Le 30/07/2017 Ã* 10:57, jacobnavia a écrit :
It has been a long time since any professional telescope
had a large lens, nor do I think it's the case any more that the
optics are the most expensive part of the instrument -- mjh

OK, now we use mirrors, I should have been more precise.

But the mirrors, and the associated machinery for moving them, is quite
a BIG part of any modern telescope budget...