Before you read this, make sure you have read the previous post on Aperture, it’s quick and easy to understand.

When we take a closer look at something, especially as we get older, we squint and by half-closing our eyes we can see more detail. We are closing down the aperture in the lens of our eyes and by making the hole in the lens smaller we create more detail in our vision. Similarly in the camera by closing down the aperture in the lens, by making the hole in the lens smaller, it creates more detail in a photograph.

The glass elements in the camera’s lens only focus on a very narrow area which is called the point of focus. Closing down the aperture extends or spreads the area that is in sharp focus. This spread happens, both in front and behind the point the camera is focused on. We use the term “depth of field” to talk about the levels of focus achieved through using the aperture.

The grey areas in these illustrations are a rough representation of how much focus is extended with a depth of field for a large aperture F2, a midrange aperture F8 and a small aperture F22. Don’t forget, aperture is just another word for a hole.

Deep depth of field

I focused on the tree then with a small aperture F22, extended the area of the image that appears sharp. This is known as a “deep” depth of field. Everything from the foreground to the background is acceptably sharp. Aperture with a large number = small hole in the lens = deep depth of field = more of the image appears sharp.

Shallow depth of field

A larger aperture F2, reduces the area that appears sharp and is called “shallow” depth of field. Aperture with a small number = large hole in the lens = shallow depth of field = less of the image appears sharp. The point of focus is the only part of the image that is sharp.

Shallow depth of field only a very narrow section of the subject to appear sharp and creates the most beautiful soft gradations of tone and colour known as bokeh. Point sources of light become circles and there is a wealth of stunning possibilities with both natural and artificial light sources. 

Shallow depth of field can be used to reduce the impact of parts of the image by leaving them blurred and bring greater attention to the sharp part of the composition. 

Deep depth of field brings a crispness to an entire scene offering detail from the foreground to the background. You’d need deep depth of field if you have important components from the foreground to the background.

It’s your call

There is no “correct” aperture, just options of how to best represent the image or tell the story in front of you. For a while try shooting deep, middle and shallow depth of field and then through editing make decisions of which ones worked best and why. Over time you will be able to assess what it is the subject requires from experience.