[rollei_list] Re: shutters
----- Original Message ----- From: "Peter J Nebergall" <iusar4s@xxxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Sunday, September 30, 2007 8:32 AM
Subject: [rollei_list] shutters



Shutter Question:
I have a number of older pieces, Rollei and Zeiss, with Compur-Rapid shutters. My Cord 5 has a Synchro-Compur. I've been told the 2 types are internally different. My question is performance. Does the Synchro-Compur do a materially better job? How accurate is a 
Compur-rapid in good nick?

PeterNebergall
Deckel made a number of shutters under the Compur name. The earliest ones had a small dial at the top to set the speeds. About 1930 these were replaced with a shutter with the speeds set by a ring aroung the case. These also have a somewhat different mechanism. The Compur-Rapid was a rim-set shutter with the addition of a booster spring for the highest speed. This allowed speeds greater than 1/200th. The first Synchro-Compur shutters were similar to the Compur-Rapid but had the addition of a delay mechanism for flash synchronization with flash bulbs. Compur shutters with the LVS sytem on them are based on the shutter developed for the Hasselblad camera. These use a clock-motor type spiral spring instead of the helical springs used in the rim-set, rapid, and synchro shutters. Curiously enough the old dial set Compur used a similar drive spring. Although weak springs get blamed for slow speeds the more usual cause is dirt. Note that like nearly all shutters the higher speeds of Compurs of all types is the _effective_ speed for the full shutter aperture. Since the shutter blades take a finite time to open and close, and block some light when partially open, the top speeds are marked as being faster than they measure when you make the measurement at a small area at the center of the aperture. For smaller Compurs the difference in speed is typically about 20%, that is, at small apertures, or on a simple shutter tester, the top speed of 1/500th will measure a bit more than 1/400th when the shutter is working normally. The difference becomes less for longer shutter times because the opening and closing times are constant for all shutter speeds. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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