You're right, IMO. I've never seen any horizontal shutter rated faster than
1/2000 of the OM-3/4. All the shutters rated higher are vertically
travelling metal "blinds" shutters. And they go as high as 1/12,000 on the
Minolta Maxxum/Dynax 9! Geez, that sucker must have a tiny slit width!
Skip
From: Jez.Cunningham@xxxxxxxxxx
Reply-To: olympus@xxxxxxxxxxxxxxx
To: olympus@xxxxxxxxxxxxxxx
Subject: Was: [OM] Digital Camera that takes OM lenses (READ!) Is now:
Sync speed vs. fastest speed
Date: Wed, 21 Nov 2001 12:22:50 +0100
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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