Definition: Aperture

Definition: Aperture | Glossary entry


Aperture sizes

Diagram showing the relative aperture sizes against the F-stop numbers for each. A wide aperture also creates a shallow depth of field.

The term aperture has two meanings:

  1. The aperture is a hole in the ‘diaphragm‘ (a partition) in the camera lens. The size of the aperture controls the amount of light passing through the lens.

  2. We use the term ‘aperture’ to describe the size of the opening when a picture is taken.

Aperture size is important. Each aperture size creates a different DoF. A wide aperture creates a shallow DoF – sharpness in a very slim band of the image. A tiny aperture creates a deep DoF – the picture is mostly/all sharp.

Aperture size can be controlled in a number of ways. In a DSLR it is normally controlled by overlapping blades in a fan-like arrangement around the aperture mounted on the diaphragm. See the ‘Iris Diaphragm‘.

Aperture size is expressed in numbers called f/stops. Low f/stop numbers indicate wider aperture openings. In the sequence that follows each succeeding f/stop halves the light through the aperture…

Wide:                                               :Narrow
  f0.7; f1; F1.4; f2.8; f4; f5.6; f8; f11; f16; f22; f32;

The aperture size controls the ‘DoF‘, the range of sharpness in the image. As the aperture gets wider the depth of field gets shallower. A range of notional values for a 50mm prime lens might be:

f/stop Notional aperture Notional DoF
 1.4  Extremely wide open  Extremely shallow
 2  Very Wide open  Very shallow
 2.8  Wide open  Very shallow
 4  Broad  Shallow
 5.6  Medium  Medium
 8  Narrowing  Local Area
 11  Restricted opening  Long Distance
 16  Tight opening  Far distance
 22  Extremely restricted  Virtual infinity

Although the aperture size is measured in f/stops modern cameras allow great flexibility. Most modern lenses and cameras work on thirds of f/stops. So in the table above some of the stops are one third measures of a full stop. You camera will probably have all the one third stops available for the whole range. The table is only a notional example. It only shows some of the settings to give a guide.

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