Re-Aluminization of the 200-inch Primary Mirror of the Hale
Telescope at the Palomar Observatory  Time-lapse movies:
Washing the 200-inch mirror filmed October, 2006 (17.7 mb)
October, 2006 full aluminizing movie with narration (Warning:
Large File! ~352 mb) Here's a smaller version posted at YouTube.
June, 2005 aluminizing filmed June, 2005 (~150 mb)  Telescope
mirrors get a lot of use.  The 200-inch Hale Telescope at the
Palomar Observatory is used on average about 300 nights a year. 
Even with weekly cleanings, mirrors periodically need to be
given a new coat of reflective aluminium.  It is a process that
takes several days.   How do you re-coat a 14.5 ton mirror? 
What follows is how it happens at the Palomar Observatory. 
Click on the images to see them at full size.   First the
astronomical instrument located in the Cassegrain focus at the
bottom of the telescope is removed.  The instrument cage and all
wiring are also removed from the telescope (left).  This exposes
the mirror cell (right) that hol