Quote Originally Posted by silveror0 View Post
I assembled a sensor, based on Ralph's tester, and then made a jig out of MDB to hold both a lens-on-lensboard and a 75W flood in position, carefully aligning the sensor to the lens axis. Then used free download of the Audacity program to record the waveform on my PC screen. Then the program is able to measure the time from halfway up the rising wave (shutter opening) to halfway down the falling wave (shutter closing). All six of my large format lenses in leaf shutters checked out within tolerance, except for a couple of speeds, which I then labeled on the lensboard so I could make exposure corrections when using those speeds. I did, however, see a frequency of 120 Hz superimposed on the Audacity wave (which did not affect the ability of determine the shutter speed), but I was curious to learn the cause. So I contacted Chris Woodhouse (co-author of Way Beyond Monochrome 2nd Ed., WBM2) who is the electrical guru of this checker. His response to my query:

"It is the mains - but you commonly get 2x the mains frequency (100Hz in the UK and 120 in the US). It normally comes from the fact that any power supply that has a bridge rectifier will cause current bumps 120 x per second."

I've not tried my setup with a battery-driven light source yet to see if this oscillation goes away, because I'm satisfied with the results I got.
Yes, Chris was thr electronic brain behind the shutter tester shown in WBM2nd Ed.it works wellwith audCITY AND I use it regulary.