Bresser National Geographic PORRO Mode D'emploi page 10

Binoculars ABC
MAGNIFICATION
The magnifi cation value always is mentioned fi rst in the model name (e.g. 7x50). With a magnifi cation of
7x, the observed object appears one-seventh of the distance away that it really is. Zoom binoculars have an
adjustable magnifi cation. For example, the amplifi cation can be altered between 8x and 24x magnifi cation
in an 8-24x50 model.
OBJECTIVE DIAMETER
The lens pointing towards the object is called the objective lens. In the model name (e.g. 7x50), the second
number stands for the objective diameter in millimeters. The objective lens diameter is an indicator of the
amount of light that can enter the binoculars.
An objective diameter of 20 mm is suffi cient for observations during the day. In twilight conditions, an objec-
tive diameter of 50 mm or larger is recommended, as the lenses can gather much more of the remaining
light.
TRANSMISSION
The value of the ability to let light pass through optical systems is called transmission.
OCULAR
The ocular is on the side of a pair of binoculars pointing towards the eye and is often composed of three to
six single lenses that form an achromat. The ocular is one of the factors that determines optical quality (i.e.
color fi delity, sharpness and image distortion).
EYEPIECE FOR SPECTACLE WEARERS
An eyepiece for spectacle wearers allows for a full fi eld of view with and without eyeglasses. Its main aim
is the adjustment of the distance from the eye to the ocular (eye relief). When an observer sees a circular
image through the binoculars, the eye relief is set correctly. Without glasses, the optimal distance can be
adjusted by three different ways:
eyecups with a sliding mechanism, eyepieces with a twist mechanism and folding rubber eyecups. For use
by spectacle wearers, these eyecups should be folded down or brought to the fl atest possible position; non-
spectacle wearers should use binoculars with eyecups in their extended positions.
BINOCULAR
Optical systems with two oculars are called binocular (hence the name binoculars).
MONOCULAR
Optical systems with one ocular are called monocular.
TWILIGHT OUTPUT
The twilight output number quantifi es binocular visual performance and detail visibility in twilight conditions.
Formula:
√Lens diameter x magnifi cation
10