Learn Photography Series - Aperture 101: Aperture and Depth of Field

In my whole decade-plus of photographing families and children, my go-to lens has always been Prime lens. Prime lenses are camera lenses where the focal length is fixed requiring you, the photographer to move your feet more often, getting all the Steps in!

In this series, we will explore the 101 on photography starting with Aperture. We won’t go into shooting in Raw vs Jpeg or shooting in Manual vs Aperture mode or others in this post, but that will come in a later blog post. I know it probably seems unconventional to start a series on beginner photography with aperture instead of a piece on shooting modes, but this will be our intro piece! I like to be different.

So what is aperture, why is it important in photography, and how does it affect your images? Read on to find out.

But first, a little note of caution: All blog posts are my personal opinion and expertise. I am not a professional or credentialed educator of photography. Everything written and mentioned is based on my experience as a portrait photographer and what has worked for me. These are things I have learned over the years.

What is Aperture?

In photography, aperture refers to the opening in the lens for which light enters. The wider the opening, the more light that enters the lens, therefore the brighter the photo. Aperture, along with shutter speed and ISO are the main 3 components in exposure and photography. In another post, we’ll go over how the 3 components create the image exposure.

Aperture is represented by the f stop. The larger the opening, the smaller the f-stop number.

Depth of Field

Depth of Field in photography refers to how in focus your subject is compared to the background. A shallow depth of field will have your subject sharp, and the background blurry. Blurriness in the background is referred to as bokeh. Opposite of a shallow depth of field is a deep depth of field. A deep depth of field will have more of the surroundings in focus as well as the subject.

Aperture and Depth of Field: How They Affect The Subject of Focus.

You have now learned that the Aperture is the amount of light that enters the lens and that the wider the opening, the more light. You have also learned that a shallow depth of field means the more focused the subject is to the background creating bokeh. Now, you will learn how they are important to each other.

When you set your aperture to be wide open, your depth of field becomes more shallow. With this setup, you’re more likely to get a beautiful bokeh, especially with busy backgrounds. However, if you have more than one subject you want in focus, you will run the risk of either subject being out of focus. This is due to occur when you have multiple subjects and they are not on the same plane.

While in this photo, it was purposely done to keep the children in focus and parents out of focus but still recognizable, it’s a great example of different planes.

If unable to get multiple subjects on the same plane, to avoid being out of focus, you will need to increase your aperture f stop. Increasing your f-stop means having a smaller opening and enabling less light to come in. Your exposure will be darker, therefore you will need to adjust other camera settings such as shutter speed or ISO to get the right exposure. In result, having a smaller aperture means a deeper depth of field. When you do this, more of the background will also be in focus, but so will all your subjects. Note that in the image below, some parts are out of focus, but this is due to movement which is also an important factor we will discover later.

In the below example, the aperture setting is 1.4f. The focus point is on the boy in each photo. With a setting of 1.4f, a creamy beautiful bokeh is formed with what was busy background is pretty much unrecognizable. Note the cup in the foreground of the first photo is more in focus. Why do think that? Yes, because it’s closer to the focal point.

In this next example, my three wiggly kids are on slightly different planes, therefore I increased the aperture setting to 3.2f to ensure all three are in focus. At 3.2, everyone is in focus, but the background also is more identifiable.

Here is a great image guide to show the different F stops, and how it affects depth of field. All images were taken on the same lens, same distance between camera and subject, and same distance between subject and background. The largest difference to spot between the aperture setting is the trees in the background and the wooden fence she is leaning on. You’ll noticed in the wider aperture, the trees and immediate fence panel is less in focus and they become more in focus as the aperture gets smaller.

In this photo, the subject is right against the branches of a tree. You can see that as the f stop increases, the branches, and many more of them are more and more in focus.