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Test results for an old shutter



 
 
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Old August 9th 09, 10:18 PM posted to rec.photo.equipment.large-format
David Nebenzahl
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Posts: 1,353
Default Test results for an old shutter

Moving closer to my goal of actually taking pictures with my antique
wooden camera (Rochester Optical Co. "Universal" 5x7), today I tested my
shutter so I can know how to estimate my exposures. Here are the results.

The shutter is a Rochester Optical & Camera Co. (R. O. & C. Co.)/Bausch
& Lomb "Victor", carrying a lens marked only as a "SYMMETRICAL 5x7" [1].
It's a pneumatic shutter with 5 (nominal) speeds + B & T. The shutter
has been completely overhauled and cleaned (by me), so it works as well
as it's ever going to.

I measured the speeds with my homebrew electronic shutter tester (see
description below), which I know to be accurate based on tests against a
known time base (clock-counter circuit). Each time is the average of 10
tests.

Here are the results:

nom. speed mS actual speed
-------------------------------------
1 470 ~1/2
1/2 435 ~1/2
1/5 261 1/4
1/25 30 1/30
1/100 15 1/60

So the first thing that's apparent is that this is actually a 4-speed
shutter masquerading as a 5-speed. Fine, I can live with that: I don't
think I'll need to do much shooting at 1 second anyway. What I'll do is
make a little card that has the actual speeds listed.

Other than that, the results seem none too shabby, especially for a
century-old piece of machinery. There is, of course, some variability in
the results, but not so much as to make it unusable. A scatter plot
would show pretty tight grouping of results.

And yes, I know about the issues about measuring shutter speeds, having
to do with the time it takes for the blades of a leaf shutter to open
and close, etc. I think I can safely just ignore these subtleties, based
on the way my shutter tester works, which is as close to the way film
responds as to make no never mind.

The shutter tester is fairly simple: a phototransistor connected to one
of the ports of a SX-28 MPU (similar to a PIC for those familiar with
microprocessors), and a simple program to sense when the transistor goes
"on" and count time until it goes "off", plus some code to convert to
milliseconds (the gizmo has a 1 MHz clock, so it's pretty damn accurate)
and display it on an LCD.

So, any comments appreciated.


[1] We'll see how well it actually covers 5x7. Looks OK in the ground glass.


--
Found--the gene that causes belief in genetic determinism
 




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