I was browsing the OM2 repair manual and an extract of Mannheim's 'The OM
way' and between them they provide the answer to why sync is marked at
1/30th not 1/60th for manual operation. Apologies if anyone has posted this
answer and I missed it.
Imagine for a moment that at 1/60th, the shutter is fully open for just
enough time for a complete flash dump. There is a delay between the release
of the closing curtain magnet and the actual curtain starting to move. This
means that the magnet will release at some point during the shutter -
fully - open period. The connection between the quench contact and the
magnet is permanently wired, which means that the flash will receive a
quench signal at some time during its 'full dump' period. This signal will
not be related to a light measurement, as the shutter is in manual. The
flash is therefore reduced in guide number by an unspecified amount.
Even if you put the flash into manual mode, it will still receive the quench
signal and act on it.
I have no data on the actual timings involved, but they surely vary from
camera to camera, and therefore it would be impossible for Olympus to
guarantee correct flash operation at 1/60th using a QA310 or T series flash.
Since the shutter and X sync circuits are identical to the OM1, 1/60th
should present no problem for a flash with no quench contact.
In auto mode, the same timing problem exists, meaning that even with perfect
correlation between the viewfinder meter and TTL, the gun would be quenched
early at 1/60th. With the N series, the second contact forces the shutter to
1/60th or thereabout. I presume that this is a bastardised 1/60th, more akin
to the 1/40th of the OM10, so that the shutter - fully - open time is enough
for a full dump plus the delay time on the magnet.
Julian
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