PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Howdy:
I have a 16" coater but that is not big enough of course so I am planning to build a bigger one after I got a quote of $1000 for coating and shipping my 22". It seems like we get ripped off a lot in S. California so I plan to do this for myself and to help others. I have flat bottom 20" coater base and believe I can use a 42" 550 Gallon propane tank after I reinforce it and coat the insides with nickle and chrome. I will make some discoveries and am always looking for some tips. I am looking for doable alternatives to a turbo pump and an ion beam. Of course someone with good used parts may want to join in.
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Even though I have done some coatings in the past, I am always learning things. I haven't seen the reflection specs. for 45 degree reflections. It seems to me that it does not matter if the coating on a diagonal is 89% or 98% reflective because as light approches Brewster's Angle the smoother coating should be close to 100% anyway. If this is so an AlO2 coating should give a better reflection than a 40 layer dielectric coating. I have heard AlO2 protected aluminum is a very durable 95% reflective coating and I need four reflections for a special project. Two will be right angles so I still should be above SiO2 overcoated Aluminum with just one reflection. Yes? -Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Hey if your interested you can find a mirror restorer and have your mirror coated with raw silver. It will need to be burnished but the chemicals are already mixed and you just spray it on. I have done this with great success but in California, our air became acidic after going to the catalytic converters. My last raw silver only lasted three days and I was out in the countryside of San Diego County. I did not like dealing with varnish but now there are some low VOC conformal overcoats. Still the thinnest will be hundreds of times thicker than an oxided overcoat which probably was fine for small long focus Newtonians but not relative fast and large reflectors of late.
Edited by PitchHitter (09/28/09 11:26 PM)
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rboe
Reged: 03/16/02
Posts: 45307
Loc: Phx, AZ
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A good roughing pump and a diffusion pump will work too. Not as fast as your turbo though. 
How good of a vacuum do you need?
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Cary
Vendor (Optic Wave Labs)
Reged: 07/07/04
Posts: 398
Loc: Rancho Cordova, CA
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If you want to keep your cost down to less than $10K for the deposition electronics then you will have to stick with Aluminum with a silicon monoxide overcoat. You can deposit these coatings with a tungsten filament for the aluminum and a "baffle box" for the SiO. You can get these from RD Mathis in So. Cal.
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Cary Chleborad
http://www.opticwavelabs.com
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3529
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our club used to have a working coating chamber. we were charging members $10 to recoat.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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DanNie
journeyman
Reged: 11/18/08
Posts: 6
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While I applaud the do-it –yourself spirit , just as ATMs are cautioned to start small with grinding and polishing mirrors, I would point out some reasons why large vacuum coating projects are seldom done by amateurs and even less often successful. I have known a few individuals that achieved some success in garage-type coating operations, and I worked in the field myself on-an-off for several decades.
• The atmospheric pressure on any large vacuum tank is truly enormous, reckoned in hundreds of tons on a 36” square box coater, for example. Flat walls are to be avoided, otherwise “over-engineered” to provide a large margin of safety. Repeated small flexures on weld joints can lead to chamber leakage or worse, failure. Without a helium leak detector at hand, chasing after small high-vacuum leaks is a royal pain.
• Large coating chambers require fast, clean high vacuum pumping systems with large conductance. Since coating adhesion failure is most commonly caused by unclean substrate surfaces (atomically speaking), in turn frequently caused by dirty vacuum, “slow-and-dirty” pumping is a waste of effort and money. A large diffusion pump is the usual low-cost answer for large aluminization chambers, provided diff oil vapor and moisture is cryogenically trapped out. One should aim for at least 10^-6 torr vacuum.
• Adhesion success is much more likely if in-chamber glow-discharge cleaning or ion-beam cleaning of the substrates immediately precedes coating. These are generally better than simple substrate heating.
• Large-scale multi-layer dielectric coatings are pretty much off the table for amateur operations. The monitoring and control requirements imposed by tight tolerances on the individual layer thickness and index dictate the use of in-situ thickness monitors and automatic control of e-beam, ion-beam, or sputter deposition sources. These requirements usually equate to big bucks.
