What Spot Metering Is and When to Switch to It
Your camera decides how bright to make a photo by measuring the light in the scene, and it gives you a choice of how much of the frame to measure. Most of the time it reads almost the whole frame and evaluates the scene as a whole, which works well for ordinary, evenly lit scenes. But some scenes fool that approach badly, and that is where spot metering comes in. It is the mode that tells the camera to ignore everything except one tiny patch and expose for that. Knowing what it does, and the handful of situations where you should reach for it, will rescue a lot of shots that would otherwise come out as silhouettes or muddy gray.