Understanding Depth of Field: A Practical Guide
Depth of field (DoF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp. Mastering DoF gives you control over where the audience looks and how they feel about what they see.
The Three Factors
Three variables control depth of field on set:
Aperture (f-stop): A wider aperture (lower f-number like f/1.4) produces a shallower depth of field. A narrower aperture (higher f-number like f/16) keeps more of the scene in focus.
Focal Length: Longer lenses (85mm, 135mm) compress the background and produce shallower DoF at the same aperture. Wider lenses (24mm, 35mm) keep more in focus.
Subject Distance: The closer your subject is to the camera, the shallower the depth of field becomes. This is why macro photography has such razor-thin focus planes.
Sensor Size Matters
Larger sensors require longer focal lengths to achieve the same field of view, which indirectly produces shallower depth of field. A Full Frame sensor at 50mm f/2.8 will have noticeably shallower DoF than a Micro Four Thirds sensor at 25mm f/2.8, even though the field of view is similar.
Circle of Confusion
The mathematical basis of DoF calculations relies on the "circle of confusion" (CoC)---the maximum size a point of light can be blurred before it appears out of focus. Different standards exist, but the common formula is:
CoC = Sensor Width / 1500
