How a camera works

Every camera does three things: a lens gathers light, the aperture and shutter let a measured amount reach the sensor, and the sensor turns it into a picture. Here the parts sit in a row, in the order the light meets them.

The same parts, packed into a mirrorless camera, the most common kind today. DSLRs add a mirror for an optical viewfinder, and phones shrink it all into a module a few millimetres thick.

The focal length decides how much of the scene fits in the frame. Short lenses see wide, and long ones see a narrow slice that brings far things closer.

Ultra-wide 14–20 mm

Landscapes, buildings and small rooms.

Wide 24–35 mm

Everyday photos. Most phone cameras are about 24 mm.

Standard 50 mm

Close to what your eyes take in.

Portrait 85–135 mm

Flattering faces with a soft background.

Telephoto 200–600 mm

Sport and wildlife from far away.

Macro 60–105 mm

Small things, shown life-size.

Fisheye 8–15 mm

Up to 180°, with curved lines.

A prime has one focal length, and a zoom covers a range. Phones switch between two or three fixed cameras instead.

The curved glass bends light from each point of the scene back to a point. When those points land on the sensor, the photo is sharp. Focusing just moves the glass, and autofocus does it with a tiny motor.

A ring of blades opens and closes a hole. The f-number is the focal length divided by the hole's width, so f/2.8 is big and f/16 is tiny. Each stop halves the light, and a smaller hole keeps more of the scene sharp.

Two curtains set how long light reaches the sensor: one opens, the other closes. 1/1000 s freezes motion and 1/30 s lets it blur. Phones do the same thing electronically.

Millions of pixels each measure the light that lands on them, under red, green or blue filters. A bigger sensor gathers more light. ISO amplifies the readings, which brightens the photo but adds noise.

The processor fills in the colours, fixes white balance and noise, and saves a JPEG to the card. A RAW file keeps the untouched readings for editing later.

Light from the scene is focused by the lens, measured by the aperture and shutter, caught by the sensor and turned into a photo. Aperture, shutter speed and ISO together set how bright it is, and each has a side effect: depth of focus, motion blur and noise.