Depth of Field

Depth of field (DOF) refers to the zone of acceptable sharpness on either side of the focus plane. Anything inside that zone reads as sharp; anything outside it slips progressively into blur. Three factors determine it: the aperture of the diaphragm (f/), the focus distance between the camera and the subject, and the focal length of the lens. The wider the aperture (f/1.4), the shorter the distance, the longer the focal length — the shallower the DOF. Conversely, f/11, a distant subject and a wide-angle give you a generous DOF. Technically, DOF rests on the circle of confusion (CoC), the maximum blur point still perceived as sharp: about 0.03 mm on a full-frame sensor. The simplified formula reads DOF ≈ 2 × N × c × (d/f)², where N is the aperture, c the CoC, d the distance, and f the focal length. Henri Cartier-Bresson often shot at f/8 or f/16 in hyperfocal — a focus calculated so that everything, foreground to infinity, stays sharp. A precious discipline for catching the decisive moment without losing a second.

Three concrete scenarios to understand how DOF behaves in context.

Portrait — 85 mm at f/1.8. Two meters from the subject, the sharp zone is only a few centimeters thick. The eyes are sharp, the ears already soft, the background dissolves into creamy bokeh. It's the signature look of fast primes: total subject isolation, cinematic separation. Watch out: if the subject moves even slightly toward you, focus slips. Better to lock onto the nearest eye and engage continuous AF.

Landscape — 24 mm at f/11. Here you want the opposite: everything sharp, from the pebble in the foreground to the mountain in the back. The hyperfocal becomes the key tool. At 24 mm and f/11 on full frame, focusing around 2 m, the sharp zone runs from 1 m to infinity. Don't forget to balance with your exposure triangle — closing the diaphragm often means raising ISO or slowing the shutter speed.

Macro — 100 mm at f/2.8. At 1:1 magnification, DOF is no more than 1 to 2 millimeters, even closed to f/8. Many macro shooters practice focus stacking: several images stacked to reconstruct a sharpness impossible in a single frame.

f/1.4 on a group portrait. The classic beginner mistake from someone in love with their fast 50 mm. Wide open on three people side by side, only one face will be sharp — usually the middle one, sometimes nobody if focus drifted. Simple rule: for a group, count roughly f/4 minimum for two people, f/5.6 to f/8 once there are more. The DOF needs to cover the depth of the group, not just the main subject's nose.

f/22 on a landscape "to get everything sharp." Intuitively appealing, technically a loss. Beyond f/11 (sometimes f/16 on full frame), diffraction degrades overall sharpness: light scatters as it passes through too small an aperture. You gain a few centimeters of DOF but lose bite everywhere. For a landscape, f/8 to f/11 remains the optimal aperture on most modern lenses.

Forgetting that distance matters as much as aperture. Stepping back two meters sometimes doubles DOF more efficiently than stopping down one click. Before touching the diaphragm, ask: can I move farther away? That discipline changes everything, especially in street photography where responsiveness comes first.