I have both these instruments which I use with a Celestron C11. SCT are perfect with the LHIRES which is optimised for an 8-12 inch f10 scope and where you are normally looking at a narrow wavelength range where defocussing due to chromatism is not not important.
With the ALPY it depends on how critical you are. I manage to get good results with the ALPY using it with a focal reducer to match it to the fast f5 optics of the ALPY but an SCT is not ideal for fast spectrograph optics and a wide spectral range though due to the chromatics aberrations, mainly from the reducer. This makes it more difficult to get an accurate flux calibration (shape of the continuum) which can change dramatically with focus due to the selective sampling of wavelengths at the slit. This means you have to be very careful that nothing changes between measuring the target and reference. (The focus of my old metal tube C11 is not particularly stable with temperature either, new carbon fibre models might be better.) More on the effects of chromatism (both from the telescope optics and the atmosphere) on Christian Buil's page here
Most people use what they have or chose a telescope based on other requirements but if starting from scratch specifically for spectroscopy I would go for a fully reflective design or perhaps a good quality APO refractor with a decent aperture though that would be much more expensive. See Christian Buil's page here for examples of telescopes which are optimum for the ALPY (in french but google etc translate well)
and what can be done with a small aperture quality APO
Edited by robin_astro, 20 February 2021 - 07:46 AM.