Part 1 of this series explains how the focal length of lenses control depth of field and background perspective.How does this apply to the photographs you want to create?  Once you master controlling your depth of field you will be able to control what is in focus; you can purposely throw your background out of focus so only your subject(s) are in focus or you can choose to have your background in focus to include it in your portrait to compliment your subject(s).   A portrait, by definition, is a portrayal; to depict, written or visually an image or group of images that tell a story about a specific subject or subject matter.  You can feature an individual or a group of individuals in your portrait. Selecting the proper lens and settings are essential in telling the story.

We have previously determined how the focal length of a lens, the  the f-stop (aperture) you select, and, the distance between your lens and the subject you are photographing determines your depth of field. The distance of your subject to the background is another factor to consider when you want your background to be sharp or blurry.

Controlling Depth of Field – Keeping your backgrounds in focus

For the sake of applying theory with real numbers let’s say you are using an 18mm (smaller). After mounting the camera to my tripod, I stood approximately 10 feet from the rider and her horse  when I created this portrait. As a result, everything from 3.07  feet and beyond is in focus.

	Infinite
3.07 feet		Infinity

Example 1

Focus Point is to the subject distance is 10 feet,
Focal Length is 24mm
Aperture is f22

Controlling Depth of Field – Creating blurry backgrounds

Let’s apply theory with real numbers; for argument sake, you are using the same 18mm-135mm zoom lens and full frame camera. Now you decide to take some close-up portraits of your children.

Since a portrait is supposed to tell a story about your subject, it is imperative to cast the focus of attention to your children. You decide you want to make your background extremely blurry in order to limit background distractions. To accomplish this you are going to want to use a longer focal length, say 135mm, and, a larger aperture, let’s say around f/2.8. You are standing 20 feet from your children when you take your photograph and about 3/4 of a foot of depth of field and everything beyond 20.4 feet is going to be blurry.

 

Example 2

Focus Point is to the subject distance is 20 feet,
Focal Length is 135mm
Aperture is f2.8

	0.7 feet
19.7 feet		20.4 feet

 

Fortunately you can also determine how blurry your background is by using lenses with a longer focal length. When creating example 2, I selected  a longer focal length lens. Longer focal lengths compress the background and shrink the depth of field so this toddler just pops out at you. Choosing to have the background further away from your subjects will also help to blur the background.

You can see how selecting the right lens and aperture can greatly impact the images you create. Remember that wider angle lenses tend to create a greater depth of field than a telephoto (longer) lens. As mentioned previously, lenses are like your iris, larger number/smaller aperture openings, increases depth of field and smaller number/larger aperture openings decrease depth of field.

Larmon Photo offers individualized training. If you are interested in receiving hands on private mentoring visit us online at larmonu.larmonstudios.com. You can also give us a call at (215) 887-1248 for more information.