graywolf http://www.graywolfphoto.com "Idiot Proof" <==> "Expert Proof" -----------------------------------
Jens Bladt wrote:
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."
