Ralf,
As a non-expert I understand that the factor that controls the flash sync time
(1/60) is determined by how long it takes the leading and trailing shutter
curtains to go from one side of the frame to the other. You have to get the
front curtain all the way
across, fire the flash, and then start the trailing curtain moving. The time
the film is exposed is the time beteen the leading one passing and letting
light through to the film, and the trailing one passing and blocking it off.
(Vertical curtains have
an advantage with less distance to move than horizontal so even at the same
speed of curtain movement they have an advantage. Should we call horizontal
ones CURTAINS and vertical ones BLINDS?!)
The factor the controls the fastest shutter speed (1/2000) is to a small part
related to the speed of the curtain movement, but more importantly how narrow
the gap is between the back of the leading curtain and the front of the
trailing curtain. For all
speeds faster than the flash sync speed, both curtains move together with an
open slit between them. The width of the slit determines the exposure time:
narrow = fast. Accuracy of that high speed is determined by tolerances in the
gap, related to the
accuracy in the timing of the release of the two curtains.
So we can assume that the curtains in the "more modern cameras" move at the
same speed as the earlier OMs, hence the same 1/60 sync speed, but the width of
the slit is more accurately controlled in the modern cameras and 1/2000 is
reliably achieved. I'm
sure it would have been possible to set the electronic shutter release timings
for 1/4000 or 1/8000, but I expect the manufacturing tolerances meant that they
could not reliably meet the exposure accuracy specification so they settled for
1/2000.
Now the experts can correct me...
best regds
Jez
>The sync (1/60) speed is limited by the use of a horizontal cloth
>focal-plane shutter. The benefit of this shutter is reduced camera height,
>I believe.
>Sincerely,
>Roger Key
>By the way, I cannot explain why the sync time (1/60) is still the same in
>the modern cameras (OM-3/4)
>whith shorter exposure time (1/2000) than the old ones (OM-1) with 1/1000
>Ralf Loi
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