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RE: [Rollei]shutter speed question

At 10:09 AM 06/08/2000 -0400, you wrote:
 >Hello all,
 >I just read in Mannhiem's rollei book that if you are using a fast shutter
 >speed (like 1/500 sec, 1/400 sec), the shutter speed should be set before
 >the film crank is wound to the next frame. He gives no reasons for this but
 >suggests that when it is done, less effort is needed to set the film speed
 >but also prevents shutter damage. Is there any truth to this?
 >I know nothing about the internal workings of shutters but is there a
 >difference if the shutter is left cocked at a high shutter speed as opposed
 >to a low shutter speed as the manual suggest that the shutter should not be
 >left cocked for any extended periods of time.
   It depends on the shutter. Older Compur-Rapid and Synchro-Compur 
shutters have an additional spring which is tensioned by the speed cam at 
the highest speed. If you attempt to set the shutter to the hights speed 
after its been cocked you stand a chance of jamming the spring under the 
speed cam. You can set it to a lower speed after cocking. The extra spring 
puts quite a bit of force on some parts of the shutter so its a good idea 
to avoid changing the speeds of these shutters when cocked.
   The later Compur, as used in Rollei E's and F's and on Hasselblad lenses 
does not have an extra spring. These shutters can be set for any speed 
whether cocked or not.
   The business of not leaving shutters cocked is mostly due to a 
misunderstanding of springs. Springs wear by fatigue rather than by being 
tensioned, provided the tension does not exceed the elastic limit of the 
material. On many shutters there is some extra force on parts of the 
shutter when left cocked. Probably older Compur and Kodak shutters with 
booster springs should not be left cocked in the highest speed for this 
reason. The late type Compure is intended to be left cocked, as it must be 
in a Hasselblad, they are pretty much bulletproof. The resting tension of 
the springs in these shutters is pretty high even when uncocked.
- ----
Richard Knoppow
Los Angeles,Ca.