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What the f/stop? An introduction to Aperture and Depth of Field (DoF)...

Updated: Apr 7, 2023

Let's start at the beginning. Everyone in the photography world talks about the "Exposure Triangle".

But what is aperture and how does it effect an image?

A camera’s aperture setting controls the size of the opening in the lens, which then regulates the amount of light reaching the film or digital sensor. It works like the pupil in your eye - when the light level is low, it can expand to let in more light, and when there is a lot of light it can close up tight to prevent too much from getting in.

It also impacts the depth of field, or how sharp the subject of an image is compared to it's surroundings.

We've broken this down into two parts if you wish to skip through:

What the f/stop..?

The apertures are described based on a size scale called f-numbers, or f-stops.

Your camera may have displayed something on the screen like f/5.6 or f/8 when you were taking a photograph. The "f-number" refers to the lens aperture, indicating the ratio of focal length to effective aperture diameter. A camera lens typically comes with a set of marked "f-stops,” settings you can use to select an f-number you wish the camera to use.

The "f-number" is a term used to describe the lens aperture, indicating the ratio of focal length to effective aperture diameter.

Each f-number up or down either doubles or halves the amount of light being allowed in.

Opening the aperture up one stop lets twice as much light through, which makes the picture brighter, while closing the aperture down one f-stop makes the picture darker by cutting the amount of light going through by half.

Measurement of Aperture

The f-stop scale looks a little something like this...

The full range of f-numbers is broader than this, going larger and smaller at either end. Also, some cameras have half or third stop settings in between these - but we don't need to worry about those yet. Your camera should have some or all of the f-numbers on this chart – they are the most common ones used in a wide variety of cameras.

Aperture range

This sounds backward, but the larger the f-number the SMALLER the aperture – and the LESS light is going through it.

  • The lower the f-number, the larger the aperture opening - this lets more light reach the image sensor or film, resulting in pictures with greater exposures.

  • Higher f-numbers mean smaller aperture openings, less light reaching the film or image sensor, and pictures with lower exposure.

Depth of field (DoF)

The Depth of Field (DoF) is also controlled by the aperture. Depth of Field is the area that is maintained in sharp focus - the subject of the photo and the in-focus areas before and beyond them. The Depth of Field is influenced by 3 factors:

DoF: The lens aperture

Deep DoF