153 replies to this topic

[SandyHouTex]

Machines can make parabolic mirrors pretty easily and for little cost.  I have an excellent SkyWatcher solid tube 10 inch with great optics.  The difference, when a mirror is machine made, is whether the figure is actually checked and any errors remediated before it goes out the door.  That costs more money, and I don't know, and I don't know that anyone here does.  It's also true that I don't know how many come of the machine at 1/4 wave, 1/8 wave, etc., etc.  Again I don't think manufacturers share their data on accuracy with anyone.  Will the polish be any better than a machine polish?  By definition, no.  Probably a 60/40 scratch/dig.

 

What you get with a Zambuto is a laser polish, 10/5 scratch/dig, so much less scatter.  He also does not sell you a mirror until all of the rays go into the Airy disk at the focus.  Basically a perfect optic, but you have to pay for this of course.

[barbie]

When I had my 6" mirrors tested, they came back with an excellent test report which also indicated a very smooth polish to the surface with no zones or TDE.  These mirrors were my current 6 inch F8, an 8"f6, and a 10"f5.  All of these mirrors were made within the last 10 years so I think that the Chinese have gotten the art of fine figuring in hand.  Are Zambuto's nice?  Sure!  But not thousands nicer than what I currently have.

Edited by barbie, 09 August 2018 - 10:12 AM.

[X3782]

I understand there are several volume companies who can potentially compete with each other on paraboloid mirrors, though I have seen no description of the exact method, only rumors. But if they use similar CNC techniques as described in that video and advertisement links, it is based more on grinding than polishing to achieve the high speed and low cost. Particularly if there is an additional polishing step involved, the surface would be quite smooth........ but not quite as microscopically smooth as the time-consuming and careful polishing, also there can tend to be more undulations in the mid-spatial frequencies because the grinding tool has a certain size, which would get aggravated the more the process needed to be speeded up. Of course such effects would be subtle at the eyepiece, a bit more contrast, a bit more sharpness.

 

When I first heard of these machines, they were originally used for, e.g., very high end research optics or semiconductor lithography optics using fused silica or glass-ceramic materials with low thermal expansion, but if one does not need lithographic grade, I suppose corners can be cut appropriately, because machine time adds to cost. I think production will tend to be more efficient for slow f-number optics.

 

I admire what they have achieved with the optics quality, sure, 20 years ago I would have thought such things weren't possible. But it was funny to me that some companies in mainland China start to advertise probably for the domestic market, "Every mirror of our company is slow speed hand-crafted by the special techniques of masters with more than 10 years of experience", the word slow seems to appear many times in the product description. In every country I guess there is a certain fraction of the customers who want that and feel the same way.

Edited by X3782, 09 August 2018 - 03:02 PM.

[JonTeets]

In my 7 years in China, I spent a fair amount of my working hours reviewing Chinese engineering, manufacturing processes and management.  There is a tremendous amount of variation as one might well imagine when a sizable proportion of the country barely has a foot out of subsistence farming whilst many others are doing far better than they have historically, including a many who are very wealthy.   Few of the people producing items for export consume them.  When I'd bring my teams back to the US for meetings, they'd invariably buy products that where made in China but weren't available there.   

Owning the supply chain end-to-end or being close to most of it provides a great advantage for Chinese companies, as does being close the the tool-makers and raw materials.   Inspection checklists can and do go a long ways, but they substitute the what for the why, meaning often the only innovation is cost innovation.  There is value in that, to be sure, and it is necessary, but progress is rooted in the why, in close connection with the consumer.  

There is a difference in the custom optics produced here and the mass-produced imports, and it is clear in side-by-side comparisons.  Is it worth the difference in cost?  YMMV, of course, but I believe so.  For me, there's an additional factor to consider.  I repeatedly saw cases where Chinese companies substituted easily-acquired and often dangerous substances for what had been contracted, and I saw vendors all along the chain do the same while the stateside procurers -- when they noticed it -- looked the other way.  It's a problem even for the huge vendors of premium products, so I wouldn't know if I could trust the paint on the tube, the metal deposited on the mirror, what might be mixed in with the glass or the materials next to where I'd put my eye.  On the other hand, I do know that money I give to the likes of TEC, Lockwood, Teeter, Zambuto, et. al. is going to meet certain quality (and safety) standards, and is going to come with the guarantee of a pulse at the other end, even if it takes some time.   They'll also push the envelope of what's possible so we'll not only end up with cheaper versions of stuff we've come to cathect, but novel offerings and solutions for problems we don't recognize we have.   

