Developing Your Observation Skills
 

Binocular Basics

A good pair of binoculars is a must for most NatureMapping bird monitoring projects. Certainly, you can observe birds and other wildlife without the aid of binoculars, such as at a feeder right outside your living room window, but with them you will see more detail. Binoculars don't have to cost you a lot of money, but should adequately magnify birds and have a clear image to aid in proper identification. Many 7 x 35 or 8 x 42 power binoculars are affordable and good for bird watching. Purchase what your budget will allow, but if you can afford it, don’t buy anything costing less than $100.00, as quality usually suffers in these models and you don’t have to pay very much more in order to get a decent pair of binoculars. A good pair of binoculars will cost you between $150 and $400. There is a lot of variation in features among binoculars, including the quality of lenses, mirrors, prisms, etc., all of which affect the price and quality of the image that you see. Seek out literature to learn more about the materials and construction of binoculars. Ultimately, the pair of binoculars should be easy and comfortable for you to use and meet your expectations for quality. You can buy binoculars through sporting goods stores, catalogs, and the Internet. Make sure to try out different binoculars in retail stores before purchasing them. This is the only way to be absolutely sure they are right for you.

How to use binoculars
Your eyes are your best tool to rely on when observing wildlife in the field. Binoculars are merely an extension of your eyes, allowing you to view things close-up without having to move closer yourself, an obvious benefit when viewing birds. First, use your naked eye to find the bird you are observing. Once you have detected movement and/or can see the bird, focus your eyes in that direction and then slowly raise the binoculars to your eyes. You may have to relocate the bird again, but with practice, this transition from naked eyes to binoculars will become smooth. Once you have the bird in sight, you will look for details of a bird’s “field marks.” Everyone’s eyes are different, so before you raise the binoculars, you must calibrate them for your eyes.

How to Calibrate Binoculars
1. Binoculars hinge at the center between the two large “barrels,” allowing the eyepieces to fit the width of your eyes (See Illustration Below - A). Pivot the hinged barrels so you see a single circle-shaped image, rather than a double-image when looking through them. The distance between the eyepieces is called the “interpupillary distance.” If this is too large, you will see two images. If the barrels are as close together as they go and you still see two images, you may need to find another pair that fits you better. The number on the hinge post (angle) will always be the same for your eyes, no matter which binocular you use (A).

2. Each of your eyes sees with slightly different levels of clarity (your prescription varies in each eye), so your binoculars must be calibrated to accommodate the difference (Illustration - B). Calibrating binoculars brings both eyepieces into sharp focus. Most binoculars have a focusing wheel in the center. It adjusts the focus of both eyepieces (what you see with both eyes) at the same time. Most binoculars also have a separate “diopter” adjustment, which allows you to focus (turn) one eyepiece independently, to accommodate the differences in your eyes (B). Depending on the binoculars, this adjustment can be on the left or right eyepiece (usually the right). Marks similar to the following symbols (+ … O … -) are on the eyepiece. Note: the remainder of these instructions assumes you are using binoculars with a right-eye diopter adjustment. For binoculars with a left-eye adjustment, reverse the side of the binoculars indicated.

3. Turn the center focusing wheel to the right as far as it will go (if it is an external focus binocular as in the illustration) (B). Turn the adjustable eyepiece (diopter adjustment)
counterclockwise, moving it as far out from the body of the binoculars as possible (B). Both eyepieces should now be out of focus. Stand about 30 feet from a sign (street signs work well) with clear lettering. Cover the end of the right binocular barrel with your hand so that you just see out of the left side (B). With both eyes open, turn the center focusing wheel until the lettering comes into sharp focus. Turn the center focus wheel past sharpest focus and back again to ensure you have the sharpest image.

4. Next, cover the left barrel, keeping both eyes open, and turn the right eyepiece clockwise to bring the lettering into focus (B). Again, turn the eyepiece beyond the point of sharp focus and back to find the sharpest image. Remember to keep the center focus wheel in the exact position you left it in step 3. Uncover the left barrel. Your binoculars should be in perfect focus and calibrated to you eyes. Some fine-tuning may be necessary, however. Remember the position that the right eyepiece is set. This will not have to be changed unless your vision changes. You may want to place masking tape around the eyepiece so it can’t be turned. From now on, you will only need to use the center focus wheel to adjust both eyepieces.


A Note for teachers:
This exercise will greatly enhance the experience of watching wildlife, and taking the time to teach students this method is passing on an important skill. However, it may be preferable to keep the right eyepiece in the center (not adjusted) for younger students. Most young people have little or no need to adjust the eyepieces independently. This will reduce confusion for younger students, but the decision is up to you.

Information taken from Classroom BirdWatch, Teacher’s Guide, FeederWatch Module, Copyright, 2001, Cornell Lab of Ornithology; adapted from “How to Calibrate Binoculars For Your Eyes” by Steve W. Kress, National Audubon Society biologist. Binocular drawings by Jason O’Brien, 2002, Iowa NatureMapping.

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