Re: ATM A Visit to Griffith Observatory

[ab866@freenet.durham.org (ric rokosz)]

Richard Schwartz writes:
> 
> -- [ From: Richard Schwartz * EMC.Ver #2.5.02 ] --
> 
> Today I visited Griffith Observatory.  When there, I informed my wife that I
> first ground glass in the basement ATM workshop there, 25 years ago.
> 
> The 40" hole from the Palomar 200" has been demoted from its original shrine
> .  Half of the reflective coating has been stripped to reveal the interior
> of the glass.  
> 
> What a MESS!!!  It has striae, dirt clods, internal cracks, a grogzillion
> bubbles, edge and surface chips, and every other imaginable defect.   You
> can clearly see the different layers of glass that result from the several
> pours into the mold.  I think it a miracle that a working telescope could be
> made of that piece of garbage!
> 
The 72 inch mirror at the David Dunlop Observatory outside of Toronto was
one of the test blanks done for the Hale 200 inch and it has similar
problems,of slight cracks,and bubbles;but this blank was figured and is
still in use.This is a full thickness blank and the technician told me it
never reaches temperature equilibrium;in July the blank is still cold to
the touch.They tried fans but......

Ric

--