Sorry - on the way home from breakfast I had a “flash” of inspiration. I made a basic mistake in the explanation posted last night. I must have been asleep already!. The disk does not turn in 1/23 second but rather in 1/8 th of a second. It makes 23 impressions in 3 seconds so in 1 second it only makes 8. So the result is that the individual exposures are not 1/1666 of a second but rather 1/555 second. and during the 3 seconds the stationary parts of the subject receive an exposure of 23/555 second or 1/24 second. The ratio of exposures between stationary and moving parts is still 1 to 72 though. Now I’ll check if anyone caught the mistake earlier. Andy > On Jan 5, 2019, at 7:40 PM, Andrew Davidhazy <andpph@xxxxxxx> wrote: > > Roy, not quite. The rotating disk has a 5 degree or so slot cut along one radius. It rotates 23 times in 3 seconds and each time it passes the lens the camera catches a glimpse oof the scene in front … and if this moves it is recorded onto different portions of the sensor. Overexposure of stationary parts is a byproduct of the method as the moving arms get exposed for a much shorter time than the stationary body. > > Let’s see 5 degrees.. so 1/72nd of a full circle. It takes the circle 1/23 second to make 360 degrees … so the slot passes light for 1/72 nd of 1/23 rd or .00060 seconds and that is 1/1666 second … pretty good action stopping time! So the moving arms in this case only get exposed for 1/1666 second but the stationary parts of the body get exposed 23 three times during the 3 second exposure. So 1/1666 times 23 or 1/72nd of a second. So 1/1666 compared to 1/72 and so exposure is 72 times longer for the stationary parts compared to the moving parts and so if arms are properly exposed the body will be quite overexposed. (That is if I have not messed up in my “calculations” or lost my train of thought in the process!) > > I once wrote and article about this device, its construction and calibration and one application. Read it here: http://www.davidhazy.org/andpph/text-mechanical-strobe-inst.html > >> On Jan 5, 2019, at 6:37 PM, photoroy6@xxxxxxx wrote: >> >> Andy, >> >> In other words you put a flash unit on a rotating disk and had the flash tripped somehow 23 times in 3 seconds as the model moved her hands and arm from the top to her sides? >> >> Roy >> >> RE: The PhotoForum members' gallery/exhibit space was updated with new photographs on JAN. 06, 2018. >> Authors with work now on display at: http://people.rit.edu/andpph/gallery.html include: >> >
