Olympus E-1 Reference Manual page 101

Slow synchronization (1st curtain)
The slow synchronization flash is designed for slow shutter speeds. Normally, when
shooting with a flash, shutter speeds cannot go below a certain level to prevent
camera movement. But when shooting a subject against a night scene, fast shutter
speeds can make the background too dark. Slow synchronization allows you to
capture both the background and the subject. Since the shutter speed is slow, be sure
to stabilize the camera by using a tripod so as not to cause the picture to be blurred.
1st curtain
Usually, regardless of the shutter speed, the flash fires right after the shutter fully opens. This is
called 1st curtain. Unless you change it, this is how the flash always fires.
Slow synchronization (2nd curtain)
2nd curtain flash fires just before the shutter closes. Changing the flash timing can
create interesting effects in your picture, such as expressing the movement of a car by
showing the tail-lights streaming backwards. The slower the shutter speed, the better
the effects turn out. The slowest possible shutter speed depends on the shooting
mode.
P mode : 2 sec.
A/S/M mode (Bulb is also available) : 60 sec.
When the shutter speed is set to 2 sec.
2 sec.
2nd curtain
Shutter closes
2nd curtain flash fires
SLOW
SLOW 2nd-CURTAIN
2 sec.
1st curtain flash fires
Shutter fully opens
Flash mode
0
1st curtain
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