Good luck if you decide to press ahead, and let us know how it goes.
Dan Niebauer (S. California)
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Brian Engel
member
Reged: 08/25/09
Posts: 89
Loc: Cincinnati,Oh
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I would tend to agree. I am Mr. DIY but the risk and cost of making a vacuum chamber to make a quality coating on a large mirror is just not worth it if you are coating onesy-twosy mirrors from time to time. Not only the risk of a bad coating but also being injuried/killed from a large vacuum chamber imploding.
I just look at it like it doesn't matter if you have a beatiful 1/20 wave surface on the *glass* of your mirror if the coating doesn't conform perfectly to it.
OpticalMechanics.com charges $600 for a 22" mirror and does a really good job (including free null test foucault/ronchi-grams). Also, L&L optical is in Santa Ana CA.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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I have a Helium leak detector although building one does not seem that complicated. I also have a complete 16" Varian but it does not have the glow discharge cleaning except maybe at the base.
I want to build a larger chamber. I believe a sputtered aluminum coating followed by a blast of pure O2 will produce a durable protected Aluminum coating of 95% reflectivity. My roughing pump is three times larger than the original and of course the system has a diffusion pump but boosted turbo pumps can actually draw more than diffusion pumps which I would like to get away from. Protected silver only brings up the Blue-UV spectrum and lowers the IR irradiation. Actually Aluminum is the best photopic choice and its pure oxide is both durable and highly reflective so SiO and SiO2 overcoats are redundant and at the cost of about 5% reflectivity.
I believe I am closing in on having functional knowledge and a system that can handle my scouts mirrors as well as my own and cooperating participants.
We used to have some decent coaters on the West Coasts and a few will slip an amateur's mirror in as a favor but that is getting rare too. I lost my 16.25" that way and got it back years later with the figure ruined by a fire and improper storage for seven years. I don't want to be at the mercy of favors and contrived prices.
Anyway that is the reason for the post, to share and find knowledge. Best, Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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BTW there is no danger from an imploding metal chamber. Heavy wall metal is just going to collapse not implode. Glass is entirely another experience as it shatters into sharp shards that will pass through center and keep on going. I've decompressed metal drums and cans before. It can be a shock if one is unprepared but it is no big deal! The only reason I would need to weld support is to make sure the hatch stays true.
Addressed to no one in particular....When you don't know something it is best to ask because when you state an opinion as fact you are ruining your credibility and the purpose of the forum. I may be off on the values of the aluminum reflectivity because that is the posted values, not what I have duplicated and that is part of the experiment. BUT! I have watched cans and tanks and tubes implode, know there is a difference between glass and metal and that in this thread I have already had naysayers claiming a danger that does not exist. There is far more danger of inhaling glass dust so where would we be if we just bought our mirrors? BTW Bob Goff, friend and alumni was a PRO that did inhale glass dust.
For the rest of this post, please state facts from experience, express opinions, ask questions and question your doubts.
I am not suggesting one never use a commercial coater but if I could come up with an inexpensive and safe way for a small club to do coatings on marginal, experimental and junior made optics then this post will be worth the time.
Cheers,
Rick
Edited by PitchHitter (09/29/09 06:56 PM)
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Quote:
our club used to have a working coating chamber. we were charging members $10 to recoat.
Thanks! Now that is they way it ought to be and actually a raw aluminum coat lasts five years when I worked at Palomar. No protection and about 90-92% reflective.
I hear one club uses aluminum foil in a tungsten boat inside a converted 13" diameter propane cylinder and discharge cleaning by using spark plugs.
Way to go!. Hope you will point some of the guys doing that to this forum post.
Did you do the glass on that 30"er?
Clear Skys -Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Quote:
A good roughing pump and a diffusion pump will work too. Not as fast as your turbo though.
How good of a vacuum do you need?
I have those pumps but turbo pumps boosted by a roughing pump now go to -8 and I am told -5 is enough.
Your question is a good one though because if the surface is truly clean then it is a matter of energy transfer and molecular displacement. Pin holes could occur if a stray molecule were in the path but it would be pushed aside so my thought is pinholes are not from a bad vacuum but low energy particles on the surface. This will be an area to experiment and search for mitigations to low vacuum or higher pressures to be technical.
