Want to look at spark structure? Use a streak camera.
Terry Fritz and I had concurrent projects in competition in 2012.
Some details:
Rotating mirror giving 300 m/s camera recording as the spark "moves" through
the field.
So not an independent frame but a record on a moving film as it were. Think
of a seismograph printing on moving paper.
Ideal for microsecond events.
Camera was my then Nikon D300 DSLR exposed in darkness for 2 seconds
exposure. (i.e. NOT fast frame)
Here is a single green LED running a 100 kHz calibration. These are 10 us
apart and have sharp images.
Resolution is 100 ns/pixel. Hence with this setup with small fast mirror,
one can resolve spark microsecond events easily.
There is a 100 kHz ring down with at least 5 clear sparks of decreasing
intensity following.
The left electrode gives a more constant blue glow from the copper wire
which has strong blue spectral lines.
Lots of other stuff about streamer growth and ring up of streamers prior to
the main spark.
Structure of sparks shows some odd things. A lot different to what you
expect.
I have one shot that I interpret as a spark hitting a dust mote.
Later I have used a series red LED with a 2 foot spark to it with a 4 inch
mirror running at a fearsome 2000 rpm. These LED's (red only) are bullet
proof.
They more clearly show the second resonance at about 8-10 kHz on top of the
200 kHz.
Also sparks ringing down for perhaps 10 cycles are clearly seen by the LED
and not by the camera.
Streamers ring up and sparks ring down - easy to remember.
See the full details on the streak camera topic on my old tesladownunder
site - unfortunately still not altered after 7 years to include everything
I've done since.
Could you use a lesser camera? Certainly. Could you use a smartphone? For
bright events, I think you probably could if you can do at least a one
second exposure.
Particularly if a red LED is used as well.
I have taken 1200 FPS with a Nikon 1 V2 of small sparks onto my hand but
this is direct video recording detail 1000 times slower.
It's not all about the megabuck equipment.
Enjoy.
Peter Terren
Tesladownunder
-----Original Message-----
From: Chris Boden
Sent: Wednesday, June 6, 2018 9:30 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] High FPS cameras
Hi Nick, Matt, greetings :)
The 240FPS you're going to get from an overcranked Sony won't show you
anything but mellow flowing arcs. We tried that with a Rx100MkV (it's what
the Captain's Blog series is shot on) and even with our big FS-100. 240
Frames is great for slow-mo at human speeds, but not this stuff.
Even at 17kFPS we can't get much of what we want. We were trying for
stepped leaders, Project Thumper discharges, and Project Groucho's Marx gap
going off.
Our next step will be getting a serious high speed camera (up in the
250,000FPS and faster range). But those come with 6-digit pricetags and
it's a long, long way down on the budgetary wishlist.
I support anyone who wants to try this, when it comes to shooting arcs in
high speed I certainly wish you the best of luck trying to figure out the
lighting. We've never really figured out how to do it well.
I think that just means we need to screw around with it more though. :)
On Tue, Jun 5, 2018 at 2:58 PM, Matthew Sweeney <msweeney23@xxxxxxxxx>
wrote:
Hey Chris, well that is certainly far above the frame rate I expected. I
am
most interested in observing the stepped leader effect in a controlled
environment (if possible), similar to an actual lightning strike.
Therefore this might apply more directly to static discharge from a VDG?
Thanks!
Matt Sweeney
On Mon, Jun 4, 2018, 10:30 PM Chris Boden <cboden@xxxxxxxxxxxxxxxx> wrote:
> We can do up to 17kFPS here at the lab. Is there anything in particular
> you'd like to see? I know we've shot some high framerate video of our
coils
> in the past. If you dig through https://www.youtube.com/user/
thegeekgroup
> you'll likely find some.
>
> On Mon, Jun 4, 2018 at 3:50 PM, Matthew Sweeney <msweeney23@xxxxxxxxx>
> wrote:
>
> > It seems like people are starting to post slow motion videos online of
> > lightning using new consumer cellphones.
> >
> > I've seen up to 1000fps if you can time it just right (you only get .2
> > seconds), or 240fps with less need for precison.
> >
> > Due to the controllable nature of a Tesla coil (and VDG to a certain
> > degree), I'd be very interested to see any such footage if members
happen
> > to have those devices.
> >
> > You may not even realize you have a cellphone with such capabilities
> > so
> you
> > might want to check just for your own benefit :)
> >
> > Matt
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxxxxxx
> > https://www.pupman.com/mailman/listinfo/tesla
> >
>
>
>
> --
>
> Chris Boden
> President
> The Geek Group National Science Institute
> www.thegeekgroup.org
>
> --
>
>
> This email may contain confidential and privileged material for the sole
> use of the intended recipient. Any review or distribution by others is
> strictly prohibited. If you are not the intended recipient please
> contact
--
Chris Boden
President
The Geek Group National Science Institute
www.thegeekgroup.org
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