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Equipment Discussions >> Reflectors

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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Why are high-quality mirrors so expensive? new [Re: Starman1]
      #5717470 - 03/06/13 10:49 PM

Quote:

And there is also a difference in materials. Many inexpensive mirrors are made of plate glass or BK7 or some less-expensive material. High end mirrors are made of Borosilicate glass or fused quartz or ULE materials or zero-expansion glass types, which can literally be 10-20X as expensive (and more).




Even in things as innocuous as pitch and cerium oxide.

Or in letting a mirror set in the stand for three hours before testing, vs. 30 seconds.


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Achernar
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Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: Why are high-quality mirrors so expensive? new [Re: Dragonwatcher]
      #5717482 - 03/06/13 10:54 PM

The final adjustments to the mirror's surface have to be done by hand, IF you want a mirror to be as smooth and well corrected as possible. Machines do very well for hogging out the curve, and the initial polishing. The figuring is best done by hand because when a person does it the figuring strokes are somewhat random, which keeps roughness and errors to a minimum. Figuring a large and or fast mirror is no small task, let alone the testing to see what needs to be done next or if the mirror is finished. That can take quite some time. Also, premium mirror makers can make your mirror from any sort of low-expansion glass or glasslike material you want. That alone is quite expensive, but worth it because they are easier for the optician to work on, and you won't have to deal with the mirror's figure shifting when the mirror is cooling down to ambient temperature.

Taras


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Why are high-quality mirrors so expensive? new [Re: Achernar]
      #5717541 - 03/06/13 11:53 PM

When I make 12.5" f/2 primaries of elliptical figure, getting that last 10% of finesse takes at least 80% of the time devoted to aspherizing. And that's in spite of the substrate being fused silica, which allows virtually instantaneous testing due to its low coefficient of thermal expansion. Initial removal of glass can proceed quickly, with robust action of the tool. But as the final figure is approached, the pace slows down considerably so as to bring about a smooth surface of good correction.

A graph of time spent vs volume of glass removed over time would show a curve which very rapidly deflects to near horizontal for most of the process, due to the relatively minuscule amounts of glass polished away during the last 80+ per cent of work on aspherizing.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Why are high-quality mirrors so expensive? [Re: Dragonwatcher]
      #5717818 - 03/07/13 07:24 AM

Quote:

Perhaps you are correct. I was under the impression that one NW mirror maker does, it's done in China, and when I go to the site for Veritas Optics I see the message "Veritas Optics is currently implementing robotic figuring/testing systems to produce the highest quality medium to large aperture primary mirrors. Availability expected mid 2013."




"Highest quality" is probably subjective.. Reading that interferometer and deciding where to make the corrections would seem difficult to automate. If you want Roland Christen or Peter Ceravolo quality optics, someone like Roland or Peter or ... better be at the helm.

Jon


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Why are high-quality mirrors so expensive? [Re: Starman1]
      #5717854 - 03/07/13 07:51 AM

Time. It's very time intensive.

Pete


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turtle86
Pooh-Bah Everywhere Else
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Reged: 10/09/06

Re: Why are high-quality mirrors so expensive? [Re: azure1961p]
      #5718066 - 03/07/13 10:31 AM

Quote:

Time. It's very time intensive.

Pete




Yes. Quality takes time and time is money.


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kfrederick
Carpal Tunnel
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Reged: 02/01/08

Re: Why are high-quality mirrors so expensive? [Re: turtle86]
      #5718096 - 03/07/13 10:40 AM

The nice thing a great mirror lasts more than a lifetime . We are blessed that there are such good mirrors to be had .

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Cary
Vendor (Woden Optics)


Reged: 07/07/04

Loc: Rancho Cordova, CA
Re: Why are high-quality mirrors so expensive? [Re: Starman1]
      #5718236 - 03/07/13 11:42 AM

Quote:

Quote:

I've quickly scanned the thread and have this:

There are a number of misconceptions:

#1 Mirror makers are using robotic equipment. Not so, not so, not so.... show me one mirror maker that caters to the amateur market that is using "robotic" equipment to figure mirrors. I only know of ONE person that claims so but has shown no evidence of doing so.


