In any shooting mode except for manual, the camera calculates at least one of the shooting parameters for you. To do so, it measures the light coming in Through The Lens (TTL). Cameras have several ways of measuring and calculating the amount of light in a scene, which are called Metering Modes. Which modes are available depends on the camera model, but most olympus cameras have the following modes: Digital ESP, Center-weighted, Spot, Highlight spot, Shadow spot. These will be discussed later on but first we'll look at how metering works in general.

When taking a picture, you focus on a specific distance. In theory only points that are this distance from your camera are perfectly in focus. In practice however we find that points some distance closer and some distance farther away are also sharp. They aren't exactly in focus, but they are "close enough" for us not to notice. The range in front and behind the focus distance where focus is "close enough" is called the depth of field.