Mirror Re-coating

[OzEclipse (Joe Cali)]

Originally Posted by gb_astro

HI Mark.

I think you will find that both his standard and enhanced overcoats use Silicon Dioxide, which is Silica rather than Quartz.

gb.

GB
The chemical formula of Quartz is silcon dioxide SiO2. They are the same thing.
Joe

[gb_astro]

Originally Posted by OzEclipse

GB
The chemical formula of Quartz is silcon dioxide SiO2. They are the same thing.
Joe

Yes appologies for getting that wrong. Thought the formula for quartz was SiO4. Now see it's SiO2 in a tetrahedron structure.

gb.

[alocky (Andrew lockwood)]

Originally Posted by OzEclipse

GB
The chemical formula of Quartz is silcon dioxide SiO2. They are the same thing.
Joe

True - but crystalline quartz and its polymorphs are composed of tetrahedra, and are more properly SiO4...
picky picky, I know!
Also to be picky, quartz is at 7 on the hardness scale, so it's not super-hard, and can be scratched by hardened steel. So don't use steel wool to clean your mirror.
cheers!
Andrew.

edit: ha ha - snap!

[gb_astro]

"edit: ha ha - snap!"

Close though.

So just to clarify, in the coating process silicon monoxide goes into the chamber
and SiO2 in a tetrahedran structure (Quartz) is formed on the mirror surface?
Is that right?

gb.

[alocky (Andrew lockwood)]

Originally Posted by gb_astro

"edit: ha ha - snap!"

Close though.

So just to clarify, in the coating process silicon monoxide goes into the chamber
and SiO2 in a tetrahedran structure (Quartz) is formed on the mirror surface?
Is that right?

gb.

Interesting point - all the phase diagrams I can find for quartz are around geological pressures, not near vacuum. At the temperatures and pressures in a coating chamber I don't think you'd be forming quartz, but presumably someone who actually knows can chime in!
cheers,
Andrew.

[Me2 (Mark)]

Hmmm.... interesting discussion but my mirror is on it's way to Wayne and I need to make up my mind between the pros and cons of Aluminium + Quartz R>91% vs. Aluminium Enhanced R>95% coatings.
He intends to do my secondary at the same time. I seem to remember that secondaries should be enhanced. Is that correct?

Cheers,
Mark

[OzEclipse (Joe Cali)]

I don't see why secondary needs to be more reflective than the primary. The total transmission is the product of the two. ie two 91% coatings will give a net transmission of 83% while two 98% surfaces will transmit 96%. So you can combine them any way you like. A 91% primary with a 98% secondary will transmit 89% as will a combination of the reverse coatings.

You always buy the highest spec diagonal flat you can afford because the light is incident at 45 deg, wavefront errors are "magnified" for want of a better word over orthogonal incidence. Perhaps that's what you are thinking about in terms of higher spec for the secondary.

Joe

[AstralTraveller (David)]

I think the logic was that you pay less for a secondary to go from standard to enhanced than for a primary. So enhancing the secondary gives more bang for the bucks. The truth is that that the increase isn't all that much for either - only $30 for A 16".

Two questions.
(1) How are people packaging their mirrors for transport? I doubt there is an off the shelf box for a 16" mirror. Does everyone build their own transport box?
(2) What is the turn around time?

[gb_astro]

Originally Posted by Me2

Hmmm.... interesting discussion but my mirror is on it's way to Wayne and I need to make up my mind between the pros and cons of Aluminium + Quartz R>91% vs. Aluminium Enhanced R>95% coatings.
He intends to do my secondary at the same time. I seem to remember that secondaries should be enhanced. Is that correct?

Cheers,
Mark

Just contacted Wayne to clarify the differences between his two Al coating techniques.
Looks like my previous description of Wayne's process was out of date or just wrong.

So:
Both use his low pressure ion assisted deposition method.
Both apply a 200nm aluminium layer.
The Aluminium + Quartz applies a 200nm layer of SiO2 as the overcoat.
The Aluminium Enhanced applies multiply layers of Titanium and Tantalum Oxides as the overcoat to a thickness of 15O nm.

Wayne says the enhanced coating is harder than the quartz coating although it is thiner of course.

As to which overcoat would protect the mirror better is a tough call.
Thiner/harder verses thicker/ softer.
Probably turn out to be the same.

gb.

[Me2 (Mark)]

I've mailed it off and chosen the enhanced coating as Wayne said it also lasts well. I'll be more vigilant about keeping moisture away when not in use. Thanks for all of your answers etc.

