Mini Assignment #5 – DOF

First things first – Just what is Depth of Field?  In simple terms it’s the amount of your image that is in sharp focus throughout the scene from front to back.   Why is it important to control your Depth of Field (DOF)?  Understanding how to manage DOF will allow you to get the entire scene in sharp focus or let you isolate your subject while blurring a distracting background.  Creative use of Depth of Field can be used to create a sense of depth in a photo or direct the viewer’s eye to a specific focal point.  In short, skillful use of DOF can take your image from “average snapshot” to “WOW!”

A shallow depth of field is one where your main subject is in focus, but the surrounding background, and possibly some of the foreground are soft and blurred. The segment of your image in focus, from front to back, is very shallow.  This can be very effective when shooting nature or portraits.

A greater depth of field is one where you have sharp focus throughout the full range of your image.  Your foreground, as well as the background, is all in sharp focus.  This is often the choice for sweeping landscapes and images where your subject matter is at varying distances.

So, how do you control this? Depth of Field is controlled through adjustments to the Aperture, the Focal Length and the Distance from the subject.

Before reading further, pause to watch this short video that demonstrates how these three factors can impact your depth of field.  Depth of Field – Adorama TV

Welcome back!  Now let’s continue on with a few more points on Depth of Field then we’ll head out to give it a try ourselves.

Let’s recap the three points.  The Focal Length of the lens (ie: 50mm or 200mm) and the Distance from the subject are easy concepts to grasp.   Zoom in or zoom out with your lens or physically move closer or further from your subject.  Aperture settings can be a bit more difficult to comprehend.

Aperture settings are referred to by f/stop settings and they are measured in numbers, such as f/2.8 or f/18.  When I was starting out, my biggest struggle was trying to understand and remember the relationship between the f/stop numbers and the effect they would have on Depth of Field.  Small numbers are referred to as a large aperture and large numbers are referred to as a small aperture.  I won’t get technical as to the why’s here – just think of it like this for now:

  • Small # f/stop (f/2.8) = Small (shallow) DOF = a smaller area in focus, with the main subject as the focal point.
  • Large # f/stop (ie: f/22) = Large (greater) DOF = foreground and background in focus

Aperture settings (f/stops) are automatically set in the Auto and Picture modes.  You’ll want to use one of the creative settings, such as Manual or Aperture Priority to control your depth of field.  Aperture Priority is a favorite of many photographers because you select the desired aperture based on the results you want to achieve and your camera will select the correct shutter speed.

One last thing – most cameras have a DOF Preview Button.  When you’re setting up your shot, the image seen through the viewfinder may not be an accurate rendition of the depth of field your settings will render when you press the shutter button.  I won’t get into the technical aspect of why that is in this lesson (it has to do with light passing through the lens and stopping down the shutter), but grab your camera manual and read up on the DOF Preview Button – you’ll be glad you did.

Now that you’ve learned a few of the basics head out and try it for yourself. For this exercise let’s use the Aperture Priority option.  Select Aperture Priority on the dial (“AV” on Canon, “A” on Nikon cameras – check your manual if necessary for more information on Aperture Priority settings for your particular camera).   Find someone willing to pose for you, or find an inanimate subject that will stay put while you experiment.  Start first by keeping your distance and focal length the same, but change your aperture (f/stop) settings.  Then try changing your focal length or your distance from the subject.  Come back and share the results with us via Mr. Linky and post your comments and questions.


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