Quote:
Originally Posted by Paul Haese
A fast Newtonian ... f4 and below might as well be in the impossible range.
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I'd agree with that having built a 12.5" f/3.7 and a smaller f/3.5 long ago when I had a workshop and the tools to make a decent secondary cell and spider. Not quite impossible, but certainly damn difficult.
The 12.5" was intended to be a classical Cassegrain - I got as far as figuring a secondary but never finished the scope when I realised how massive the mount would have to be. Its temporary configuration as a very fast altaz newtonian became permanent.
Never again. f/7 - or close to it - is nirvana IMHO for fast reflectors and refractors, apart from lunar and planetary which is where the larger maks from 7" and up have a whole game to themselves.