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Choosing Binoculars

Choosing Binoculars

Ingrid using binocularsUnless he’s perched on a feeder right outside your window, it’s pretty darn hard to see a bird close up. If you are going to identify these beautiful creatures farther afield you need a decent pair of binoculars. Compact binoculars, while handy to own, are not powerful enough to satisfy a growing interest in bird identification for long. Full size binoculars provide steadier images and a wider field of view, so they’re great for bird watching. They come in many styles and sizes, differentiated by a variety of numbers. What do all of those numbers mean?

Basic Numbers

Binoculars are usually described by two numbers, such as 10×42 or 7×50. The first number indicates the magnification. A magnification of 10 for example means that the object will appear ten times closer than it would to the naked eye. The second number refers to the size of the front, light-gathering lens.


While more powerful magnification may seem better, this is not necessarily true. Large magnifications make the binoculars difficult to hold steady. The birds already twitter enough. You don’t need your binoculars adding to this challenge. low magnification provides a wide field of view and is easy to hold steady. Although magnifications of 10, 12 or higher are available, 6, 7, and 8-power binoculars are easier to use and give you a wider field of view. This is very helpful in locating the object with your binoculars.

Objective Lens Diameter or Aperture

The second number used in binocular identification refers to the diameter (in millimeters) of the objective lenses (those farther from your eyes; those closer to the bird being viewed). The diameter of the objective lenses largely determines how much light your binoculars can gather. More light means a brighter view, particularly in low-light conditions, like dawn or dusk.

Binoculars Goslings

Exit Pupil

The exit pupil refers to the diameter of light leaving the binoculars. This number is related to the perceived brightness of the image. It is calculated by diving the aperture by the magnification. Thus a pair of 10×40 binoculars and an 8×32 pair will give the images the same brightness as both have an exit pupil of 4mm.

Field of View and Apparent Field of View

Field of view is how wide in feet you can see at 1,000 yards. Apparent field of view gives the image size as an angular measurement. The biggest is not always the best as sometimes the image appears fuzzy at the edge.

Binoculars - Harlequin Ducks

Eye Relief

This refers to the distance from the eyepiece to the eye. This is important for eyeglass wearers. Good eye relief is between 11mm and 15mm.

Close Focus

Another key feature of a good birding binocular is a relatively close focus.  While all binoculars can focus to the horizon, the closest point to which they can focus varies from model to model. An ideal birding binocular should be able to focus on an object within 10 feet.


Porro-prism (left) and Roof-prism (right)

Binocular Types

Binoculars come in two basic designs. Porro-prism binoculars are a good value and may have equal or better performance than a more expensive roof-prism pair.

Most binoculars are waterproof and fog-proof. If you plan on birding around wetlands or intend to watch birds in diverse weather conditions and climates, you want to make absolutely sure your binocular has this feature.

Which Binoculars Should I Buy?

Buy the pair that feels comfortable to hold and use. This is most greatly affected by magnification and aperture. For birding, the most popular are 8×42 and 10×40. With the 8×42, you will have a larger exit pupil of 5.25mm, making the object appear brighter and the colors more vivid. A 10×40 pair will give you stronger magnification, but will be a bit heavier.

The price range for binoculars is huge. While the adage, “You get what you pay for” does apply to a certain extent, you do not need to buy the most expensive brand of binoculars to get the best quality. It is helpful to read reviews online and try out different types at a local birding or outdoor store. Buy the best pair that you can afford, and you will enjoy years of birding with them.