| Binoculars are one of most popular optical instruments
for the hunters, astronomers, fishermen, boaters, sports fans, and military
troops. Binoculars are available in hundreds of specifications and with
a multitude of different features. How to choose a binocular that best
fit your needs? This buyer's guide is intended to help our customers who
need some basic information about binoculars.
Quality of Binoculars
Quality is the most important "feature" of binoculars. In many
cases the brand name is a guide to quality. Companies like Celestron,
Leica, Minolta, Nikon, Pentax, Steiner, Swarovski, and Zeiss have spent
decades earning a reputation for high quality optical products, and they
are unlikely to produce a clearly inferior product. Other companies, like
Tasco, Jason, and Bushnell have built a reputation on low price.
Binocular Lenses
The lenses of a binocular serve to collect light, thereby enabling the
high-resolution observation of distant objects. In a quality binocular
each objective lens typically is manufactured of two separate glass elements,
the so-called crown and flint elements. The refractive specifications
of these elements permit the objective lens to image objects free of false
colors.
Binocular Prisms
Since the objective lenses form images that are both upsidedown and reversed
left-for-right, prisms are required to invert the primary image. Most
commonly, binoculars utilize either porro prisms or roof prisms for this
purpose. Porro prisms give binoculars their familiar zig-zag profile,
while roof prisms permit a straight-line design. Either type of prism,
properly manufactured, yields excellent optical results.
Collimation of Binoculars
Collimation refers to the optical and mechanical alignment of the binoculars.
If a pair of binoculars is out of collimation, after prolonged use it
may feel as if they are trying to suck your eyes out of your head. Cheap
binoculars are often (perhaps usually) shipped from the factory out of
collimation. Good binoculars are carefully collimated, often with laser
instruments. This requires time and expense at the manufacturing level,
and raises the price at the retail level.
Binocular Eyepieces
The most basic function of an eyepiece, or ocular, is to magnify the
image formed by the objective lens, in fact the eyepiece also largely
determines the binocular's field of view, edge-of-field image resolution,
and other characteristics.
Binocular's Magnification
Magnification, or power, is perhaps the most misunderstood term of binocular
optics. While higher powers can be useful, power by itself does not increase
the level of observable detail; image resolution is a function of objective
lens diameter, not of binocular power. Higher powers result in images
that are less bright and in a binocular that is more difficult to hold
steady in the user's hands. Powers of 7x to 12x are by far the most popular
among regular binocular users. Binoculars with magnifications above about
16x are generally not recommended for use without a tripod.
Binocular's Field of View
A binocular's field of view is measured in degrees of arc or as field-width
(in feet) at 1000 yards distance. Other non-wide-angle binoculars have
fields of view of perhaps 270 ft. at 1000 yds. Depending somewhat on the
observer's intended applications, wide-angle binoculars are generally
well worth the relatively modest additional cost involved.
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