Metering Modes: Evaluative, Center-Weighted and Spot

Your camera's meter reads the light reflected from the scene and assumes the world averages out to a mid-tone of roughly 18% grey. Every metering mode is a different answer to the question of which part of the frame gets measured. Evaluative (Matrix on Nikon, Multi-segment on most others) divides the frame into dozens of zones, weighs them against a database of typical scenes, and is the best default for landscape, travel and general shooting. It is hard to fool, though a very bright sky or a large patch of snow can still pull the exposure down.

Center-weighted metering averages the whole frame but gives the middle 60-80% most of the weight. It is predictable and consistent from frame to frame, which makes it a good match for portraits where the subject sits in the centre and the background is brighter than the face. Photographers who learned on film often still prefer it for exactly that steadiness.

Spot metering reads only 1.5-3.5% of the frame, usually tied to the active AF point. It is the precision tool: meter the cheek of a backlit portrait, a performer in a spotlight against a black stage, or the moon, and the camera ignores everything else. The catch is that it obeys whatever you point it at - meter a white dress and it turns grey, meter black clothing and it turns grey too. Some bodies add partial metering, a wider spot of about 6-10%, and highlight-weighted metering that protects blown whites at weddings and stage shows.

In practice, choose Evaluative for everyday shooting, Center-weighted for portraits with a bright background, and Spot when the subject is much brighter or darker than its surroundings. Whichever you pick, meter a mid-tone - grass, asphalt, a grey card - and then recompose, and check the histogram after the first frame rather than trusting the rear screen. Exposure compensation is your correction dial: about +1 to +2 stops for snow, -1 to -2 stops for a dark stage.