OK, now let's start playing further with this toy. Brightest object in the sky happened to be Venus. Grabbed a spectrum of that and decided to compare it to the Sun. After all, Venus mostly reflects Sunlight. Nuisance: the Sun is an extended object using my setup. So I took a Solar spectrum the next morning using my Rough Science Spectrograph, same equipment but in a cardboard box with a slit ( http://www.samirkharusi.net/spectrograph.html ). Click "original" below right to see a large version of the above spectra. Because the Sun's spectrum was obtained with the lens focused only a few inches away (see how nice a macro lens can get?) and Venus' at infinity, I had to stretch one horizontally to match the other. They do match quite well in the visible wavelengths, but for some strange reason, at longer than 7000 Angstroms the spectral scales diverge. If I align the extreme ends of the spectra, the mid-wavelengths mismatch. OK, ultimate pixel-peeping, and we are using the lens most definitely at wavelengths it was not designed for (near Infra Red) and if there is some kind of differential, wavelength-dependent, geometrical distortion between when the lens is focused at 8" and at infinity, Canon couldn't care less for the Near IR. Also, diffraction gratings are meant for parallel light, and my Rough Science Spectrograph has its slit at a few inches, without any collimating lens... Of course I could easily warp or multi-point align the whole scale so everything lines up perfectly, but I thought you might also be intrigued by this little phenomenon. To get the Solar spectrum to show up in full colorful splendor I spliced two exposures with a gradient transition. The upper half, with longer exposure, goes deeper into both the UV and IR ends. Somewhere in there, Venus is supposed to demonstrate CO2 absorption, but I have no clue as to whether such CO2 absorption lines would fall within my visible-to-Near IR range :-(