Wayne Wrote:
Any chance of us Brits seeing a copy? I'd be quite interested in having
a go at building one. The more usual, simple method is to use a
photodetector connected to an oscilloscope and put it behind the
shutter. This will measure exposure time at one point in the frame.
You could detect differences in curtain speed by testing at different
points along the curtain travel, of course.
Wayne and the rest,
I built a version of the tester shown on this page:
http://www.geocities.com/Yosemite/2131/shspeed.html
It has the disadvantage of needing a computer with a sound card to run,
but seems pretty accurate. I had some difficulty finding the specific
diodes noted but with help from the clerk found a suitable substitute.
In brief, it uses photo diodes to trigger a sound card in your
computer. Using Cool96 share/free ware to do some simple signal
processing (ie. Timing). The version I built takes advantage of both
the left and right channels of the sound card. The left ch. sensor is
at one edge of the film plane and the right ch. the other. This gives a
timing pulse for the edges of the film plane and the difference in
start/stop times is converted to the speed of each curtain. I mounted
the two diodes 35mm apart to give a known distance to calculate the
curtain speed from.
I have never tested the shutters of any of my cameras to verify. I
simply did a timed shutter about 10 seconds long to calibrate. My OM-2s
agreed very closely with the "theroetical" calcuations whereas my OM-1
strayed abit but still close (no more than 10%). The curtains speed was
about 1/90th of a second as I recall. All this gave me confidence in
the measurements.
Since I read the digest version of this list, a new digest has come in
as I write so hopefully this is not duplicating somebody elses work.
I put the diodes a on/off switch and a AAA battery is a 35 x 54mm
plastic box availible at "Shadio Rack".
I too would be interested in seeing the circuit that started this thread
though, It might be a lot easier to use than the one mentioned above.
--
Mike Butler
Chief Mechanic / Engineer
Team FCAR
http://home.earthlink.net/~teamfcar/
Dublin, California
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