What is the diameter (objective size) of a pair of binoculars?
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. Hence, a 7x42 binocular has an
objective lens of 42mm.
Objective size (diameter) is
marked on many pairs of binoculars.
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.
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.
What is the eye relief for binoculars?
relief is the distance (in millimeters) that a binocular can be held
from the eye and the full field of view can still be comfortably
observed. It measures the spacing from the last surface of the eye lens
of an eyepiece to the plane behind the eyepiece where all the light
rays of the exit pupil come to a focus and the image is formed. Your
eye should be positioned here to see the full field of view of the
Eye relief should be at least 10mm, 15mm for the best comfort, maybe more if you wear eyeglasses.
your binoculars so they are just in front of your eyes to take
advantage of its eye relief. You’ll lose field of view if you place
your eye farther away and may even move your eye out of the beam of
light from the eyepieces. Getting too close will prevent you from
blinking and may also cause a black ring to appear around the field of
What is the field of view of a pair of binoculars?
binoculars field of view is the width of the area you can see. It’s
usually described in two ways: angular field of view and linear field
Angular field of view is the true angle seen through the optics and is usually measured in degrees. The
linear field of view is the width of the area seen and it’s given in
feet observed at 1000 yards. A larger number for either angular or
linear field of view means you see a larger area.
Angular and linear field of view
field of view can be used to calculate the linear field of view. Just
multiply the angular field by 52.5. For example, if the angular field
of a particular binocular is 8 degrees, then the linear field at 1000
yards will be 420 feet (8 x 52.5).
of view is related to magnification. In general, a greater
magnification yields a smaller field of view. A large field of view is
especially desirable in situations involving motion – birds in flight
or you are on a boat or in a car.
I want to know: what determines the brightness of the image in my binoculars?
Brightness is important to consider when comparing different pairs of binoculars. It impacts your overall ability to see things (sky objects, animals and landscapes) in low light. The quality of the image contrast and color also depend on brightness.
The physical factors determining a given pair’s image brightness are the objective diameter or front lens size, the light transmission of the optics and coatings used on the lens surfaces and prisms throughout the binocular and the magnification. A larger objective will gather more light. Modern coatings allow more light to pass through the optics. When comparing two pairs of the same objective size a lower magnification will have greater brightness (a 7x50 binocular will have a brighter image than a pair of 15x50s).
If you want to compare numbers before looking through actual binoculars, there are several calculations used for brightness or the effectiveness of binoculars in low light. The first is twilight factor, found by multiplying objective size by magnification and taking the square root of the resulting product. (The twilight factor for a pair of 7x50s is 19.) The larger the twilight factor, the easier it is to see detail in low light. A second measure is the relative brightness index, RBI, which is the square of the exit pupil (exit pupil is the objective size divided by the magnification). Those same 7x50s would have an exit pupil of 7 and a RBI of 51. Finally, RLE is used when comparing coated to uncoated (vintage) binoculars. Just increase the value of the RBI by 50 percent. The RLE for coated 7x50s is 77. Binoculars with higher RBI and RLE numbers deliver brighter images.
CHOOSING THE BINOCULAR BEST SUITED FOR YOUR INDIVIDUAL NEEDS IS FUNDAMENTAL IF YOU WANT TO ACHIEVE THE BEST RESULTS.
Every binocular is identified by two numbers, for example 8x21, 10x50 and so on.
The first number before the "x" indicates its magnifications. A 8x21 binocular brings objects 8 times closer. A lOx5Omm binocular brings objects 10 times closer.
The second number after the "x", indicates the measurement of the diameter in millimeters of the objective lens (the lens furthest from the eye). This size determines the amount of light which reaches the eye and the brightness and definition of what you see. The greater the objective size, the greater the brightness.
The field of view is a measurement of the width in feet or meters that can be seen through the binocular, at 1000 yards or meters.
Coated, fully-coated, multicoated, fully-multicoated, phase-coated binocular optics. Why are these important?
Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. Binoculars may have 10-18 glass surfaces, each one contributing to scattered light, so coatings make a big difference in what you see. Coated optics will have a less shiny, even dark appearance when looking into the barrel or tube. You may see a greenish, bluish or brownish tint as well. Most coatings are magnesium fluoride or calcium fluoride and work by destructively interfering with certain colors or wavelengths of light, eliminating their reflection. More light gets into your binoculars and more light is able to pass through to your eyes. Almost all modern consumer optics have some kind of coating on most of the optical elements. However, there are different levels and qualities of coatings.
Coated optics means that at least one of the major optical elements has a coating on at least one surface. Fully-coated means that all lenses and glass surfaces have a coating layer. Multicoated means that at least one of the major optical elements in a fully-coated binocular has multiple coatings of antireflective compounds on at least one surface. Fully-multicoated means all glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95 percent, bright, sharp and contrasty images.
Some roof prism binoculars feature phase coatings. Because the light travelling through the prisms in these binoculars takes a slightly different path in one prism, it's shifted by one-half its wavelength and contrast is lowered. By applying a special coating that compensates for this shift, the contrast loss is eliminated, giving phase-coated binoculars brighter and more vivid images.
What is the exit pupil for binoculars?
exit pupil is width of the beam of light leaving the eyepiece. It’s
usually measured in millimeters. A large exit pupil is advantageous
under low light conditions and at night because the larger the exit
pupil, the brighter the image. For astronomical applications, the exit
pupil of the binocular should correspond with the amount of dilation of
your eye's pupil after it is fully dark-adapted. This number will be
between 5mm and 9mm. 9mm of dilation is the maximum amount for the
human eye. Maximum dilation tends to decrease with age. By age 50, the
exit pupil may be close to 5mm. An exit pupil larger than your dilation
just wastes light from the objective, since the outside of the beam
just falls on your iris and doesn't go into your eye.
The exit pupil is
the width of the
beam of light
from the eyepiece.
calculate the exit pupil, simply divide the size of the objective lens
by the magnification of the binocular. For example, the exit pupil of
7x42 binoculars is 42 / 7 = 6mm.
What is the resolution of my binoculars?
Resolution is a measurement of a binocular’s ability to distinguish fine detail and produce a sharp image. Better resolution also delivers more intense color and often higher contrast.
Resolution varies in relation to the size of the binocular's 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. Actual resolution is determined by the quality of the optical components, the type and quality of the optical coatings, atmospheric conditions, collimation (proper optical alignment), and the visual acuity of the user.
Allows you to focus precisely on far and near objects.
These binoculars have a special construction without the focus ring and can therefore provide bright images from 20m/60ft to infinity. They are ideal to follow fast moving targets, for example while watching a sport event.
In these binoculars, both the right and left eyepiece have an individual diopter ring. To focus them, it is therefore necessary to close one eye at a time and rotate the other eyepiece until the image is sharp, then repeat for the opposite side while looking at the same target. This system provides unsurpassed precision in focusing adjustments and is more reliable and accurate than the standard center focusing, thus enabling the user to get the highest performance out of his binoculars
Some binoculars called "wide angle" have special optics that add extra width to what you see. While a standard 10x50mm binocular has a field of view of approximately 90mt (300ft), a lOx5Omm binocular wide angle has a field of view of 120mt (400ft).
Zoom binoculars have two power numbers (e.g. 8x-24x) which represent a range. You can focus on anything, at any power between 8 and 24.
Designed for nautical use or wet environments, these binoculars provide excellent luminosity and are impervious to water thanks to their nitrogen purged construction. Some models also include compass and floating strap.
Binoculars with high magnification and very large objectives greater than 60mm (2.36"), these binoculars are ideal for astronomy or general observation.
How do I mount my binoculars on a tripod?
Most Celestron binoculars have built-in 1/4x20 female threads (socket) to use with Celestron’s binocular tripod adapter or similar aftermarket accessory to support your binoculars.
For most pairs, look at the front of the central hinge for a cap that may or may not have the Celestron logo on it. This cap will either unscrew or pry off to expose the 1/4x20 socket. Attach the binocular tripod adapter, which in turn will be attached to a standard photo tripod with a 1/4x20 screw.
The 80mm and 100mm SkyMaster pairs have a tripod adapter rod that has a similar socket. Simply screw your tripod’s 1/4x20 bolt into the rod’s threaded socket.