Jostien. The discribed metod is very similar to the one I came up with. I just don't believe that 60 rounds pr. second (= 3600 RPM) is enough to measure flash durations as short as 1/50.000 sec. At 3600 RPM/60 RPS the disc will only turn app. 2,5 degress in 1/10.000 of a sec. and 0,5 degrees at 1/50.000 sec., which is probably not really enough to measure properly.
Tomorrow I'll try out the other method I described, firering a flash directly into the camera at perhaps 1/6000 secs. I will post my experiences. Perhaps someone can figure out how slim or wide the slut in the focal plane shutter of the *ist D is at different speeds? Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Jostein [mailto:[EMAIL PROTECTED] Sendt: 12. december 2004 00:40 Til: [EMAIL PROTECTED] Emne: Re: flash duration Kevin, Jens; Maybe this is worth reading? http://www.hiviz.com/activities/guidebook/hsptutor.pdf It contains a passage on how to test flash duration. Jostein ----- Original Message ----- From: "Jens Bladt" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, December 12, 2004 12:09 AM Subject: 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." > > > > >
