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UltravioletPhotography

Lit charcoal and "yellow" flames


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Today my dad and I tried to cook some chestnuts on a "barbecue" (a little more than a pan with charcoal). It was a fail, since the chestnuts were too dry. But it provided material for invisible light imaging.

[color=#282828][font=helvetica, arial, sans-serif]Camera: [/font][/color][color=#282828][font=helvetica, arial, sans-serif]Full-spectrum Panasonic DMC-F3[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Filter: Hoya R72[/font][/color]

Lit charcoal glows IR-blue, since its blackbody radiation is heavily weighted towards longer wavelengths, and peaks in the deep SWIR-early MWIR region (roughly around 3 [color=#282828][font=arial, helvetica, sans-serif]µm).[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]F-stop: f/2.8, ISO 200, 1/30 s exposure.[/font][/color]
[attachment=20552:P1000206.JPG]

[color=#282828][font=helvetica, arial, sans-serif]F-stop: f/2.8, ISO 200, 1/13 s exposure.[/font][/color]
[attachment=20553:P1000227.JPG]

[color=#282828][font=helvetica, arial, sans-serif]F-stop: f/2.8, ISO 400, 1/15 s exposure.[/font][/color]
[attachment=20554:P1000258.JPG]

Then I noticed some flames were IR-yellow. That's odd for a flame. We initially used a chemical to help the flame going (not exactly healthy, but it hopefully burned out, even if we didn't eat the chestnuts), and I think it has an emission line in the 700-800 nm range. Sometimes flames change color depending on the chemical burned. I have seen cyan-green flames when burning some thin residues of plastic from a metal wire I heated to cut a plastic bottle. Yeah, avoid this experiments indoor.

[color=#282828][font=helvetica, arial, sans-serif]F-stop: f/2.8, ISO 400, 1/400 s exposure (both images).[/font][/color]
[attachment=20555:P1000274.JPG]

[attachment=20556:P1000275.JPG]
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Beautiful study Stafano, I like the violet/blues you have captured. The yellow is interesting, a diffraction grating would have been handy....
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Thanks colin. Yes, it would have been interesting to see the spectrum of the flame. If I had a diffraction grating with me I would surely have given it a try.

 

I was once in a supermarket and I was curious whether the ceiling lights were LEDs or HID. I found a diffraction grating in my pocket and took a look. I saw a discontinuous spectrum, which indicated they were HID lamps.

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Standing on uts own, I like your last image.

Yes you might have been seeing contaminant in the wood or from your lighter fluid. I remember as a kid throwing in powders into the fire to change the visible color.

Atomic absorption/atomic emmission is fun chemistry.

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Channel swapping (BGR) gives this:

 

post-284-0-89961900-1603718354.jpg

 

post-284-0-78816300-1603718366.jpg

 

In this image I also tried to fix the color of overexposed areas (which is not white since there is a white-balance apoplied) by replacing it with white (tolerance 10):

post-284-0-53147200-1603718388.jpg

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