Optical Physics: Depth of Field (DoF)
In photography, Depth of Field refers to the distance between the nearest and the farthest objects that are in 'acceptably sharp' focus in an image. Controlling DoF is one of the most powerful creative tools in a photographer's arsenal, allowing for the isolation of a subject (shallow DoF) or ensuring an entire landscape is sharp from the foreground to the horizon (deep DoF).
The Four Pillars of DoF
- Aperture (f-stop): The larger the aperture (smaller f-number, like f/1.8), the shallower the DoF.
- Focal Length: The longer the lens (e.g. 200mm telephoto), the shallower the perceived DoF.
- Subject Distance: The closer you are to the subject, the shallower the DoF.
- Sensor Size: Larger sensors (Full Frame) produce shallower DoF than smaller sensors (Micro Four Thirds) at equivalent fields of view.
The Circle of Confusion (CoC)
The 'sharpness' of a photo is relative. Because lenses can only focus perfectly at a single distance, every other point is technically a small blurred circle. If that circle is small enough, our eyes perceive it as sharp. The maximum size of this circle is called the Circle of Confusion.
Hyperfocal Distance (H) = f² / (N * c) + f
The '1/3 - 2/3' Rule
At most standard distances, the depth of field is not distributed equally. Typically, the area of sharp focus extends 1/3 in front of the focal point and 2/3 behind it. As you move closer to the subject (macro photography), the distribution becomes nearly 50/50.