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John Cribbin
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 21, 2005 - 12:41 pm: | 
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Hi folks,
As a collector of former Soviet Union rangefinder cameras, I have undertaken a fair ammount of maintainance over the years. However there is one area where I have never been able to get my head around.
Many models have a separate slow speed mechanism, normally 1/30 and slower. I have observed on many occasions, that while both curtains run fine at higher speeds, at lower speeds the second curtian is slow in closing.
To my mind, both curtains are closed by releasing the energy stored in the springs. So delaying the release of the second curtain, should have no effect on the speed at which it travels once released. But as it obviously does, is there something I'm missing?
Thanks. |
Jon Goodman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 21, 2005 - 03:48 pm: |
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On those Soviet cameras...On the faster speeds, the two curtains run across the opening together, with a slit of varying width (depending on shutter speed) between them. So, in effect, curtain no. 1 will help draw curtain no. 2 along with it. Keep in mind curtain no. 1 will have a slightly greater spring tension and the shutter ribbons between 1 and 2 will have some degree of drag (friction) between them...geese flying in formation v goose flying alone, and so forth. However at speeds of 1/30 and below, the first shutter curtain has finished its travel when no. 2 starts moving. So, if no. 2 is prone to be a little slow, that slowness gets magnified. There is no momentum "help" from curtain no. 1 and its shutter ribbons any longer. In fact, at that point, curtain no 1's ribbons are not moving and as such provide some drag to the ribbons of no 2. In a good shutter, the second curtain should have enough tension to travel across the opening crisply, but not with extreme speed or force. I'd say there could be dried lubricant in the spring roller of curtain no. 2, or the spring tension could be off. Further, in some Soviet cameras, (Zenit SLRs) I've seen a situation where curtain no. 2 will drag against something in its path, and this can worsen things.
Jon |
Ed
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 22, 2005 - 04:13 pm: |
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Typically, on a shutter of this type, the slow speeds (below 1/60) are controlled by a speed escapement--never worked on any Russians, but that the way the Japs and Germans do it. If that is the case, possibly the escapemtn needs a CLA. |
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