Neil Baird Photography

Your camera's light meter

In the early days of photography photographers would use a handheld light meter to gauge the brightness of the light they were shooting in, and work out what settings they might use to get a good exposure.

These days almost all cameras – and all digital cameras – come with a built in light meter to do the same thing. The light meter is so much a part of the camera that some of us forget (or don't know) that there is a light meter at work behind the scenes whenever we go to take a shot.

This is very convenient and very very helpful, as without it we would have to guess what the light levels are and then guess at what our settings should be. And most of the time the light meter does the job its paid to do, and deserves some praise. Sometimes though it just can't get it right – usually under specific circumstances that it finds difficult to understand. Its been told that it should read the light level and then make adjustments to the camera settings to ensure that the overall balance of light throughout the scene averages out to mid-tones. But in situations where there are a lot of bright tones, and some dark tones (like a figure back-lit by a large bright sky) or a light object on a dark background, the meter and camera together will often get it wrong. That's when we might use Exposure Compensation to adjust the settings suggested by the camera.

But there's more…

Your camera's light meter also has different ways of reading the light, and each of these can produce different results under different circumstances.

Most cameras by default are set to Matrix metering (Canon calls it Evaluative, and Sony call it Pattern) where the whole scene is taken into account in the evaluation of the light. And this works well in many cases, but not all.

The other modes are Centre-weighted, where the whole scene is analysed but more emphasis is given to the centre section. and Spot, where a much smaller area in the centre of the frame is measure, and everything else ignored. Canon also has a mode on some cameras called Partial, which is like Spot metering but the area measured is larger.

You can get away with keeping your camera in Matrix as long as you know what it's limitations are likely to be, and can therefore make adjustments to the camera's suggested exposure settings when you need to. The same is true for all the modes.

But in order to really master exposure its a really good idea to learn to use the other modes so you understand how they work in real situations, and so know when you might turn to them. You can only really get this with practice – so practice in situations where you can take the time to experiment.

Symbols for the different modes

Your camera may not tell you what the name of the mode is on the symbols that you see, so you need to get familar with them if you are going to be using them from time to time.

And what do they actually do?

The red/pink overlays on the following images show the approximate area evaluated by the meter in each of the modes...

Metering Mode Experiments

I wanted to see how my Canon 5d mkiv would cope shooting a simple image on a white and then on a white background where the subject is a different size in the frame using different metering methods. I shot them all in Aperture Priority and made no Exposure Compensation adjustments. It might surprise you to see how the same subject in the same scene and under the same lighting conditions can turn out so different.

 Can you work out why they came out as they did?