#2. Don Pensack made a statement of "time and materials". Nope... it's just time. My materials cost for figuring mirrors is insignificant. PITIFULLY SMALL. Its the time and therefore the overhead of my shop that drives the cost.





so far as I know, commercial scopes from China do not use fused quartz, Zerodur, ULE materials, and I'm not even sure they use borosilicate glass.
So there would, indeed, be a significant difference in materials cost.
Admittedly, though, materials are not a significant part of the difference in price between premium mirrors and those in commercial scopes from China.




Correct if we are talking about super premium mirrors, however I was thinking in terms of amateur astronomy. You just don't see any zerodur or ule mirrors in dobs and such. There are a few Asian manufacturers that do use borosilicate but most are BK7. One thing that befuddles me on the use of the BK7 is that it is torturous to anneal properly. The energy costs of annealing large chunks of bk7 is about 10 times that of borosilicate. If they find this more cost effective then Asian energy prices must be almost free.


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Cary
Vendor (Woden Optics)


Reged: 07/07/04

Loc: Rancho Cordova, CA
Re: Why are high-quality mirrors so expensive? [Re: Starman1]
      #5718285 - 03/07/13 11:58 AM

I received a P.M. from a moderator that my comments above had been edited because they violated the TOS. I had commented on the optical quality of mirrors coming out of Asia. Since I am considered a competing manufacturer I am not permitted to do so even though I rarely make new mirrors. My primary business has evolved into re-figuring these very mirrors.

So my thought is that I'm one of the very few people on earth who has handled, tested, and re-figured many hundreds of these optics. The count is in the thousand plus range now.

It's quite likely that I have the best understanding of the optical quality of the various manufacturers parabolic mirrors yet I am not allowed to bring any discussion about it into the public light. Doesn't seem right.

I'll risk saying that after ten years of testing mirrors of all makes, manufacturers and vintages the "public" would be shocked at the results.


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Why are high-quality mirrors so expensive? [Re: Cary]
      #5718319 - 03/07/13 12:18 PM

Cary,
Don't forget that your sample is "pre-selected" to exclude the better mirrors. People aren't going to send you a mirror for refiguring unless there is an issue with the mirror, i.e. the owners are not getting the results out of the mirror they think they should.
You aren't going to be sent the 16" LightBridge mirror I star tested as having one of the most perfect figures I'd ever seen on a mirror. That, of course, wasn't the average mirror, but does show the issue.

I grant you, though, that the brand names of the mirrors you are sent in significant quantities would be enlightening.


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KerryR
Post Laureate
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Reged: 12/05/07

Loc: SW Michigan
Re: Why are high-quality mirrors so expensive? [Re: Starman1]
      #5718333 - 03/07/13 12:25 PM

On the other hand, when you send a mirror to OWL for re-coating, testing is free, isn't it? I suspect most folks sending their Asian mirrors in for re-coating would have this done. So, it'd seem likely Cary would see the figure of nearly everything coming in, re-figuring or not.

No?


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Cary
Vendor (Woden Optics)


Reged: 07/07/04

Loc: Rancho Cordova, CA
Re: Why are high-quality mirrors so expensive? [Re: KerryR]
      #5718443 - 03/07/13 01:31 PM

Don, you may be correct. I do get the feeling that there is some pre-selction going on but as Kerry points out I get a lot of mirrors in for coating that get the free optical test too. Among those mirrors are some premium made mirrors (big names I cannot mention) that test out differently than expected.

I can also say that there is a brand/make selection process going on. I get mostly all of one asian made brand (we'll call it "Brand X") coming in for testing and refiguring and the other of the two major brands very rarely is sent in for an test / refigure. Of those "other" brand mirrors that come in for testing, only a handful (about 8 all time) warranted refiguring. When most people guess about which brand is which they almost always guess wrong. I guess this is the power of marketing? Who knows. I can say that the difference is so large that I personally would never purchase a scope with "Brand X" mirrors in them.

