video/film of coils..Re: Hybrid-Maggy

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

Watch out for some strange things going on when videotaping or filming  a
TC.  For almost all recording devices, there's an effective shutter
interval, when it's collecting light, and a time when it's not.  A standard
motion film camera has a 50% or 25% duty cycle, so if a spark occurs when
the shutter's closed, it won't show up.

If the camera speed is slightly different from the 60Hz that the coil is
running at, the image on the recording may fade in and out, as the shutter
phase moves against the power line phase.

Solid state cameras have a similar phenomenon, that can be even worse.  In
bright light, the camera does automatic exposure control by reducing the
exposure time (down to around 1/10,000 sec). That starts getting you into
the 1-2% duty cycle, making it even harder to capture the spark.

As a practical matter, this might be useful for examining spark growth,
because it's kind of a like a vernier, or a microwave sampling head, slowly
sliding the sampling window past the underlying waveform.

There are cameras that can be locked to an external source (i.e. the power
line or video sync) but they are the exception, rather than rule, in
consumer gear.  Pro gear almost always makes a provision for shutter sync
(film) or gen-lock (video).

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, January 12, 2004 6:27 AM
Subject: Re: Hybrid-Maggy


 > Original poster: Harvey Norris <harvich-at-yahoo-dot-com>
 >
 >
 > --- Tesla list <tesla-at-pupman-dot-com> wrote:
 >  > Original poster: Bart Anderson
 > So, I
 >  > set it up and shot some video of sparks as well as
 >  > some other tid bits
 >  > regarding this system. Next week I'll take the video
 >  > to work and convert it
 >  > to windows media video for on-line viewing.
 >  >
 >  > Take care,
 >  > Bart
 > A useful tool of these VHS tapings is to view the
 > arcing that is taped frame per frame, which shows
 > 1/60th of a second time intervals. This is typically
 > done by pressing pause on most tape selectors.  In one
 > of my early tapings both the primary and secondary
 > arcs positions could be seen in the same frame, and
 > these do not seem to correspond in time.( Showing that
 > primary and secondary arcing are separate in time)
 > Tapings of Mark Metlicas large coil showed that frame
 > per frame,many empty periods of non arcing exist,
 > which seem feasible for a very low natural res
 > frequency of long wire length. It might be useful to
 > also know that a mpeg conversion is translated to a
 > selection of 30 frames/sec from the VHS copy, and this
 > might result in a differing final copy of your
 > original VHS. I found this out by VHS taping a rapid
 > neon blink discharge to earth to find its frequency,
 > which could be found by counting the empty vs lit
 > frames on VHS tape review. Doing that with the VHS
 > taping itself showed 12 hz, but the Dazzle mpeg copy
 > showed a lower frequency when put through the same
 > frame count tests. From these frame count tests, it
 > seems at least like several 60 hz AC cycles go by
 > before secondary arcing is seen on taping.
 > HDN
 >
 >