Lesson 8: Metering and Shooting Modes

By now you can set aperture, shutter speed and ISO yourself. But a camera also has to decide how much light is the right amount — that is metering — and it offers several modes that decide how much of that work it does for you. Understanding metering and shooting modes is what turns the exposure triangle from theory into photographs you can take quickly, in real situations, without missing the moment.

Metering is how the camera measures the light in a scene. The light meter reads the brightness through the lens and suggests settings that would make the scene a middle grey — an average tone. Most cameras offer three metering patterns. Evaluative (also called matrix) metering divides the scene into zones and weighs them together, and is the best default for most situations. Centre-weighted metering gives priority to the middle of the frame. Spot metering reads only a tiny area — usually the focus point — and is the right tool when your subject is much brighter or darker than its surroundings, such as a person backlit by a window.

Why the Meter Can Be Wrong

The meter's weakness is that it assumes the world averages out to middle grey. Photograph a snowy field and the meter will darken it to grey; photograph a black cat on a dark sofa and it will brighten it to grey. This is why cameras have exposure compensation: a dial or button, usually marked +/−, that tells the camera to make the image brighter or darker than the meter suggests. Snow needs about +1 to +2 stops; a dark subject may need −1. Checking the histogram — the graph of tones in your image — after the shot tells you whether the highlights or shadows are clipped, which is information the small screen alone cannot give.

Shooting Modes

The mode dial decides who controls what. In auto mode the camera chooses everything. In program mode it chooses aperture and shutter speed but leaves ISO and other settings to you. In aperture priority you set the aperture and ISO, and the camera picks the shutter speed. In shutter priority you set the shutter speed and ISO, and the camera picks the aperture. In manual you set all three, with the meter as your guide. There is no prize for using manual mode: professionals use aperture priority for most of their work, because it controls the look of the image while the camera handles the arithmetic. Use manual when the light is constant and you want every frame exposed identically, such as in a studio or for a panorama.

The practical skill is choosing the mode for the job: aperture priority for portraits and landscapes, shutter priority for sport, manual for the studio. Learn the meter's habits, learn exposure compensation, and you will spend your attention on the photograph instead of the settings.