[rollei_list] Re: 2.8C shutter speed
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 4 Oct 2006 16:21:02 -0700
----- Original Message -----
From: "ERoustom" <eroustom@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, October 04, 2006 2:46 PM
Subject: [rollei_list] 2.8C shutter speed
Hello all,
My 2.8C can only be put into or taken out of 1/500 speed
when the shutter release trigger is at rest (between
shutter releases). The self timer won't set in 1/500
either. My manual is in French - I was bad at French
through nine years of school with the kindly nuns of
Lourdes, and still am. C'est normal?
Thanks,
Elias
Its normal. The older, non EVS, Synchro-Compur and
Compur-Rapid shutters have a second spring to boost power
for the highest speed. Its partially tensioned by the speed
cam, thats the extra resistance one feels when going from
1/250th to 1/500th and is also the reason for the long space
between these two speeds. This spring is fully tensioned
when the shutter is cocked. There is very considerable force
on the end of the spring that contacts the speed cam. This
can cause wear if the speed is shifted to a lower speed from
1/500th often. If you try to move it to 1/500th when the
shutter is cocked the end may be forced under the speed cam
jamming the shutter and requiring the shutter face plate to
be removed to fix.
There is no particular problem in shifting among other
speeds while the shutter is cocked although more force is
applied to some parts than when the shutter has been fired.
While leaving the shutter cocked does not harm the
springs (contrary to the popular wisdom) the force applied
internally, particularly at 1/500th, is considerable. I
would not leave the shutter cocked at the highest speed for
very long periods (days).
The later LVS/EVS shutter uses a different kind of spring
motor and is, in fact, quite different in other respects.
These shutters use a single spiral spring similar to a clock
motor. It is always under partial tension so cocking the
shutter simply increases the steady tension somewhat. There
is no booster spring and none of the speed regulating parts
is subject to constant pressure from the motor while the
shutter is cocked so speed change can be made at any time.
These shutters were developed for the Hasselblad and are
meant to be left cocked all the time without damage.
A note about springs: Springs are weakened by the fatigue
caused by constant flexing. Constant compression or tension
does not change the shutter provided its within the elastic
limit of the spring material. Generally slowing of the
higher speeds of a shutter is due to increased friction due
to wear or to dirt. Also, the top two speeds (at least) of
most shutters are marked for the _effective_ shutter speed
for the full clear aperture of the shutter. Since the
opening and closing time of even very good shutters is
considerable (a total of about 1/1000 for Compurs) the
efficiency become rather low at high shutter speeds.
Typically, for a Synchro-Compur or Compur-Rapid shutter of
small or medium size the total open time of the shutter will
be about 20% longer than the effective speed for maximum
aperture. So, when measuring shutter speed with a simple
interval timer like the Calumet Shutter Tester, which tests
total open time, the indicated speed will usually be
significantly longer than the marked speed even when the
shutter is operating perfectly. For the Compur total open
time at the speed marked 1/500th will be around 1/390th
second for a perfect shutter. This error in measurement can
cause people to think shutters are running slow when, in
fact, they are not.
Slow speed operation is regulated by a clockwork
mechanism which is subject to lubrication problems and dirt.
At least up to about 1/100th the measured total open time
should agree with the marked speed. Compur shutters, even
very old dial set ones, are surprizingly accurate and
repeatable.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
Rollei List
- Post to rollei_list@xxxxxxxxxxxxx
- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
in the subject field OR by logging into www.freelists.org
- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
'unsubscribe' in the subject field OR by logging into www.freelists.org
- Online, searchable archives are available at
//www.freelists.org/archives/rollei_list
Other related posts:
