40X with a StackShot rail

[rjlittlefield]

The shape of flash pulses is strange enough to make me somewhat skeptical about assigning a single number for a flash pulse's width, especially if comparing different units or even the same unit at different nominal power levels. The old standby of Full-Width-at-Half-Maximum seems a bit simple for this task.

In recognition of this problem, Advanced Photographer magazine has taken to determining estimated flash duration by looking at pictures of moving fan blades, comparing flash with mechanical shutter.

--Rik

[Pau]

A good article about flash duration with experimental graphs:
http://eosdoc.com/manuals/notes/discharge/

[AndrewC]

...
In recognition of this problem, Advanced Photographer magazine has taken to determining estimated flash duration by looking at pictures of moving fan blades, comparing flash with mechanical shutter.

--Rik

That's also the way I used to figure out shutter delays - used an old computer fan spinning at a known rpm, triggered an exposure from a photo interrupter and then measured how far the blade had rotated before the flash went off.