The Basics of Buying Binoculars

Thinking about upgrading your optics? Researching your options with binoculars can be a daunting task, but the basics are all you really need to know in order to make the correct choice.

Price range: There are three cost ranges of binoculars: low, medium, and high. In general with binoculars, you get what you pay for; the best quality costs the most. Zeiss, Leica, Swarovski, and Brunton all have high-end optics that retail around $1500--well out of the price range for many birders. Rest assured, however, that a thoroughly enjoyable and birding career can be had without Zeiss and Leica. If this is your first pair of binoculars for birding, or your first upgrade, plan on spending at least $200 to avoid being continually frustrated with poor images.

Magnification: This is fairly straightforward: magnification is the first number written on the binoculars. A pair of 10x40 binoculars magnifies an object 10 times (10x). The greater the magnification, the closer the image appears in the binoculars. Generally, the greater the magnification, the greater the price and weight of the binoculars. See "Field of View" for more on selecting the proper magnification.

Light Transmission: Most people assume that binos with greater magnification inevitably produce better images, and are therefore better binos. But this is not necessarily true. Higher magnification always produces bigger images, but also has a lower light transmission. This means generally that the greater the magnification, the darker the image.

Light transmission is determined by the amount of light exiting the "eyeball end" of the binos. This amount of light, called the exit pupil size, is calculated by dividing the size of the objective lens (the second number written on the binoculars) by the magnification. This means that 10x40mm binos have an exit pupil size of 4mm (40 divided by 10); 7x35 binos have an exit pupil size of 5mm. Obviously, the larger the exit pupil size, the greater the light transmitted, and therefore the brighter the image.

So, greater magnification gives bigger images, but lower magnification tends to give better light transmission. Keep in mind that light transmission is a concern only in low-light birding situations, such as birding at dusk for owls or at dawn for rails. In ordinary daylight, binoculars with the same quality lenses will be equally bright, despite differences in magnification and objective lens size.

Field of View: Field-of-view is simply the width of vision seen through the binoculars. This is generally expressed at 1000 yards, which isn't that helpful since field-of-view matters at close range. To better understand field-of-view, move the decimal point two digits to the left: a field-of-view of 350 feet at 1000 yards means a field-of-view of 3.5 feet at 10 yards. At 10 yards, field-of-view becomes a vital factor in how quickly a birder can find and follow birds, especially when they are in thick brush.

Field-of-view is most closely related to magnification. The greater the magnification, the smaller the field-of-view. For this reason, most Eastern birders use 7x and 8x, giving them a larger field-of-view to bird effectively in the denser foliage of the East. In the West, where distances are greater and the foliage is sparser, 10x and even 12x binoculars are the norm--especially for hawk watching and shorebirding.

Close Focus: Many birders are also becoming interested in butterflies, which require very close-focusing capabilities. Close focus is also important for watching birds at window feeders. There are several brands of binos that feature extremely close focus (around 5 feet). For birding purposes, get a close-focus of no greater than 10 feet for maximized use with small brush-loving birds like sparrows and warblers.

General Advice:

1. Consider what type of birding situation you will be in the most: dense brush or open spaces (Eastern U.S. or Western)? This will determine the magnification you need.
   
2. Will you be doing a lot of low-light birding? If so, purchase a bino with a larger exit pupil size for brighter images. (By the way, the lens coating on more expensive binos also increases brightness.)
3. Do you need extreme close-focusing capabilities?
4. Once you determine your magnification, light transmission, and close focus needs, go to a store that sells binos with these specs and test them by taking them outside (with their permission) and "field-testing" them. While you're there, try out some high-end binos as well to get a feel for their quality. You should also experiment with different magnifications.
   
5. Watch out for gimmicks and bargains. Quality binoculars cost money, and don't also take pictures, walk the dog, or make coffee. (Although Leica does have a very excellent pair of range-finding binos.)
6. Buy the very best binos you can afford. You will have these for a very long time and become very attached to them. Buyer's remorse is painfully intense when the possible life bird flies unidentified into the distance because you were overly frugal.