Binocular Terminology
The brilliance and sharpness of the image you see through a particular
binocular is determined by a number of different
factors, including the combination of these factors. Magnification,
optical coatings and lens diameter are just a few of the factors
influencing how a binocular performs.
However, the single most important performance feature will always be
the quality of the optics. Steiner offers optical excellence through
careful consideration of quality in the glass and lens coatings used,
precision manufacturing processes, and uncompromising quality control.
Please consider the following factors when choosing a binocular:
Magnification (Power)
Magnification is the degree to which the object being viewed is
enlarged. For example, with an 8x42 binocular, the number 8 represents
the binocular "power" or magnification. A binocular of the
power 8 magnifies an image to eight times the size it would be when
viewed by the normal, unaided human eye. The level of power affects
the brightness of an image, so the lower the power of a binocular, the
brighter the image it delivers will be. In general, increasing power
will reduce both field of view and eye relief, which are also
discussed here.
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Diameter of Objective Lenses
The objective lenses of binoculars are the front lenses. The diameter
of one of these lenses, given in millimeters, will be the second
number describing a particular binocular. An 8x42 binocular has an
objective lens of 42mm. The diameter of the lens determines the light
gathering ability of the instrument, with the greater light gathering
ability of a larger lens translating into greater detail and image
clarity. This is especially useful in low light conditions and at
night.
Doubling the size of the objective lenses quadruples the light
gathering ability of the binocular. For instance, a 7x50 binocular has
almost twice the light gathering ability of a 7x35 binocular and four
times the light gathering ability of a 7x25 binocular. This might lead
you to assume that bigger is better when it comes to the diameter size
of the objective lenses, but in reality the size of the lens must be
considered along with exit pupil and intended usage to determine the
best binocular for you.
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Field of View
The size of the area that can be seen while looking through a pair of
binoculars is referred to as the field of view. The angular field of
view is indicated on the outside of the binocular, in degrees. The
linear field of view refers to the area that can be viewed at 1,000
yards, and is expressed in feet. A larger field of view translates to
a larger area seen through the binocular.
Field of view is related to magnification, with greater magnification
creating a smaller field of view, in general. A large field of view is
especially desirable in situations where the object viewed is likely
to move, a large terrain area is viewed, or when the user is moving.
You can use angular field to calculate the linear field by multiplying
the angular field by 52.5. For example, if the angular field of a
particular binocular is 8° then the linear field will be 420 feet,
i.e. the product of 8 x 52.5. Or, you can divide the linear field by
52.5, e.g. the binocular has a field of view of 390 feet at 1,000
yards, so 390 divided by 52.5 is 7.43°
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Exit Pupil
The diameter, in millimeters, of the beam of light that leaves the
eyepiece of a pair of binoculars is the "exit pupil". The
larger the exit pupil, the brighter the image obtained will be. Having
a large exit pupil is advantageous under low light conditions and at
night. For astronomical, marine or low light applications, the exit
pupil of the binocular should correspond with the amount of dilation
of your eye's pupil after it has adapted to the dark. This number
will be between 5mm and approximately 7.5 mm. 7 to 8mm of dilation is
normally the maximum amount for the human eye, and this number tends
to decrease with age.
To calculate the exit pupil, divide the size of the objective lens by
the magnification of the binocular. For example, the exit pupil of
7x50 binoculars is 50 ÷ 7 = 7.14mm.
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Eye Relief
This refers to the distance, in millimeters, that a binocular can be
held from the eye and the full field of view can still be comfortably
observed. Eyeglass wearers in particular benefit from longer eye
relief. Normally, a minimum of 15mm will be needed to use the
binocular while wearing eyeglasses.
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Inter Pupil Distance or "IP" Distance
This refers to the distance, in millimeters, that a binocular
can be used by users with both eyes viewing a complete viewing
picture. In other words minimum distance for viewers with narrow eye
distance and the maximum distance for viewers with eyes that are
farther apart. Normal optics industry standards range at a minimum of
58 to a maximum width of 72mm. To accommodate a wide range of users,
most Steiner models offer a minimum of 56 to a maximum of 75mm or
more
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Brightness
The binoculars' ability to gather and transmit enough of the
available light to give a sufficiently bright and sharp image defines
its brightness. The brightness of a binocular also enhances color
differentiation in the image observed. R.B.I. (Relative Brightness
Index), Twilight Factor and R.L.E. (Relative Light Efficiency) are
common indices used in the binocular industry, but are all somewhat
flawed in their design and often prove fairly meaningless as both high
quality and low quality binoculars will gather the same result.
