How Aperture Works in Preset ModesMacro
Macro mode is an automatic setting mode where the camera is predisposed to use the large aperture to compensate for the DOF compression of close-up shooting. In this mode you can not set the exact aperture you want but you can lessen your chances of an out of focus close up subject by using this mode.
Landscape mode is basically a large DOF mode. Landscape is programmed to give the smallest aperture (largest F-Stop) possible in order to ensure a large depth of field. This means that the shutter speed will be slower. If your camera does not allow Manual or Av mode and you are wanting to shoot a subject where the background is in focus, try the Landscape setting.
Portrait mode uses a large aperture to create a small DOF. Portrait is programmed to have a shallow depth of field (large aperture/small F-Stop) and use a slow film speed in order to throw the background out of focus and obtain a very fine film grain. Use this setting anytime you want a blurry background.
Manual setting is marked "M" on newer cameras and is, in effect, the only setting on manual cameras. Manual mode means that you are fully in charge of the settings of your camera. If you set the aperture/F-Stop while in M mode, you will need to make an adjustment to shutter speed yourself in order to maintain a correct exposure. Use your camera's light meter to ensure the values are in balance.
The setting on your camera marked "Av" is called Aperture Priority mode. This means that if you use Av mode and set the aperture/F-Stop, the camera will adjust your shutter speed value to maintain a correct exposure.
Program mode is marked by a "P" on the few cameras that have this option. In program mode, your camera responds to some preset conditions you programed through the menu. Generally, this mode allows you to set either the shutter speed or the aperture while the camera adjusts the other setting to maintain proper exposure.