From: "Frank Q" 
To: "Richard Schwartz" ,
        "Vladimir Galogaza" ,
        "ATM shore" 
Reply-To: "Frank Q" 


Hi All

For the situation described below, any random piece of window glass might
be flat for your purposes

Cheers
Frank Q


>
> The trick here is that for a given star only a tiny spot of the diagonal
is
> used.   Surface errors beyond the boundaries of that spot are meaningless.
> So the diagonal can be badly warped, but will still function well if it
has
> a smooth curve, as was shown by Anthony Stillman.   I am looking at having
a
> minimum obstruction scope with the diagonal just far enough from focus to
> avoid seeing the dust on it.   A relay lens or gregorian secondary will
> re-form the image where it can be accessed by eyepieces.
>
> . . . Richrad

--- BBBS/NT v4.00 MP