It does seem a shame that I am barred from sharing my ten years of experience with testing these mirrors and the public goes uneducated.

Edited by Jarad (03/08/13 08:23 AM)


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CosmoSat
Pooh-Bah


Reged: 07/24/09

Loc: India
Re: Why are high-quality mirrors so expensive? [Re: Cary]
      #5718494 - 03/07/13 01:55 PM

That "X" word might be misleading here too, it might well have been "Y"...

Clear Skies!

Edited by Jarad (03/08/13 08:27 AM)


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FirstSight
Duke of Deneb
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Reged: 12/26/05

Loc: Raleigh, NC
Re: Why are high-quality mirrors so expensive? [Re: Cary]
      #5718504 - 03/07/13 01:57 PM

Quote:

I get mostly all of one asian made brand (we'll call it "Brand X") coming in for testing and refiguring and the other of the two major brands very rarely is sent in for an test / refigure. Of those "other" brand mirrors that come in for testing, only a handful (about 8 all time) warranted refiguring.




Another way to look at it is that the viable continuation of your refiguring business is dependent on Brand X's lax approach to quality control of their mirrors, as well as their continuing commercial success despite that incorporating that factor into their business model. This observation is not at all intended as a negative comment about you; after all, you are being as bluntly frank and forthcoming about the true state of things as the CN TOS permits in this forum, and amounts to nothing more than a particular application of the obvious fact that if all mirrors were well-figured there would be none left to be re-figured.

Edited by Jarad (03/08/13 08:26 AM)


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Why are high-quality mirrors so expensive? [Re: CosmoSat]
      #5718514 - 03/07/13 02:04 PM

Quote:

That "X" word might be misleading here too, it might well have been "Y"...

Clear Skies!




I have a very good brand "%^&&&&^%##@@" mirror but the Baytronix scope/mirror I had was horrible.

Jon

Edited by Jarad (03/08/13 08:27 AM)


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Cary
Vendor (Woden Optics)


Reged: 07/07/04

Loc: Rancho Cordova, CA
Re: Why are high-quality mirrors so expensive? [Re: FirstSight]
      #5718526 - 03/07/13 02:13 PM

Quote:

Another way to look at it is that the viable continuation of your refiguring business is dependent on Brand X's lax approach to quality control of their mirrors, as well as their continuing commercial success despite that incorporating that factor into their business model. This observation is not at all intended as a negative comment about you; after all, you are being as bluntly frank and forthcoming about the true state of things as the CN TOS permits in this forum, and amounts to nothing more than a particular application of the obvious fact that if all mirrors were well-figured there would be none left to be re-figured.




They've already made and sold more mirrors than I could ever refigure in my remaining lifetime.

Edited by Jarad (03/08/13 08:28 AM)


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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: Why are high-quality mirrors so expensive? [Re: Jon Isaacs]
      #5718608 - 03/07/13 02:56 PM

Quote:

Reading that interferometer and deciding where to make the corrections would seem difficult to automate.




Well, that would be exactly the wrong way to automate the process. The correct way uses deterministic figuring that converges on the desired curve, not error correction after the fact.

The OP asked about robotic mirror production and why that hasn't resulted in lower cost high quality mirrors. It really won't result in that as far as I can see, given the expenses involved. But it will increase my production capacity many fold, while allowing the same time and attention to ultimate surface quality.

It's not as simple as putting a blank in the slot and pulling out a finished mirror, though of course I don't really believe the OP ever thought that.

It still involves a large number of steps in a complicated process. But by automating the time consuming testing and figuring steps - linked in one feedback and prediction loop - the process converges under robotic control on the desired figure. Which is all anybody really wants to see anyway.

