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Buying Binoculars
Whether you want binoculars for bird watching,
general nature study, sports, or sightseeing,
there are a number of factors to consider.
- Magnification. How close the binoculars make
a distant object seem is called "magnification."
For example, magnification of 8X (often called
"8 power") makes an object 80 feet
away appear as if were only 10 feet away.
Is more magnification better? Not necessarily.
These is a downside to greater magnification:
- Hand Tremor - no one can hold binoculars
perfectly still. As magnification increases,
you are more likely to notice that the image
shakes. Windy conditions or on a boat (as
in whale watching) only increases the problem.
- Field of View - people with normal eyesight
have a field of vision that radiates roughly
160 to 170 degrees in both the left-right
and up-down dimensions. Most 7X binoculars
have a field of under 9 degrees, which shrinks
to about 5 degrees with 10X binoculars. With
a smaller field of view it becomes harder
to find an object, especially a moving one
like a flying bird.
- Depth of Field - people with normal eyesight
(or good eyeglasses) can look off in the
distance and see everything from a few feet
away to the horizon with roughly equal clarity.
With binoculars, once you focus on a distant
object, other objects more than a few feet
in front of or behind your subject will be
out of focus. At greater magnification, the
in-focus range usually becomes narrower.
Therefore for most purposes, 7X or 8X binoculars
are safer bets than 10X. Note, however, that
field of view and depth of field can vary
between instruments with the same magnification
based on the quality of manufacture.
- Size of Objective Lens. Binoculars are identified
as "8X40" or "7X42" or
"10X50," for example. The number
before the X is the power, or magnification,
and the second number is the diameter of
the lens at the front of the binoculars in
millimeters. The larger the front lens, the
more light your binoculars will collect and
the more detailed the image should be. Lens
size around 40 is normally optimal. The largest
you'll usually find is 50, generally in a
10X50 instrument. Compact binoculars with
lenses smaller than 30 often give you too
small an image to be worth considering.
- Size, Weight and Comfort in Your Hands. Old-fashioned
porro-prism binoculars (the lenses are set
farther apart than the eyepieces) tend to
be bulkier and heavier than roof-prism models
(their lenses are aligned with the eyepieces).
However, quality porros are are roughly one
third the price of quality roof models.
- Close Focus Capability. If you are interested
in up-close views of small objects,
like
butterflies, look for binoculars
that can
give you a sharp look at things only
a few
feet away.
- Weatherproofing. Higher-end models will be
sealed from outside air that can fog interior
surfaces in humid or rainy weather.
- Eye Cups. To shade users' eyes against the
sun, the eyepieces have either soft
rubber
or hard plastic cups. If you wear
glasses,
you must either roll down the soft
rubber
or push in the hard plastic to get
your eyes
closer to the eyepieces for an adequate
view.
- Other qualities to look for include
- Ease of Focusing
- Sharpness of Image
- Trueness of Colors
- Brightness of Image in Twilight
- Glare-Reducing and Scratch-Resistant Lens
Coatings
- Durability (Shock Resistance)
Personal preference also plays a major
role
in choosing binoculars. After researching
the features of binoculars, you are
well
advised to get some hands-on experience
with
various models, preferable out in the
field,
before deciding on which to buy. |
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