P, S, A, and M modes are referred to as "exposure modes" because they let you control settings that determine exposure, namely shutter speed and aperture. Each of these modes offer different degrees of control over shutter speed and aperture.
Exposure Mode: Mode P (Programmed Auto)In mode P, the camera automatically adjusts shutter speed and aperture for optimal exposure. You can, however, choose other aperture and shutter speed combinations that will produce the same exposure: this is called "flexible program". Choose programmed auto for snapshots and in other situations in which you don't want to miss a shot.
P (Programmed auto)
Exposure Mode: Mode S (Shutter-Priority Auto)You choose the shutter speed and let the camera automatically adjust aperture for optimal exposure. Use to emphasize motion.
S (Shutter-priority auto) Faster shutter speed (1/100 s)
S (Shutter-priority auto) Slow shutter speed (1/13 s)
"Shutter speed" is the time the shutter is open during an exposure. It is usually expressed in seconds or fractions of a second: 1 s, 1/2 s, 1/4 s ... 1/250 s, 1/500 s. Fast shutter speeds reduce the amount of light that reaches the image sensor, while slow shutter speeds increase it.
S (Shutter-priority auto) Slow shutter speed (1/125 s)
Exposure Mode: Mode A (Aperture-Priority Auto)You choose the aperture and let the camera automatically adjust shutter speed for optimal exposure. Use to control background blur.
A (Aperture-priority auto) Wide aperture (f/1.4)
A (Aperture-priority auto) Small aperture (f/5.6)
Aperture controls the amount of light reaching the image sensor and is usually expressed as an "f-number": f/1.4, f/2, f/3.5, f/5.6, f/8, f/11, f/16, f/22, f/32.
Changing the f-number changes the size of the opening through which light enters the camera (the aperture) and thereby changes the amount of light passing through the lens. High f-numbers stop the aperture down, allowing less light into the camera, while low f-numbers increase the size of the aperture and let more light into the camera. Going from an aperture of f/4 to f/5.6 reduces the amount of light entering the camera by half and halves the brightness of the image on the image sensor.
A (Aperture-priority auto) Wide aperture (f/3)
A (Aperture-priority auto) Small aperture (f/9)
Exposure Mode: Mode M (Manual)
The camera offers a choice of the following shooting modes.
P：Programmed auto
S：Shutter-priority auto
A：Aperture-priority auto
M：Manual.
Mode P (Programmed Auto)
Flexible Program
In mode P, different combinations of shutter speed and aperture can be selected by rotating the command dial (“flexible program”). Rotate the dial right for large apertures (low f-numbers) and fast shutter speeds, left for small apertures (high f-numbers) and slow shutter speeds. All combinations produce the same exposure.
Rotate right to blur background details or freeze motion.
Rotate left to increase depth of field or blur motion.
While flexible program is in effect, a
indicator appears in the viewfinder and information display. To restore default shutter speed and aperture settings, rotate the command dial until the indicator is no longer displayed, choose another mode, or turn the camera off.
Mode S (Shutter-Priority Auto)
Choose a shutter speed.
Rotate the command dial to choose the desired shutter speed: rotate right for faster speeds, left for slower speeds.
Mode A (Aperture-Priority Auto)
Choose an aperture.
Rotate the command dial left for larger apertures (lower f-numbers), right for smaller apertures (higher f-numbers).
Mode M (Manual)
Choose aperture and shutter speed.
•Shutter speed:
Shutter speed is selected by rotating the command dial (right for faster speeds, left for slower).
•Aperture:
To adjust aperture, keep the 
button pressed while rotating the command dial (left for larger apertures/lower f-numbers and right for smaller apertures/higher f-numbers).
View information on functions related to P, S, A, and M Modes.
