Re: Re:High speed Tesla spark photographs - new superimposed frequency

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

Well, I've taken well over 500 photos today and have whittled them 
down to 100 for a closer look.

There is a little mirror aberration giving ghosting due to flex of 
the mirror in the support giving horizontal displacement. Seemed to 
get worse during the day so needs a new design with no stress and 
epoxied in place. Possibly a proper mirror.
I now have had full 2 foot spark with a spark that is 3 pixels wide 
(1 pixel per microsecond in these shots). This was a daytime shot and 
in retrospect was probably sharper than the night shots as it was f18 
and 1/10 sec. Night shots were f3.5 and longer duration.
I got quite interested since almost all of my photos showed the 
negative LED firing well, but I expected it was due to some asymmetry 
in the LED's as it seems to be just happening today. Makes you wonder 
though as I was using slow ASRG rates today.
I did try a current meter but I have had problems with it. Possibly 
overvolting the metal film 1.8 W resistors. Certainly looks like one 
resistor is open circuit here. They should fire at 0.01, 0.1, 1 and 
10 amps respectively but the 1 amp LED is firing too readily. The 
100A and above LED's never fired. (but did with a capacitor on a 
rectified ignition coil setup).
I was intrigued by a streamer shot showing a second and possibly 
third group of streamers following.
I added a spark arrestor and a disposable camera xenon flash in 
series with unprotected LED's and got an interesting but blurred 
streamer shot showing a remarkble 6 streamer groups that the camera 
and LED's weren't picking up. Seems like there is a another frequency 
superimposed of perhaps 8-10kHz. I presume that this is the 
difference between primary and secondary resonances (the "notch"). I 
am running it a bit out of tune still so that may account for that. 
It could actually explain a row of negative only ring down sparks as well.
Pics here
http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography%20-%20large%20mirror

Peter


> Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> Nice Peter!  Just mounting a single mirror close to the spinning 
> axis is a nice way to go.  My block mirror does get along 
> "aerodynamically" better though since it is less of a flying 
> wing.  Back surface mirrors should not be too bad since we always 
> take the pictures at a significant angle where direct reflections 
> are not a problem.  Common mirror distortions and some lens effects 
> will be there, but I don't think we would really notice for this 
> work.  A common cheap plate glass mirror might do perfect fine!
>
> "I" have not made any progress these last days due to other stuff going on...
>
> Cheers,
>
>         Terry
>
>
> At 10:38 AM 10/1/2006, you wrote:
> > I have been a bit busy with other pursuits such as picking up some 
> > big old discarded physics equipment and attending the Tesla 
> > exhibition. A week without new developments has been a long time in 
> > the high speed Tesla photography field.
> > I was however able to obtain a new higher quality mirror of 10 x 15 
> > cm which although rear silvered, does not show any distortion 
> > visibly when viewed from a distance. It is well centered but moves 
> > a fearsome amount of air and has some vibration at 3000 RPM (250 
> > VAC) but 2000 RPM (85 VAC)seems comfortable. It is a big mirror to 
> > spin fast but the aluminium supports seem to hold it firmly without 
> > adding too much weight or obstructing the view.
> > The reduced revs should be countered by the much clearer and wider 
> > view. Still needs to be tested in use though.
> > http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography
> > I have also done some testing on a 7 stage LED meter to get the 
> > feel for how it will work. Now have to make a reverse copy to 
> > indicate the opposite polarity then run things with the new mirror.
> >
> > Peter
> >
> >
> > > Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
> > > Hi Peter,
> > > .......
> > > The mirror was spinning at 7500 RPM in those photos but "cheap 
> > > cam" made it look "still"...  I have been pushing higher RPMs now 
> > > to separate the lead up leaders...  If anything gives way, I get 
> > > to go buy a "new" camera ;-))
> > > ......
> > > Cheers,
> > >
> > >         Terry
>
>
>
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