[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: High speed Tesla spark photographs



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Gary,

A correction. Peter says that the dimmer stripes occur "after", not before, the main arc. So the situation looks like this:

http://drsstc.com/~piranha/PIRANHA/Corrected-PetersPictureWComents.jpg

The arc channel does not appear to be loaded much after the main arc but perhaps the ionization is easy to keep flashing or something... I don't know.

Peter's picture here:

http://tesladownunder.com/HVRotMirrorTeslabigSparkElectrodeglowDelay.jpg

Shows the light and dark bands but with the terminal ionization (vertical blue strip on right) fairly constant. Those ions probably can't recover as fast. The actual arc can also be isolated all by itself as show here:

http://tesladownunder.com/HVRotMirrorTeslabigSpark1SingleFullPowerArc.jpg
http://tesladownunder.com/HVRotMirrorTeslabigSpark1SinglePartPowerArc.jpg
http://tesladownunder.com/HVRotMirrorTeslabigSparkPowerArcGaps.jpg

The bright arc is burning a "lot" of power. Perhaps if the camera were more sensitive (higher ISO) then the arcs would look much more constant. This picture does show smearing.

http://tesladownunder.com/HVRotMirrorTeslabigSparkElectrodeglowDelay.jpg

A flash lamp, like the super high speed ones, just use a power arc. So the "flash" can be very fast. Scientific American had an amateur scientist article on flash lamps once.... I should try and find it...

Peter is running the coil normally and taking many pictures hoping a few will catch the arc at just the right time. I am not sure what his ratio of successful pictures is but it is low. I have four mirrors for my setup and a wider field of view so I am hopping to get a high yield of cool pictures as opposed to the floor ceiling etc...

Peter explains his setup here:

http://tesladownunder.com/HighVoltage.htm#High%20speed%20spark%20photography

http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography

I know he has been trying all kinds of camera settings so I am not sure if it has found the "good" ones yet. Here are my "guesses" for my setup but I have never done it yet so don't believe me ;-)

Aperture - How big that iris thing is. I think it should be kept as wide open as possible to catch as much light as possible. It is really the only light control we have. Mine goes from 2.7 to 11.0.

Focus - Have to set it up. There is nothing for the camera to focus on when the mess is running. Peter said it was hard getting the focus just right.

ISO - As high as possible. For digital cameras, ISO or film speed is fixed and the ISO settings are software tricks. If one hits a limit for aperture setting this might be another way to adjust the light further.

Shutter speed. Not sure... Mine goes to 1/800 second. It could probably be far slower based on the BPS of the coil. It would be very hard to accidently superimpose two bangs...

Color balance - Manual probably daylight. The auto setting does not work in the dark and can't adjust to a fast arc. Peter was having trouble with odd colors at first due to this I think.

Mirror speed - Mine goes from very slow to 24000 RPM so I have it covered ;-)) Peter's is 3000 RPM sync motor (50Hz) I think.

Zoom - I figure you can zoom close to the arc and loose the frame a lot, or go wide angle and catch more arcs...

I looked hard at "cheap cam" (Olympus D-395) and it does not have many (hardly any) of the mentioned settings as "manual". My old Olympus C-3000 can do everything manually if you read the instructions enough ;-)

So that is what "i" know at this "moment"...

I got the motor for my setup today and mounted it up with the mirror block:

http://drsstc.com/~piranha/PIRANHA/TerrysCam-01.JPG

http://drsstc.com/~piranha/PIRANHA/TerrysCam-02.JPG

The block is machined to about +- 0.002 inch and it runs smooth even at like 25000 RPM!! Although that is a pretty scarry speed in general!!! I just saw that the motor is rated 24000 RPM at 12 V and I was running it at 25 V :o))) It is a 1/2 HP peak motor at 148A stall... But nothing bad happened... The motor is the Mabuchi Speed-550 a little down the page here:

http://www.robotmarketplace.com/marketplace_motorsmisc.html

A very nice place and got it sent priority mail super fast!!!

Here is the spinning block at 1/800 sec shutter speed:

http://drsstc.com/~piranha/PIRANHA/TerrysCam-03.JPG

There is a giant (1.2M) picture here that show the block in the zoom mode at full resolution. Probably close to the way it will be run. It is just a big blur so not worth downloding it you don't care.

http://drsstc.com/~piranha/PIRANHA/TerrysCam-04.JPG

I also made the calibrator today. Just a LMC555 CMOS timer in the 50% mode calibrated to flash a high brightness red LED at 100.00KHz.

http://drsstc.com/~piranha/PIRANHA/Cal-01.JPG

http://drsstc.com/~piranha/PIRANHA/Cal-02.JPG

It uses the same timer cap from my TCT. Don't by one since I have 75 here on my desk for free ;-)) The LED is 20mA but I run it at 30mA with a 220 ohm resistor to the +9V and ground to pin 3 for +50mA capable drive. 30mA at 50% duty is about the same power as 20mA DC. It is very bright!!

So I am just waiting on the four front surface mirrors now to be glues to the block....


Many many more questions than answers ;-)))

Cheers,

        Terry




At 05:53 PM 9/13/2006, you wrote:
Hi Terry, Peter:

I'm not "getting" something.  For Peter's image
http://tesladownunder.com/HVRotMirrorTeslabigSpark1Singel.jpg

I get how each vertical trace is displaced due to the rotating mirror,
but I don't get why it's dark between each trace.  I would have guessed
that it would show up as a smooth vertical smear for the duration of the
bang.  Isn't the arc luminosity more or less constant during the
duration of a bang?  Sure, it starts at zero, increases to some peak
value, and decays, but I wouldn't guess that it oscillates from zero to
peak at Fres.

Is there some other opto-mechanical chopper in addition to the sweeping
mirror?

Also, Peter - what film speed and lens aperture did you use?  I'm
wondering if a garden-variety digicam is fast enough.  I assume the coil
operated in single shot mode?

Thanks, Gary

> At 05:54 PM 9/11/2006, you wrote:
> >I have been working on a setup to show high speed streak photos of
> >Tesla sparks. Setup is a 3000 RPM synchronous motor with a single
> >mirror which reflects the sparks image to my Nikon D70s with 180mm
> >lens. I can resolve the 100kHz ring down sparks readily with about
> >1us resolution. 1 camera pixel is 100ns. Calibration is
> >geometrically and with a LED at 100kHz.
> >With this running on a 6 inch spark to ground I can see detail of
> >the central channel of the initial spark, details of the 5 or so
> >ring down sparks, gaps in the spark channel, immediate and delayed
> >electrode ionisation effects and (I think) a spark hitting a dust
mote.
> >Photos and details here:
>
>http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark
> %20photography
> >Terry is also working on a more advanced purpose built setup.
> >
> >Peter
> >http://tesladownunder.com
>