Definition: Aperture

Definition: Aperture | Glossary entry

Aperture

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 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

Size size of the hold 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
Aperture – can be measured in 1/3rd of a stop

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. Your 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 settings as a guide.

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