[ATM] Vacuum coating, was Silvering Woes

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Jason Hissong" <jhissong@gmail.com>


> James,
>
> We may be getting an old vacuum chamber going again up at the observatory 
> where we do mirror making sessions.  We need to get a new diffuser pump and 
> such. But I had a question in regards to the protective coating.  How do you 
> put a coating of protective silicon over the aluminum?  In a similar fashion?

Well, I don't 'YET' :)

Personally I feel that a non overcoated surface appears to provide a performance 
boost in contrast.  But it is just a feeling based on observation of a few 
mirrors I coated for club members, who later had the same optic professionally 
coated.

Like I said in the beginning, it is just a 'FEELING', devising a method to test 
this condition is beyond my abilities, but I am open to ideas! Unprotected 
aluminum is good for a few years if you can keep the dew off, which is rather 
difficult down here in balmy Florida.

With regards to your question, SiO can be evaporated in a Tantalum boat using 
resistance heating.  Alternatively it can also be evaporated in a crucible with 
an E-Beam gun, but this might be beyond a home built system.

The trick isn't so much the evaporation part, but knowing how thick the coating 
is on the surface of the optic.  For this we need quartz film thickness 
monitors, another Ebay item, but they are a little pricey.

Honestly, my motivation for creating overcoated optics is currently rather low. 
Primarily because I have the chamber in the garage, and if the optic even looks 
a little grungy, I just recoat it instead of cleaning it.  (both take about the 
same amount of time and labor, roughly 1 hour to re-coat the two 16" primaries 
on the bino-scope).


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge




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