About Binoculars
For Binocular Terminology, please see HERE
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General Description: A binocular is an optical precision instrument providing a magnified 3-D-picture to the eyes of the user making the observation object appear closer.
Binoculars always have two tubes whereas telescopes have one tube and provide a 2-D-picture only.
Difference is made between two technical systems which can be recognized at first glance by their typical design: |
- Porro prism (left picture)
- Roof prism (right picture)
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The optical process
The light-rays hit the objective lens go through the set of prism thereafter meet the ocular which creates the actual magnification and reach the eye by the exit pupil
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 Important: The picture made by the objective lens
is reversed and upside down. The function of the prism is to reverse the picture.
Prisms also reduce the construction
size of the binocular. |
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Porro prism
Named after Ignatio Porro who first used this technique in Italy in 1854 to reverse the picture which comes reversed from the objective lens
The system allows a perfect 3D image because objective lenses are wide set.
While passing the prism the light is not changed, the optical quality stays very good.
In a special procedure STEINER connects the prisms with glue; this means less glass-to-air surfaces and additional ruggedness |
Superior light transmission as the light has to pass less glass-to-air-surfaces.
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Roof Prism
This kind of prism is named after its distinctive form, similar to the edge of a roof.
Binoculars with roof prism system normally have a slim and straight construction.
Because of the construction of these kind of prism, colour fringes have to be corrected with additional special coatings and lenses.
High-precision mechanism necessary for focussing. |
Roof prisms consume more light and
require complex technology for
achieving high-precision images.
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Coating
Visible light is an electromagnetic radiation with different wavelengths, determining which colours we see.
When light passes normal glass up to 10% gets lost through reflection.
Coatings reduce reflections and increase light transmission so more light can reach the eye.
Quality and efficiency of coatings depend on coating technology used and the number and combination of coating layers.
Only of all lenses and prisms are coated a light transmission of higher than 90% is possible. |
Important:
Coatings reduce changing of colours
and increase light transmission
(Example: High-Definition-Optics from STEINER)
Low-Quality binoculars absorb
up to 60% of the light |
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Sports-Auto-Focus
Once adjusted everything will be sharp and clear from about 20m to infinity.
A tremendous advantage especially in bad light conditions, in the dusk and at sea.
Moving objects can be observed without refocusing at varying distances
Very comfortable use in the frosty cold, while wearing gloves or in the rain.
Basic setting
Search a point far away from you and adjust both oculars - one after the other - until you see a sharp picture
The basic setting you have to do only once. |
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Centre Focussing
In most cases the focussing is done by moving a lens or the ocular with the help of a centre focus/focus wheel.
Usually there is a ring on the left or right ocular to adjust the individual difference in eye sight. Most people have a difference in their eye’s performance |
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Sports-Auto-Focus (Porro-System)
vs. Centre focus-adjustment (Roof system)
Advantages of the Sports-Auto-Focus:
Once adjusted everything will be sharp and clear from about 20m to infinity.
Perfect sharp picture even at fast varying distances.
Extremely rugged
Superior use at day and night and at sea! |
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Oculars for eyeglass wearers
By reduction of the distance between eye and ocular you can also use the binoculars with eyeglasses.
Foldable eyecups reduce the eye distance.
The small projection of the folded down eye cups enables a noiseless, agreeable position of the ocular to the eyeglass.
Eyeglass wearers set each eyepiece to “0”
Scratching of the eyeglass is not possible! |
In this case: reduction of the eye distance
by folding down the eye cups.
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The Figures on a Binocular
Binoculars are specified by numbers such as 7x50.
The first number is the magnification, the second number is the objective diameter in mm. |
Example 7x50: A 7x50 binocular has a magnification of 7 times and an objective
diameter of 50 mm.
Important: The figures are mathematical terms only, not quality features. If you want to know the quality of a binocular, you should check the coating, ruggedness and the optics! |
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Objective Diameter
The objective lenses of binoculars are the front lenses and their diameter is specified in millimetres, e.g. 7x50 => 50mm.
Larger objective lens diameter means more suitable for use in low light and at night |
Example 7x50:
Objective Diameter = 50 mm |
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Magnification
The magnification of most of the binoculars is between 7 and 10 times.
In general: for a distance far away you need a higher magnification.
Optimum for use on a boat is a 7 times magnification (steady picture). |
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Exit pupil
The bright spot seen from a distance of 25 cm behind the ocular. The diameter of this spot is measured in mm.
The exit pupil is important for the use of the binocular under difficult light conditions.
Binoculars for the marine use should have a exit pupil as big as possible e.g. 7x50.
Daylight: During the daylight the diameter of the human pupil is 2 until 3 mm.
That means that only a part of the light reaches the retina. The quantity of light is higher than effectively needed.
Twilight / night: In the dark the pupil is growing up to approximately 7mm. It can absorb all of the light which comes through the 7,14 mm exit pupil. The picture seems much brighter.
Important: While growing older the ability of the pupil to be wide open decreases. |
Example 7x50:
Exit pupil = 50 / 7 = 7,14 mm
Important; Exit pupil =
Objective diameter / magnification |
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Geometrical luminosity
Like the twilight factor the geometrical luminosity also is a mathematical term.
Combined they give an indication if the binocular is suitable for difficult lightning conditions:
The higher the value, the higher the brightness in the twilight! |
Example 7x50:
Geometrical luminosity = (7,14)2 = 51,0 |
Twilight Factor (TF)
It is calculated with magnification and diameter.
The result is a mathematical term.
It can- in combination with the size of the exit pupil- be an indication for the use of the binocular under difficult light conditions. |
Example 7x50:
Twilight Factor = √ 7 x 50 =18,708
√ magnification x diameter |
Field of view (FOV)
The linear FOV determines the area seen at a distance of 1000 m
That means: the FOV describes the observing field in a distance of 1000m from the observation point.
The FOV is no mathematical term. It is determined by the binocular construction |
Example Commander V 7x50:
FOV = 130m
The larger the FOV, the smaller the magnification |
The Housing
Binoculars should be constructed in a rugged and waterproof compact construction method.
Use of reinforced non-corroding polycarbonate: Macrolon® of BAYER.
Advantage: extreme rigid and unbreakable, absolute shock-resistant. |
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Nitrogen Pressure System
Binoculars filled with regular (humid) air will fog when temperature changes rapidly. The fog (water) will leave dots and spots on the surface of lenses and prisms and the optical system will be damaged.
With STEINER´s unique high-tech solution, condensation inside binoculars is impossible. Even temperature variations from -40° to +80° C do not influence the functionality of nitrogen-pressure-filled STEINER binoculars. |
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Sealing
Nothing can get inside the binocular (dust humidity, water …). Fungus cannot penetrate the binocular and ruin the optics.
Professional binoculars also maintain the sub pressure e.g. in planes.
The binocular is water pressure proof down to 5m (depends on the binocular model).
(all STEINER marine-binoculars are water pressure proof) |
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Steiner Nano Protection
Offers unsurpassed clear vision at any time.
Gives the lenses a dirt and water resistant surface shield, protecting them against aggressive environment effects. Water and dirt roll off the objective and ocular lenses.
Rain, snow and moisture etc. just disappear from the field of view. Cleaning is considerably simplified.
The ultra thin surface treatment on the ocular and objective lenses is extremely robust. |
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Tips for selecting the right binocular:
Before buying a binocular you must know, when you use it.
Most important criteria:
Optical performance
Ruggedness and water proofness
Size and weight
Handling |
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