Best,
Mark


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Jarad
Postmaster
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Reged: 04/28/03

Loc: Atlanta, GA
Re: Why are high-quality mirrors so expensive? [Re: mark cowan]
      #5718672 - 03/07/13 03:26 PM

On the topic of vendors:

The rule about vendors commenting on other vendors products is there for several reasons:
1 - To protect both CN and the person posting the comments from potential lawsuits.
2 - To prevent the person being commented on from being unfairly denigrated without the opportunity respond.
3 - To preserve CN as a place where anyone (including vendors) can participate in civil discussions.

A vendor cannot claim to be unbiased about their competitor's products. There is a financial incentive to convince potential customers that a competing product is inferior. This rule goes both ways - they are also protected from being commented on by other vendors.

So let's move away from comments about a specific company's mirrors, and back to the original topic about why it costs money to achieve high quality. A vendor's experience and insights into the process are welcome, and allowed by the TOS.

Thanks,

Jarad


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Jarrod
Pooh-Bah
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Reged: 01/20/13

Loc: SE USA
Re: Why are high-quality mirrors so expensive? [Re: Jarad]
      #5718702 - 03/07/13 03:39 PM

-----
Good
Cheap
Fast

Pick two.
------

Remember this relationship. It applies to almost every product or service. Including, I expect, to telescope mirrors where "fast" could mean two things (production speed or f-ratio), both of which still make the relationship true.

Edited by Jarrod (03/07/13 03:42 PM)


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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Why are high-quality mirrors so expensive? [Re: Dragonwatcher]
      #5718713 - 03/07/13 03:50 PM

Quote:

This is probably a dumb question, but I'm sure many can tell me why it is. As I understand it, many mirror makers use or will soon be using robotic equipment...




The term "robotic equipment" covers a lot of territory.

Traditional CNC machinery is often called "robotic" - it makes precise motions following a precise set of instructions for movement. Such a system provides no feedback at all to the control system, and does not have any adaptive behavior of its own.

You can't make large precision optics ONLY using a system like because it could never be precise enough to cut a final surface. Precision optics requires feedback from an iterative measuring process that guides the figuring to make the final surface.

SSG/Tinsley that makes big mirrors, and mirrors out of exotic materials, for NASA and the military uses a precision CNC system for this:
http://www.asphere.com/CA_CCOS.html

What they do is make precise measurements of the deviations from the desired figure (where and how much) then uses the CNC system to grind each mapped area down by the calculated amount, and repeats the process until the figure is final.

All this high precision stuff costs a lot of money.

More recently "robotic" systems have added adaptive behavior of their own - using optical or mechanical sensors to guide what they are doing, some even doing automated task learning. This requires a lot more computer processing power and more sophisticated software which is why it is only emerging now. This type of robotic equipment is now taking over manual tasks that resisted the former precise control paradigm.

Traditional mirror making used mechanical equipment to generate (rough out) the surface to its overall form, and then used hand guided techniques to figure it. Since humans can't do anything precisely or consistently a very different strategy of using randomized movements which inevitably combine (if truly random) to produce a very smooth unbiased surface.

The measuring process that guides this does not need to be as high-tech as the system used by SSG/Tinsley since qualitative measurements are about as useful as precise quantitative ones.

A robotic system in the recent style could do this also. Computer control would allow highly randomized figuring movements, much better than what a human can do.

One can imagine a commercial production system using such a machine and the same type of semi-qualitative measurements. With sufficient sophistication of the software, the figuring machine would use the test images directly to guide its operation.

In a mass production environment mirror cooling between measuring figuring runs would not be a problem since a number of mirrors would be in process at once, and the machine would rotate which one it was working on.

It has been pointed out here frequently that the thing that makes a premium mirror "premium" is really the consistency of the manufacturer. And this requires excellent quality control of the final product no matter how the mirror is finished.

Mass market mirror makers are under pressure to get the mirror out the door with a limited fixed amount of work invested in it to keep costs low. An adaptive system that can converge efficiently on a high quality figure could change this calculation. It would discharge a mirror from figuring once it hit the necessary quality level (and only then) and only the average amount of work per mirror would need to be considered for the cost.

I have no knowledge of such a system being developed or installed anywhere, but would be surprised if one does not eventually appear.


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