Advanced Video Camera and Editing

Depth of Field

Simply put, depth of field is the focus range of the lens. Also known as the focus range, depth of field is the area between the nearest and farthest objects that appear sharply in focus. Anything outside of this range loses focus becoming gradually more imperceptible. However, in some cases it may become more desirable to use depth of field to de-emphasise portions of the image while keeping the most important parts in focus. 

Depth of Field may be described in two ways:

  • Greater - where foreground, mid-ground and background elements are all in focus. This depth of field is achieved using a wide angle lens, or when the telephoto is zoomed out to its widest.
  • Shallow - only a limited area is in focus, such that the foreground may be in sharp focus, but the background is rendered a blur. 

Three methods for manipulating the Depth of Field:

  • Changing the focal length (adjusting the telephoto from wide to narrow) allows you to change the depth of field from Greater to Shallow. Zooming in and focusing on a subject in the foreground can cause the background to go blurry. The extent to which the background is blurred depends on the lens. 
  • Changing the distance between the camera and the subject. In most telephoto lenses, you should be able to achieve an acceptable shallow depth of field if the camera-to-subject distance is adjusted. The closer you zoom in to focus on an object, the shallower the depth of field.
  • Adjusting the aperture is probably the easiest way to manipulate depth of field. To make depth of field more shallow (decreasing), open up the aperture; to make it greater (increasing), close down the aperture.

Greater Depth of Field. The shot is achieved by zooming out,  

Shallow Depth of Field. Zoom in on the subject and focus. The closer you zoom in to focus, the shallower the depth of field.  

Effect of Aperture

  • Reducing the size of the aperture (less light enters the lens) increases the Depth of Field
  • Increasing the size of the aperture (more light enters the lens) decreases the Depth of Field

The following images courtesy of Creative Commons 

At f22 (the lens is nearly closed), the Depth of Field is greater. 

Opening the aperture to an f8 starts to render the background a soft blur. 

At f4, the depth of field is more noticeably shallow. 

At f2.8 (more light enters the lens) the depth of field is very shallow. Compare this picture with the one taken at f22 when less light was able to enter the lens.  

Here's a video made by The Slanted Lens that offers a nice explanation of how you can use depth of field creatively.
Depth of Field as a Creative Tool: A Lighting Tutorial