I must admit depth of field has been a fundamental photography concept that has been difficult for me to master.  Although I am far from mastering it I have managed to take the first step, which is understanding it.  So I figured I would give the “Cliff Notes” version of depth of field for anyone else who is struggling to understand it.

What is Depth of Field?

Depth of field refers to the portion of an image that is in focus or sharp.  It is a great tool to tell the viewer what part of the image is most important by only having that part in sharp focus.  It is generally divided into two categories; narrow or shallow depth of field and great depth of field.  Narrow or shallow means that a very limited (or narrow) part of the image is in sharp focus and the rest of the image, in front of and behind the main subject of the image, is blurred.  Great depth of field is just the opposite.  A greater portion of the image including the space in front of and behind the main subject is in focus.

How do you control depth of field?

There are three factors that affect the depth of field of your photograph.

  1. Aperture Size
  2. Focal Length
  3. Lens-to-Subject Distance

Aperture Size

Put simply, the smaller the aperture (the larger the f-stop #) the greater the depth of field and the larger the aperture (the smaller the f-stop #) the shallower the depth of field.  So if you have three objects lined up at varying distances from each other and you want to capture the front object in sharp focus while blurring the others open your aperture way up to whatever your smallest f-stop is for the focal length you are using (f/5 for example) and focus on the front object (top photo below).  If you want all three objects in relative focus close your aperture down to your largest available f-stop (f/22 for example) (bottom photo below).

Example of Narrow Depth of Field Photograph

large aperture/small f-stop = shallow depth of field

Example of Great Depth of Field Photograph

small aperture/large f-stop = great depth of field

Focal Length

Shorter focal lengths lenses result in a greater depth of field while longer focal length lenses result in a more shallow depth of field.  For example if you are using a 35 mm to 70 mm zoom lens and focus on your subject at 35 mm with an aperture of f/8 you you will get your subject as well as more of the foreground and background in focus (top photo below).  Then when you change the focal length to 70 mm at the same f/8 aperture the resulting depth of field will be narrow, meaning a blurred background and foreground and sharper subject (bottom photo below).

Example Photograph with Great Depth of Field

short focal length (~50 mm) = great depth of field

Example Photograph with Narrow Depth of Field

long focal length (~200 mm) = shallow depth of field

Lens-to-Subject Distance

The further you are from your subject the greater your depth of field will be.  Conversely, the closer you are to your subject the more narrow your depth of field will be.  For example, taking a photograph of a group of people in front of a scenic background from 20 yards away will result in both the people and the background being in focus.  While moving closer to the people, say 5 yards, will result in the people being in more sharp focus while the background begins to blur.

further away from subject = great depth of field

closer to subject = shallow depth of field

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