Learn How the Exposure Meter Behaves

Monday 1 September 2025, 16:32 by Nando Harmsen | 3,996 views | 2 comments

This article was translated from Dutch with the help of AI. Read the original.

Every photo requires the amount of light to be measured. The aperture and ISO setting then determine a shutter speed. Learn how your camera measures light and where the pitfalls are.

Modern cameras often have three or four different metering modes. These roughly consist of an average reading across the whole image, an average reading across a small part of the image, or an average reading from a small spot.

Canon's metering methods. You can use them, but first learn how your exposure meter behaves. Learn to walk before you run.
There are different names for these, and there are sometimes variations. For convenience, I distinguish three types. From large to small, these are average metering, partial metering and spot metering.

Partial metering and spot metering take a reading from a small part of the image. The rest around it is not measured and does not count. This allows you to take a reading from a very specific area.

The major disadvantage is that it is very important for the area or spot being measured to be in exactly the right place. If you move off by even a small amount, your reading may already be wrong. This can lead to unpredictable results.

Spot metering measures an extremely small part of the image. Keep the spot on your subject, otherwise the results will be unpredictable.
If you want to get to grips with measuring light and learn to anticipate certain lighting situations, my advice is to use average metering. I always use it and know when I need to compensate.

If you know that the light is measured across the whole image, you can assess at a glance whether the result is correct. The amount of light and dark areas in the image will then be roughly equal. A rough estimate is sufficient.

If there are more dark areas than light ones, you know that the light meter will make the exposure too long. The photo will be too light. The more dark areas there are, the lighter it will be. You compensate by using a shorter exposure.

For this photo, I deliberately underexposed by 1 2/3 stops, otherwise the light trail in the photo would have been overexposed. I knew this beforehand because I can see what is going to be measured.
If there are more light areas than dark ones, the light meter will make the exposure too short. The photo will be too dark. The more light areas there are, the darker the photo will be. You compensate by making the exposure longer.

Most of the image is bright sky. Because I use average metering, I know before I point the camera that I need to overexpose to avoid a silhouette.
How much shorter or longer the exposure needs to be depends on the ratio of dark to light. If roughly 3/4 of the image is light, you can use an exposure that is one stop longer. If there is even more light, choose two stops. For dark areas, it works the other way round.

You need to practise this, and you need to learn to see it. Doing it often is the key to success, and you also have the LCD screen to assess the result immediately.

By sticking to average metering across the whole image, you learn to assess the lighting situation. You learn to anticipate and to use exposure compensation based on what you have in the frame.

An unedited photo. Half light and half dark. Exposure compensation is not needed. With more sky in the frame, it would be. Just as it would be if there were more ground in the frame.
It does not matter at all whether you use manual exposure settings or leave some of the settings to the camera. In manual mode, you adjust the shutter speed by hand. In, for example, aperture priority mode, you use the exposure compensation button.

Whatever you use, you have the same amount of control over the exposure and the end result is exactly the same. but the most important thing is to learn how your exposure meter responds to the available light.

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