Depth of Field

Depth of field is the zone of acceptable sharpness in a photograph. Objects at the precise focus distance are rendered at maximum sharpness. Objects closer or farther are progressively less sharp, and beyond a certain distance in each direction they become visibly blurred. The depth of field is the total range between the nearest and farthest points that remain acceptably sharp in the final image. A shallow depth of field keeps only a narrow zone sharp with strong background blur. A deep depth of field keeps a wide range of distances sharp simultaneously.

Three factors directly control depth of field: aperture, focal length, and focus distance. Wider apertures (lower f-numbers like f/1.4) produce shallower depth of field. Narrower apertures (higher f-numbers like f/11) produce deeper depth of field. Longer focal lengths produce shallower depth of field at the same f-stop and shooting distance. Closer focus distances produce shallower depth of field than distant subjects. Changing any one of these three factors changes the depth of field, and all three interact simultaneously.

Sensor size affects depth of field through its relationship to focal length. A smaller sensor like M43 requires a shorter focal length to achieve the same field of view as a larger sensor. Shorter focal lengths produce deeper depth of field at the same f-stop. As a result, producing shallow depth of field on M43 requires wider apertures than on full-frame to achieve the same visual effect at the same framing. An M43 lens at f/1.4 produces approximately the same depth of field as a full-frame lens at f/2.8 for the same field of view.

Background blur, often called bokeh, is the out-of-focus rendering of areas outside the depth of field. The character of this blur varies between lenses based on optical design, aperture blade count, and the lens's transition from sharp to blurred. Background blur is achievable on M43 with fast primes at close focus distances, but is generally less extreme than on full-frame systems at equivalent fields of view. The m43lab Depth of Field Calculator computes near and far focus limits and hyperfocal distance for any M43 focal length and aperture combination.