| 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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