C.H. wrote:
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0.001s tol. means around 8%, it is a bit high, but what is the reason
for such tol.?
<snip>-----------------------------------------------
C.H.
This is an excerpt from a post I made in February:
<snip>-----------------------------------------------
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 (i.e.. 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.
<snip>-----------------------------------------------
I have since played with the parameters in the "Cool96" and can up the
resolution to at least .0001s using a "Custom" time setting of 10000
samples per second. This works pretty nice, and I can go back to the
stored data and re-measure the data at a later date. The scan rate is
for sound/music 44100 samples/sec. at 16 bit. But for ease of reducing
the data I stopped at 10000 samples on the time scale.
If you have any specific questions feel free to contact me off line.
Mike Butler
Dublin, California
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