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Public Lab Research note

Webcam brightness testing for Oil Testing Kit

by warren | September 12, 2014 15:44 12 Sep 15:44 | #11133 | #11133

What I want to do

We've had trouble getting bright enough spectra in the Oil Testing Kit with the SANM webcam that ships in the current Desktop Spectrometry Kit, but other cameras seem to do all right. @mathew and I are testing a range of cameras to see if we can solve the brightness problem primarily through camera choice, but also using reflectors and other design modifications to maximize brightness. We need to do a lot better than this: https://spectralworkbench.org/analyze/spectrum/33804, and @mathew and I have been going for over 25% intensity.

My attempt and results

I tried both a Creative Live Notebook webcam and the old SYBA cam with a UV ultro-micro cuvette. The results were really solid; peaks were close to 50%. Note that none of the spectra on this page are calibrated; the graphs are just to show relative intensity and are not aligned by wavelength:


Aligning the cuvette wasn't super easy by hand, but if we create a shelf or guide it should be pretty easy to get the laser aligned just right.

Questions and next steps

I'm also curious about how we're combining color channels; the percentage exposure per channel is much better, and if we could have a better means of combining them, maybe we'd be more confident in the data:

Creative Live webcam w/ 'nail polish' bottle


Creative Live webcam w/ cuvette


Syba webcam w/ cuvette


Here are all the links to the spectra themselves:


Oh, edit: the Creative had a wider than usual slit -- maybe 1.25mm or so. So maybe the clipping in the blue channel wouldn't be as bad with a little less brightness.

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Actually, kind of amazing -- for the Creative webcam ones, not enough laser was actually reflected into the spectrometer to get the 405nm peak... crazy! Maybe we actually need to be sure some laser is reflected in just to get that peak aligned...

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@JSummers was commenting that the light path on my gel caps was never going to be consistent enough to compare to the laser peak. this seems to be a case of similar. How important is it to have a consistant relationship between the laser and the slit to normalize the laser peaks?

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Do you (or jack) mean getting the laser to be in the same place each time with relation to the slit? If the laser is fixed in place by the cardboard frame, I don't think it'll be hard to get it to align with the slit perfectly. I understood Jack to mean that the curved surface will deflect the laser, which a square-sided container wouldn't do.

Have you checked the fluorescence of an empty gel cap after you found the paper about gelatin fluorescence?

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I tried to find gel caps but CVS didn't have them; I was going to order online but saw your note about the fluorescence... should I still order them?

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I will test an empty gelcap for fluorescence now. I searched google maps for a "compounding pharmacy" in my neighborhood and found one close by. They were the ones with cheap gelcaps, but there were a bunch of them around.

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poop. the caps fluoresce.


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