Aperture 101

Photographers use aperture for a multitude of things from getting the proper exposure to creating a specific depth of field. Understanding how it works is essential to being able to use aperture to your advantage and taking the photographs you envision in your mind. In this quick primer, John Cripps breaks down the ins and outs of aperture and lets us know what it’s all about:

What Is An Aperture?

Simply put, an aperture is the opening in a lens that allows light to enter and, conversely, blocks light from coming in depending on which setting it is on. If you hold a lens up to the light and move the aperture ring (or arm depending on your lens) you will see the aperture diaphragm opening up and closing down. That is your aperture.


Aperture is the hole that lets light into your lens.

How Can You Use Aperture?

Let’s say you want to take a photo of a tree, but the tree you want to photograph is surrounded by a bunch of other trees. How do you isolate the chosen tree from the others to draw the viewers eye to it? Simple. Just adjust your aperture. Look at the two photographs below. They were taken using Aperture Priority Mode, which locks your aperture to a setting that you control and automatically adjusts the ISO and shutter speed to get the proper exposure.

aperture settings

At f/4, a narrow aperture, the depth of field is shallow, effectively isolating the tree in the foreground.

aperture priority mode

At f/22, a lot more of the trees are in focus, making it harder to decide which is the subject.

What Does the F Number Mean?

The F number (i.e. f/4, f/8, f/22, etc.) represents the ratio between the focal length of your lens and the diaphragm of your lens. But there’s no need to memorize any complicated formula. Just remember, the bigger your F number, the more depth of field you will have, even though it’s actually a smaller sized aperture opening. A wider aperture (small f number) lets in more light and results in a more shallow depth of field. Think of it this way:

“Say you have a horde of screaming tweens at a Justing Beiber concert trying to get backstage. If you only have 2.8 security guards holding them back, well, there’s a lot space in between them for those teeny boppers to get through, but if you have 22 guards holding rank, there’s a lot less space for those Beliebers to make it past.”

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One Comment

  1. Claude B. says:

    Interesting indeed, but on the argentique cameras (35mm), there was a button to see the real depth of field on the pictures, it was very handy but at f/16 or 22, it was very dark to make an opinion.

    But now with the DSLC if there is a way to check that before to do the click?


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