Brightness is one criteria to be considered when purchasing
binoculars, but is not always the most important factor. Given in
order of importance to the overall brightness of a binocular, the
following factors are worth investigating: objective lens diameter,
magnification, the type and quality of the objective lens glass, type
of lens coatings and type of prisms used. In general, large objective
lenses, low magnification and fully multicoated lenses are the most
desirable. At Steiner, all low light binoculars are tested to perform
to the highest "light transmission" this means that light is
brought into the objective side and then measured at the exit, the
eyepieces. The percentage remaining is "light transmission".
Good low light binoculars will have high light transmission across the
whole spectrum of color, evenly to produce good color fidelity and
best low light results. Binoculars with spikes in their transmission
at certain wave lengths are designed for brightness and contrast,
Steiner also offers models for these types of specific applications.
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Resolution
Resolution is a measurement of the binoculars' ability to
distinguish fine detail and produce a sharp image. Better resolution
also delivers more intense color. Resolution varies in relation to the
size of the binoculars' objective lenses. Generally, a larger
objective lens will deliver more detail to the eye than a smaller
objective lens, regardless of the magnification of the binocular.
However through technological advancements in production, there are a
number of compact models available that deliver detail as good as
larger models. Actual resolution is determined by the quality of the
optical components, the type and quality of the optical coatings,
atmospheric conditions, collimation (i.e. proper optical alignment),
and the visual acuity of the user.
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Contrast
Refers to the degree to which both dim and bright objects in the image
can be differentiated from each other and from the background of the
image. High contrast helps in observing fainter objects and in
discerning subtle visual details. The same applies to differences in
color especially in darker or difficult light conditions. High quality
optical coatings provide better contrast in an image. The other
factors affecting contrast are: collimation, air turbulence, and
objective lens, prism and eyepiece quality. Steiner offers several
high contrast coatings such as the Predator Series for spotting and
viewing wildlife against a foliated or wooded background or the
Navigator Series which reduce haze and excessive blue light to product
a sharp high contrast image while viewing over water or similar
conditions.
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Close Focus
The distance between the binocular and the nearest object you can
focus on, while maintaining a good image and sharp focus, defines the
close focus distance of a binocular. This term is normally applied
only to center focus models which may need to focus both near and
farther distances. Close Focus distance is a critical issue with bird
watchers and observers of close subjects that tend to move around at
varying distances quickly. Steiner offers "Fast close
focusing" on its lines of roof prism binoculars including the
Merlin, Wildlife Pro, Peregrine and Predator Series.
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Lens Coatings
The optical elements of the binocular are coated to reduce internal
light loss and glare, which in turn ensures even light transmission,
resulting in greater image sharpness, brightness, color fidelity and
contrast. Choosing a binocular with good lens coatings will ensure
greater satisfaction with the binocular you select. Lens coatings
range in quality or applications as follows: coated -- fully coated --
multicoated -- fully multicoated. Coated lenses are the lowest
performance and basically will not result in much satisfaction. Fully
coated lenses are quite economical and can work well for you,
depending on your needs. Multicoated or fully multicoated lenses are
both very good choices. Fully multicoated lenses give the best light
transmission and brightest images, and are therefore the most
desirable. Steiner offers only multicoated and fully multicoated
lenses using a variety of proprietary mineral source substances to
produce outstanding viewing results.
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Prisms
A binoculars' prisms serve to invert the image and come in one of
two basic designs: Roof or Porro prisms. By design, roof prisms are
more lightweight and compact, for portability. Porro prisms are
designated either BK-7 or BAK-4. Both are economical and highly
effective designs. The finer glass in the BAK-4 design is of high
density and virtually eliminates internal light scattering, producing
sharp, well defined images. Steiner uses only BAK-4 prisms in their
binoculars.
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Construction
A critical factor in the performance of any binocular is its
construction. The security of the barrel alignment and proper internal
mounting and alignment of the optics are crucial to producing a
binocular that's mechanically reliable, smooth functioning and
long-lasting. This is a special strength in Steiner models: By
starting with the most durable design and then combining that with
very strong materials that will hold the optical elements in place
securely not allowing them to shift, therefore not to cause flaws or
discomfort in the viewing experience. The proper design, materials and
construction will also assure that the binocular is sealed to not
allow intrusion of water or moisture.
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Collimation
Collimation is the alignment of the optical elements of the binocular
to the mechanical axis. Good collimation prevents eyestrain,
headaches, inferior and double images while improving resolution.
Unfortunately, proper collimation is almost impossible to achieve in
very low priced binoculars that lack quality components and design.
All Steiner models are collimated to exceed universally acceptable
standards so as to produce a very comfortable viewing experience for
longer periods of time.
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