Hey almost a neighbor!
Best,
Rick 
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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DanNie
journeyman
Reged: 11/18/08
Posts: 6
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I don't believe that the "quick blast of oxygen" will do what you want. On a cold (room temp) freshly aluminized substrate still in the coating chamber, oxygen will only develop a very thin self-limiting oxide film, similar in optical and mechanical properties to what develops when fresh aluminum is exposed to air. This would yield 87% reflectivity at best. If you had an oxygen ion source, you could implant oxygen deeper of course. The other problem is pumping anything but a smidgeon of pure oxygen can lead to explosive results in any vacuum pump that has combustible working fluids, including backing pumps.
An earlier suggestion about a controlled thickness (several hundred Angstroms - the exact thickness should be optimized for maximum reflectance in a program such as Film*Star) of silicon monoxide/dioxide, using a resistance-heated oven is both proven and practical.
BTW, I have had good results on at least three mirrors recoated by L&L Optical, for what it's worth.
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Quote:
If you want to keep your cost down to less than $10K for the deposition electronics then you will have to stick with Aluminum with a silicon monoxide overcoat. You can deposit these coatings with a tungsten filament for the aluminum and a "baffle box" for the SiO. You can get these from RD Mathis in So. Cal.
Thank You Cary:
My 16" machine was being used to lay down about 14 dielectric coatings. I did not get the thin film monitor so I am going to have to see if I can find the place I got it from or buy or build another one.
If the information I have gleaned is correct. Oxidized Aluminum is the best Photopic coating available and my machine has the gas induction system. This means one firing of Aluminum followed by a blast of pure O2. But even without the O2 a one shot Al would be as good as what is used on most of the large telescopes. So I have the electronics just really no need for them. If pure O2 is the first gas to hit the coated surface it produce an extremely hard and smooth coating with even greater reflectivity. SiO is not as smooth or reflective. I was told this by a 3x Ph.D. in Applied Physics and 27 patentsin the coating field. I have an idea of my own for the Al and Ag metals.
Cheers,
Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
Edited by PitchHitter (09/29/09 08:08 PM)
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Quote:
I don't believe that the "quick blast of oxygen" will do what you want. On a cold (room temp) freshly aluminized substrate still in the coating chamber, oxygen will only develop a very thin self-limiting oxide film, similar in optical and mechanical properties to what develops when fresh aluminum is exposed to air. This would yield 87% reflectivity at best. If you had an oxygen ion source, you could implant oxygen deeper of course. The other problem is pumping anything but a smidgeon of pure oxygen can lead to explosive results in any vacuum pump that has combustible working fluids, including backing pumps.
An earlier suggestion about a controlled thickness (several hundred Angstroms - the exact thickness should be optimized for maximum reflectance in a program such as Film*Star) of silicon monoxide/dioxide, using a resistance-heated oven is both proven and practical.
BTW, I have had good results on at least three mirrors recoated by L&L Optical, for what it's worth.
Thanks:
The O2 has to be applied before air is introduced for the affect to happen according to two professional sources. As I point out the O2 charge is optional, after all most of the professional observatories use raw aluminum as the only coating. At Palomar the 200 inch was very exposed and yet coated about once every five years. How well 02 works will be a question our experiments will answer.
As for the O2 being combustible or explosive? Nope, one, it never gets to a high enough pressure and two, there is nothing to combust in the chamber. Now the diffusion pump might have a combustible oil but I believe it would require 5PSI or more and that is never going to happen. The main valve is closed prior to coating and not opened until it is time to repressure and the diffusion pump valve is not opened until it is needed agian. What system did you use that would allow you to coat while the diffusion pump was opened to the coating chamber? Same goes for the roughing pump, it is closed off before O2 goes into the coating chamber.
