• Ultraviolet Photography

A sweet multispectral set.

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#1 Mark


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Posted 26 September 2017 - 01:29

As summer comes to an end, and the ensuing floral subjects inevitably disappear with the changing seasons, I find myself already turning to back again to photographing foods/edible subjects. And here I'll start the season off with something sweet: gummy bears! Mini gummy bears, that is. As usually happens after these shoots, yes, all of the subjects displayed below (and then some) were promptly consumed.

Let's start with the usual, VIS reference image. Sitting on a sheet of black open-cell foam with an aluminum foil background, it was only a matter of time before they were to become a delicious snack.
Attached Image: 09-24-2017_19-19-32_s8612.jpg

Now, the UV image(s) turned out to be a decent illustration of the difference in transmission profiles for two of my UV filters. The top image was taken through an Asahi ZRR0340 filter, while the bottom was taken through an AndreaU-MKII filter. The latter has some bleed above ~400 nm, which clearly shows in the purple bear to the far left. How about that... gummy bears as a filter transmission profile test!
Attached Image: 0340-vs-andreaU.jpg

On the other end of the spectrum, they all look equally clear in IR, whether imaged at 720 nm, 830 nm, or 1000 nm (top, middle, bottom, respectively: Hoya R72, Xnite830, EO1K/Xnite830 stack). I bet a MW-IR camera would pick up some variation between the flavors (that's been on my wish list for a long time now - the camera, I mean).
Attached Image: r72-v-xn830-v-eo1k.jpg

Back to the VIS spectrum, but this time as UVIVF. This was surprising - just how fluorescent they are! (they were very bright as I saw them by eye.) And note that the fluorescence of each does not always match their normal VIS color. Here again I found a good illustration of the difference between two filter stacks I have to choose from for UVIVF imaging. The top image was made through a GG420 longpass / Baader UV-IR cut filter stack, while the bottom was made through a GG420 / S8612 filter stack. Notice how much more the S8612 cuts down into red than the Baader (the Baader filter has very steep cut-on/cut-off slopes both on the low and high ends; thus the increased purple and red captured).
Attached Image: s8612-vs-baadercut.jpg

Finally, as my multispectral sets tend to include these days, I shot UVIIF images as well. Included are 720 nm, 830 nm, and 1000 nm (top to bottom, respectively: Hoya R72, Xnite830, EO1K/Xnite830 stack). Yes, the IR fluorescence is brightest around 720 nm, but, let me just say - what is going on with that blue gummy bear!?!
Attached Image: r72-v-xn830-v-eo1k_uviif.jpg
(note: the bottom image, at ~1000 nm, had ~4x exposure compared to the other two due to very low fluorescence.)

Such a rewarding subject :)

Shooting info:
- Nikon D750 [broadband] + 50 mm Nikon Series E lens + 12 mm extension tube
Lens filters
- UV: AndreaU-MKII / Asahi ZRR0340
- VIS & UVIVF: EO 420 nm longpass + Baader UV-IR cut / S8612 [stack]
- IR & UVIIF: Hoya R72 / Xnite 830 / EO 1K nm longpass + Xnite 830 [stack]
- VIS: White LED bulb
- UV & UVIVF: 4 x 18" T8BL-B + FL-02 glass

- UVIIF: 2 x [MTE-U303 + Hoya U340]
- IR: 40 W incandescent clear glass bulb
- ISO320 (1@ 640)
- f11
- 1/6-20s, as needed

#2 OlDoinyo


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Posted 26 September 2017 - 03:07

The differences in IR fluorescence could be just differences in intensity--the most intense specimen has output detectable over the greatest range. I suspect this emission is not from the dye, but rather from some other ingredient. The dye could modulate intensity by absorbing more or less incoming light and/or acting as a sensitizer for the actual luminophore.

#3 nfoto

    Fierce Bear of the North

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Posted 26 September 2017 - 15:46

Interesting test, for sure. And with a subject you can digest later ... now, this is photographer-friendly testing. Just don't eat all of them at once :D
Bjørn Birna Rørslett, Ph.D.
Just call me Birna

#4 Andrea B.

    Desert Dancer

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Posted 01 October 2017 - 19:56

Mark, this is so funny -- and interesting. I love it!!!!

It certainly does make me wonder about all those interesting dyes in our Bayer filters.
And in our candies!

I'll bet Blue Bear contains some kind of betanin dye (see Pokeberry post). WikiP mentions it is used as a food coloring. Hence the strong UVI-IR fluor. Just guessing though...
Andrea G. Blum
Often found hanging out with flowers & bees.

#5 Hornblende


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Posted 12 October 2017 - 01:32

This is very interesting, keep up the cool experiments :)