• Ultraviolet Photography

Buttercups show SWIR patterns that match UV!

Infrared Multispectral
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#1 Andy Perrin


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Posted 10 June 2019 - 02:36

I found that a buttercup (exact species of Ranunculus to be determined) shows patterns in SWIR that match the ultraviolet pattern.

First the visible image, taken with the Sony A7S using BG38 2mm under an "energy saving" halogen light. WB was off PTFE.
F16 0.8" ISO50
Attached Image: _DSC1909 halogen Noflexor35mm BG38 F16 0.8%22  iso50 UVP.jpg

Next the UV image, same camera, using S8612 1.75mm + UG11 2mm and a Convy S2+ torch. WB again off PTFE.
F16 6" ISO1000
Attached Image: _DSC1904 ConvoyS2+ Noflexar S8612 1.75mm + UV11 2mm F16 6%22 iso1000 UVP.jpg

Then the standard, featureless NIR rendition using a nameless Chinese IR1000 filter (obviously the exact cutoff is unknown since it's a no-name). Halogen again.
F16 2.5" ISO80
Attached Image: _DSC1908 halogen Noflexor35mm IR1000 F16 2.5%22  iso80 UVP.jpg

Finally the SWIR results using the TriWave Ge-CMOS camera under halogen. 1500-1600nm Thorlabs bandpass filter
Attached Image: Buttercup SWIR denoise_res4.jpg
Attached Image: ICA1_res.jpg
Attached Image: Buttercup SWIR denoise 2_res.jpg

Edited by Andy Perrin, 10 June 2019 - 02:42.

#2 JMC


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Posted 10 June 2019 - 08:23

How interesting. I wonder if this the same compounds that are absorbing in the UV and the SWIR, or if it different things which are present in the same areas? Could there be more water in those parts of the flower, leading to the greater absorption in the SWIR?

#3 Andy Perrin


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Posted 10 June 2019 - 19:04

Someone posted a paper on here awhile back about showing that Raniculus's colors come from physical interference effects between layers, rather than pigments (mostly, anyway). I suspect that the same structural color thing might be going on here too. Sometimes interference effects repeat at multiples of the wavelength, like how the colors on oily water repeat themselves.