Canon 10x30 IS II Manuel - Page 11

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3) Twilight Coefficient

Watching a bird from a distance at night, you would use a 300

mm f/2.8 instead of a 50 mm f/1.4 lens, even if the brightness

were cut in half. The amount of gradation which the human

eyes can see is very large, and with experience, will be able

to distinguish between the colors. In this way, although the

eyes may be weaker when bright, the higher the magnification

(resolving power), the more detail the eyes will be able to

distinguish. A simple calculation rule:

Twilight Coefficient =

For example, if you compare the brightest binoculars for general

use, those of 7x50 (exit pupil: 7.1 mm) and 12x36 (exit pupil:

3.0 mm), the binoculars of 7x50 are brighter. But with the

twilight coefficient:

As a result, using 12x36 binoculars at night will provide more

detail.

Even with binoculars with the same exit pupil, the brightness

may not always be the same. This is due to the amount of

light reflected by the lens. With uncoated lenses, about 8% of

incident light is reflected. The more light is reflected, the lower

the brightness of the images will be, in addition to a decrease in

image quality.In order

to prevent the incident

light from being

reflected, Canon uses a

"super spectra" coating,

which has been highly

praised for its efficacy

with Canon' s EF lenses.

Canon also coats the

prisms as well to ensure

bright and clear images.

Magnification x Available Aperture of Objective Lens

(the brightness is limited to a certain point)

7x50=18.7

12x36=20.8

Left: lens not coated. Right: lens coated. The lens

on the left looks white because light is reflected.

Exit Pupil/Available Aperture of Objective

Lens/Twilight Coefficient