[pure-silver] Re: old rollei over exposing
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 17 Feb 2005 23:13:21 -0800
----- Original Message -----
From: "Richard Urmonas" <rurmonas@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, February 18, 2005 7:59 AM
Subject: [pure-silver] Re: old rollei over exposing
> Quoting "Koch, Gerald" <gkoch02@xxxxxxxxxx>:
>
>> It
>> is extremely important not to leave a shutter cocked for
>> long periods of
>> time.
>
> The manufacturers of the older leaf shutters generally
> recommend
> the shutter be left cocked. From a mechanical point of
> view, the
> cocked state will result in less chance of the shutter
> misbehaving
> (going sticky) as the driving spring is much stronger than
> the return
> spring, so there is more force available to 'break free'
> any sticky parts.
>
> Richard
> --
> Richard Urmonas
Well, I've never seen such a recommendation. If a spring
is not tensioned beyond its elastic limit it probably
doesn't matter if its tensioned or not as far as losing
strength with time.
Many shutters do work as you describe. When the shutter
is cocked the restoring spring on the retarder winds the
retarder to its starting position. This usually brings the
speed control peg up against the speed cam. When the shutter
is tripped the retarder is forced over by the full strength
of the drive spring. If the retarder mechanism is glued
together sufficiently by old lubricant it might just not
move enough to allow the shutter to close again. Hard to
know. I would not leave shutters with booster springs in
their highest speed position because that puts a lot of
force on some of the parts and I suspect the booster springs
may be close their limit.
Springs wear pretty much because of work hardening due to
cycling rather than constant tension or compression.
The Compur shuttes used in Hasselblads and the similar
shutter used in EVS Rollei cameras was designed to be left
cocked all the time, they must be in Hassy cameras.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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