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Re: High speed Tesla spark photographs



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

I have taken pics of a 12 inch streamer growing and forming a spark to a grounded object. Noisy as anything and much harder to catch and only perhaps one in 5 shots were useful. Difficult to know at the time though because they all appear dark on the viewscreen of the camera. Time axis is downward.

http://tesladownunder.com/HVRotMirrorStreamerHit1.jpg

Pic setup is of about 12 inches of an 18 inch spark from the toroid side on the left. I was throttling the variac back to try to just get streamers and few hits.

Streamer shots are quite different to the high current ground shots where the initial spark is bright and there is a ring down of a number of weaker sparks. The initial streamer sparks (the top one) can be broken into perhaps 6 consecutive channels (5us apart = 2 pulses per 100kHz). Although it is difficult to be sure, only the last one makes it across the screen then a 10us gap then the main arc hits. Interestingly there is no ring down on the main arc, however the distances are greater and intensity is down. I speculate that the 7th channel which is faint or absent is a harmonic effect and the spark fires because it has a higher energy for the same reason.

I guess the new information from the rotating mirror stuff is that streamers enlarge with successive cycles and ring up leading to a spark that connects. Sparks that connect (often) have a ring down. Not really unexpected from the CRO pics but nice to see it directly. So streamers ring up and sparks ring down - easy to remember.

Other pics and info at the bottom of the topic on my site.
http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography

Peter


> Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dan,

At 07:46 AM 9/16/2006, you wrote:
Terry,

A "dark" frame will only remove non-random noise such as hot pixels.

That is a big problem in my case. The old CCD sensor has significant hot pixels and the "fixed" noise floor has risen over time. This camera does not have a built in function to remove that. The software fix really cleans up super dark photos well.

To
remove random noise generated by the sensor itself, you basically would need
to take multiple exposures of an identical object (such as stars for
example) and then average those frames to remove random noise.

The software just does a 2nd order low pass function which is surprisingly good at this type of noise. It has a lot of various filters but this one does fine. It does chew up the good image just a little but not bad.

Of course,
our arc is not a constant image, so you cannot do that.

Dan

It should be good enough right now.  I will just have to see what happens.

Cheers,

        Terry