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UltravioletPhotography

Candle Flame with UV Imager


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Below are my series taken using the KSS UV Imager with 60mm lens at F4 with Olympus 30mm Macro at F4 on a Panasonic GM5 positioned on the back imager.

 

No filter:

post-188-0-40599800-1603483682.jpg

 

First image 254.3bp25 UVC image:

post-188-0-02453200-1603483697.jpg

 

303bp10 with U340 2mm to block all IR:

post-188-0-06778500-1603483713.jpg

 

313bp25 with U330WB80improved to block all IR:

post-188-0-09408800-1603483727.jpg

 

313bp25 only (Some IR leak even with this):

post-188-0-60372400-1603483740.jpg

 

335bp10 with U330WB80improved to block all IR:

post-188-0-70734400-1603483753.jpg

 

370bp15 with U330WB80improved to block all iR:

post-188-0-50992600-1603483767.jpg

 

395bp25 fitler:

post-188-0-92749300-1603483780.jpg

 

Lp 720nm filter only:

post-188-0-94972000-1603483793.jpg

 

Last image 254.3bp25 UVC image (incase I could see hot spot in wick):

post-188-0-09720100-1603483812.jpg

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Two things:

It seems the candle is inside a casing. Can its material influence UV images, especially at shorter wavelengths?

 

Your UVC images are similar to those taken by Wilhelm, but not "equal". In particular, the tip of the flame is not bright.

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No the imager looks above the glass dish, so no influence or glass restrictions.

 

Sadly my images are not the same as Wilhelm's. I now thik his are IR leakage at 254nm. Mine are the same as here with UVC on the edges of the flame:

http://photographyoftheinvisibleworld.blogspot.com/2016/12/deep-uv-ultraviolet-reflected-light.html?m=1

 

I wonder now if the 2020BSI is too IR sensitive and not enough UVC sensitive. Jonathan showed that BSI sensors were 2x to 3x more IR sensitive than FSI sensors. So I don't know if its the sensor being more sensitive to IR than UV and really bad IR leak on his 250bp filters or if the sensor isn't strong in UVC sensitivity.

 

Also he had dark water at 313nm. Thats not right. That is clearly IR high band leakage.

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Wilhelm, if you are reading this, try to put an IR longpass filter (such as Hoya R72) on the lens, with your UV filters, and see if you can see something and in case you can, how much leakage you have. As Steve (Cadmium) says, if you see something with the same settings, you have a leak.
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WiSi-Testpilot

David, please take the 250 nm image again, but in front of the sky. At 254/25 nm the sky is dark. Maybe there is some leak. I have documented the full spectrum leak and think it’s ok.

Stefano, I will try it tomorrow.

Best regards,

Wilhelm

 

Leak test at high gain.

post-210-0-24773100-1603489581.jpg

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WiSi-Testpilot, the thing is that the ratio of IR to UV of the candle matters a great deal here. If there is only a little UV and a lot of IR (as one might expect), the IR could dominate, regardless of what the tree/sky/roof look like. The IR from the lighter might be much stronger than all of the above, and the UVC negligible in the relative sense.
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I will see if I can squeeze that in tomorrow. Are you using a butane lighter? I think I only have matches and candles. I may have some butane that I could light though. Will have to look through my chemicals.
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Andy or Stefano,

How do we calculate the area signal?

Lets assume the quantum efficiency x fill factor plot to be correct for the 2020BSI sensor. Now lets assume OD3 blocking in IR for Wilhelm's filters, as thats common and 30% sinal as indicated in his plots.

How much IR is comming through over the sum of 700nm to 1100nm vs area under the 250nm peak?

I wonder if its very close

 

As in 400 x IR leak x QE vs 25 x 30%peak x QE.

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WiSi-Testpilot

I will see if I can squeeze that in tomorrow. Are you using a butane lighter? I think I only have matches and candles. I may have some butane that I could light though. Will have to look through my chemicals.

Thank you, I'm very excited. I think it doesn't matter if you take a candle or a lighter.

How long is your exposure time at 250 nm?

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My exposure for the candle was 1/2.5 at ISO 200. My exposure for the LP 720 filter was 1/30 at ISO200. The sensitive is significant less at IR than UV for the imager.

I would assume about 6 stops more IR than UVC in the candle.

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Andy or Stefano,

How do we calculate the area signal?

Lets assume the quantum efficiency x fill factor plot to be correct for the 2020BSI sensor. Now lets assume OD3 blocking in IR for Wilhelm's filters, as thats common and 30% sinal as indicated in his plots.

