Binocular ABC

Magnification and lens diameters

8x21, 12x26 or 7x50 – what does it all mean? The first figure is the magnification factor; this is the amount by which an object will appear larger or nearer compared with a naked eye observation.
The second figure is the diameter of the objective lenses (front lenses). The larger the number, the greater the amount of light that can enter the instrument and therefore the brighter the image.

Field of view

The field of view is generally stated in meters at 1000 meters, or as an angular figure. So if the field of view is stated as 96m at 1000m, then at a distance of one kilometer the user will see an image 96 meters across. The greater the field of view, the better the instrument for surveying a large area or a fast-moving object.

Exit pupil

The exit pupil describes (in millimeters) the size of the image that is presented to the eyes at the observer’s end of the binoculars (the oculars). The larger the exit pupil the brighter the image will appear. From a distance of a few centimeters the exit pupil can be discerned as a bright, sharply delineated circle.

Twilight factor

The higher the binoculars’ twilight factor the more suitable they are for observations in fading light. A twilight factor of 22.4 means that, in theory, one could still recognize an object adequately at a distance of 224 meters.

Lens coating

This is the process of treating the surface of the lenses (by metallic salt vapor deposition) to prevent unwanted reflections and enhance the light transmission to achieve a brighter, clearer image. The greater the surface of the lens that is coated, the higher the image quality.

FC - Fully Coated:
simple coating on all external surfaces of the lens

MC - Multi Coated:
multiple coatings on at least one external surface of the lens

FMC – Fully Multi Coated:
multiple coating on all external surfaces of the lens

Prism systems

Binoculars made with traditional Porro prisms can be readily identified by their relatively short and squat form. The path of the light is broken a number of times, as in a reflex camera. Roof prisms have enabled newer designs that, by using precisely ground prisms, achieve an almost linear light path. Binoculars with this construction are particularly slim and convenient. Although there are no differences in quality between the two designs, the manufacture of roof prisms is more demanding.

Focusing systems

The central focus system uses a centre drive, an adjusting wheel mounted on the centre axis that moves both ocular lenses in the same direction at the same time to sharpen the image. With ocular adjustment (individual focus), turning the scale ring on each ocular adjusts the sharpness of the image for each eye. To balance the different powers of vision of each eye and to enable observation without spectacles, many binoculars also have a dioptre adjustment.

Binocular choice

The ideal binoculars suitable for every conceivable mission do not exist. In choosing binoculars, considerations of size, weight, quality and of course price all have their part to play.
The chief criterion should be, however, the application that the binoculars are to be used for. Whilst a yachtsman will place an emphasis on wide field of view and waterproof qualities, powerful equipment that also has good twilight properties will be needed for observing animals in the wild. Compact (folding) binoculars with low magnification are lightweight products that fit in a pocket and are ideal for travel, hiking, sports and cultural events.

COMPASS ABC

The magnetic hiking compass is a measuring instrument for determining direction. It must be held horizontal so that the degree scale can rotate freely and indicate north. Magnetized objects and objects made of metal can cause false readings. When taking bearings, do not place the compass on bridge railings or other items made of metal, and never use it adjacent to your mobile phone.

Orient the map

As a rule, the top of any map is north. To determine a route direction the map must therefore be oriented towards north.

• Open the compass fully.
• Lay the compass with its scale along the edge of the map.
• Turn the sight glass so that the yellow line forms a line through the sight and cross hairs.
• Finally turn the map with the compass so that the north pointer corresponds with the long yellow line.

The map is now oriented north, and the map and environment are fully aligned for direction.

Read off route direction and head for destination

First orient the map north.

• Find your present location and destination on the map.
• If necessary sketch a line between your actual location and the destination on the map.
• Lay the compass scale along this line.
• Turn the sight glass so that the long yellow line corresponds with the north pointer.
• Using the sight and cross hairs the route direction can be found across the surrounding country. Set the sight and cross hairs up vertically. Orient the compass so that the long yellow line corresponds with the north pointer. Then using the sight and cross hairs aim for a landmark (e.g. a church spire or mountain peak) that lies on the line of sight (= route direction).

Go to this point and on arrival, keep the set route direction and head for the next landmark (and so on until you reach your destination).

Walking along a route

This method is used if the destination can no longer be seen during the walk, e.g. when traversing a fold in the ground.

• Just before losing sight of the destination (e.g. peak), take a sighting on the destination and adjust the long yellow line so that it corresponds with north.
• Now head in the direction of your destination and keep a constant check that the yellow line and north still correspond.

Determining position

First orient the map north as described earlier.

• Take a sighting of a target (e.g. a tall building) that is indicated on the map and adjust the long yellow line towards north so that the line corresponds with the north pointer.
• Lay the compass on the map and adjust it so that the scale intersects with the target and the long yellow line still corresponds with the north pointer.
• Next project a line from the target along the scale in the direction of your own approximate position.
• Repeat this procedure for another target that lies in another direction. The exact present location is at the point on the map where the two lines cross.

Determining distance

The centimeter scale along the edge of the compass is marked with figures 2 000, 4 000 and 6 000. On a 1:50 000 scale map these values can be directly read off in meters. On maps drawn to other scales the distance can be calculated using the centimeter scale and the scale details of the map.