Bresser FERNGLAS, Operating Instructions Manual

Page: 11 / 44

EN
11
The result is evaluated purely mathematically and is only of interest when comparing differing types of bin-
ocular (e.g. 8x30, 7x50 and 10x50). The number calculated disregards binocular performance increase
due to optical treatment, top-quality glass types and the like. See luminous intensity for more information.
DIOPTRIC COMPENSATION
In binoculars with centre wheel focusing, the right eyepiece (in zoom binoculars, usually the left) can be
adjusted.
This compensates for the user’s eyesight defi ciencies. In models with single eyepiece adjustment, both
eyepieces can be turned, as they also serve to adjust the focus.
RUBBER ARMOUR
Binoculars with rubber armour are advisable for rugged, professional uses. The black or olive green rubber
armour protects the instrument against splashing, dropping and impacts. The armour on our instruments has
fast colouring and is proof against sunlight.
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) quantifi es 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: 50/7 = 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 / magnifi cation)
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 fi eld of vision over 120 m/1,000 m is called ‘large fi eld’, and one with a fi eld of vision
over 140/1,000 m is ‘wide angle’. Wide angle instruments are particularly suitable for viewing moving ob-
jects such as footballs or horses.