L&L no longer takes amateur mirrors they told me. I do have a resale lic. and do repair optics so they quoted me $660 for my 22" plus $60 tax and shipping was going to be around $350 with a weeks wait in between. With packing materials that means it would cost me about $1,100 not including more time to crate and administer the shipping. If I paid myself $100/hr, with material and power my cost would be about $75 to do it myself and then there will be the products of my Scout class and local ATM class. Finally there is this educational value as well. We are losing our skills and floating an economy in the hands of amoral paper pushers.
Cheers, Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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Gordon Rayner
scholastic sledgehammer
Reged: 03/24/07
Posts: 965
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" Bob Goff inhaled glass dust". But he died of heart failure, no? Or, was that problem caused or abetted by the glass dust?
Robert E. Cox, longtime Sky&Telescope's Gleanings for ATMs department editor and contributor, warned us about glass dust in Berry's Telescope Making, and then reportedly died of silicosis or something like that.
What is the solution? Total enclosure of curve generators? Water curtains?
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Your right as usual Gordon. As I understand, Bob Cox died from pancreatic cancer after silicosis caused lung cancer migrated to his pancreas. Bob Goff died of cardio-pulminary failure attributed to damage caused by silicosis of the lungs. Point Blank he told me the dust had killed him a little while before he passed. In my avatar you can see my grinding pendulum. The wheel was always under water and the backsplash was scrap cardboard. I wore the full face mask and there was no dust until it dried. This was the year before I bought my eyepiece from you... shhh I don't want any one to know my real age because I still hope to find a fertile mate.... 
I have a two meter bent beam diamond generator I am building. The diamond tool will have a total shroud that runs under water and the water will have a collection system. I will collect the glass and incorporate it into a firing for my vitrified tile tools. If I did not have the kiln I would mix it in concrete work. My lab I am working on now will have curtains in the curve generating room and hepa filtration.
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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DanNie
journeyman
Reged: 11/18/08
Posts: 6
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A pity about L&L no longer doing ATM mirrors. They did a fine job on mine.
Which brings us perhaps to the central issue: ATMs getting reasonably priced optical coatings, or doing it oneself. There are fewer and fewer such services available, and I suppose this reflects (!) fewer DIY glass-pushers.
Rick, I truly appreciate what you are trying to do. When I was a bit younger I myself entertained notions of setting up a mirror coating system in my garage, egged on by occasional availability of nickel-on-the-dollar surplus vacuum equipment. But having designed and operated thin film coating systems, what I knew made me reluctant to do it without a ready pile of cash. It is mainly the cost of new capital equipment and the cost of skilled operators that makes coating services expensive for individuals. A large enough group of motivated ATMs could possibly remedy the situation, setting up a coating facility for themselves, Boy Scouts, and maybe the occasional commercial job as well. In my estimation, it is not so easy for an individual.
Aluminization is simple enough, and the requirements for an evaporator aren't prohibitive. Silicon monoxide protective overcoating isn't arcane. However, the difficulties go up as some power function of the size to be coated. Enhanced coatings or multilayers for reflection, antireflecting, or optical filters, require well-controlled, optically significant (>1/10 wave thick)dielectric coatings. This raises the stakes and costs. Such coatings as Al2O3 and TiO2 are best done by reactive evaporation, sputtering, or ion beam, which in turn requires pressure and flow controls, monitors, and preferably instrumentation like ellipsometers. Then you have to get some jerk to design the stack and analyze the results.
Many roughing/backing pump manufacturers specifically warn about pumping pure oxygen. The danger is in the high pressure stages, the hot oily internal surfaces of the pump may be exposed to compressed oxygen. There are several expedients to reducing the danger: bleed sufficient nitrogen into the pump ballast, use mixed argon/oxygen in the process(e.g. reactive sputtering), use (expensive) Fomblin oil in the pump, or (most expensive) use a dry pump.
Tell us more about your 16" coater, if you care to.
Regards,
Dan
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Dan McConaughy
member
Reged: 11/11/06
Posts: 81
Loc: LA
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L&L did my 16" Cass optics last Feb. They did a great job. I live close enough to them that I got to drive over and see the operation. I think they stillcoat mirrors but just don't advertise as they do a lot of industrial and Government work that is far larger than the amateur astronomer market.
