Experimental Setup for Measuring Discharge Graphs of Electronic Flash

In February 1997, Jeremy Stein, an amateur photographer and physicist working in Albuquerque, New Mexico, measured the light output of the Canon 430EZ and 380EX electronic flash units. He describes the procedure as follows:

The testing started with a fresh set of batteries, and I waited until the red ready light was on before flashing the unit manually. The testing was not done in any linear fashion, and there was no evidence of serious differences in the flash timings measured as the batteries wore down or heated up. By the end of the tests, after maybe 100 flashes, the time to recharge at full power was getting to be long enough to be annoying.

I used a Tektronix probe (TEK P6701 o/e converter) intended for the purpose of converting the light in an optical fiber to an electrical signal. This unit has a bandwidth of 700 MHz, so I felt it would be plenty fast enough. I connected this unit to an oscilloscope (TEK 210) and fired the flash unit into the fiber port of the sensor. I filtered the incoming light enough to avoid saturating the sensor (overdriving it into nonlinear response), and I printed the scope traces on a computer printer directly from the oscilloscope. The scope I used was not capable of sending the data to a computer for further analysis. When I do the more accurate setup, I will be able to do numerical analysis of the data directly on the computer, but the results are rather interesting even now. I extracted the following data from the scope printouts by measuring levels and timings with a pair of dividers and a ruler.

The data were taken with a TEK 210 digital sampling oscilloscope. For a 250 microsecond per division sweep speed, the scope takes one sample every microsecond. For a 2.5 millisecond per division sweep speed, the scope takes a sample every 10 microseconds, etc. The scope has a maximum sampling rate of 1 Gigasample per second, and its overall bandwidth is 60 MHz.

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