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Al,
just my comment but spectra work with a SA is mainly done in the range of 3500 - 7000 Ang. To go outside that range would require a much more sophisticated spectroscope with a slit, higher resolution reflective grating and imaging selected areas of the spectra at a singe time.
The image below is of Fomalhaut taken with a DSI II mono and a ED80. The line at the tail of the spectra is atmospheric O2 + H2O. The hydrogen lines, H alpha, H beta and H gamma, are at the left hand side of the spectra and are of more interest.
A f/3.3 focal reducer would probably be overkill. A short f ratio will increase the "fishtail" effect of the wavelengths coming to different focus points, blurring the overall image. You can use it, but the total spectra would probably need multiple exposures as you focus on specific regions.
I experimented with the gear I had to see what effect / improvements I could get.
I'll be upgrading to a 120mm f/8.3 in the short term future.
cheers
Mark
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