In February 1997, Jeremy Stein, an amateur photographer and physicist working in Albuquerque, New Mexico, measured the light output of the Canon 430 EZ and 380EX electronic flash units. This page shows the results for the dependence of flash output on the duration of flash charge time.
Jeremy writes: I just finished testing (retesting) the 430EZ, and learned a lot more about its behavior. This thing is SMART!
On another day, the tests were repeated for the 380EX: The series consists of data taken on a Canon 380EX, attached to an ElanIIE body, and flashed by the camera at various times after the red flash ready light came on. The times were: when the light came on, 5 seconds after, 10 seconds after, 15 seconds after, and 30 seconds after. The change in peak intensity is from 1.9 volts fired at the instant the ready light came on to 2.8 volts when fired 30 seconds after the ready light came on. Note also that the half peak level time for the first shot was about 950 microseconds, while the same measurement on the shot fired 30 seconds after the light came on was about 1150 microseconds. Nothing else changed during this series, so the scope data differences are due solely to level of charge. The batteries were nearly new, but I expect that the timings would be different for older or newer batteries. The data should probably serve more as a warning that it is best to wait a while after the flash says it's ready, although I suspect the difference will never be seen in the pictures. [Ed. note: "volts" means volts as measured from the output of the light-to-electrical signal converter. We expect to have a linear correspondence between the "volts" and light levels, but the numerical relationship between the two is not known to us.]
Thus the observation also stated in the Flash FAQ that full GN is achieved long after the "ready" light comes on is also true for Canon flash units.
All images are Copyright © Jeremy Stein, 1997. Unauthorized reproduction prohibited.
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