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| Old and New. An 1890s 12x30 field glass next to a current Zeiss 8x30. |
Binoculars are the one essential piece of equipment for the birdwatcher and are a great boon to most other outdoor activities. The history of these elegantly simple instruments started in 1608 when the Dutch spectacle maker Hans Lipperhey built a “telescope for both eyes”.
This was essentially
two telescopes joined together, producing an inverted image. Significant
advances in the technology beyond the basic Galilean design of two
lenses at either end of a tube came later in the Seventeenth Century
with the addition of erecting lenses to correct the inverted image.
These additional lenses made the glasses much more practical for
terrestrial use but increased the length significantly.
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| Ernst Abbe 1840-1905. Father of the prismatic binocular. |
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| The Porro prism design. |
In 1854 the Italian
artillery officer Ignazio Porro developed a telescope that erected
the image by using two prisms. The Porro prism design (and other
arrangements of prisms) effectively folds the light-path allowing
much shorter instruments to be made. When independently reinvented by
Ernst Abbe in 1870 (who worked in association with optics company
Carl Zeiss in Jena) this much more compact design formed the basis of
modern prismatic binoculars. During the Twentieth Century advances
in optical understanding and technology included coated lenses to
increase light transmission and colour fidelity, nitrogen filling for
fog and water proofing and more recently fluorite crystal lenses with
their very low dispersion and excellent light transmission.
These days there are
essentially two types of binocular widely available: roof prisms and
Porro prisms. The majority of modern binoculars are of the roof
prism design which has a more slim-line shape and when combined with
internal focusing gives good waterproofing and shock resistance. Schmidt type roof prisms are the most commonly used |
| The Nikon E II 8x30 |
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| Dialyt (left) and Schimidt (right) type roof prisms |
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| Top of the range. A cut away Zeiss Victory FL 8x42 with Schmidt type roof prism |
Although Porro prisms are mostly at the cheaper end of the market due to there simpler construction, there are still some high-quality examples available such as the Nikon E II and the Swarovski Habicht. Modern top of the range binoculars are ultra-precise and constructed under laboratory conditions using exotic materials, complex and time-consuming process and rigorous testing.
Here are some of the
terms associated with binoculars that you might come across and what
they mean.
APO.
Abbreviation of apochromatic. A completely apochromatic lens system
corrects all chromatic aberration (colour fringing). Leica's APO-Televid scopes also have fluorite lens elements.
BK-7 and BAK-4
prisms. These are two grades
of glass, boroscilicate BK-7 (generally in cheaper optics) and barium
crown BAK-4 (delivering better sharpness)
ED, HD, HR. Terms
used to denote higher-quality glass models, HD standing for High
Definition, ED usually standing for Extra-low Dispersion, and HR
standing for High Resolution. These terms are not standardised, one
companies standard glass can sometimes be as good as another's HD.
With Leica and Swarovski HD denotes models with fluorite lenses.
Eye relief. This
is the distance that your eye should be from the eyepiece lens to get
the optimum image. Spectacle wearers often need a longer eye relief
when using binoculars with there glasses on.
Nitrogen filled.
Waterproof binoculars are often
filled with a dry, inert gas (most commonly nitrogen or argon) to
prevent internal fogging.
Phase correction.
Coatings applied to the surfaces of roofprisms to
reduce dispersion, giving sharper images with better contrast and
reduced chromatic aberration (colour fringing).
Cley Spy
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