I went into the garden today and - believe it or not - the sun was shining. Again. So instead of photographing ants or chasing the dog around the garden I took my spectrometer out and photographed plants and spectra. Here is the first:
A nice white spring flower. And here is its spectrum:
Very bright but not overexposed this time. As mentioned before, when it gets overexposed in green and red the yellow will come out much stronger. But its a pretty smooth spectrum over all colours with a slight dip at 590 nm.
The next "pictures" I took of green leafs of grass:
Great. We have proven that the main colour in a green grass spectrum indeed is green. Probably not a surprise to most of the scientific world, but as long as no one measures it everyone just has to guess or believe it... We have a broader range of blues but a higher peak of red than of blue. Perhaps there were a few yellowish leafs. Thats the problem with the setup. You can't know for sure what exactly you are taking the spectrum of when you just point and shoot somewhere.
And now for a nice yellow flower:
Isn't it pretty? We should get a lot of yellow from that one, shouldn't we?
First thing you might notice is the flickering "waterfall" image. There was some wind that let the flower tumble a bit. But for the curve I used one of the brighter lines in the middle. The second thing you should notice is that there is almost no yellow at all! Where green and red curves should overlap to give us some nice yellow the curves are strictly separated! We have a very strong blue and green section but only a little red and still it adds up to a strong yellow in the photo. Perhaps I did not properly aim at the yellow part of the flower? Okay, lets take another spectrum. This time with a stillstanding flower and aimed right at their yellow heart:
That's more like it! Green and red dominating, adding to yellow. Seems it was a targeting problem.
To avoid that we would need a kind of "sights", preferably a direct photo through the slit and a "two picture monitoring image" on the computer screen. One image of what the spectrometer "sees" and one image of what it measures, in real-time, of course. And it shouldn't raise the price of the spectrometer too much. A second web cam inside? A prism to part the light? Let's challenge the tech wizzards here!
Okay, last but not least a nice blue flower:
In fact it is a bit violet, so in the spectrum we see the dominant blue and a good amount red adding up. Interesting here is the blue "plateau" on the red hand side of the spectrum. Again: shouldn't the diffraction grating send the blues to the left and the reds to the right?