[barbie]

I have absolutely no problems buying and using Chinese made telescopes, or other products for that matter!!  I've seen Chinese scopes give American made ones a serious run for their money!! Oh, as for hazardous materials, I have yet to develop any physical ailments from using Chinese scopes!!

Edited by barbie, 09 August 2018 - 06:11 PM.

[X3782]

At the risk of offending, one of the things that has always amazed me about the US market is the preceived willingness of consumers to switch brand loyalties and go for the highest value for the money even with an unknown foreign brand. So even the established market leaders have to continue providing good cost performance, otherwise they might quickly be replaced. My own home country, as well as many European countries that I have lived in for that matter, can be more conservative in our buying habits, we can tend to be less willing to accept something new (again a generaization). This might be why the US is more friendly to innovation, and why a mature nation can stay dynamic. It is also the characteristic that maybe helped our own country to export to the US to get us out of poverty and utter ruin maybe 70 years ago.....  I don't have enough experience with the Chinese market, but I think we should share some of the same cultural characteristics in terms of tending to first ask which brand is generally the oldest and considered "best".

 

So I can almost guarantee that in some years a fraction of Chinese consumers will crave the "real thing", which in the case of Dobsonians will be US mirrors, accessories, TeleVue eyepieces, etc. When I go home I see unending swarms of tourists coming from there, going to the most "authentic" out-of-way places and snapping up even a bit pricey things that I thought only locals knew about.

Edited by X3782, 09 August 2018 - 08:16 PM.

[NHRob]

My mass-produced 16" GSO mirror is tested at 1/14th wave p-v, and it beats the heck out of my 11" Zambuto.

 

 

[X3782]

In machine mass-produced optics, particularly for the type based on NC, the deviation of the surface height of each identical-looking mirror from some predefined target shape can be important to control the average product quality, and quickly reject "bad mirror copies" that stray too far away from the pack. This can best be measured by interferometer in terms of fractions of a wavelength against some reference mirror artifact that the manufacturer defines as "their standard". But the exact values of the highest and lowest deviations, i.e., peak-valley (p-v), will depend on how the interferometer is set up and the wavelength of the laser used and temperature excursions during the measurement, the defined "good" outer boundary of the mirror and the reference shape in the program, and how the data is analyzed and smoothed out. If one goes into details, it can depend on how high the pixel resolution of your imaging sensor in the interferometer was, or the degree of coherence of your laser beam, or if you mounted everything on a rigid table or an actively vibration-stabilized optical table. So while in practice the program may show precise-looking numbers, I think it can be hard to get accurate robust values that do not vary between manufacturers or measurement conditions, particularly below lambda/8 or so for a large paraboloid, unless an impractical amount of time and effort were used. The mass manufacturer might properly say, "today we produced 100 mirrors and the average p-v was l/4 under so-and-so measurement condition, but yesterday it was l/6 under similar conditions measured with the same device in the same way, clearly we have drifted away from where we want to be, so let's adjust the process a bit to get us back". In this way they can ensure that the mirrors produced today and those produced in 5 years will be virtually identical, with smaller and smaller variations in quality compared to their reference as the production process became better controlled. But it can be far more problematic to compare the p-v of mirrors from different suppliers that would have been measured and calculated in slightly different ways, and say A should perform better than B at the eyepiece because the p-v is slightly smaller.

 

I think in traditional mirror making and optics testing methods, based on classical ray tracing of polychromatic incoherent light rather than lasers, the symmetry of each unique mirror against itself in terms of allowing the maximum energy of star light into the Airy disk (and thus sharpest image at the eyepiece) is important. The exact absolute shape of the mirror compared to some rigid theoretical one that exists inside a computer is not usually an important design goal, it's not a method designed to produce 100 identical mirrors of the same height distribution. Instead, if each different mirror can be made to perform the best it can on an individual basis, the optician does not usually care about scoring the best p-v numbers under some slightly-arbitrarily set criteria, because that is not how the mirror will be used under the stars.

 

So I think it can be hard to compare the two kinds of mirrors and say, this mirror is better than that one based on a single number like p-v obtained in such a convoluted way. Besides the question of, "What does the mirror do between the peak and the valley, maybe the root mean square (RMS) value is a better criteria?", fundamentally the underlying philosophy and goals are also too different to begin with.

Edited by X3782, 10 August 2018 - 04:15 AM.

[waso29]

i have been involved with manufacturing (including toys) in prc for over 2 decades, i concur with jon's experience.

my extended family in prc are challenged daily in finding quality products and truthful information.

 

but with wages stagnating stateside, i understand why i too have fallen for the china price.

i plan to take my orion xt10g to the grave.

