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Aperture Explained

Aperture Explained


The aperture is the hole in the lens though which the light comes through.


It is constructed from a number of blades which move in unison in order to change the size of the hole.

This is an aperture ring that I removed from a malfuncting Canon 50mm f1.8 lens.

The bigger the aperture, the more light hits the sensor, and the more exposed the final image is.

Aperture is measured in 'f-stops' of 'f numbers'.

A wide aperture will have a low f number, and a small aperture will have a high f number:

                
f1.8 f2 f3.5 f8 f16 f22


The aperture has other effects beyond exposure, the most significant being the depth of field.

You may have used a pinhole camera at some point in your life. A pinhole camera has no lens at all, however it still manages to produce a 'focused' image.

This is because the aperture (the hole made with the pin) is very small.

Likewise, a very small aperture in the lens of a conventional camera will result in almost everything being in focus. This is know as 'wide depth of field'

A large aperture will have the opposite effect, with only objects a specific distance away in focus, and everything else out of focus. This is known as 'shallow depth of field'

Large aperture, shallow depth of field: Small aperture, wide depth of field: