• Ultraviolet Photography

Pyrrharctia isabella

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#1 Mark


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Posted 02 December 2017 - 15:15

The other night I happened upon this wooly worm (Pyrrharctia isabella), making its way across the sidewalk in front of me. I was a little surprised at this find, as it just seems way too cold to be out in this near freezing weather without a hat and gloves. But then, maybe that fuzzy coat it has is enough to keep it warm. ;)

It was lethargic, as it should be lulling away the winter right now, so photographing it over a multispectral set wasn't a problem. Shown here in VIS on bits of hydrangea leaf:
Attached Image: 2017-11-26_18-08-54_flash-visstack.jpg

Under IR (~1000 nm) the luminosity of my little friend isn't much different from VIS, though the leaf bits are characteristically bright:
Attached Image: 2017-11-26_18-18-35_inc-lp1knx830.jpg

That rich brown band in the middle disappears into a uniform dark/black under UV:
Attached Image: 2017-11-26_18-21-22_s2-andrea.jpg

While the leaf bits again demonstrate characteristic UVIVF (along with lint & debris!), there is still the struggle to separate UVIVF from ambient/contamination VIS. Here, for example, the middle brown segments of the caterpillar faintly come through in the image. My presumption, for the moment, is that the induced fluorescence(s) in turn self-illuminate the scene, thus showing some the original VIS image. I have yet to figure out a way to effectively separate the two (aside from digital subtraction - which I like, and is highly effective, but not exactly the one-shot 'analog' I'd like).
Attached Image: 2017-11-26_18-10-10_mte-visstack.jpg

Shooting info:
- Nikon D750 [broadband] + 50 mm Nikon Series E lens + 12 mm extension tube
Lens filters
- UV: AndreaU-MKII
- VIS & UVIVF: KV418 + 420 nm LP + Baader UV-IR cut [stack]
- IR:
Xnite830 + 1K nm longpass [stack]
- VIS: handheld flash
- UV: 1 x Convoy S2+
- UVIVF: 2 x [MTE-U303 + Hoya U340]
- IR: 40 W incandescent clear glass bulb

- 0.6-3.0 s
- ISO320
- f 8.0

#2 Andy Perrin


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Posted 02 December 2017 - 16:35

Pretty critter! I love the IR here, even though it's black and white. I wonder how it'd look in the ~720nm band?

#3 Andrea B.

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Posted 03 December 2017 - 22:19

This is the canonical Wooly Worm we looked for as kids! Nice to see how it looks in alternate light. This one must have been living in a warmer micro-climate somewhere. There's always a non-conformist in every population. :D

It is possible the red pigment in the caterpillar hairs is slightly fluorescent? Just a thought. But I agree with your observation that visible fluorescence can light up other non-fluorescent parts of the scene. In that recent thread of mine where I was trying to determine what was lighting up a certain scene, some later photos showed visible fluorescece reflecting off part of the standards.
Andrea G. Blum
Often found hanging out with flowers & bees.