Light meter

The measurement of light falling on the subject using a meter with a 180 diffuser cone positioned over the light sensor. This type of meter reading is not affected by the subject's reflectivity so can often be more accurate.

A meter used to measure the light that is emitted from an electronic flashgun. The meter suggests what aperture should be used to obtain a correct exposure. Some meters are purely for flash, others are multipurpose.

Cameras and exposure meters can take readings of the light levels in a number of ways, from basic to advanced methods. The most basic is Centre-weighted (CW) or average metering that takes a measurement from most of the image area. A more sophisticated version of this is Partial (P) metering that has a narrow area of measurement that is still based on the centre of the image and Spot (S) that can measure from as little as 1 of the image. The most commonly used in more advanced cameras now is Matrix, also known as Multi-pattern (MP) or segment metering, that takes readings from several parts of the scene and produces a calculated average. Buying advice In most cases the basic metering with an auto camera is fine, especially if you have the sun behind you or it is overcast. But when you start to try more advanced shots, such as the sun behind the subject for a backlit halo effect or an archway with light streaming through the pillars or a spotlit subject against a dark background, you may find the standard meter will let you down. If you can see yourself shooting subjects like this, buy a camera that lets you switch over to spot or multi-pattern metering.

A button or lever on the camera or exposure meter used to lock the automatically measured light reading into a memory while you recompose.This is ideal for backlit subjects because you can move closer to the subject, take a reading without any background in the view, lock the exposure and move back to the original position to take the photo.It's also fine for landscapes when there's an expanse of bright sky. Point the camera down to the ground, lock the exposure, recompose and shoot.Use this to bias the exposure to one area of the scene or to maintain a consistent reading when lighting conditions are variable.