Correcting your exposures

Why your camera meter can get things wrong – and steps you can take to deal with it

Trying to achieve a good exposure with a digital camera is world away from the occasional fingercrossing that came with shooting film. Being able to preview the results on your Canon’s rear LCD screen and check the brightness range with the histogram means that you know exactly what you’re getting straight out of the camera, and can make any exposure adjustment to ensure good results.

And you will need to make exposure adjustments at some point. Despite a top-of-therange Canon body, such as the 5D Mark IV, being loaded with a 150,000-pixel metering sensor that can recognize colour and faces as well as brightness – it is, in effect, a miniature imaging sensor – it can still get things wrong.

Rather than measuring the light that’s falling onto the subject of a photograph, your camera measures the light that’s reflected by the subject into the lens, and it’s this that can lead to exposure errors. Camera meters are tuned to approximately 18% grey

– they assume that the world is a midtone grey that reflects approximately 12-18% of the light that falls on it. Although many scenes average out to an overall midtone, there will be plenty that are either darker (and reflect less than 18% of the light that falls on them) or brighter (which reflect more than 18%). Your camera, however, still wants to make an exposure that’s closer to midtone, which can sometimes result in dark scenes looking too bright and bright scenes looking too dark.

If the scene or subject is bright, then you’ll need to add more light to keep it bright in the photo. Do the opposite when metering a dark object – take light away, essentially, to keep it dark. If you don’t, then the camera will assume that the bright object or the dark object should appear as a midtone in the image.