By Carl Runge
One great feature about taking up the hobby of birdwatching is how little equipment you need. A good field guide and a pair of high quality binoculars is all it takes to get started. This article will describe how to go about selecting the right pair of binoculars for you.
The most important feature of your binoculars is fit. They must be comfortable for you and easy to maneuver. Size is important! Binocs can range from 18-50 ounces. A comfortable weight for most people is 24-32 ounces. Both the small compacts and the bulky marine binoculars should be avoided as they are too difficult to hold steady. You must be able to adjust the lens distance between your eyes so that you see a single image.
The focus mechanism bears your attention. Buy only binoculars with a center focus wheel, easily reached with your index finger. Avoid those with a focus lever or bar, as they will be less sensitive to your touch. Your binocs should have an individual eyepiece adjustment on one side, usually the right, so that you can correct for possibly different acuity between your left and right eyes. Avoid separate eye piece adjustments without a center focus. Do not buy permanently focused binoculars which make your own lenses do all the work of focusing. Do not buy zoom binoculars which have a narrow field of vision at all powers, and a rapid decline of image quality as you increase the power.
What about the optical features? Here we are considering the glass elements, the lenses and prisms. The lenses should be made of BAK-4 barium crown glass and should be fully multicoated to prevent light loss. Avoid lenses made of boro-silicate glass or plastic.
Binoculars have either porro or roof prisms. Both have advantages and disadvantages. Porro prism binocs are the wide-bodied, clumsier looking ones. They are less rugged and durable than roofs, but they are simpler in design and offer better image quality at a lower price. Roof prism binocs are sleeker, fit better, are easier to use and more rugged. They are more expensive. To get a porro prism quality image with roof prism binoculars, you need to spend at least $200-300.
What is the ideal magnification? Contrary to popular opinion, higher is not better. The magnification is indicated on the binoculars by the first of the numbers designated. For example, in 8x40 (spoken 8 by 40) binoculars, 8 is the magnification power. This can range from 7x to 12x. The most versatile and easy to use for most birdwatching is 7x or 8x. Higher magnification binoculars are more difficult to use because they magnify the distortion caused by unsteady hands, they decrease the field of view and the depth of field, and they increase light loss. Field of view, or the width of the field seen, is also included with the binocular information, and should be at least 330 feet at 1,000 yards.
What does the second number, the 40 in 8x40, mean? This is the width of the objective, or more distal, lens in millimeters. The larger the width, the more light enters, a desirable feature. The relationship between the lens width and the magnification is an important indicator of light coming in and overall image quality. This is expressed as the “exit pupil” and is measured as the objective lens width divided by the magnification. In our above example it would be 40/8 = 5mm. This number should be at least 3.75, with 5-6 being more desirable.
When buying binoculars, always test before you buy. Your binoculars should be comfortable to handle and have the features indicated above. You should be able to find in the binoculars what you see with your eyes, quickly and easily with a clear, sharp, single image. Buy the best quality you can afford. Binocular prices range from around $30 to $2,000. You can get good quality binoculars for birdwatching for $200-300. If you are spending less, you might do better with porro prism binoculars.
If you want to learn more about binoculars, read the book which was my primary source for this article, Pete Dunne on Birdwatching, by Pete Dunne, Houghton Mifflin Company, 1st ed. 2003.
