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Recording High energy discharges

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rp181

Sun Feb 07 2010, 02:05AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Hello,
I have posted a thread before, but I still have no insight on this. On every single high energy discharge I have done, starting with the 5.6kJ bank, I have gotten a purple frame. I have seen it on other peoples videos, with varying magnitudes.
4336470500 D7ce737a73

I think EM pulse can be ruled out, as this was recorded over 15 feet away. This is also interesting as the middle seems to be where the projectile hits the rails, yet there is a very much opaque garolite enclosure.

Any insight?

klugesmith

Sun Feb 07 2010, 03:03AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Does the camera show a flash where none is visible to the eye?
If you can see the flash then there are several possible explanations for the apparently purple extension:

1) In color CCD and CMOS cameras, the blue detectors generally have a spurious response to near-infrared wavelengths. Red-hot sources like outdoor gas heaters, or electric toaster elements, appear purple to the camera; the IR emitter of a television remote control appears to glow light blue (try it!)

2) possible blooming of an overexposed image area on the detector array. But that usually runs in columns or rows.

3) Light from an overexposed area landing elsewhere after scattering or spurious reflections in the lens.

Sun Feb 07 2010, 03:05AM

Registered Member #2372 Joined:
Location:
Posts: 62

well, your camera is definitely being saturated where the bright spot is. Put some dark filters in front of it and take a shot to see if it is just the camera saturation or something else.

Hon1nbo

Sun Feb 07 2010, 03:08AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

the dynamic range of your camera is too small - it will overexpose for the most part, but the blues on cameras tend to be more sensitive than others, and sometimes less sensitive - in the less sensitive case it could explain why only that color didn't blow out, look up your camera and find the spectrum response graphs and see what you can find

-Jimmy

rp181

Sun Feb 07 2010, 05:23AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I am doubting it is response issues, as on one occasion I got this clearly defined picture:
(5.6kJ, ETG)
100 1947

and the frame after:
Etg3 3

tesla500

Sun Feb 07 2010, 06:23AM

Registered Member #347 Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106

rp181 wrote ...

I am doubting it is response issues, as on one occasion I got this clearly defined picture:
(5.6kJ, ETG)
100 1947

and the frame after:
Etg3 3

This blue or purple may be explained if your camera has CMOS sensor. When exposure of one frame is completed, the data is stored as analog voltages in tiny capacitors in each pixel. The next frame is exposed at the same time as the voltages on the capacitors are being read out and converted to digital values. During this time, the circuits around the caps are slightly sensitive to light. Extremely bright light can change the voltage read from the caps, causing apparent brighter areas in a frame right before an extremely bright frame.

David

klugesmith

Sun Feb 07 2010, 09:15AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

tesla500 wrote ...
Extremely bright light can change the voltage read from the caps, causing apparent brighter areas in a frame right before an extremely bright frame.

Interesting explanation, and I think quite plausible.
To explore that, rp could record a video close-up of, say, a xenon flashlamp firing. Get several flashes, which would peak at various phases of the video frame cycle, and see if there's a pattern of light "aliasing" onto the previous frame. If the camera or lamp is moving, so the apparent position changes with each frame, you can discriminate the "aliasing" from a flash pulse that actually straddles two frame periods.

Back to my original suggestion: if this is a railgun or electrothermal gun, the plume could have a luminous spectrum very different from "ordinary" light sources, and fool the camera's color filters which are supposed to match human visual response.

Bjørn

Sun Feb 07 2010, 11:43AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

If you post pictures larger than 400 pixels you need to use the width=400 tag to avoid oversize pictures in your post.

Digital cameras will often show bright IR light as purple, try to filter out the IR with an external filter and see if it reduces the purple. Also try the opposite, use an IR pass filter and see if only the purple is left.

Steve Conner

Sun Feb 07 2010, 12:27PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You can see the aliasing effect, or at least one like it, in this video still of a Tesla coil. Notice the lines of little dots coming from the spark gap electrodes.
30incher

There's a similar effect in this Youtube video:

MinorityCarrier

Sun Feb 07 2010, 07:07PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

For NTSC interlaced video, you can extract the "odd" and "even" frames from the original interlaced frame (if you have a good video editing program) and you may find what you want.

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