Field Of View - Bresser National Geographic 7-21x40 Instrucciones De Uso

COLLIMATION (double image)
This term means the parallel alignment of both halves of a pair of binoculars. If an instrument is subjected to
any major impact or dropped, the prisms may become misaligned, making the instrument out of collimation.
Observation through such an instrument yields double images, as the contours seem to the observer to be
displaced.
Readjusting for eyesight can compensate minor maladjustment of this kind. However, a headache may result if
such an instrument is used for any length of time. Such instruments should always be sent in for repair.
LUMINOUS INTENSITY (general information)
The luminous intensity (LI) quantifies the brightness of a pair of binoculars. Under normal circumstances, a 7x50
pair (LI 51) yields much greater intensity than a 10x50 pair (LI 25). To exploit the greater intensity of 7x50s, the
user's pupils must be dilated to the size of the instrument's exit pupil [EP] (in 7x50, EP = 7.14). In people over
age 50, the pupil often doesn't fully dilate. In such cases, the higher luminosity cannot be exploited.
LUMINOUS INTENSITY (geometric)
The geometric luminous intensity is the mathematical brightness value of a pair of binoculars. Models with
higher luminous intensity are especially suited to observation at twilight.
Formula for calculating luminous intensity:
(Lens diameter / magnification)
2
e.g. (50/10) 2 = 5 x 5 = 25
This calculation disregards any features improving performance, such as BaK-4 prisms, multicoating or optical
glass quality.

FIELD OF VIEW

This is understood to mean the visible image at a distance of 1,000 metres from the object being observed. This
measurement is usually given in metres.
If given as an angle, 1° = 17.5 m.
An instrument with a field of vision over 120 m/1,000 m is called 'large field', and one with a field of vision over
140/1,000 m is 'wide angle'. Wide-angle instruments are particularly suitable for viewing moving objects such
as footballs or horses.
TRIPOD CONNECTION
Many binoculars have a tripod thread built in. These binoculars can be screwed onto a tripod using an adaptor,
which guarantees a static image.
COATING
Normal optical lenses reflect part of the light falling on them.
This causes a loss of light and a reduction in contrast due to light scatter.
Coating the lenses by steaming a reflection-reducing mineral layer onto them greatly reduces reflection and
increases light transmission (permeability).
This is a coating of 7 to 15 layers of ruby-coloured mineral steamed onto the objective lens. It increases image
contrast in sunlight, as the red spectrum is mainly filtered out. However, the luminous intensity of the instru-
ment is reduced by approximately 7%. Fully coated binoculars let approximately 60% more light through than
uncoated ones. Special coatings (UV, multilayer) can be used to increase luminous intensity even further.
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