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This is how the camera adjusts the shutter speed and aperture to ensure the right amount of light reaches the film or CCD. Early cameras only had a manual mode (M) where the user had to select the aperture and shutter speed manually to ensure the correct exposure. Over the years cameras have become more sophisticated and now offer several automated modes including Program (P) - a fully automatic exposure mode that sets the aperture and shutter speed; Aperture priority mode (AP) where the user selects the aperture and the camera sets the necessary shutter speed; and shutter priority (SP, or Tv on some cameras) where the user selects the shutter speed and the camera sets the necessary aperture. Auto bracketing (AB) takes a pre-selected number of photographs, one at the suggested exposure and one to either side, so you can be sure of one accurate result. There are also several subject-based program modes that we haven't listed here that tailor the camera for particular subjects such as sports (action), landscapes, portraits, or flowers (close-ups). Some digital cameras have black & white and sepia modes. Buying advice A full auto program mode is ideal for point-and-shoot photography, but it's also useful to have some control over the exposure. The beauty with digital is that you can see whether the camera has got the shot right by previewing the image on the LCD. If not, you try again. If there is no manual control you can often preset the exposure using an auto-exposure lock or exposure compensation. The subject based program modes are often a waste of time and don't really bring much to the package. Special effects modes on digital cameras are also throw-away because all these can be created using the computer later.
Many cameras now have a built-in flash that is used to take pictures inside when the light levels are low. The camera detects when flash is needed and automatically fires it, there are usually several other modes to increase the flash's versatility. Red eye reduction fires a pre-flash to prevent large red eye pupils appearing. 'Off' turns an automatic flash off so that the camera can be used with a long shutter speed for night photography. 'On' forces the flash to fire as a fill-in for daylight pictures that have harsh shadows or to illuminate a close subject in a night scene. Slow sync fires flash and records the ambient exposure, which is great for creating image trails and creative subject movement.
Cameras and exposure meters can take readings of the light levels in a number of ways, from basic to advanced methods. The most basic is Centre-weighted (CW) or average metering that takes a measurement from most of the image area. A more sophisticated version of this is Partial (P) metering that has a narrow area of measurement that is still based on the centre of the image and Spot (S) that can measure from as little as 1 of the image. The most commonly used in more advanced cameras now is Matrix, also known as Multi-pattern (MP) or segment metering, that takes readings from several parts of the scene and produces a calculated average. Buying advice In most cases the basic metering with an auto camera is fine, especially if you have the sun behind you or it is overcast. But when you start to try more advanced shots, such as the sun behind the subject for a backlit halo effect or an archway with light streaming through the pillars or a spotlit subject against a dark background, you may find the standard meter will let you down. If you can see yourself shooting subjects like this, buy a camera that lets you switch over to spot or multi-pattern metering.
A display for modes and features in the viewfinder or top-plate of many cameras. Most display the number of photos you have left along with the battery condition and exposure mode. More advanced cameras also have the metering mode, exposure mode and flash mode displayed.
An accessory shoe on a camera that has electrical contacts to trigger and synchronise a flashgun when the camera's shutter fires. More sophisticated cameras have several connection pins for advanced communication between the camera and flash. As well as setting the camera's correct shutter speed, these dedicated pins can also control exposure and focusing modes.