The Lens Aperture - Leica M2 Instructions Manual

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The Lens Aperture (11)

Turning the lens aperture ring opens or closes the iris diaphragm. This may easily be observed
by looking into the front of the lens. Like the pupil of your eye which opens or closes to adapt
itself to weaker or stronger light, the lens diaphragm is used to regulate the amount of light
reaching the film. To cut down very bright light we "stop down" to a small lens aperture. In very
dim light, on the other hand, we "open up" to a larger lens aperture which transmits more light
to the film.
The aperture f/numbers (stops 1.4 — 2 — 2.8 — 4 — 5.6 — 8 — 11 — 16 — 22 — 32*) follow
an internationally recognized scale. This scale has been designed in such a way that closing
down the aperture one stop cuts the light passing through the lens to one half. Conversely,
opening up one stop doubles the amount of
light that will reach the film. One aperture
interval on the lens corresponds to one shutter
speed interval on the shutter speed selector
dial.
Remember: The larger the f/number, the
smaller the aperture.
* The length of this scale depends on the lens type
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