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UltravioletPhotography

Sigma camera for UV reflectance imaging


Adrian

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Found the old Sigma links at the now Fotozones

https://www.fotozones.com/live/index.php?/forums/topic/14805-uvvisir-multispectral-with-just-one-shot-yes-we-can/&do=findComment&comment=119134

top histogram is unprocessed linear RAW and lower is standard Sigma processed RAW histogram.

https://www.fotozones.com/live/index.php?/forums/topic/8897-uv-capabilities-of-the-sigma-sd-camera-foveon-cmos-sensor/

unfortunately in the archiving of these posts some text seems to have gone missing..but the top image is the B channel, middle the G channel and bottom the R channel. As you can see most UV fell into the B channel as expected, with a little falling into the G channel and none in the R channel.

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Theoretically, UV should be in the blue channel which it was primarily, and IR in the red channel which certainly wasn't the case. Sigma processing showed IR data in the blue and red channel but none in the green......not possible! Further investigation bypassing Sigma processing revealed that it occurred in all 3 channels increasing in intensity from blue through to the red channel but certainly not confined to the red channel only.

 

Welcome to the wacky world of Sigma firmware! I wonder how you managed to bypass the processing. I was never able to do that on the SD14 I used to have.

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Shane,

Thank you for those historical links! The first one is very similar to my thoughts. Reading through it took me a long time as there seemed to be a bunch of off topic discussions with posts missing, so following it was fun. Also since the main players seemed to have fallen here now.

 

I think software has gotten better but the leakage through layers will be the problem. Will be like specral unmixing of fluorophor channel signals, like in a 6 color flow cytometer. But may be possible, just need lots of control images, which may elimate the point really. I am still thinking about it and will see if the Quattro files are better.

 

The terminology we use may also be a problem. I do find Sigma cameras good for uv. They are really sensitive. However their range is really limited. I found that my SD14 is great from 370 to 400nm section of the UV spectrum. Equal to a well converted Bayer camera. But the Range is limited to a maximum of just 350nm. Whereas my well converted Olympus Em1 can quite easily see to 300nm. But I purchased my SD14 for the cost of converting my Em1. So if you were just interested in great uv monochrome signal response, the early Sigma cameras are still good. If you want broad range or mixed color uv with various filters, then No don't buy an earlier Sigma. Testing the new Quattro should be fun. But I think the range will be similar.

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The major advantage of the Sigma SD14 is it was the last camera model fully supported by almost all software. You can open Raw files in dcraw, lightroom, and convert to dng using Adobe free dng converter software. Using the DNG converter is how you can make a linear uncompressed DNG file, which maybe what you used.

 

The files can also be opened in ImageJ. The Sigma photo pro software is a pain to use, but does have the best artistic output.

 

The revived Photivo, may be the best free software to fully manipulate Sigma files though now.

https://photivo.bouchier.be/en/pages/Download.html

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