Exposure is the amount of light which falls upon the sensor of a digital camera. Shutter speed and aperture are adjusted to achieve optimal exposure of a scene. Most digital cameras offer a variety of exposure modes — from fully-automatic to semi-automatic to full manual control. Scene modes have factory optimized settings for different subjects and scenes.
In fully automatic mode, when the shutter release button is pressed halfway, the camera selects all settings depending on the type of lighting and brightness of a scene. The camera also focuses automatically. When light is low or insufficient, the flash fires automatically.
Digital cameras with Program AE mode (P mode) set the shutter speed and aperture automatically. However, the user can adjust some settings such as ISO and white balance.
Aperture priority mode (AV) – Select the aperture (lens opening) and the camera automatically sets the shutter speed.
Shutter priority mode (TV) – Select the shutter speed and the camera automatically sets the aperture.
You have complete control by selecting both the shutter speed and the aperture. Digital cameras with manual modes have a manual assist indicator that indicates whether or not exposure is adequate.
Scene modes let you choose from a variety of pre-programmed modes suitable to photograph a given subject such as a portrait, landscape or fireworks. The camera settings change when moving a dial to a mode that matches the scene you plan to photograph.