 

note: i will NOT buy prc-made toys for young kids.

Attached Thumbnails

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Edited by waso29, 10 August 2018 - 10:32 AM.

[Cosmosphil]

I have been following this thread for these past few days and had a funny feeling it would slowly turn to some geo-political / Econ discussions and various personal back and forth.   These "premium vs mass market" threads always do.   Lots of good thoughts here.

I used to be a little more of a "hothead" when I was younger and posting in all the forums. 

Age has mellowed a lot.   I try to look at a bigger picture now in my personal pursuits and hobbies.  

 

Going all the way back to the OP I believe for where I'm at now with the hobby I'd go with the premium 6" scope and call it a day.   The reasons are not really if the GSO 10" is better because its bigger or less than because it is mass market.   But, similarly like Barbie, I'm older now and getting some health issues that prevent me from grabbing a 16 or 20" truss dob and venturing several hours to a dark sky site to chase

Hickson and Abell objects, etc.    I'm going to try and see how the 11" STS works for moving around.

It's much lighter and smaller than my current 15" beast but still enough aperture to enjoy most of the objects I can still see in the modest dark skies 90 minutes or so from the house.  It will be used much more in the yard and at public outreach on the planets, lunar and bright DSO objects.  Giving more detail when seeing permits than the refractors I have and easier to set up.  

 

But, my reasoning for purchasing a premium 6" is more along the lines of supporting local artisans, opticians and sub contractors.  I like the idea of Rob Teeter, Mr Lightholder, etc getting to ply their craft and monies going directly into their local economies and folks' pockets.     I know that mostly today the overseas mass market makes very suitable products that can either match or maybe even exceed local premium products at a sometimes ridiculously lower price.  And, we all know the various reasons why.  I mean I love my little ED80.  I don't know why this particular optic is so good but it is.   I paid hardly nothing for it used but I'd put it up against any 80mm out there.   Great little scope.   So, mass market Chinese is fine for certain things. 

 

Finally,  I really don't know or care if the latest Chinese made 5" or 6"  3 element  APO is "as good" or "beats" my TEC140.   I just know I enjoy the fact that a group of Russian expatriates ply their old world craft over in Colorado and hand build a beautiful instrument.   I smile every time I pull it out to use it.  My friends who look through it smile as well.   I could of saved thousands yes.  But, It just isn't where the heart goes and long as the wallet can follow......     

[gwlee]

In my 7 years in China, I spent a fair amount of my working hours reviewing Chinese engineering, manufacturing processes and management.  There is a tremendous amount of variation as one might well imagine when a sizable proportion of the country barely has a foot out of subsistence farming whilst many others are doing far better than they have historically, including a many who are very wealthy.   Few of the people producing items for export consume them.  When I'd bring my teams back to the US for meetings, they'd invariably buy products that where made in China but weren't available there.   

Owning the supply chain end-to-end or being close to most of it provides a great advantage for Chinese companies, as does being close the the tool-makers and raw materials.   Inspection checklists can and do go a long ways, but they substitute the what for the why, meaning often the only innovation is cost innovation.  There is value in that, to be sure, and it is necessary, but progress is rooted in the why, in close connection with the consumer.  

There is a difference in the custom optics produced here and the mass-produced imports, and it is clear in side-by-side comparisons.  Is it worth the difference in cost?  YMMV, of course, but I believe so.  For me, there's an additional factor to consider.  I repeatedly saw cases where Chinese companies substituted easily-acquired and often dangerous substances for what had been contracted, and I saw vendors all along the chain do the same while the stateside procurers -- when they noticed it -- looked the other way.  It's a problem even for the huge vendors of premium products, so I wouldn't know if I could trust the paint on the tube, the metal deposited on the mirror, what might be mixed in with the glass or the materials next to where I'd put my eye.  On the other hand, I do know that money I give to the likes of TEC, Lockwood, Teeter, Zambuto, et. al. is going to meet certain quality (and safety) standards, and is going to come with the guarantee of a pulse at the other end, even if it takes some time.   They'll also push the envelope of what's possible so we'll not only end up with cheaper versions of stuff we've come to cathect, but novel offerings and solutions for problems we don't recognize we have.   

I spent most of my career designing products in the US, marketing them internationally, and manufacturing them offshore in various places. I found that getting consistently high-quality widgets manufacured in China was always a challenge. The prototypes might be great along with the first runs, but consistency was vey difficult to achieve for various reasons. It could be done if the volume of business was large enough to justify an expensive, long-term investment in the manufacturer, but it was far too expensive an investment for a small business that imports a few hundred widgets a year. 

