Protected silver vs protected aluminium coating for 14.5" Quartz primary mirror?

[mbaddah (Mo)]

Mark Suchting has just completed my 14.5" f4.8 Quartz mirror and it will be shipped off to the coaters at Saintech this week. I have the option of protected aluminium or 99% reflective protected silver coating to be applied. Based on my primitive reading online, most still recommend protected aluminium due to following reasons:

- Enhanced coatings reduce contrast and increase light scatter
- Aluminium is more durable
- Silver is a difficult substance to remove and recoat when it needs to be done later down the track, possibly ruining the figure on the mirror

I haven't read anything yet to show that the enhanced reflectivity of the silver equates to brighter image at the eyepiece? I'd love to hear anyones experience with both and what they recommend. Thanks

[blink138 (Pat)]

you would think the mirror maker himself if he has any curiosity would already have compared the two coatings on two identical mirrors!
silver has a higher reflectance but is more prone to oxidation, if it can be suitably protected and some sort of warranty or guarantee then i would be tempted the silver road
pat

[gb_astro]

mbaddah, with silver it seems to be all about the coatings.
Apparently Saintech think they have something pretty special.
Pity we need a guinea pig to find out.
Have you spoken to Sainteck directly?

gb.

[Satchmo]

Originally Posted by blink138

you would think the mirror maker himself if he has any curiosity would already have compared the two coatings on two identical mirrors!

For your info Pat the 99% enhanced protected silver coating has been offered by a new coater as of a few days ago. No one is under any obligation or pressure to use it !

I have never viewed with a silver coating - its being offered by Wayne Sainty of Saintech for the same price as the standard overcoated aluminium. it was developed by Wayne when at CSIRO running the thin film coatings for mant year - as a robust high reflective coating for the SUSI stellar interferometer which has many 200mm celiostat flat mirrors which are uncovered in roll off sheds under the harshest conditions at Narrabri- as far as I know all or most of the coatings are still going strong after 22 years.

If you would like to satisfy _your_ `curiosity' as about Silver coatings then why not give Wayne an email wayne@saintech.com.

Mark Suchting

[Satchmo]

Originally Posted by gb_astro

Apparently Saintech think they have something pretty special.

Pity we need a guinea pig to find out.

gb.

I think the 22 year old SUSI Stellar Interferometer is one massive guinea - pig... ;-)

[gb_astro]

I posed two of the questions mention above to Wayne at Saintech:

Q. Enhanced coatings reduce contrast and increase light scatter.
A. Wayne implied that the higher scattering of silver mirrors was due to older methods of metal deposition rather than the overcoats. Saintech use Ion Assisted Deposition (IAD) that can results in coatings "with very fine crystallites with very low scatter".

Q. Silver is a difficult substance to remove and re-coat when it needs to be done later down the track, possibly ruining the figure on the mirror.
A. Removal of old silver-based films is easily accomplished with nitric acid. Providing the mirror is not left for long times in the acid, there is no damage to the mirror surface or figure.

Wayne said he is hoping to produce an information sheet on his coatings.

gb.

[LightningNZ (Cam)]

I'd trust the CSIRO guys. I work opposite them at ANU and there are some awesomely bright men and women there. There's some great materials and space tech research jointly going on between the two institutes.

Cheers,
Cam

[mbaddah (Mo)]

I managed to get in contact with Wayne yesterday, lovely guy and took the time to answer all the concerns that I had read about silver coatings. Most of criticisms against silver coatings comes down to its method of application. They are not an issue if applied correctly.

In the end I was convinced to go ahead with silver protected coating 99% reflectivity!!!

[torana68 (Roger)]

is this the guys at Gladesville?

[gb_astro]

Originally Posted by torana68

is this the guys at Gladesville?

Yes they are, or were.
Mark said Wayne was moving to Taree, NSW.

gb.

[torana68 (Roger)]

Originally Posted by gb_astro

Yes they are, or were. Mark said Wayne was moving to Taree, NSW. gb.

well that explains the phone not working, perhaps someone has contact details?

[strongmanmike (Michael)]

Originally Posted by LightningNZ

I'd trust the CSIRO guys. I work opposite them at ANU and there are some awesomely bright men and women there. There's some great materials and space tech research jointly going on between the two institutes.

Cheers,
Cam

Funny, many don't seem to trust what they say about other topical science though

sorry couldn't help it....

I'd be temted by the silver coatings myself....go for it, worth the risk

Mike

[blink138 (Pat)]

quote "If you would like to satisfy _your_ `curiosity' as about Silver coatings then why not give Wayne an email wayne@saintech.com"
funny_ tone_ ya have there mark! i am not the one that is curious, i am saying the mirror maker surely would have compared the two
i actually dont give a rats one way or 'tother!
pat

[Jbunky86 (Jason)]

Hi guys anyone know around about how much it costs for a 12" gso mirror Recoat with this mob? I'v flicked Wayne an email, waiting on a response.
Anyone know if this mob would be better or cheaper than that Isac bloke?

Cheers

[erick (Eric)]

Looking forward to hear of experiences with this coating.

[Jbunky86 (Jason)]

Waiting waiting waiting waiting
No response waiting waiting waiting
Hmmmm waiting waiting waiting.................

[xstream (John)]

Jason, You could always do the research yourself, instead of being impatient.
Maybe no-one knows your answer or they haven't been online.

[mbaddah (Mo)]

Hi Jason,

Last I spoke to Wayne he said he will be on leave for 4 days so that could be why he isn't responding.

[clive milne]

Originally Posted by Jbunky86

Hi guys anyone know around about how much it costs for a 12" gso mirror Recoat with this mob? I'v flicked Wayne an email, waiting on a response.
Anyone know if this mob would be better or cheaper than that Isac bloke?

Cheers

I'm pretty sure it will be cheaper and also better.
To the best of my knowledge, the coating that Wayne has developed will be have higher reflectivity, less light scatter and be more durable.

[Jbunky86 (Jason)]

Oh cool sounds good thanks
Haha I ment waiting for email response from Wayne
I realize forum members have better things to do than answer my every query.


As soon as I get some info I will
Reveal

Cheers Jas