Leica M3 - The Lens Aperture

The Lens Aperture
Hold the lens of your LEICA up to your eye, and rotate the aperture ring . You can then
see
how the aperture opens and closes. It works rather like the iris of your eye which also
opens or closes to adapt itself to weaker or stronger light . The lens aperture has a similar
purpose, namely to cut down very bright light by "stopping down" - i. e. the use of a
smaller lens opening. Conversely , in poor light the use of a larger aperture admits more
light to the film. At the same time the depth-of-field changes.
The
apertures or f-numbers 1.4 - 2 - 2.8 - 4 - 5.6 - 8 -11 -16 - 22 - 32 *) are a
measure
of the amount of light reaching the film . They are chosen in such a way that
closing down the aperture from each number to the next reduces the light by one-half.
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Similarly on opening up, each aper-
ture passes twice the light of the
next smaller one . So remember: a
high
aperture number signifies a
small opening, and vice-versa.
*) The length of this numer ical sca le de -
pends on the type of len s
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