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RE: [TCML] Camcorder Gap Syncronizing

Jeff -
   
  I've watched your video clip over and over, and there is something odd going on, but I don't know if your explanation is correct.
   
  Using RealPlayer V10.5 to "play" the clip, I do see that the spark at the center of the doorknob electrode seems to "disappear" at around the 15 second mark if the clip is played through without interruption. However, if I step through this part of the clip frame-by-frame, the spark is clearly present.
   
  I can't think of any way that the camera would not "see" the actual spark, but would capture the reflection of the spark. Regardless of any timing issues with the CCD detector in the camera being synchronized with the spark, I don't think its possible for the camera to not be able to see the spark, but to see its reflection only.
   
  Also, do you remember why the sound of the spark changes during this clip? There is a distinct change to the sound at the end of the "invisible" spark segment.
   
  As to your question about using a stroboscope to see fine details of a rapidly rotating object, I can assure you it is easily done. A few years back I was working on a new data storage technology. We were using a very high-speed, short duration stroboscope along with a very high power video microscope to see (and count) interference fringes occurring as spinning magnetic read-write heads pressed against clear tape (magnetic recording tape that had not been coated with the magnetic media). A circular array of read-write heads was spinning at 10,000 RPM, and the magnetic tape was slowly drawn across the array of heads. There was a few millionths of an inch air gap between the magnetic heads and the tape, and you could very clearly see the interference colors (like oil on water) as the air gap between the heds and the tape varied. The intent was to measure the thickness of the air gap by interpreting the colors of the interference fringes. The very expensive stroboscope was
 perfectly synchronized to a pulse from the motor driving the magnetic head array, and the flashlamp, pulse capacitor, and the capacitor charging power supply in the stroboscope were all of the highest quality and very tightly controlled so the duration of each flash was very consistant. After the flash tube was warmed up, at 10K RPM there was absolutely zero visible "jitter" in the image. It looked just like you were viewing a perfectly stationary object, except that the interference fringes around each magnetic head slowly varied in size and shape. This whole setup cost many tens of thousands of dollars, with all the optics being the best available in the world (Leitz), the video camera the highest resolution available at the time, etc, etc. All in all, the tiniest microscopic details of each read-write head could be clearly seen, all while spinning at 10k rpm.
   
  Regards,
  Herr Zapp
  

Jeff Behary <electrotherapy@xxxxxxxxxxx> wrote:
  
David,

I've had this happen by accident with a stationary gap! 
http://www.electrotherapymuseum.com/2007/ExtensionlessPointLimitlessPlane/EPLPMovie.wmv

About 14 seconds into the movie, the spark in the spark gap disappears! The camera only caught the reflection of the spark on the shiny metal pieces! I guess it was somehow in sync with the 30 frames a second...
I didn't even notice in putting the clips together until after the movie was made.

I always wondered if you could use a strobe light when working on a lathe to check the finish of parts, while they are spinning. I'm not sure though, is what you see when the motion "stops" the actual object (as it would be if stopped) or is it just an optical illusion of sorts?

Jeff


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