I made a 6mm plywood box 80mm deep. I put a layer of 15mm 80kg/m^3 pvc foam in the bottom then the 55mm mirror then another layer of 15mm foam on top. There is another layer of pvc foam cut out to the mirror diameter around the mirror. I glued three softwood wedges for the mirror edge to sit on, upside down in the box. This keeps the reflective surface a few mm above the foam. a couple of layers of dressmakers wadding liner on the back of the mirror keeps it all snug. The disadvantage of this method is having to put the mirror in upside down without touching the mirror surface. I found disposable rubber gloves help grip the edges, or the inverted box could be lowered over the mirror. I loosely wrapped the secondary in toilet paper and snugged it in with the primary.

There are Youtube videos on packaging mirrors but they all rely on the newly coated surface being in contact with tissue in cardboard boxes. I realise I've done that with the secondary. My box took about 1 hour to make ready for posting.

Wayne didn't give me a turnaround time though he did say he would still do it even if it was the only one to do. Now may be a good time to get yours done.

[gb_astro]

The wooden box/wooden wedges method is not recommended these days.
There is always the chance of the wedges coming loose and if the box is dropped there can be a lot of force applied to the mirror at those small area contact points.

The cardboard box with stiff foam method seems to be preferred.

http://www.galaxyoptics.com/images/1...structions.pdf

http://www.spectrum-coatings.com/Tel...or_Packing.htm

gb.

[Me2 (Mark)]

I did wonder about that but my wedges are about 20mm wide and well glued to pvc foam. The foam would absorb a lot of impact, it's the foam I use to build 40 foot catamarans hulls.
I seem to remember my Parks mirror originally arrived in a cardboard box 15 years ago.

[Me2 (Mark)]

To up date progress:
Wayne Sainty coated my mirror but noticed some marks so cleaned it off and coated again. Marks were still there so he didn't overcoat it. He kindly sent it back no charge despite all his work. The marks are a bit strange as they don't look like roughness. When I sent the mirror it was quite badly corroded so I assume this had affected the glass somehow. I am rebuilding my telescope so can't test it till it is finished.
Question: If the mirror needs polishing, what would be the best way to go about it? I'd like to do it myself as paying someone doesn't seem worthwhile considering a new mirror can be had for $650 these days.

Cheers,
Mark

[chunkylad (David)]

Great thread.
I had been putting off getting my 12" mirror refinished since CQin went missing from the scene. Now this thread has provided a solution.

Cheers.

[billdan (Bill)]

These guys in Sydney appear to offer a recoating service.

http://www.astro-optical.com.au/mirror.php

Not sure how up to date their website is though.
Regards
Bill

[Satchmo]

Steer clear of any coaters like Astro Optical that don't do a protective overcoating of your mirror ( their chamber is about 50 years old and just not capable of it )

Saintech are your best bet for Australian based coating , and CQin still do coatings but he waits until he has a number - ships them to China and then goes over to coat them so the wait may be longer .

[frank farrell]

Well, I got my 10" mirror back from Mr Sainty. Great service, we are blessed to have him in Australia. Quick, friendly. Protective coating over enhanced aluminium. Cost was spoilt by having to post it. Otherwise, an affordable operation. If you live near to his business it would be a same day service.

[mark3d]

Frank, can I get an indication of the postage method you used, and cost?

[Leo.G (Leo)]

Originally Posted by billdan

These guys in Sydney appear to offer a recoating service.

http://www.astro-optical.com.au/mirror.php

Not sure how up to date their website is though.
Regards
Bill

Charged me $200 plus return freight to coat my 8" mirror.
Took 2 weeks longer than promised with nothing but BS excuses, sent it back in old dusty foam and, to top that, they returned it by post using the last 4 digits of my home phone number as the post code.

After contacting these guys several times asking if they'd addressed my package properly and being told every time they had, I contacted Australia post and they eventually found my mirror in Newcastle (NSW). That's a long way from Lithgow where I live.

After receiving the mirror and inspecting it I noticed it was severely scratched and have never bothered since. All this after a 3 hour train ride, a lot of cash (for me) and a couple of weeks waiting, it being posted to the wrong town plus, the $30 freight they charged me up front came in at $12.

I was ripped off for an inferior product done by people with inferior ethics and practices.

I'd originally found them through this forum (I honestly thought I'd joined years ago) but not only would I not recommend their service to anyone, I'd go down there and....Never mind!

I'm now in the process of spending another $200+ for a new mirror for my GSO through Bintel who, now stock the mirrors. The scope will end up being worth more than a 10" equivalent but that's how this game is.

I've just learned through another forum that these incompetent people are no longer in business, GREAT news!

At the time when I got my mirror re-coated, Bintel weren't selling new F5 mirrors for the GSO scopes so I had no choice but to get it re-coated. Biggest regret ever.

At least I still have my old 6" refractor (skywatcher achromatic (1200mm focal length, the old blue series), an 80mm Megrez (achromatic) and, an 130mm Celestron reflector to play with.

I've just acquired an old Starlight Xpress MX5-C camera and am interested in playing but that's a whole different story. Maybe after I replace the mirror with a new one, till then I'll settle for closer imaging through the Megrez.