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David,
In your original post you mention guiding after centering the Zero Order star image. Yes, this will work on spectroscopes like the Spectra-L200 but not all slit spectroscopes allow access to the Zero order star image.
All the commercial instruments use fixed width reflective slits, so the image of the focused star on the front of the slit can, with additional optics, be used to position and guide on the target.
An adjustable slit has the advantage of allowing the spectroscope to be used in "Slitless" mode; the slit being much wider than the target star/ asteroid. The resolution will then depend on the linear size of the seeing disk. A 20 to 50 micron slit if set to 80% of the seeing disk still allows >80% of the light to contribute to the spectrum but at significantly improved spectral resolution.
Using a guide scope and guide CCD works well with the Spectra-L200.
Ken
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