Overexposure

The technical description is a picture where all the tones are squashed into the brighter end of the tonal scale and where the highlights may be completely ‘clipped‘ (lost). The artistic description is a photo that’s lighter than the photographer intended.

Zone System

A system developed by the great landscape photographer Ansel Adams for measuring the light levels throughout a scene and allocating them to ten brightness ‘zones’. The idea was to develop the film to a specific level of contrast that captured the full range of tones and make appropriate artistic interpretations with dodging and burning during the print-making process. It worked well with the very exposure tolerant sheet films of the day, where each negative was processed individually, but it’s mostly of academic interest today since digital sensors don’t offer this extended exposure latitude.

Zebra pattern

A visual warning that image highlights are being overexposed and used especially during video recording. The overbright areas are marked by moving diagonal stripes (hence zebra) leaving you to decide whether to reduce the exposure or to leave it if the highlight areas are unimportant.

Underexposure

Where a picture comes out darker than you expected because of the way the camera has adjusted the exposure, or where you deliberately make the photo come out darker for dramatic effect.

Time (T) exposure

A close relative of the bulb (B) shutter speed setting and, like bulb mode, it’s used for long exposures. With time (T) exposures, though, you don’t hold the shutter button down all the time – you press once to start the exposure and a second time to end it.

Spot metering

A metering mode where the camera measures the light from a very small area of the scene. This might be right in the centre or, on some cameras, it’s directly beneath the selected autofocus point.

Smart Lighting (DxO)

A feature in DxO Optics Pro that attempts to optimise exposure levels and highlight detail retention in RAW files. You can adjust the strength of the effect and apply exposure compensation at the same time, to get the ideal result.

Shutter speed

The length of time the shutter is open during the exposure and usually quoted as fractions of a second. Each shutter speed is half as long as the one before, for example 1/30sec vs 1/60sec. This exposure ‘halving’ is the basis for balancing up lens aperture and ISO settings. A few cameras have external shutter speed dials but most simply display the shutter speed on the LCD display – you turn a control dial to change the speed.

Shadows

The darkest tones in a picture. A pretty vague term (like ‘highlights’) but usually taken to mean the darkest areas where you can still see some image detail. Digital cameras often retain more shadow detail than you can see initially, and this can be brought out later on a computer.

Multi-pattern metering

This is the most sophisticated form of light metering used by cameras. The light values are measured at many points across the frame and compared to ‘known’ scenes so that the camera can work out what the subject is likely to be and the best way to expose it properly.