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16" F/12 R-C with optics figured by Paul Jones mounted on Byers Research Grade Series II mount with Gemini GOTO housed in 11.5' Sirius Observatory.
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droid
rocketman
Reged: 08/29/04
Posts: 4030
Loc: ohio
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Rick ;I think this is wonderfull.For many years Ive suspected amatuer astronomy was going the way of all hobbies, to the well to do and the semi or better wealthy.
I have a 13 inch mirro being made by another cloudy night member, but I could not have afforded to buy one if I had too.
Coating will be my next hurdle,lol.
I wish you well the hobbie needs people such as your self to help those who cant afford the " real coaters ".
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102mm Celestron C102HD
Tasco 7TE5 60mm Classic
Tasco 9TE5 60mm Classic
Celestron Ultima 2000 SCT
Remains of an 8 inch dob
Celestron Comet catcher(orange tube)
1960 Edscorp Space Conquerer 6inch f/8
10x50 Bushnell Binoculars.
11T 4.5 inch Tasco reflector Lunograsso?
60mm Telescope Club
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Venetia2004
sage
Reged: 08/27/05
Posts: 260
Loc: Lynnwood, WA
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Quote:
L&L did my 16" Cass optics last Feb. They did a great job. I live close enough to them that I got to drive over and see the operation. I think they stillcoat mirrors but just don't advertise as they do a lot of industrial and Government work that is far larger than the amateur astronomer market.
I recently contacted L&L to have my mirror set coated. I received an e-mail from them with a Excel file attachment that I could not open because I use an older Excel version . I e-mailed them back twice explaining that I could not open their file but I receved no reply. It seems that they do not care about the ATM's any more... Do-it-yourself if possible or a smaller company that provide coating services to everyone is the way to go.
Vic
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2156
Loc: salem, OR
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For glass dust? Water - the mud is easy to handle safely. If it dries wet it down again before cleanup. You can mix it with concrete, or run it through your local garbage service, but leave it wet.
This is an interesting discussion. I'd like to hit one or two points - in almost any discussion I have with people with experience about coating the same point comes up time and again - mirror preparation by coaters who serve the amateur market. The best coatings can only be applied to clean mirrors, and that really calls for ion beam cleaning as the final prep stage. Horror stories abound of coaters who've used their own particular, uhm, methods to clean precision mirrors...and left them damaged.
Secondly, pure Al works, it will gradually oxidize on exposure to air, obviously. It has to be treated with care during that stage, which I believe takes on the order of a month or so. From what I understand it cannot be handled at all at first though, and appropriate care would need to be taken.
Is there a difference in reflectance or more importantly, spectral response for Al alone vs Al + SiO2 (or the admixture generally achieved Si2O3)?
Best,
Mark
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grendel
sage
Reged: 04/12/09
Posts: 241
Loc: Canterbury, Kent, UK
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Have you tried open office - its free and will probably handle the newer excel files OK.
Grendel
Quote:
Quote:
L&L did my 16" Cass optics last Feb. They did a great job. I live close enough to them that I got to drive over and see the operation. I think they stillcoat mirrors but just don't advertise as they do a lot of industrial and Government work that is far larger than the amateur astronomer market.
I recently contacted L&L to have my mirror set coated. I received an e-mail from them with a Excel file attachment that I could not open because I use an older Excel version . I e-mailed them back twice explaining that I could not open their file but I receved no reply. It seems that they do not care about the ATM's any more... Do-it-yourself if possible or a smaller company that provide coating services to everyone is the way to go.
Vic
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Venetia2004
sage
Reged: 08/27/05
Posts: 260
Loc: Lynnwood, WA
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Hi Grendel,
Thanks for the suggestion. No, I have not. I expected to hear back from them in a "regular" e-mail. However, it's too late now, I shipped my mirrors to another company.Silence is an answer...
Vic
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3529
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Quote:
Quote:
our club used to have a working coating chamber. we were charging members $10 to recoat.
Did you do the glass on that 30"er?
