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UltravioletPhotography

Lime, NIR and IRG


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I wanted to try out the IRG photos, and I lucked out with this lime, which looks striking in IRG.

 

halogen, Asahi Super-Takumar 50mm/1.4, NEX-7 body

 

Visible photo, using 1.75mm S8612, F11 1/30" ISO100

post-94-0-08424500-1486518537.jpg

 

NIR photo, using Hoya R72, F11 1/200" ISO100

post-94-0-56932100-1486518604.jpg

 

IRG from the above images, with a re-white balance off the stove top:

post-94-0-13350000-1486518682.jpg

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I like the crisp results from the IRG version. I also shot a lime recently, in a multispectral set (image below). While limes, like other fruits, look rather unappetizing under UV, their fluorescence is quite colorful (though I wouldn't exactly say that looks appetizing either!). On the outer skin, I wonder whether the dark spots are dark because they are IR transparent (thus dark because of shadowing in pits/holes) or IR absorptive. If its something absorptive I wonder whether that would indicate emission somewhere else on the EMS, perhaps even further up into IR? If I was rich I'd buy a SWIR camera and start adding a fifth shot to my multispectral sets ;).

 

Just to be clear - are your "IRG" images a composite of IR in the red channel, Red in the green channel, and Green in the blue channel?

 

Here's my multispectral lime:

 

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Apologies, I must have missed something...IRG ?

 

Just to be clear - are your "IRG" images a composite of IR in the red channel, Red in the green channel, and Green in the blue channel?

Yes, that's right. I took the IR from the Hoya R72 and did "desaturate" in Photoshop, then I made a new document with the desaturated IR in the red, Red in the green, and Green in the blue. After that I did a one click white balance in PhotoNinja on the stove top.

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I also did a UV using my Tuofeng torch, which is fairly narrowband around 365nm. Saturation is increased a lot to try to deal with that.

 

2mm "UG11" (there are some doubts about whether this is a Chinese glass or not), 1.75mm S8612, Noflexar lens

F8 30" ISO100

post-94-0-79305400-1486656931.jpg

 

And finally, my SWIR (shortwave infrared, 1480nm-1600nm) photo, using the halogen light source, the Edixa Auto Cassaron lens, a Thorlabs SWIR long pass filter that blocks both visible light AND near infrared out to 1200nm, and a fluorescent screen that has the following manufacturer-supplied absorption spectrum: post-94-0-11860800-1486657299.jpgpost-94-0-10029700-1486657402.jpg

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Andy, how was your SWIR image photographed? My understanding is that CMOS and CCD image sensors are photo blind above 1200 nM.

 

You are correct. The cutoff is actually closer to 1125nm.

 

So the SWIR is photographed using a fluorescent screen that upconverts SWIR photons into NIR photons. Physically, it is the anti-Stokes effect.

post-94-0-73754100-1486682155.jpg

post-94-0-45292900-1486682173.jpg post-94-0-85689000-1486682536.jpg

post-94-0-03673900-1486682234.jpg

 

(I believe this to be the cheapest SWIR camera setup in existence! ...and it was still too damn expensive. :( )

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Interesting how the wood takes a nice red tone in the IRG picture.

 

(I believe this to be the cheapest SWIR camera setup in existence! ...and it was still too damn expensive. :( )

Is it even possible to possess a dedicated SWIR camera? I heard it is only reserved for military application in the US.

 

EDIT: I was wrong, these cameras are also commonly used in research...

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Yes, you can buy one, but even on ebay the cheapest I could find is about $9000. This setup (not counting camera body) is <$500.

 

They are used extensively to examine the underdrawings of paintings, too! Lots of museums have them.

 

I have created a new thread for the SWIR stuff. Please reply there.

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Dim! 8" at ISO1600 and F2 or so, and a 600W quartz tungsten halogen lamp at close range. The lime was rather dry by the time I finished!
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Dim! 8" at ISO1600 and F2 or so, and a 600W quartz tungsten halogen lamp at close range. The lime was rather dry by the time I finished!

 

My experience with such light sources is that they tend to ignite the subject matter! Surely art conservators could not use them on high-value pieces, and incandescence from heated subjects could be a contamination problem.

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HEEE, no, art conservators don't use my LOW COST SWIR setup. If I had $15,000 ($9000 used on ebay), I could buy a new InGaAs camera, or a germanium one, both of which can cover SWIR with a great deal more sensitivity and with no flames. :-P

 

The quality is so much better -- someone here posted a photo using a TriWave:

http://www.ultraviol...ndpost__p__2288

 

Compare to my self-portrait, taken in sunshine (my ability to focus has improved since taking this, but you get the idea):

post-94-0-05586400-1487003756.jpg

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