On Wed, 10 Oct 2007 15:49:48 -0700, Fred the Red Shirt
wrote:

On Oct 9, 11:53 pm, Steve Hix
wrote:
In article .com,
Fred the Red Shirt wrote:


...

Obviously you have not seen how a telescope mirror ages over the
years.

Guess again.

Well then you should have observed that the transparency increases
between cleanings.


It's easy to recoat the mirror, so it's not so much of a problem,
certainly less of one than dealing with silver corrosion.

While it is not a technologically daunting task, it is not cheap for

IF you have the equipment (vacuum chamber, heater for vaporizing
Aluminum) it's relatively simple. One of our Astronomy club members
does up to 10 or 12" for the locals. IIRC his favorite source of
Aluminum is peeling the foil off gum wrappers although regular
Aluminum foil works. It just takes more power.

It doesn't take a super high vacuum either. Just one high enough to
develop a plasma although that's not part of the process.

On local used the chemical process for coating which worked pretty
well, but the coating isn't nearly as even as vacuum deposition.

larger mirrors especially when you consider shipping. I have a 17.5"
mirror that will need realuminizing when I finally get around to
putting
it into a scope. It has been cleaned exactly once, but the coating
is nearly gone entirely after 30 years in storage.

Offhand, do you know anyone who recoats mirrors that size?

Not that size, but there are a number of labs that do the work and I
think I saw a couple of links listed.

Roger (K8RI).