As an experiment today, I took five minutes to use an LED and oscilloscope as discussed earlier. With the lens wide open and an LED torch pointing through the lens, the signal was about 200mV, but clearly showed that the 1/250th second was a shade slow at 4.2ms (should have been 4.0).
So this is a viable option. Note that (also as discussed) if the lens is stopped down not only will the signal get smaller by 50% per stop (though a brighter light will help) but the shutter will get faster. I didn't measure the rise- and fall-time of the signal - it was a very quick test
- but it was under a hundred microseconds for each. The LED should have a response time in microseconds or faster.
Neil
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