What’s the difference between depth of field and depth of focus?

Depth of field and depth of focus describe tolerance on opposite sides of the lens.

• Depth of field is the range of subject distances in the scene that appear acceptably sharp. In other words, it describes how much your subject can move toward or away from the camera and still look in focus.
• Depth of focus is the range over which the image plane can shift and still remain acceptably sharp. That means movement at the film/sensor plane rather than movement in the scene.

In practice, depth of field is the term photographers use most, because it affects what parts of the subject look sharp. Depth of focus is usually extremely small—often less than a millimeter—so it mainly matters in situations where the film or sensor position can vary, such as:

• poor film flatness in a film camera
• bellows or other adjustable lens-to-film setups
• freelensing
• lenses with built-in bellows-like movement

So yes, the distinction is real: depth of field concerns the subject side, while depth of focus concerns the image plane side. Confusing them can be misleading, especially in technical discussions, but for everyday shooting, depth of field is usually the more relevant concept.