I learned this past week that C# can be played by using L3 and R123 on my alto. (Forgive me if that is not the proper way to describe it, and please indicate the proper description of this method.) It is not on my fingering chart. It does seem to make a darker tone than not pressing any keys. I'm sure it has been discussed here many times but was a real eye-opener for me. Using the octave key doesn't appear to make any difference. Why would that fingering not be generally taught? Do any of you find yourself using that alternate and when?