Hi David,
I modified my ALPY using a 200l/mm grism in place of the standard 600l/mm. This gives a lower resolution but still sufficient for SN classification for example. (I estimate this gives perhaps a 1.5 mag increase in sensitivity over the standard ALPY. I have been down to mag 17.5 supernovae in favourable conditions with this setup on a 280mm aperture C11 so mag 15-16 supernovae should be reachable with an unmodified ALPY)
The modification is fairly straightforward and reversible but requires a bespoke grism which Paton Hawksley (manufacturers of the Star Analyser and the supplier of the grism used in the ALPY) made for me. There are more details of my modified “ALPY 200” on my website here.
http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm
Cheers
Robin