10 MINS
Your camera’s metering system plays a vital role in picture-taking, by working out how much light should enter the camera to make a correct exposure. Be warned, though: while it’s very clever, it’s not completely foolproof. The problem with metering is that it takes an average reading (either of the entire frame or part of it, depending on which metering mode you’re in), and this reading is assumed to be a midtone, halfway between white and black.
More often than not this assumption comes out about right, but the metering system can struggle when a frame is dominated by areas of extreme brightness or darkness. For example, imagine a person standing in the snow wearing a white coat. The frame will be dominated by whites, but your metering…