When photographers talk about ‘taking a reading’ or ‘metering a subject’, they’re usually talking about taking a Spot or Partial meter reading from a specific area in a scene and locking the exposure in. This guarantees that the subject you’re metering for will be exposed correctly.
However, you need to make sure that the area you’re taking a reading from is a midtone. If the area is dark in tone, and you don’t dial in ‘-’ exposure compensation to make it dark, this area will be set as the midtone, and the picture will be overexposed.
If the area is bright in tone, and you don’t dial in ‘+’ exposure compensation to make it bright, then this area will be set as the midtone, and the picture will be underexposed.
In our examples below we show you the effects of different metering modes and where within the frame you should take your reading.
Evaluative has done a good job here, although the highlights are slightly blown.
How Evaluative metering gets it wrong
Your Evaluative metering mode is reliable and accurate in the majority of day-to-day shooting situations. However, the exposure it comes up with is linked to the focus point (and AF points that have almost achieved focus), and this can cause problems if the subject in focus is very dark or very light in tone.
The solution, as always, is to check the histogram, and dial in exposure compensation if required (What is exposure compensation? See our cheat sheet).
Spot metering – highlight
Taking a reading from the white area makes the picture underexposed.
Spot metering – shadow
Taking a reading from the black area makes the picture overexposed.
Taking a reading from the grass (a midtone) creates a balanced shot.
Exposure and metering adjustments
Capturing the optimum exposure in-camera is critical if you want to get the best-quality results, and whichever metering option you choose there will often be some room for improvement. Your DSLR has a wide range of features that you can take advantage of to ensure you end up with the best-possible exposure, even in the most demanding of lighting conditions.
By rotating the Quick Control dial or pressing the ‘+/-’ button and turning the control dial (depending on the camera), you can apply compensation in 1/3 or 1/2 stop increments up to +/- 5EV. Reset to 0 when you’re done.
Your AE Lock function enables you to lock an exposure setting independently from the focus, then re-frame the shot. Dab the shutter release to activate the metering system, fill the frame with the subject you want to meter, then press the ‘*’ button and recompose the shot.
The auto exposure bracketing (AEB) function enables you to take three consecutive shots: one as-metered, one slightly overexposed and one slightly underexposed. You can set the bracketing increments, and use AEB in conjunction with exposure compensation.