Light Metering Modes – Measuring Light for Photography
For your camera to make decisions about which aperture, shutter speed and ISO settings to use, it needs to measure the available light in the scene you are trying to photograph. When you are in Automatic Mode, you cannot influence this. However, in Manual Mode, P Mode, A (Av) and S (Tv) Modes you can change how the camera measures the light and calculates the settings. We will now look at the various light metering modes normally available to you to choose from.
You will normally have a choice of 3 metering modes if your camera allows you to change this:
- Evaluative or Matrix Metering
- Centre-Weighted Metering
- Spot Metering
Some more recent high end cameras also have a highlight priority metering mode.
Evaluative / Matrix Metering
This mode looks at the whole scene and measures the light to create an average for the scene. The way your camera chooses to evaluate a scene is based upon 18% grey. This average is designed to give a balanced exposure. It means that your camera looks at the scene and tries to average everything out at about 18% grey in terms of darkness from black to white. Evaluative or Matrix Metering tries to do this over the whole scene. This mode is useful for much general photography and landscapes where you want an even metering of the whole scene.
The symbol for evaluative/matrix metering tends to be something like this:
This form of metering forces the camera to take its readings from the centre area of the frame. It is usually slightly wider than just the central focal point. This can be useful if your subject is in the centre and you want to be certain that it will be correctly exposed. Especially when the rest of the scene is quite contrasty, this can help you get more accuracy in the centre.
The symbol for centre-weighted metering tends to look like this:
If you have a very contrasty scene and your subject is not in the centre of the frame then you can use spot metering. This forces the camera to measure for its exposure at the point where you have placed your focal point. This mode is helpful in situation such as live music photography. It can enable you to keep your subject properly exposed whilst not worrying too much about the background.
The symbol for spot metering tends to look like this:
Highlight Priority Metering
Some cameras also have an additional light metering mode that helps you to protect the highlights from burning out. Highlight priority metering forces the camera to set the exposure so that any highlights in the frame are not burnt out (don’t go to pure white). This can be useful in very contrasty situations when you still want to keep some detail in the bright areas.
The symbol for highlight priority tends to look something like this:
Cameras that allow you to alter the metering often have a button that looks like the evaluative/matrix symbol that allows you to cycle through the various modes. You can find out more about how to use a separate light meter for studio photography in my blog post on how to use a light meter
© Joe Lenton, April 2016