In another thread
, we got way off topic and touched on stuff you can do with an IR-converted camera. John posted a cool link to a discussion of NDVI on the PLOTS web page
. Among other things, the PLOTS page mentioned the "Superblue" filter, which passes blue and IR wavelengths. The graph on the PLOTS web page seemed to show that the Superblue filter is actually a Schott BG3 filter. I have one of those at work, so I stuck it in our spectrophotometer to take a look. While I was at it I stuck in a Schott UG1 UV filter and my Hoya R72 IR filter:
Both the UG1 and the BG3 have peaks at both the blue and red ends of the spectrum. The R72 turns on around 720nm and just keeps going.
UG1's blue peak turns off right around 400nm, and its red peak turns on right around 700-720nm, same as the Hoya R72. So for the purpose of an unconverted camera, it's essentially black with a little red leak.
BG3's blue peak turns off a little later, closer to 450nm, and its red peak also turns on right around 700-720nm. So for the purpose of an unconverted camera, it's got marginal blue and red leaks. Just for fun I stuck it on my Canon T2i and took a picture:
That's our courtyard at work in more or less direct sunlight. I uploaded the picture full size.
Looking at the curves for the image, there's a fair bit of light in the R and B channels, and practically nothing in G. Which makes sense given the nature of the filter. I'm not sure what I can do with it on my camera, but on a modified camera you should get a fair bit of IR at the red end, and a bit of UV at the blue end.
Given what's on the PLOTS page, it may be possible to get something similar to an NDVI image off of a single frame by doing:
Pixel = (R-B)/(R+B)
I'm going to ask around at work tomorrow to see if we have any modified cameras sitting around. But if anyone can think of anything to do with this using an unmodified camera, please let me know. I can go out and get whatever pictures you'd find useful and upload them for some sandbox play time.