not always as portable as one might desire.

Compact Binoculars:
Compact binoculars have less than 30mm of aperture, and are more portable than full-size models. However, due to their limited light gathering capability, they are best when ample light is available to the viewer.

What is the field of view?

When you look through your binoculars, the widest dimension you can see is known as the field of view. Some binoculars will feature unique lenses to provide a "wide field" that is greater than normally seen through binoculars of the same magnification.

A wide-field binocular is desirable for observing in close quarters, deep woods or picking up anything that is moving quickly across your viewing area.

Note: The field of view decreases as magnification increases, so select a binocular with lower magnification if a wide field of view is important to you.

What about light transmission and optical coatings?

Light transmission describes the percentage of available light that passes through your binoculars. The amount of light can be increased with the use of anti-reflective coatings on binocular lenses. When an anti-reflective coating is applied to the glass surface of a binocular it increases the amount of light that reaches your eye.

The more complete and complex the coating scheme is, the brighter and sharper the binocular image will be. Better coatings on a binocular allow more light to reach your eye, improving brightness and overall binocular performance.

What is eye relief, and what if I wear eyeglasses while using binoculars?

Many models of binoculars will allow you to view in comfort while wearing eyeglasses or sunglasses. These binoculars have been designed to provide you with longer eye relief.

Eye relief refers to the distance images are projected from the eyepiece out to its focal point, measured in millimeters. If you want to use your binoculars with eyeglasses or sunglasses, look for binoculars that offer at least 15mm of eye relief, including the Audubon 8x25 and 10x25 compact, and the Audubon 8x40 Intrepid.

Note: Without proper eye relief, the eyeglass wearer will not see the full field of view.

When using your binoculars be sure you understand the correct use of the eyecups. All binoculars will allow you to adjust the eyecups. There may be a rubber eyecup that can be folded down or a newer type that either twists or slides up and down on the eyepiece of the binocular.

If you're an eyeglass wearer using binoculars, you always want to be sure you have the binocular eyecup rolled back (placed in the down position) while using your binoculars. This will allow you to see the widest possible field of view through your binoculars. Conversely, if you don't wear glasses, you'll enjoy your binoculars more if you leave these eyecups fully extended (placed in the up position). Doing so will help block out lateral light.

Do my binculars need to be waterproof?

Binoculars are used outside in all kinds of weather. If you expect that you will be using your binoculars in rainy, wet weather (or if you use them around water), consider a pair of waterproof binoculars. You'll pay a bit more for this feature, but you'll also be able to use these binoculars without fear of repairing or replacing them just because they got wet.

Waterproof binoculars are literally submersible and any water damage would be handled under the manufacturer's warranty for the binocular.

Note: If waterproofing isn't necessary for your hobby, then you can find good quality binoculars at lower prices.

What makes a binocular appear brighter?

Brightness in your binoculars can be affected by several things. Contrary to what many binocular users believe, big objective lenses are not the only factor to consider. The quality of glass used in binocular prism and lens construction along with the quality of the lens coatings on the binocular contribute more to brightness than do big objectives.

Lens coatings are thin layers of chemicals applied to the glass surfaces of the binoculars. These coatings improve light transmission through the binocular. Coating quality is affected by the number of coatings and whether all binocular lenses, inside and out, are coated with several layers of coatings.

Ideally, you should purchase binoculars that are fully multi-coated, which means both sides of every binocular lens are coated with at least several layers of the anti-reflective chemical. High quality lens coatings will appear as fairly light, subtle shades of blue, green or violet.

A word of caution, beware of a binocular using heavily colored lenses. These lenses will only cut down on light transmission through the binocular.

Note: If all other things are equal in two binoculars, a binocular with a larger objective lens will yield a brighter image, but at the cost of greater size and weight. Higher quality binoculars with a smaller lens may very well be brighter than less expensive binoculars with larger objective lenses.

How do I clean my binoculars?

Use common sense in the care and maintenance of your binoculars. Always attempt to blow off any visible dust or dirt from the binocular lenses before brushing or rubbing anything on the glass of your binocular. Next, use a lens cleaning tool like a Lens Pen or lens cleaning tissue to gently wipe off any remaining marks or spots from the lens of the binocular.

Remove stubborn things like dried water spots from the lens of a binocular by lightly fogging the binocular lens with your breath. If your waterproof binoculars are badly soiled, you can even clean them by placing them under lightly running water (to minimize any possible damage).

Note: Do not use your shirt tail or pocket tissue to clean your binoculars. These fibers may contain material which will scratch the coatings on the binocular lenses.

Keep binocular eyecups and focus mechanisms free of dirt and oil. An occasional wipe with rubbing alcohol will extend the life of rubber eyecups on the binocular. Check your neckstrap and its attachments for wear or slippage, too. You don't want your bino to come flying off and hit the ground!

What about the light gathering ability of my binocular?

Your eye is uniquely designed to gather more or less light as conditions change, but your binoculars are not. Since the light gathering ability of a binocular is fixed, it is important to select a model that best meets your eye's need for light as viewing conditions grow darker.

The exit pupil is the magnified image in the eyepiece as it leaves the binocular to enter your eye. It is an indicator of how well you will see an image through your binoculars on a bright day, at twilight or at night. Almost all binoculars gather more light than is needed by your eye for viewing in bright conditions. For the best viewing at twilight, you'll want a binocular with a minimum exit pupil of 4mm.

Determining the Exit Pupil:

To determine the exit pupil of a binocular, simply divide the objective lens by the magnification of the binocular. If we use an 8x42 binocular as an example, the 42mm objective lens divided by the magnification of 8x gives us an exit pupil of 5.25mm. This tells us that an 8x42 binocular is a good configuration for low-light viewing.

In contrast, if we look at an 8x25 binocular, we find that 25mm divided by 8x leaves us an exit pupil of only 3.12mm. This means that an 8x25 binocular will give sufficient brightness for daytime viewing, but the image will not be as bright as you would like at dawn and dusk.

How do I properly adjust the diopter on my binocular?

All quality binoculars will allow you to separately adjust the focus on eyepiece (usually the right eye) with a diopter. This is done to compensate for any differences between your eyes, providing the clearest image possible through your binoculars. When adjusting the diopter, pick a stationary object to focus on that is beyond the close focus distance of the binocular, approximately 50 yards away. Initially, while covering the right objective lens with your hand, use the center focus of the binocular until the target appears clear.

When adjusting the diopter, pick a stationary object to focus on that is beyond the close focus distance of the binocular, approximately 50 yards away. Initially, while covering the right objective lens with your hand, use the center focus of the binocular until the target appears clear.

Once you've got the left eye focused as sharply as possible- carefully, without moving the center focus of the binocular and covering the left objective lens, see if image sharpness through the right eye improves by slowly moving the diopter adjustment back and forth. Once you've found the setting that gives you the sharpest image, note where the setting is and leave it there -- you're done. From this point on, you simply use the center focus to adjust both eyes while viewing.

Note: You should properly set the diopter adjuster when you first use your binocular (make a note of your setting). Check the diopter setting on your binocular every so often to be sure your eyes haven't changed. Always check it whenever you share your binocular with someone else.

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