User Guide

The Iris Diaphragm
The Iris DiaphragmThe Iris Diaphragm
The Iris Diaphragm
Hold the lens of your LEICA up to your eye, and rotate the aperture ring. You can then
see through the lens components how the iris diaphragm opens and closes. It thus works
rather like the iris of your eye which also opens or closes to adapt itself to weaker or
stronger light. The iris diaphragm of the lens has a similar purpose, namely to cut down
very bright light by "stopping down" — i.e. the use of a smaller lens aperture.
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 aperture 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.
Similarly on opening up, each
aperture passes twice the light
of the next smaller one. So
remember: a high aperture
number signifies a small
aperture, and vice-versa.
*)
The length of this scale of numbers
depends on the type of lens.
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