Clear Skys -Rick
no our chamber only went to 18", my 30 was last done by intermountian
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Ion cleaning would energize the low potential residual on the mirror and that would be nice. I believe only the Keck out of hundreds of professional observatories does that and I am not sure for a fact they even do. I was priced $25,000 for a broken Ion Gun at a surplus shop in San Diego County. I would like to have one but I am not going to let having less than the best keep me from having the freedom to do a pretty darn good coating when I want it. I also have an idea I want to test that may be more effective than an ion gun.
I have no intention of being a commercial coater. If someone wants a coating they will have to bring their mirror and do it themselves under supervison of course.
Best,
Rick
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
Edited by PitchHitter (10/03/09 06:12 PM)
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PitchHitter
member
Reged: 09/23/09
Posts: 23
Loc: Southern Sierras
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Quote:
Hi Grendel,
Thanks for the suggestion. No, I have not. I expected to hear back from them in a "regular" e-mail. However, it's too late now, I shipped my mirrors to another company.Silence is an answer...
Vic
This illustrates my point.Southern Californians are simply being treated wrong on their coatings and the service. I miss the old Panchro. Many local coaters are now wholesale only. They tell me amateurs are needlessly too picky for one thing. L&L coatings are available but now you must take your optic to a retail outlet that repairs telescopes.
Clear Skys
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About 20 telescopes from a 200mmAPO up
Fav is Meade 10" f:4.5 using my 3" 40mm 96°AFOV
BUT! In Progress:
14.5" f:5 grab n' go with DSCs will offer 2.4 degrees at 45 power and 8mm exit pupil (Light Bridge Buster)
16.25" f:7.5 to refigure
(20th wave ruined in a fire at the coaters)
22" f5: New mount almost done
(old all aluminum mount was stolen)
16" Varian Vapor Deposition Coater.
Looking for larger chamber.
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DanNie
journeyman
Reged: 11/18/08
Posts: 6
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Mark,
Freshly deposited aluminum oxidizes very quickly. Pure aluminum is soft; unfortunately, the naturally-developed oxide is so thin, even after a month, that it doesn't offer much protection. The main reason for the silicon monoxide/dioxide overcoat is mechanical improvement (scratch resistance). The silicon oxide overcoat may improve or degrade the overall reflectance a few percent, depending on thickness and the actual index of refraction as-coated.
Truly enhanced aluminum reflectivity usually means a two layer (low, then high index) or four layer (LHLH)dielectric coating on the aluminum. Again, these have to be deposited in such a controlled manner that the thicknesses and complex refractive indices are according to thin film design and repeatable - hence the added cost over simple aluminization.
I'm not an apologist for commercial coaters, especially regarding their attitudes towards ATM customers. However, any coater large or small has to deal with regulatory compliance or risk being shut down and/or fined (particularly in the fair state of California). Some of the cleaning and stripping chemicals are regarded as hazardous, and the used ones are regarded as hazardous waste. Again, an added cost is passed on to the customer.
Despite all this, the allure of coating mirrors at home or as a group project is strong. I for one would like to hear from some that have made a go of it: what equipment, process, and materials they used, and the degree of success and failure.
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2156
Loc: salem, OR
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Thanks for the confirmation on pure aluminum, but my question was about spectral difference between bare aluminum and Al with, variously, SiO, Si2O3, SiO2 overcoats, not enhanced coatings. 
If you want responses on home coating successes/failures, ask on the ATM List (www.atmlist.net) for plenty of views - traffic is very light currently.  Particularly check the archives (searchable back to '95) here.
The difficulty commercial coaters have with ATM mirrors is that ATM mirrors are typically heavily contaminated with pitch residue, cerium oxide, and sometimes other stuff, much of which vaporizes into the chamber and fouls it. I've heard this several times from different coaters. Hence they need to purge the chambers well, and they can't afford to do a mixed run of ATM mirrors, due to the risk of cross-contatmination, which increases their overhead.
Best,
Mark
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Venetia2004
sage
Reged: 08/27/05
Posts: 260
Loc: Lynnwood, WA
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"...L&L coatings are available but now you must take your optic to a retail outlet that repairs telescopes".
If I'd known that they had changed the way they deal with the ATM's I would have never contacted them. It's too complicated...
Vic
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