The Audubon Guide to Binoculars
A wide field of view makes it easier to find birds and to follow them when they fly. Prove this to yourself by taking a cardboard paper towel tube and holding it up to your eye while you try to find a robin. Then try to keep sight of your robin (through the tube) as it flies. Impossible, right? Next cut off two-thirds of the tube and try again with the remaining one-third. You have just dramatically increased the field of view. You will now find it much easier to locate the bird and then keep it in sight. Think of your binoculars as a pair of expensive tubes with a bunch of expensive glass inside. The wider the field of view, the easier it will be to find birds and track them as they move. Since birds move fast, being able to find them quickly with your binoculars is critical. You can find the field of view in the specifications sheet included with most binoculars. Makers describe the field of view of any given model as the diameter of the field you see from a distance of 1,000 yards. Some manufacturers instead give the angle of view, because they consider it a more useful number. To convert an angle of view to field of view, multiply the angle by 52.5 (to convert field of view to angle of view, divide by 52.5). Bird-worthy binoculars should have an angle of view of at least 6.5 degrees, which is equivalent to a field of view of 341 feet at 1,000 yards.
Making Things Perfectly Clear
Binoculars come in too many configurations to list. Models close to the following sizes are all suitable for birding: 6x32, 8x32, 7x35, 8x40, 7x42, 8x42, or 8.5x44.
Buy binoculars that have a single focusing knob located between the two barrels that turns one to one-and-a-half times. Don’t buy binoculars with separate focus adjustments on the two barrels—they’re too slow to be useful for birding.
If you pay more than $200 for your binoculars, they should be waterproof and nitrogen purged, so they don’t get “fogged” in humid conditions.
You will be using your binoculars for many hours at a time, so make sure you buy the right pair. Do they feel good in your hands? Can you comfortably reach the focus knob? Can you see the entire field of view with your eyeglasses? All binoculars have a hinge to allow you to adjust the barrels to match the distance between your eyes. If you have closely set eyes, be sure you can adjust the barrels so you can see a single image. All binoculars can be adjusted to allow you to compensate for differences in your eyes. To adjust yours, close your right eye and focus on an object 50 to 100 feet away using the center focus knob. Then, while keeping the same object in view, close your left eye and use the separate eyepiece adjustment to bring the object into sharp focus for your right eye. Your binoculars are now matched to your vision.
Don’t buy zoom binoculars or image-stabilized binoculars because they are heavy, give up a lot of brightness, and have a much-reduced field of view.
Don’t ask for advice from non-birders. Hunters, boaters, and hikers may know a lot about optics, but they have different needs than birders.
Don’t touch the lenses with your fingers. Never clean the lenses with tissue, toilet paper, paper napkins or towels, or newspaper—all contain wood fibers that will scratch and eventually destroy the lens coatings essential to your binoculars’ optical performance (and can’t be repaired or replaced). Never use commercial glass cleaners. They may contain ammonia or other chemicals that will destroy the coatings.
Clean your binoculars only with good-quality lens tissue or a micro-fiber lens cloth from an optics or camera store. Also buy a can of compressed air and lens-cleaning fluid whose label states clearly that it’s safe to use with lens coatings. First use compressed air to blow away loose dust. Next spray the lens cleaner on the cloth and gently clean the lenses. Then gently wipe them with a dry part of the cloth.
If you eat while you are birding, use the lens covers that came with your binoculars. Although they are called “rain guards,” think of them as “food guards.” Coffee, orange juice, goat cheese, and hummus are not good for your binoculars.
Do You Wear Glasses?
It’s pretty simple: If you see better with eyeglasses, you should wear them while birding. Remember, however, that your eyes will be farther away from the binocular eyepiece than they are for non-eyeglass wearers. Unless your binoculars are designed to compensate for this, you will see a much-reduced field of view. Optics engineers design binoculars to project the image a few millimeters beyond the eyepiece; this distance is called “eye relief.” Eye relief tells you the distance your eye can be from the eyepiece and still see the entire field of view. Binoculars designed for birders offer eye relief of 15 millimeters to 20 millimeters and eyecups that extend and retract so you can adjust the distance between your eyes and the eyepiece. Use the eyecups in the fully retracted position with your eyeglasses and in the fully extended position without glasses. Before you buy a pair of binoculars, make sure you can see the full field of view while wearing your glasses. Some people, because of their face shape and vision, can experience image blackout if their eye is too far from the eyepiece. They should position the eyecup between full up and full down; this will give them a good compromise between field of view and ease of use.
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