Monthly Archives: December 2010

BINOCULARS EXPLAINED INDEX

Aperture  Armoring of binoculars           Aspheric Lenses           BaK-4 (barium crown)             Basic design of binoculars: Porro prisms or roof prisms         BK-7 (borosilicate)          Chromatic Aberration         Close focus       Coating of lenses     Collimation      Contrast    Depth of field      Dielectric Coatings       Diopter         Exit pupil           Eye relief         … Continue reading

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Optical glass

Three types of glass are currently used for making lenses and prisms: BK-7, BaK-4 and SK15. SK15 is the highest quality glass available and has only recently been introduced to optics of binoculars (expensive). I found only two brand names … Continue reading

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Lenses and prisms

The optical elements of a pair of binoculars consist of lenses and prisms and could be which could be as much as 16 elements in total. Lenses are the optical elements through which the light travel, from the big ones … Continue reading

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Eye relief

For every pair of binoculars, there is an optimal distance between your eye and the eyepiece, which is called eye relief. The eye relief of a binocular is the distance your eyes are allowed to be away from the eyepieces … Continue reading

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Depth of field

The “depth of field” of a pair of binoculars refers to its ability to keep objects further towards the background and closer towards the foreground in focus without you having to adjust the focus. Stated in another way: Once you’ve … Continue reading

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The twilight factor

Some manufacturers claim that a combination of the magnification and objective lens size makes a greater contribution towards image brightness in dim light than the diameter of the exit pupil. This is known as the “twilight factor”, and is calculated … Continue reading

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CLOSE FOCUS of the binocular

All binoculars can focus on any object far away, but focusing up close is a different matter. Some binoculars cannot focus closer than 10 meters/yards, whereas some can focus as close as 1 meter! The ultimate close focus binocular, the … Continue reading

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EYE RELIEF of the binocular

Do you wear glasses? In that case the “eye relief” has to be at least 15mm. and if that’s not the case, you could end up with a pair of binoculars with severely restricted field of view. Binoculars ideal for … Continue reading

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OPTICAL GLASS AND COATINGS of the binocular

The object is to get as much light as possible entering the binoculars through the objective lenses eventually entering the viewer’s eyes. This is achieved by the optical quality of the glass used for the lenses and prisms, as well as … Continue reading

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FIELD OF VIEW of the binocular

Field of view  (FOV) is the width of the view you see through your binoculars, measured in feet at 1000 yards, or meters at 1000 meters. It can also be expressed at angle of field of view (e.g. 7 degrees). … Continue reading

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