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Re: High speed Tesla spark photographs - Terry's Now ;-)



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

Great pics for first light, Terry even if you people do things upside down compared to here in Australia (the time axis is going up). The camera is the limitation here even despite your SISG having brighter sparks. You have a larger field than me which will also reduce the available light. The 100kHz LED works well and fortunately the 4 images don't overlap otherwise you wouldn't see anything. Given your machining tolerances, I guess this is a difference due to epoxy thickness.
How long are the sparks?
I look forward to closer pics with better detail. I will look at 40M file as well.

Cheers
Peter
http://tesladownunder.com


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, September 19, 2006 10:15 AM
Subject: High speed Tesla spark photographs - Terry's Now ;-)


Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

It works!!

http://drsstc.com/~piranha/PIRANHA/pictures/Image6a-good.jpg

http://drsstc.com/~piranha/PIRANHA/pictures/Image8a-good.jpg

Here are the setup details before I forget them ;-)

Zoom - To fit the image nicely to the picture. Does not seem to affect light gathering. Optical zoom only as opposed to stupid software zoom.

Shutter speed - Does not matter much. Long enough that you get a good chance of "catching" an arc. 1/10 and 1/20 sec does well here.

Background sensor noise - Don't worry about trying to fix noise by subtraction of a dark frame or anything. Oddly, that seems to hurt more than help. If your camera does this automatically, I think it should be turned off. The key is a sensitive low noise sensor to begin with!!

Aperture - As big as possible!! You need to gather as much light as you possibly can at all costs!!

Len's - If you have a choice, one that gathers the most light.

ISO - As high as possible!!! 1,000,000 would be nice!!! Mine only goes to 400 at that is barely enough. One of those cameras that can be forced up to 16,000 whether it is good or not would be nice. You really need this one!!! As Dan and other's say, getting data out of the camera in a deep RAW format would really help here too. The cool stuff is just barely above the noise level in my case.

Distance - As close as possible just to gather more light!!

Speed - My four rotating mirror block is running at about 5000 RPM. 2000 - 6000 RPM would be fine. I think slower is a bit better since more light hits the sensor pixels that way, but you want it to be fast enough to separate the pulses.

The room should be very dark to eliminate stray light.

Flash - Be sure to turn that **^*&%* thing off!!! There you are in the dark fiddling with the camera and blammo!! Almost knocked me over.

Remote shutter is ultra nice!! If the camera can take pictures automatically at say every second that would be very nice too. But you can do the shutter button too.

White Balance - I used daylight, but it is turning out black and white mostly in my case as I super pump up the brightness and contrast.

EV - Set it up high to brighten the picture as much as possible, but it had no effect in my camera's manual mode.

Reset - Set the camera so it does not loose all the settings when the power is turned off ;-)

Focus - Manual. I just measured it and set the camera to that distance. This could be tricky, but I did not have much trouble with it.

Background - Black felt works fine.

I took about 200 pictures today. Mostly figuring out by trial and error what is good. Rechargeable batteries are good too but you don't use the flash so the battery drain is pretty low. I did keep the LCD screen on all the time.

At 5000 RPM you can just glue the mirror to the little motor shaft or whatever. No need for a fancy machined block. No need for four mirrors, just one would do fine with a longer shutter speed to catch a good arc on one of the rotations.

The stray light paths near the mirror should be blocked and all the surfaces should be painted black to eliminate stray light reflections.

So it is pretty easy. I did have to carefully increase brightness and contrast with software to see air streamers. They are barely above the noise level. However, power arcs are very easy to see. I had to go back to all the black frames and lighten them so see if there were air streamers. Power arcs show up right away.

I put a 40.5MB zip file with a lot of pictures here:

http://rapidshare.de/files/33629810/StreakCam.zip.html

At the bottom of the page select "free".
It makes you wait about 2 minutes to read the ads and then a download screen comes up. Enter the funny letters in the robot trap box and save the file. It is just a typical zip file filled with all the JPG images from the last "lucky run". Some are plain and some have been enhanced. Some of those pictures are just black too... The four read streaks to the left or the calibration LED flashing at 100kHz. Each mirror makes it's own streak depending on the fine alignment of the mirror. If the pulses are blurred out, it is because that mirror scanned twice while the shutter was open.

I "think" time increases from bottom to top. Hard to say since the camera is upside down, inverted, twisted, and the motor turns in some direction... "Hard to say for sure" #;-)) I will try to modify the calibrator so it gradually goes out to point in the right direction. The calibrator is not really needed but it does prove the speed and all.

Thanks to Peter for figuring all this out!!! I think you are even working on an improvement :-))

I don't know what the pictures "mean" yet since Just taking the pictures is the deal right now.

Cheers,

Terry