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Feature Explanation
Magnification
Prismatic binoculars are defined to a combination of numbers, here 9 x 60 mm.
The figure 9 indicates the magnification factor and the 60 represents the diameter
of the front lens in millimetres. This diameter determines how much light can enter
the optical system.
Twilight Factor
The twilight factor is an important factor to quantify the amount of details that can
be seen in dim light. The higher the value, the more details can be seen in
twilight. The factor is found by multiplying the objective lens diameter by the
magnification factor and then finding the square root of that product. In this case
the value is 23. With this feature the night binoculars are perfect for viewing
objects in dim light conditions.
Exit Pupil
The exit pupil is the size of a virtual aperture, from which rays pass through
binoculars. To find the exit pupil size, divide the diameter of the objective lens by
the magnification, in this case approx 6.5 mm. You can see the exit pupil if you
hold the night binoculars approx. 20 cm away from the eyes and look at a bright
background. You will see a bright circle in the centre of the lens. The larger the
exit pupil is, the brighter the image will be while observing the object.
Angle of Vision
The FOV (field of view) is indicated in a distance of 1000 m. The unit has a FOV
of 95 m at a distance of 1000 m and an angle of vision of approx. 5.5º.
Angle of Vision
FOV
