I am new to this game and have already made one mistake. I hope that this effort gets published.
What I want to do I would eventually like to be able to test garden soil to find out the amount of NPK in the soil; that is Nitrogen, Phosphates, and potash. I have built a home-made spectrometer from square black plastic rainwater downpipe. It is available in the UK, but I'm not sure of its availability in the USA or elsewhere. See attached.
My attempt and results I have made the spectrometer so that ambient light is excluded, and so that it will be safe to use ultra-violet within it. I have made the angle of the diffracted beam and the camera mounting adjustable; I can then measure an angle to a spectral line and from that I can deduce the wavelength that it represents. I have measured the angles to various spectral colored lines and superimposed them on a CFL spectrum fro SpectralLab. See attached. I have made the slit width adjustable to any width. It can also be measured with a car mechanic's feeler gauges. I can also alter the angle of the slit in relation to the centre of rotation of the defracted beam and camera mount.
Questions and next steps My Test 1 spectrum shows curved spectral lines and I don't know why. Th black line in the centre of the spectrum is to give me a datum line for measuring the angle of the diffraction grating and camera when I alter the angle. When I captured the Test 1 spectrum with Spectral Workbench software the graph had only a small height. To my eye the intensity of the Test 1 spectrum looked of a reasonable intensity for a good graph. Can anyone put me right? I have added an attachment about slit width, but I have yet to do slit width tests.
Why I'm interested I am intending to use a pair of cuvettes alongside each other. I hope that I will be able to have the soil test sample in one cuvette and the solvent alone in the other. The idea being that I can subtract the two spectra and thus eliminate the spectrum of whatever light source I am using and also whatever solvent I am using.
Comments would be appreciated! Angle_of_deflection_of_diffraction_Grating.doc