Bird Notes from West Houston

Tuesday, March 14, 2006


With spring migration upon us, many will be interested in getting a pair of binoculars. Whether it is your first pair or a replacement for a well-worn pair, it is important to know a little about what you are shopping for.

The first number in the binocular designation (i.e. 8x42) is the magnification. Most birders use 7x, 8x or 10x binoculars for regular birdwatching. The number represents how many times closer the binoculars will make an object appear. If you look through a pair of 8x binoculars, the object will appear to be eight times closer than it is with no magnification. Normally 10x is as high as you will want to go. While higher magnification binoculars magnify the birds even more than lower magnification, they will also magnify every little shake in your hands. For higher magnification than 10x, consider using a spotting scope with a tripod. Also, as the magnification increases, the light-gathering ability decreases.

Objective Lens
The second number in the binocular designation is the size in millimeters of the objective lens. A pair of 8x42 binoculars will have a 42 millimeter objective lens (the lens away from your eyes.) Typically the larger the objective lenses will allow more light into the binoculars giving you a brighter image. A 50 mm objective lens is usually the limit on birding binoculars because of the weight. On a bright, sunny day, the size of the objective lens will make little difference in light gathering. You will see the difference on very cloudy days, at dawn and at dusk.

Field of View
When you look through binoculars, the widest dimension that you can see will be the field of view. It is similar to peripheral vision. A wide field of view is helpful because the bird does not have to be in the center of your binoculars. You can put your binoculars in the general area and look for movement even if the bird is not in the center of the view. As the magnification increases, the field of view decreases.

Lens Coatings
The binoculars today are much different than binoculars thirty years ago. Many advancements have been made to improve the image and light-gathering abilities of binoculars. One of those advancements is lens coatings. Coatings help the light that enters the objective lens stay in one beam until it reaches your eyes. Binoculars with multi-coated lenses will provide better light-gathering than uncoated lenses with a larger objective lens.

Waterproofing and Fogproofing
Nine years ago, I had one of the most frustrating experiences of my birdwatching life. I had gone to High Island for migration and the weather was less than ideal. It was raining and cool. However, those less than ideal conditions created a spectacular fallout. The binoculars I carried were not waterproof or fogproof and fogged internally. I could not see anything. Fortunately a friend of mine had an extra pair of waterproof binoculars that she let me borrow and I could enjoy the birds. Having waterproof binoculars is great because you never know when you'll get caught in a rainstorm or be sprayed with surf at the ocean. Fogproof binoculars eliminate internal fogging from rain or from sudden temperature changes. Most roof prism binoculars are waterproof and many are fogproof as well.

These are some of the more important issues to consider when purchasing a pair of binoculars. Other issues such as eye relief, depth of field and exit pupil can be discussed when purchasing the optics. To make sure you are completely satisfied with your binocular purchase, go into a store with the optics and test them out. A good pair of binoculars is an investment. You wouldn't buy a car without test driving it first. You shouldn't buy binoculars without testing them first either. See how they feel in your hands. See how they fit your eyes. Compare the different kinds and find out which pair fits you best. Then enjoy them!

- Paul


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