Factors affecting Depth of Field

Fig. 3 - Subject-to-Camera Distance and Depth of Field
Fig. 3 – Subject-to-Camera Distance and Depth of Field
  1. Subject to Camera Distance

From Fig. 3, assume that we are using a fixed focal length (50mm for example) and same aperture.

When we move the camera away from the subject, light rays propagate in a longer path and travels slower, squishing the blue triangles into a longer path – Longer depth of field. More areas will come in focus before and after the focus point on the subject.

When camera is moved closer to the subject, the light rays propagate in a much shorter path, thus decreasing the area of the depth of field. Light rays travel much faster in a shorter distance.

Conclusion:

  • The shorter the Subject to Camera Distance, the shallower the depth of field.
  • The longer the Subject to Camera Distance, the longer (wider) the depth of field.

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