On The Mecablitz - Metz Canon SCA 3102 M3 Manual Del Usuario

mode A of the mecablitz, an LED will light up for
approx. 3 seconds as a visual "ok" signal to
indicate correct exposure.
Some flash units (mecablitz 40 MZ-2, 40 MZ-3,
40 MZ-3i, 50 MZ-5, 54 MZ-..., 70 MZ-5)
supplement the visual indication by an acoustic
signal (bleep). For further details please refer to the
operating instructions for the mecablitz.
Note:
The viewfinder of the EOS does not indicate
whether the exposure was correct!
10. Second-curtain synchronisation
(REAR)
Synchronization with the shutter's second curtain
(REAR) is particularly advantageous when shooting
moving objects that have their own source of light
with a slow shutter speed (longer than 1/30th
second). Second-curtain synchronisation gives a
more realistic impression of movement because
the light streaks behind the light source instead of
building up in front of it, as is the case when the
flash is synchronised with the first curtain.
Mount the camera on a tripod for this mode to
avoid camera shake with slow shutter
speeds.
Note:
Turn off this function after exposure, otherwise the
unwanted slow shutter speed could result in
camera shake with "normal" flash shots in the P
camera mode or in the programmed image control
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