Archived posting to the Leica Users Group, 2001/04/17

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Subject: RE: [Leica] RE: Was Medium format camera (now pit-bull arena)
From: "Austin Franklin" <darkroom@ix.netcom.com>
Date: Tue, 17 Apr 2001 20:37:13 -0400

> >I'd be curious if you happen to have the acceleration curves and/or the
> >open/close times for any leaf shutters?  That would certainly
> substantiate
> >or refute the claim that it doesn't matter.  My understanding that this
> >phenomenon does matter is apparently standard knowledge, and has been
> >discussed extensively on the Rollei and LF lists.
>
> Austin
>
> ALL mechanical shutters haver errors.  It goes with the turf.  But the
> errors in mechanical shutters, or, at least, the better ones, are within
> the permissible window the film will allow.  If your shutter is off 1/6
> stop, it doesn't matter, so long as the film will allow a 1/3 stop window.
>
> Marc

For the most part, I agree, and accuracy is obviously more important
depending on what film choice you make.

This is second hand information:

The opening and closing of medium size late version Compur shutters
takes about 1/1000 second total. For a #1 Compur the factory adjustment is
to have a total open time at 1/500th of about 1/380th second.

For shutters like the Compur Rapid, as found on Rollei cameras, the loss
is around 20% to 50%, perhaps 1/3rd stop to 2/3rd stop at most. The
effective speed for small stops for the Compur shutters used on Rolleis is
around 1/380th for the speed marked 1/500th, providing the shutter is in
good condition.