What is the diaphragm in photography?

In photography, the diaphragm is a mechanism composed of several articulated metal plates, which restricts the passage of light in the photographic lens and thus the amount reaching the digital sensor.

Rear view of the diaphragm of a 50mm Canon lens.

Click to enlarge: Rear view of the diaphragm of a 50mm Canon lens. You can see the sliding blades in the center. Image WikiMedia Commons.

It is, with the shutter, the main exposure control mechanism on most modern digital cameras.

However some simple digital cameras have a fixed aperture and so do not have a diaphragm.

The diaphragm blades are hinged so that they can slide over one another to define an aperture of variable size and near-circular shape. The different sizes of the opening are calculated so as to correspond to a predefined scale called F-Stops. For more details, please read this post.


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