Mike,
you are right, we can start counting when the first diode see the
light and then stop when the second see the light. For the second
curtain just reverse the bright trigger to dark trigger (or convert to
AC pulse trigger then no need to care about polarity). I just haven't
thought of using very slow shutter speed (or even "B") to isolate the
second curtain's influence.
0.001s tol. means around 8%, it is a bit high, but what is the reason
for such tol.? May be I can find some sensors from my drawer to do
some experiment.... oh! no! I have just thrown away the frequency
count that I built in 1980 when we moved to a new house, otherwise I
can covert it to a time interval counter and start to play with it.
C.H.Ling
Mike Butler wrote:
>
> C.H. et al,
> I built a shutter tester with two photo diodes. They were separated
> by
> 35mm in order to get the entire face of the diodes within the frame.
> The samples from my OM-1n are fairly consistant at .012s for both
> curtains. However the resolution is only +/- .001sec.
> This relates to a curtain speed of ~1/83s. That also correlates to
> the
> flash sync speed of 1/60s eg. 16.7ms total exposure 11ms or 12ms to open
> the curtain leaving 4 or 5ms for the flash to expose the full frame. I
> used this to make sure I was "in the Ball Park" for my measurements.
>
> Mike Butler
> Dublin, California
>
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