[MF3D.FORUM:452] Shutter speed testers

["Menzel, Greg" <Greg.Menzel@xxxxxxxxxxxxx>]

Speaking of shutter speed testers, I built my own a few years ago.

I used a frequency generator to create a pulse wave at 1000 Hz.

An infrared emitter is placed directly in from of the camera lens, and an
infrared detector placed centered on the film plane.

Using logic gates, the pulse wave is ANDed with the output of the infrared
detector. This signal is fed into the least significant leg of three
cascaded decade counters, each driving a BNC to 7-segment decoder-driver
hooked to 7-segment LED displays.

When reset, the segments show 000.

If you then cock and release the camera's shutter, the segments will show
the number of milliseconds the shutter was open. For example, at 1/50, the
counter should show something in the neighborhood of 020 for twenty
milliseconds.

Since I'm only using three 7-segment LED displays, the range of the display
is 000 to 999. So with the clock at 1000 Hz, we get 0.000 to 0.999 seconds
range with 1 millisecond resolution. One can easily increase the clock to 10
KHz, increasing resolution at the cost of limiting range. Or, I suppose you
could add a fourth stage to the cascaded decade counters.

My dad made a fixture specifically for a Wollesnsak Stereo 10 to hold the
inward emitter/detectors. I have since Gerry rigged the setup to work for
Reaslist and Sputnik cameras.

I was at first a little concerned that the rise and/or fall time of the
infrared emitter/detector system would be too long. To find out, I hooked up
a storage oscilloscope to find that the rise/fall time is negligible
compared to the shutter times being tested.

A fun project that works!


Regards...
Greg Menzel

P.S. Looking forward to receiving the next folio. I think I have greatly
improved my mounting (i.e. reducing vertical mounting error) and have
several good shots from Hawaii last January.