[Stefan Buda]

Sorry Peter, I've only just seen your reply.

I don't know how professional optical skills are defined, so all I can say that I've been pushing glass since 1985 when I made my first Newtonian, ready to view Halley's comet.
However I did not practice the craft for commercial reasons until recently.
The other thing is that making an f/5 mirror is not too difficult if you can measure it with an interferometer and you already have committed most of the learning curve mistakes on other pieces of glass.

Thanks for the appreciation.