A (Aperture Priority) Mode; S (Shutter Priority) Mode - Olympus E-3 User Manual

POWER USER TIP: You can set the shift function to change values in
1/3, 2/3 or full EV steps so as to speed up the shift function operation.
This will, if set to 1 EV step as an example, allow you to go from 1/125
second at f=11 to 1/60 sec at f=16 with one "click" of the dial which
can, in some cases, speed up handling.(UMPg103)

A (APERTURE PRIORITY) MODE

This option permits you to select the aperture while the camera
sets the correct shutter speed for you.
The camera will accomplish the shutter speed adjustment within
the range of available settings without reference to the lens in
use and/or any consideration of straying into the "hand shake"
zone (generally anything below 1/30 second with a 25mm 4/3
lens) so you need to keep your wits about you if you are setting
smaller apertures for deep depth of field.
If using a high ISO value and a wide aperture you may see the
shutter speed indicator blinking. This indicates that the required
value needed to balance the aperture/light level is beyond the
1/8000 second maximums peed of the camera.
POWER USER TIP: If the ISO setting is on AUTO the camera will first
push up the ISO setting to the highest possible setting before dropping
the shutter speed below 1/30 second. So, if you are using the A mode
in gloomy conditions, consider making use of AUTO ISO and limiting
the maximum setting to a level of your choice for an almost "fail-safe"
application of A mode

S (SHUTTER PRIORITY) MODE

This option permits you to select the shutter speed while the
camera sets the correct aperture for you.
The camera will accomplish the aperture adjustment within the
range of available settings if at all possible. If the aperture value
indicator blinks then it is not possible to couple the aperture with
the set shutter speed.
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