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How to Select the Right Binocular
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Meade Sports Optics Support
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While many binocular brands look about the same, there are often
important differences in performance from one manufacturer to
another. The information in this section of the Meade website will allow you to choose the right
binocular for your intended applications, budget, and personal
preferences. Every Meade binocular, incorporates quality optical components, durable optical housings, and
precision mechanical components for years of high-performance
observing. It is this Meade attention to detail and intimate knowledge of
optical design fabrication that is perhaps your best assurance of all.
Binoculars are available in hundreds of specifications and with a
multitude of different features, but all share the same three basic
components:
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- Objective Lenses: The main (objective) 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.
- 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.
- Eyepieces: The ocular, or eyepiece, design included with a binocular
has important performance implications. While the most basic
function of an eyepiece 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 listed below. Eyepieces are manufactured from two to
five glass elements.
With this knowledge of the basic components of a binocular, it is now
possible to understand the technical terminology that will enable
selection of the right binocular for you:
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Binocular Specifications: Binoculars are classified as, for example, 7 x
35mm — read "seven by thirty-five millimeters." In this case the
binocular is of 7-power ("7x") and includes objective lenses of 35mm
(about 1.38") diameter. Other binoculars might range from a tiny 3 x
14mm to giant battleship binoculars that are 40 x 178mm. The "WA"
designation after a binocular specification, such as 7 x 35mm WA,
refers to the Wide-Angle design of the binocular's eyepieces; wide-angle
eyepieces can increase a binocular's visual field of view by as much as
60%.
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.
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. Example: The Meade
8x42mm Waterproof roof prism binocular has a field of view 367 ft. wide for an
object 1000 yards distant from the observer, yielding a field of view
specification of 367 ft. at 1000 yds. 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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Field of view (inner circle) for typical binocular; field of view (outer circle)
for wide-angle binocular.
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Lens Coatings: An uncoated optical glass lens or prism reflects about
10% of the light incident on one of its surfaces, allowing only about
90% of the light to pass through. Standard coatings of magnesium
fluoride (MgF2) applied to the lens and prism surfaces reduce the level
of reflected light to about 4°, and with substantially reduced ghost
images of bright objects. More sophisticated multi-coatings of 7 to 15
layers further reduce reflected light and can result in total light
transmission through a lens or prism of 99% or more. Some Meade models are multicoated with perhaps the most
advanced multicoatings available, permitting 99+% light transmission
and extremely high image contrast.
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Eye Relief: Binocular users who wear eyeglasses for near- or
far-sightedness may remove their glasses while observing; the binocular
can fully correct for these eye defects. Observers who suffer from
astigmatism, however, may need to wear their glasses to maintain sharp
imaging through the binocular. In this latter case choosing a binocular
with longer eye relief will enable easier binocular observing with
eyeglasses.
Binocular Models
Although the nomenclature associated with binoculars varies somewhat
from manufacturer-to-manufacturer, the majority of binocular
manufacturers use the classifications described here:
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Ultra-Compact and Mini Binoculars generally include objective lenses not larger than
about 32mm in diameter, are of a straight-line roof prism design,
and are foldable for compactness and ease of transport. Mini
binoculars are small, light weight, and highly versatile in their range of
applications: as a moderately-priced gift, for example, it is a rare
person who will not enjoy, and find many uses for, a mini binocular.
Because of their relatively small objective lenses, however, mini
binoculars are not intended for high-resolution birding or other nature
applications. Example: Meade 8x21mm Folding Roof Prism.
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Compact Binoculars utilize porro prisms to invert the image and
usually are styled to form-fit comfortably in the observer's hands;
objective lenses are typically 27mm in diameter or
less. As their name implies, compact binoculars,
while larger than mini binoculars, are relatively
small and easy to carry. For sporting events, as a
gift item, or as a general-purpose travel binocular,
compacts are extremely popular, because, again, for all but the most
advanced applications, compacts provide a good trade-off between
weight, performance, and cost. Example: Meade 10x25 Compact.
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Standard Porro Prism Binoculars: Most binoculars referred to as
general-purpose are standard porro prism models. The typically larger
objective lens apertures, 35mm or more, of these models enable
bright, high-contrast images on the entire range of viewing subjects,
from sporting events, to long-range animal observation in the wild, to
high-resolution study of a bird's feather structure. A moderately-priced,
high-quality, standard porro prism model is a binocular for
almost any observing application. Standard porro prism binoculars are
available in a wide range of specifications and price points. Example:
Meade 10x50 Full-Size Porro Prism.
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Zoom Binoculars offer the convenience of zooming
to higher or lower powers at the touch of a finger.
The Meade 8-24x50 "Triple Zoom" model
permits powers from 8x wide-field to 24x high-power,
and with high-resolution imaging and sharp
image focus at all magnifications.
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Waterproof Roof Prism Binoculars: provide high-quality binocular
resolution and performance. Designed for any application where waterproof performance is desired, but not at a premium cost. Waterproof roof prism binoculars are typically of 25mm objective lens aperture or larger and include sleek, straight-line roof prism
styling. Typical applications are hunting, boating, and camping. The straight-line roof prism is comfortable to hold and offer much of the optical performance of binoculars costing hundreds of dollars more. Meade Waterproof Roof Prism binoculars are also nitrogen-purged to eliminate internal fogging. Example: Meade 10X42 Waterproof Roof Prism.
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Waterproof Phase-Coated Roof Prism Binoculars: provide professional-level binocular
resolution and performance. Designed usually for advanced applications, such as for
serious birders, expeditions, and hunting,; and incorporate the finest optical glasses, multi-coatings, phase and silver coated prisms, nitrogen purging, and multi-element eyepieces. The result is an uncompromised, bright, extremely sharp, high-
resolution images throughout the field of view, and with a level of image
fidelity unobtainable in lesser binoculars. Although premium-grade
standard roof prism binoculars are not inexpensive, they are usually
treasured for a lifetime. Example: Meade Montana 10X42 Waterproof Phase-Coated Roof Prism.
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