FWIW, and going again by memory, the typical opening and closing
times of shutters like the Compur is about 1/1000 second. The shutter
markings are for wide open. As the iris is stopped down the opening and
closing times become a greater part of the effective exposure time. At
1/500th marked the total open time, i.e. exposure time for small stops
of a Compur No.1 or similar will be no less than 1/400 second. A fresh
shutter will be around 1/380th second. Opening and closing times may be
shorter for the highest speed for a shutter with a booster spring, the
above is for such a shutter. For shutters with single springs as the
later Compur used in Rollei the opening and closing times will be
constant at all speeds so the marked speeds are closer to the effective
speeds as the speed is lowered. Effective speed is always slower than
marked speed and, as you say, speed generally decreases with age but not
for all speeds. For instance, as the lubricant for the regulator gears
gets old it may keep the gears from moving correctly so there is little
or no change between some slower speeds. At the slowest speeds, i.e. one
second, the speed can become shorter due to mis alignment of the
regulator or weakening of springs in some shutters. Considering these
were mass-produced precision machines they do pretty well.
One advantage of Wollensak and Ilex shutters is that the springs are
all hair type springs so its not to difficult to make new ones from
piano wire. Compur and Compound shutters used coil springs of various
sorts, not so easy to make.
Contrary to popular wisdom springs do not get weak with age or
constant deflection. Rather it is working that can cause the spring
material to fatigue. Using a shutter a lot may slow it down but just
leaving a shutter cocked, even for years, does not weaken the springs.
BTW, the Wollensak shutters used on Speed/Crown Graphic cameras has
an advantage over the Kodak and Compur shutters found on some, that is
that the shutter release has a constant resistance to being tripped. In
Kodak and Compur shutters, especially those with high speed booster
springs, the force needed to trip the shutter is considerably higher at
the highest speed than the others. This makes for difficulty if one is
using a solenoid type shutter tripper. To use the solenoid at the
highest speed one needs an extra battery while the Wollensak will trip
and stay synchronized (if you use it for flash) at any speed.
Wollensak made very good shutters and ho-hum lenses.
On 4/8/2017 3:49 PM, Tim Daneliuk wrote:
On 04/08/2017 04:14 PM, Eddy Willems wrote:
20 years ago I went with a lot of camera's from my studens to an Hasselblad
technician who had a shuttertester,
with most of the camera's there where problems, in ten test on the same
shutterspeed we saw an e fluctuation that could not bet tolerated.
I had also a packard shutter with mee and he was everytime just 1/25 of a second
he had 5 people asked to push the shutter and the shutter gave with everybody
1/25
it was that day the most accurate shutter
I have rehabbed many old cameras and tested quite a few old mechanical leaf
shutters. Even after a CLA, my experience is this:
- Anything below 1/250 is good if it's within 1/2 stop.
- 1/1000 and 1/500 is good if it's within 3/4 to 1 stop (usually slow).
- You cannot just measure shutter open time because the center of the opening
gets light longer than the edges. As I recall, the "real" shutter speed
test in a lab involves a bit of integral calculus to measure the "area under
the curve" of light vs. time somehow. (Engineers will recognize this as
analogous to RMS calculations for AC power.) Someone else here may know
more about this.
- Mechanical shutters - even when very well set up or even new - exhibit
variability from firing to firing.
The point is that these are mechanical devices with a normal range of
variability.
Yes, that includes the finest Copals, Hasselbalds, Seikos ... take your pick.
(If anyone doubts this, I will be happy to provide spreadsheets with examples of
how center timing various over multiple firings.)
The good news is that shutters usually get *slower* over time, which actually
increases
exposure slightly. This is great for monochrome film in most cases, OK for
color film,
and possibly deadly for transparencies.
As I have noted here often, I have a stable of elderly film cameras - I've
resurrected
the dead. Some I had CLAed, some I cleaned up myself. But with the older
shutters like
the old Supermatics on my Graflex cameras - I fire them a couple of times at
the desired
speed before pulling the dark slide, just to "warm them up a little".
