How does the Distance from the Camera to the Subject affect the Depth of Field?

How does the distance from the camera to the subject affect the Depth of Field?

 

We performed a study to determine how the distance from the camera to the subject affects the Depth of Field (DOF). As in all of our studies or experiments all of the parameters except for one are constant throughout the experiment.  The only parameter that will change in this study will be the distance from the camera to the subject. These are the parameters and a description of the study:

  • We looked at three lenses with different focal lengths (18mm, 50mm and 100mm)
  • All of the lenses were set at f/2.8.
  • It was assumed that the lenses were mounted on a camera with a full frame sensor. Cameras will a smaller sensor would have different results but the relationships and conclusions are the same.
  • We plotted the near and far focus limits on a graph for each lens. The circles represent the near focus limit and the diamonds represent the far focus limit.
  • The shaded area between the near and far focus limits is the DOF.
  • We have used the following colors to highlight the three different lenses. Yellow/gold for the 18mm lens, Reddish for the 50mm lens and bluish for the 100mm lens.

 

These are the results:

 

Discussion:

The bottom line on the graph represents the DOF for a particular lens. The left axis shows the Focal Distance which is the distance from the camera to the subject. The shaded areas represent the DOF for each lens. The three DOF charts are overlaid on top of each other. Thus the DOF for the 18mm lens includes the yellow, reddish and bluish portions of the chart. The DOF for the 50mm lens includes the reddish and bluish areas of the chart.

 

How do you interpret the data?

If you mounted your 50mm lens on a full frame camera, set the f stop to f/2.8, and focused on a subject 11 feet away from the camera, your near focus limit would be about 10 feet away and your far focus limit would be about 12.3 feet away. Changing to an 18mm lens, setting the f stop again to f/2.8 and focusing on a subject 11 feet away would result in a near focus limit of about 5.9 feet and a far focus limit of infinity.

 

Observations:

As the distance from the camera to the subject increases, the DOF increases or gets larger.  (This assumes you are focusing on the subject).  This principle holds true for any focal length lens set at any aperture.

 

See Lesson DP-112C Depth of Field to gain a better understanding of Depth of Field. Lesson DP-111C Focus will help you understand how your focus point will impact the placement of the DOF.

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