Hi, from windy (and cold) Wellington.
Another very great advantage of a slit spectrgraph is that it gives you the ability to have calibration lines from, for example, neon or thorium lamp spectra. You can also, to a degree, adjust the resolution by adjusting the slit width, e.g. narrower slit -> more resolution -> less flux -> longer exposure .... and visa versa.
The downside, as indicated above, is that the price of high resolution is the need for long exposures and, hence very careful guiding to keep the target on the narrow slit ... not easy as I can tell you from my own experience (I'm sure Ken will confirm this). In my own work on the Ha monitoring of Be stars it is usual to have to make one hour exposures in order to achieve an acceptable SNR of at least 50.
I LOVE taking spectra with a simple 'star spectroscope'
