What is Aperture? A Simple Explanation

Aperture is one of the 3 main pillars of photography, in addition to ISO and shutter speed. Aperture controls how much light reaches the image sensor of the camera, as well as the depth of field, which is the area of the image that is in focus and appears sharp.

When you change the aperture, you’re changing the size of the hole within the lense that allows light into the camera body. It’s similar to the pupil of the human eye. When the pupil expands, more light enters the eye, when the pupil contracts, less light enters the eye.

What is the F-Number?

The size of the hole within the lense is expressed in f-stops or the f-number. The F-Number represents the focal ratio. A small f-number will make the foreground of the photo very sharp, while making the background of the photo blurry. This type of setup is commonly used in portrait photography.

A large f-number will bring the foreground and the background into focus, creating a sharp overall image.

Important Cheat Sheet:

  • The smaller the f-number, the bigger the aperture
  • The smaller the f-number, the smaller the focus range will be
  • Each lense has a minimum f-number and maximum f-number
  • The minimum f-number (maximum aperture)  is the most important number on the lense.
  • The minimum f-number shows the speed of the lense.
  • Lenses with a lower f-number or a larger aperture are better for low light photography.
  • A fixed lense (non-zoom) lense only has 1 aperture.
  • On a zoom lense, the aperture often changes.

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