Turning shapes other than cylindrical

[Occasional machinist]

G'day Ulrich
If you want to use a loupe, you might be better off applying an offset to the profile rather than trying to match some form of profile to the loupe. It could be done but trying to look down a loupe while (power) feeding a lathe is for someone better coordinated than I am. Perhaps a large magnifying glass might be a compromise.
As Jon says the technique has lots of potential. I like it for it's simplicity, as well as the ability to do both inside and outside profiles.

Michael