Archived posting to the Leica Users Group, 2002/01/13

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Subject: RE: [Leica] NEW M7 MAJOR CROCK-POT CROW PARMESAN
From: John Hicks <jhicks31@bellsouth.net>
Date: Sun, 13 Jan 2002 11:46:57 -0500

>A flashbulb has an ON time that is measured in many tens of
>miliseconds.....   A ELectronic flash is tens  of
>microseconds.......different story...

  Right. Now think of a true strobe, rapidly flashing. That's how it works.
  Now...we can trigger the flash at any point in the first or second
curtain's travel simply by adjusting time at which the synch contact
closes, so the contact closes when the first curtain starts moving, the
strobe flashes while the curtains are traveling and stops when the second
curtain closes.
  The actual duration of curtain travel is the same for all speeds above,
in the case of an M Leica, 1/50, therefore the flash can strobe for a fixed
time, no need for that to change.
  The way TTL control works is to simply clip the duration of each pulse.
  I don't know what frequency Olympus uses but it's high enough that
there's no banding.

John Hicks
jhicks31@bellsouth.net

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