What I want to do or know
How are you dealing with the slit geometry and the curvature of the DVD grating?
I have built a simple spectrometer using a Canon 1000d DSLR, a reversed 50mm lens that I normally use for macro photography and a DVD grating. The slit is about 2mm long and very thin (made by making a small cut in a aluminium foil with a very sharp blade). The problem is that even though I am basically getting a resolution limited by the CMOS sensor (I can easily resolve a sodium D lines), it's only in vertically thin slice of the image. It seems that a combination of a straight vertical slit and a curvature of the grating introduces an aberration in most of the imaged spectrum (see the sample).
Does anyone know of a way of getting a sharp spectra using a DVD grating? I am guessing that I would get a sharper spectra using a point in place of a vertical slit but than I would sacrifice a lot of light. I would very much like to be able to use mote of the recorded image.
I have even bought a cheap diffraction grating film in a roll. It does have a straight grooves but the film itself is not flat and I have not come up with a way of mounting it perfectly flat. If it isn't completely flat, I get a completely unusable spectra. Any idea how I could mount it flat?