The metering modes

We have started looking at how shutter speed, aperture and ISO can affect the amount of light hitting your camera sensor. With light levels varying from bright sunshine outdoors to dark indoor scenes, it can be difficult to achieve optimum exposure. Most DSLR cameras include a light meter to measure the intensity of the light. This allows us to assess the best use of shutter speed, aperture and ISO.

The on-board meters on DSLRs use ‘middle-grey’, or 18% grey, to identify appropriate settings for shooting a subject with reflected light. A middle-grey meter does not recognise colour or tonality. It only recognises the ‘brightness’ of the colours.

Most cameras offer a range of metering modes. When used correctly, they can be very helpful with metering accuracy.

Centre-Weighted

Centre-weighted metering is a method of metering that emphasises the centre of your image as seen through the lens. The exposure is weighted to suit the brightness in the centre of the frame. It assumes that the primary focus of your photo is in the centre.

Evaluative

Evaluative metering is the primary mode used by most modern cameras. It is based on a grid or zonal system that averages exposure across sections of the scene while discarding extremes of light or dark in order to find the middle or average exposure.

Spot Metering

Spot metering takes a reading from a smaller section of the frame. Most spot meters work between 1% and 5%, but typically around about 2.5%. This is important when taking a reading of a small section of a frame, particularly when that section is darker or lighter than the rest of the frame.

Spot metering works well when shooting a speaker at a podium or in a church where the background may be dark but the speaker is lit by a spotlight. You will get an accurate reading if you place the centre point over the subject’s face because the spot meter measures from the very centre of the image. If you rely on centre-weighted or evaluative metering in this situation, the camera will overcompensate for the dark background and the light meter reading will over- expose the subject’s face.