• Ultraviolet Photography

Lit charcoal and "yellow" flames

Infrared Processing
7 replies to this topic

#1 Stefano


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Posted 25 October 2020 - 20:23

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.

Camera: Full-spectrum Panasonic DMC-F3
Filter: Hoya R72

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 µm).

F-stop: f/2.8, ISO 200, 1/30 s exposure.
Attached Image: P1000206.JPG

F-stop: f/2.8, ISO 200, 1/13 s exposure.
Attached Image: P1000227.JPG

F-stop: f/2.8, ISO 400, 1/15 s exposure.
Attached Image: 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.

F-stop: f/2.8, ISO 400, 1/400 s exposure (both images).
Attached Image: P1000274.JPG

Attached Image: P1000275.JPG

Edited by Stefano, 11 April 2021 - 12:52.

#2 colinbm


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Posted 26 October 2020 - 00:17

Beautiful study Stafano, I like the violet/blues you have captured. The yellow is interesting, a diffraction grating would have been handy....

#3 Stefano


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Posted 26 October 2020 - 00:27

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.

#4 Cadmium


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Posted 26 October 2020 - 05:49

Stefano, That looks cool! I mean hot!, I mean... :wink:

#5 dabateman

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Posted 26 October 2020 - 11:41

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.

#6 UlfW

    Ulf W

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Posted 26 October 2020 - 11:59

View Postdabateman, on 26 October 2020 - 11:41, said:

Standing on its own, I like your last image.

So do I.
It has a free-floating abstract touch and would work well on a wall in a frame.

Edited by UlfW, 26 October 2020 - 12:00.

Ulf Wilhelmson
Curious and trying to see the invisible.

#7 Stefano


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Posted 26 October 2020 - 12:46

Thank you all!

#8 Stefano


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Posted 26 October 2020 - 13:21

Channel swapping (BGR) gives this:

Attached Image: P10002061.jpg

Attached Image: P10002581.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):
Attached Image: P10002751.jpg