Best coating in Oz for 20" mirror?

[Insomniac]

Anyone got any strong opinions as to who offers the best re coating service? I'm looking for the highest reflectivity possible. I don't want silver as 2 major U.S mirror coaters have told me that even with a protective overcoat silver is still vulnerable to fast degredation.

[Satchmo]

On 30th October you wrote : "Check out this Nov/Dec S & T mag for ultra high reflectivity coatings done in Australia by Optical Coatings Associates. They seem to be a reputable bunch and have responded in detail to lots of my technical questions."

That was a good wrap . What happened ? I emailed them for a quote on a 20" coating 10 days ago and got no reply.

[astroron (Ron)]

I thought the same thing, I even checked out their web site.
Ron

[Ian Robinson]

Has anyone used them lately ?

Maybe they aren't trading anymore , or are on holidays , or are very busy , or just simply blew you off.

[Insomniac]

Post script; whilst the U.S coaters I've contacted won't touch overcoated silver because (they say) ,it is still permeable on the molecular level, the boss of Optical Coatings Associates (David) has told me that his overcoating has the problem licked because it's non porous. It would be interesting to know how long they last in practice. But David has been helpful, even offering to send me a coated sample to play with. I'm inclined to stay conservative, especially since over here in NZ I regularly get dew on the primary! I thought that was a near impossibility!

[Ian Robinson]

Originally Posted by Insomniac

Post script; whilst the U.S coaters I've contacted won't touch overcoated silver because (they say) ,it is still permeable on the molecular level, the boss of Optical Coatings Associates (David) has told me that his overcoating has the problem licked because it's non porous. It would be interesting to know how long they last in practice. But David has been helpful, even offering to send me a coated sample to play with. I'm inclined to stay conservative, especially since over here in NZ I regularly get dew on the primary! I thought that was a near impossibility!

If the overcoating is impervious and will presumeably there is no diffusion of O2 to the metal surface , then it is even less likely moisture will get through too. Lookiing at the reflectivity of standard Al overcoated with SiO2 , Ag looks pretty good for the visual band.

It's the O2 in the air that makes silver tarnish. And Silver metal is insoluble in water.

(Ksp = 1.52 x 10-8 for AgOH)

[Satchmo]

Originally Posted by Insomniac

I'm inclined to stay conservative, especially since over here in NZ I regularly get dew on the primary! I thought that was a near impossibility!

Its all matter of risk vs cost. It will be expensive to resend it if it doesn't stand up to the rigours of the reality of life in a portable amateur telescope and what life span do you consider acceptable valuable vs. your guaranteed 6 months life or replacement coating etc.

[Insomniac]

So who else does enhanced coatings for larger mirrors in Australia? I've tried contacting C Qin Pty, but he won't answer! Customer Service hasn't quite filtered through to everyone yet. Maybe the recession will focus minds & help change that...

[Satchmo]

Originally Posted by Insomniac

I've tried contacting C Qin Pty, but he won't answer! Customer Service hasn't quite filtered through to everyone yet. Maybe the recession will focus minds & help change that...

Go easy ! Issac is Chinese, his spoken English is OK , but his written comprehension isn't great so I doubt you would have any luck with an email ( I'm not even sure he knows he has one ) . Its best to call his mobile. He does a very robust Quartz protected overcoat. I have had many large mirrors coated with Quartz and no genuine coating failures in 10 years: they are all still going strong to my knowledge.