>I also want to find a way to measure the curtain speeds, but I can't
>figure out how to do (even I know how to make it, I wonder I will pick
>up the soldering iron again). When I found the exposure deviation of
>left and right side is higher than 0.3 stops I will adjust the curtain
>by trial and error, in most case it works but it takes time and
>patience.
>
>C.H.Ling
I am just using two phototransistors mounted in an aluminum block with
two holes spaced precisely 30.0mm apart. This part would be tricky
to make without access to a machine shop.
I sample the output of each phototransistor using the two audio
inputs on my computer, then I can measure the time between when
the transistors turn on to get the opening curtain speed, and the
turn off time to get the closing curtain speed.
The circuit is very simple, and I can post more details if anyone is
interested. The software side of things is a little more complicated
right now. I haven't found a decent oscilloscope program for the Mac
that does what I need, so I record the input to a file, then analyze
the file by hand to find the needed times.
Since the sampling rate of the audio input is 44.1kHz, this method is
quite accurate, easily down to +-0.1ms, and probably a little better.
Mark Marr-Lyon
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