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UltravioletPhotography

Park Sign in Three Spectral Ranges


Bill De Jager

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Bill De Jager

A couple of years ago my wife and I visited Calaveras Big Trees State Park in the Sierra Nevada of California. While there I did an experiment, photographing a park sign in visible light, infrared, and ultraviolet.

 

The visible light photo was taken with an Olympus E-P3 and the Olympus 14-42mm zoom set at 35mm and F/5.6. The IR photo was taken using a Nikon D5100 with broadband Lifepixel internal filter and the Nikon 45mm f/2.8 GN. At this point I'm not sure of the external IR-pass filter but it was probably a Hoya RM90 or similar. The UV photo was taken with the same camera and lens, and a Baader Venus filter. I don't know what aperture I used for the IR and UV photos. All three photos have been desaturated to remove the distraction of color.

 

So here are the three photos: visible, IR, and UV. The differences in information conveyed are most interesting! The scratches evident in the UV photo are consistent with forensic information I've read elsewhere: http://www.ultraviol...orensics_V3.pdf

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Bill De Jager

Covered with UV-protective plastic?

 

Great point! I hadn't thought of that but it makes so much sense. This is at about 1500m elevation so UV is even more intense than usual.

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The 'park sign' may have a clear poly-carbonate (Lexan) panel to protect the sign from both vandals & UV light damage, a cheaper clear panel like acrylic (Perspex) would not offer this level of protection.

Col

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As an interesting side note, I see that a lot of the foliage portion of the sign goes white in the IR photograph just as it would in reality. :lol:

 

These kinds of Vis/IR/UV comparisons are always interesting, Bill. Thanks for posting. I should prolly move it to 'Forensics' ??

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Bill De Jager
Andrea, I didn't know they made park signs with the same cellular structure as the interior of leaves! :lol: Yes, Forensics makes sense. This discussion is a good reminder that some materials and objects may incorporate UV protection, a possibility which we should keep in mind when evaluating our results.
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