Category Archives: BINOCULAR BASICS

Binocular Basics index

Adjustable eyepiece  Aperture  Armoring of binoculars  Bak-4  BK-7  Basic design  of binoculars Brightness of image in dim light  Central focusing  mechanism Central focusing wheel  Central focusing knob Central focusing toggle  Close focus  Coating of lenses Collimation  Depth of field  Diopter  … Continue reading

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Image brightness in dim light

Three factors determine the brightness of the image in dim light: The quality of optical coatings, a factor determined by the size of the exit pupil and finally a factor determined by the objective lens size and magnification. Lens coatings: … Continue reading

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Depth of field

The “depth of field” of a binocular 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 focused on an … Continue reading

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Focus speed

If you need the binoculars for watching wild animals, in particular birds, the speed of focus is important. While following a bird in flight, you need to change the focus all the time if the bird gets closer or further, … Continue reading

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Close focus

Focusing at a distance is no problem for any pair of binoculars; focusing at close range, however, is a totally different matter. This is important, since sometimes you will be in a situation where close focus is important, in particular … Continue reading

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Field of view

Another set of technical detail which is imprinted on the binoculars, could be something like this: 367 ft. at 1000 yds. This is the field of view (FOV), the width of the view at the particular distance. In this case … Continue reading

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Coating of lenses

Not all the light arriving at the objective lenses at the front actually passes through – some is reflected. This happens with the light finally arriving at the viewer’s eyes at the other end of the binoculars as well – … Continue reading

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Optical features of a binocular

All binoculars have the same set of optical features, whether small, normal size or big. These include lens coatings, close focus ability, field of view (FOV), focus speed, depth of view and ability to produce a bright image in dim light. These … Continue reading

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Armoring of binoculars

Some manufacturers cover their instruments as far as possible in protective rubber or synthetic housing. These binoculars are known as “armored binoculars”. This protects the instrument from scratches and – very important – from bumps, which could harm the inner … Continue reading

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Prism glass

Type of glass the prisms are made of: Bak-4 is a high density glass, of better optical quality than BK-7 and by far the best for making binocular prisms. Fortunately nowadays even cheap binoculars have Bak-4 prisms, whereas that would … Continue reading

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