As I perviously wrote, one method could be to fire a flash throug a slot in a rotating (very high speed) disc, onto a photo sensitive material and later measure the size of the exposed area/distance. To use slower speeds, the slut could be replace by a pinhole, that is moving from the centre to the edge of the disc (or vise versa) during "exposure". The light would then draw a spiral, that could be measured, on the disc. This is perhaps a little complicated to make.
Annother and perhaps better and easier solution to this probnlem, is to fire a flash directly into the lens of an SLR, using a high shutterspeed. Perhaps 1/6000 sec. The slut in the shutter will travel across the frame in perhaps 1/150 second. The fraction of the exposed frame will indicate how long the flash has lasted. The flash cannot expose the whole frame, unless the slot is 36mm wide (for instance it is at 1/150 on the *ist D). And it won't be, at speeds faster than 1/150 sec. Of course you need to know how just wide the "travelling slut" is, at certain shutter speeds. This test method cannot be to hard to carry out. All you need is a SLR/DSLR and a PC cord for the flash you want to test. And a little knowledge about how your camera works. I guess TTL is not an option in this case. Niether is "trailing curtain" sync, naturally. :-) Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Jens Bladt [mailto:[EMAIL PROTECTED] Sendt: 12. december 2004 00:10 Til: [EMAIL PROTECTED] Emne: RE: flash duration I'm not sure if I made some errors (below). Anyway, to measure (in degrees) the a flash duration of perhaps 1/50.000 second, you'll need a very fast moving object. At a speed of 1118 miles/hour just 1 cm would last 1/50.000 of a second. Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Jens Bladt [mailto:[EMAIL PROTECTED] Sendt: 11. december 2004 17:08 Til: [EMAIL PROTECTED] Emne: RE: flash duration I believe a coammonly used technique is to photograf a moving object (with a known speed) , moving past some kind of scale. Perhaps a recordplayer-plate. It runs perhaps 78 rounds pr. minute. If one round is 360 degerees, it will run 45x360/60 = 468 degrees in one second. In 1/1000 sec. it's 0.468 degrees. So, it seems a record player it not fast enough. You may want to find a faster running electronic engine and perhaps a much larger plate/disc to mount on it. I guess you could mount a disc on a fast running engine - perhaps an electric power drill (you deed to know the speed, and perhaps you'll need a gear to raise the speed). Cut a slot in the disc and mount some photopaper behind the disc. Shoot the flash through the slot in a way that the light will go through the slot no matter how far it has reached, while the engine is running, hitting the photopaper, which should NOT rotate. Do the shooting in a darkroom and make sure only the falsh light can hit the photopaper. Then develop the paper. Measure the balck part and find out how many degrees it covers. Some easy calculataions based on the speed of the disc will give you the wanted result. If the disc runs 3000 RPM this equal 3000/60 = 50 rounds in one second (RPS) 50 rounds = 50 x 360 = 18000 degrees. 18000 degrees in one second = 18 degrees in 1/1000 sec. Or 1.8 degrees in 1/10.000 sec. So you may want a faster engine, perhaps 12000 RPM, which will give you 7.2 degrees in 1/10.000 second 24000 RPM will give you 14.4 degrees in 1/10.000 second 48000 RPM will give you 28.8 degrees in 1/10.000 second So, I guess if you use a disc with a large size, you can measure the flash duratione with a slower electric engine. Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Kevin Waterson [mailto:[EMAIL PROTECTED] Sendt: 11. december 2004 13:33 Til: [EMAIL PROTECTED] Emne: flash duration Is it possible to measure the duration of a flash? Possibly in micorseconds or something? Kind regards Kevin -- "Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote."
