More than one combination of shutter speed and aperture will produce the same exposure. The various program modes choose the settings for a digital camera differently based on what is usually the best compromise for that type of image. Full manual metering is still the ultimate photographic interpretation of the scene. However, by selecting a mode the camera’s computer has more of an idea what the scene is about and what camera setting to prioritize.
Full manual metering allows the greatest creative control over exposure, particularly in unusual situations. However, modern digital cameras have un-precedented computing power and a range of adjustments to make life easier for the photographer, leaving the photographer to concentrate on composing the image.
Particularly in situations where the photographer has no control over the lighting or the subject, the speed of automatic metering can help get a good exposure when a rare moment presents itself. The cat drinking from the birdbath is an example of a chance shot where the digital camera was set to full auto operation allowing the capture of the fleeting moment.
Many digital cameras can select the sensitivity, or ISO setting, adding to the versatility of the automatic modes.
Camera manufacturers offer a range of program mode options to suit particular common situations, here are some of the common types:
Landscape: selects a slower shutter speed and a wider aperture to maximize the depth of field.
Portrait: selects a wider aperture to reduce the depth of field to highlight the subject by making the background slightly out of focus.
Macro: optimizes shutter speed and depth of field for close up shots.
Sports: sets the autofocus to continuous focus and prioritizes shutter speed to help capture fast moving action.
The photographer can dial in exposure compensation adjustment of the automatic metering in complex lighting situations, while retaining the dynamic nature of automatic metering.
The photo below of a digital camera manual page is one of a series taken using some of the mode settings to illustrate the different combinations of shutter speed, lens aperture, and ISO selected by a digital camera:
Macro: 1/90 @ f6.7 ISO 800
Landscape; 1/45 @ 6.7 ISO 400
Portrait : 1/90 @ f5.6 ISO 400
Normal: 1/90 @ f5.6 ISO 400
When set to Auto Picture mode the digital camera selected the macro mode for this shot.
When there is time, or the situation demands it, the versatility of many digital cameras allow the photographer a range of exposure controls with varying degrees of automatic assistance.
Four main exposure modes are:
Program: the digital camera selects aperture and shutter speed, although the photographer can customize the settings.
Aperture priority: the photographer sets the lens aperture and the digital camera selects the shutter speed.
Shutter Priority: the photographer selects the shutter speed and the digital camera selects the aperture.
Manual: the photographer chooses the aperture, shutter speed and ISO sensitivity.