Olympus E-3 User Manual page 64

When the flash is ready and you subject has been briefed, trip
the shutter. If using P, A or S modes, the camera will first fire a
pre-flash metering burst from the built-in unit (irrespective of the
AF ILLUMINAT setting). This is used to calculate the correct
amount of flash power needed for the main subject.
Thereafter the camera will then open the first shutter curtain and
simultaneously fire the flash. This completes the exposure of the
nearby subject. If set to P, A or S modes the camera will then
complete the exposure by measuring the ambient light behind
your subject and close the shutter once the exposure has been
completed.
As the amount of background illumination drops, the exposure
time will increase but the result will normally be correctly
calculated.
SLOW2
The problem with firing the flash as soon as the first curtain has
opened is that any ambient light available in sufficient quantities
will cause any moving object in the frame to register as a frozen
subject followed by trail of light in the direction of the movement.
This does not look natural.
However, when set to
completes the exposure and, just before the second curtain is
released, the flash is fired to "freeze" the subject at the end of
the motion trail as follows:
SLOW2 the camera opens the shutter,
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