How much IR is comming through over the sum of 700nm to 1100nm vs area under the 250nm peak?

I wonder if its very close

 

As in 400 x IR leak x QE vs 25 x 30%peak x QE.

I don't think that kind of calculation can be done without knowing the emission spectrum of the flame. Like, you would have to integrate (flame emission)x(lens transmission)x(filter transmission)x(fill factor)x(QE) I think, for each range?

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We don't know the exact spectrum of the flame, but Wilhelm linked one in his topic: https://www.dguv.de/medien/ifa/de/fac/strahl/pdf/uv_expositionen_gasbrenner.pdf

 

The lens shouldn't matter much, as it should have a flat transmission curve. Anyway it is quite a complex calculation, you have to do it for every point (like every nanometer) and then summing all points together to get the area under the curve.

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WiSi-Testpilot

Colinbm, thank you, that is very interesting.

I made images with and without a 5 mm glass plate between the camera and the candle. Before opening the other thread I had tested it with the lighter, but not with the candle.

Later I will repeat it also with the lighter and with an IR Filter.

 

I need an additional short pass filter. Which one can you recommend?

Best regards,

Wilhelm

 

270 nm, 500 ms, with and without a 5 mm glass plate

post-210-0-02334400-1603524695.jpg

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That's the problem. There isn't a good short pass filter.

At 300nm and 313nm you can use U340 on its own. That helps cut out a lot of IR, but can't use U340 below 300nm.

 

U330 allows the lower UV. But also the higher IR. Excellent IR blocking filters are hard to get. I gone back and forth with a lot.

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Thanks Colin I think you gave us the answer. That a candle flame is the best UV filter stress test. You should be able to see the IR leakage through the BaaderU filter with this test.

 

So if we assume incomplete ionizing radiation at 250nm for the 2020BSI sensor, then a pixel will have 28% qe. Assumeing 100% ionizing radiation and its 62%.

At 850nm the qe is 50%.

So for 850nm candle with an OD3 blocking filter is 0.001x0.5x0.005 mW/cm2 = 2.5x10-6.

At full ionizing radiation 0.3x0.62x0.00001 = 1.86 x10-6

 

So there is twice as much detected 850nm light going through the filter than 250nm light.

 

So lets not use candles as UV light sources.

Best to see if you can get your hands on a 254nm low pressure mercury bulb. The cost has come down. Also ypu can buy a portable one cheap, that are typically used for short wave rock hunting.

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Shouldn't the flame spectrum represent the atoms being consumed ?

Maybe I understood what you meant. If you exite atoms on a flame they will emit light according to the energy level gaps between different electron energy states. I tried a famous experiment: take some cotton or a piece of paper towel, soak it into salt water and put it on a flame. If you look at the spectrum of the flame (I tried with an "eye spectrometer" I made with a slit and a diffraction grating) you will see the 589 nm sodium yellow line. They are actually two very close lines, at 588.995 and 589.5924 nm. The difference is basically spin up/spin down. Maybe with a very narrow slit and a good eye you can see the doublet.
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I have this UVC + UVvacuum lamp, but it produces ozone, but when I wrapped the tube with 5 thousands/inch clear Mylar it was eliminated, but please treat this carefully & do your own tests to be satisfied you are free of ozone & protected from the UVC radiation.

 

https://www.ebay.com.au/itm/8W-Ultraviolet-Germicidal-Tube-Lights-Ozone-Home-Travel-Disinfection-Lamp/373046702522?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

Uncovered bare tube....

post-31-0-91004500-1603529872.png

 

Covered tube with Clear Mylar.....

post-31-0-91676700-1603530029.png

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Maybe I understood what you meant. If you exite atoms on a flame they will emit light according to the energy level gaps between different electron energy states. I tried a famous experiment: take some cotton or a piece of paper towel, soak it into salt water and put it on a flame. If you look at the spectrum of the flame (I tried with an "eye spectrometer" I made with a slit and a diffraction grating) you will see the 589 nm sodium yellow line. They are actually two very close lines, at 588.995 and 589.5924 nm. The difference is basically spin up/spin down. Maybe with a very narrow slit and a good eye you can see the doublet.

 

Yes I was mistaken, you are correct.

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The Butane Lighter flame spectrum is slightly different....

 

Bare flame...

post-31-0-89841100-1603537594.png

 

Flame with S8612...

post-31-0-56605900-1603537648.png

 

PS, unfortunately the data gets truncated at the ends as it is too small, so on the UV end it will continue along further at the lower end, tapering away....

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