Canon 10x30 IS II Manual - Página 10

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Brightness varies from one model of binoculars to another.

Brightness varies with the price and size of the binoculars.

There are many degrees of brightness according to one' s needs.

1) Exit pupil

The bright circle visible when the eyepiece lens array is viewed

about 10 inches away from the eyes is called the exit pupil.

The diameter, measured in millimeters, is called pupil aperture.

The larger the exit pupil, the brighter an image the binoculars

make, and the brightness is expressed by the square of the

aperture of the exit pupil.

Human pupils are about 2-3 mm at most (Fig. 7-a) when bright,

and the binoculars' exit pupils should be about 3 mm. At night,

our pupils dilate to about 7 mm (Fig. 7-b), so it is desirable

to have binoculars with large exit pupils if they will be used

at night.

However, the disadvantage is that such binoculars tend to be

big and heavy.

When bright

When dark

The diameter of the objective lens which the light passes

through is called the available aperture of the objective lens.

If the magnification is the same, the larger the available

aperture of objective lens, the brighter image seen through the

binoculars. This is the same effect as when a telephoto lens has

a very large lens diameter. The relationship of the three is:

Aperture of Exit Pupil =

(Fig. 7-a)

(Fig. 7-b)

Available Aperture of Objective Lens

Magnification

The exit pupil

is 3.0 mm

The exit pupil

is 7.0 mm