 

Consequently, I am a bit leary of purchasing very expensive products manufacturered by a company in China that’s unknown to me and imported by small US businesses, but all three of the telescopes that I own today are made in China. They were inexpensive and work well enough to satisfy me.

[barbie]

I've had a Chinese scope along side a premium scope and BOTH showed the same high quality image with the same details, sharpness and clarity. Both were 10 inches and BOTH were of the highest quality. This was 10 years ago!! I'm convinced that one doesn't have to buy premium to enjoy fine performance. The Chinese are making some excellent equipment at outstanding prices. There are also Chinese companies that are making junk as well!!  It all boils down to what the consumer is willing to pay.If you are willing to spend the money, then you'll get quality! If not, then you risk being less than satisfied!!

[X3782]

35 years ago it would have been unthinkable in my country to mass produce such large, quality mirrors with the technology available at the time, a 10-12 inch mirror tended to be something mounted in a GEM in a small observatory, it's great that this has become affordable for everyone now. One of the enabling technologies I think is laser interferometry (actually digital photography and computers.......laser interferometry existed before but we previously used Polaroid photography and rulers!), it lets factory workers who are not deeply trained to quickly determine the rough figure of a mirror on a computer screen. When making hundreds of mirrors quickly, it is impractical to hire enough expert eyes of specialists with traditional knife-edge based techniques.

 

The Newtonian mirror-making factories are located I think in two different Chinese-speaking countries, one is smaller (around 40 employees?) and started installing mirror making equipment and laser interferometry in the late 1990's or early 2000's as I understand, and they seem to use more traditional polishing methods to make 6 to 16 inch mirrors. A 10 inch f4 mirror+88 mm secondary mirror set costs around 600 USD, for f/5 it is 330 USD, in the past they provided mirrors for US brands like Orion (up until early 2000's?) and Meade. Photo shows the laser interferometer in the elevator hall, it's hard to tell from the photos, but this is probably designed for fast, quick-look measurements.

 

https://www.galuxe.c...ts/公司參訪gso-工廠參訪

 

A recruitment ad for mirror polishing and CNC jobs at this company? 35 employees, 95% of production exported overseas.

 

https://www.518.com....ny-3589821.html

 

The other company with the much larger market share makes every kind of telescope in a large factory at much lower prices, and tends to utilize more large-scale CNC technology (photos in the other post above). I heard about their technological advances and ramping up of mirror production in the late 2000's, but I'm not very sure.

 

This includes a bit of guessing, but the higher-priced US products tend to have higher grade glass materials (there are several glass companies providing a spectrum of glasses, even though they may use the same tradename, the expensive grades have less defects buried in the glass, higher homogeneity); better annealing (glass contains internal stress, and this can cause the optic to slightly deform when the temperature changes or very long periods of time pass, but annealing in a furnace tends to relax this stress and reduce some defects), each mirror will be followed through on an individual basis and optimized by an expert, traditional testing methods may be used (this is for me an advantage, though other people may disagree) rather than relying on laser interferometry. Longer times would be spent in polishing. Figure is often just a bit better, though I have seen only a few examples of both types of mirrors. All this may give a subtle improvement at the eyepiece, the rest is up to individual choice.

 

This is not to say, people must spend a fortune to enjoy a 10 inch telescope, this is absolutely not the case and I agree with what the others on this thread are saying.

 

It's just a bit frightening, I clearly remember around year 2000, it could cost 200,000 USD to manufacture any new ED lens element of diameter maybe 4-5 inches because of the polishing tools and measurement devices one first had to manufacture for each new lens. Now with the new grinding devices and lower-cost glass materials it seems so much awfully cheaper.... 7 or 8 inches really appears to be no problem.....

Edited by X3782, 12 August 2018 - 04:34 PM.

[gnowellsct]

Hello

Please help me with this imaginary experiment:

Imagine you own one, and only one telescope: A 6" F6 reflector, with superb, premium mirrors made by Zambuto or Royce (just imagine they made 6" please).

If someone was to tempt you, to trade that 6" premium-mirror reflector, for a mass produced Synta or GSO reflector of larger aperture.

¿at what aperture would you cave in and accept the trade?

8"?
10"?
12"?
16"?
20" Stargate?
Never?

 

 

The problem is you're asking us to set aside the LAWS OF PHYSICS.  A nice wide angle view with a two inch eyepiece doesn't really start in the Newt (or for that matter SCT) domain till you get to 8 inches, if you car about reasonable field illumination, which I do.  It doesn't matter how good Messieurs Zambuto and Royce are they aren't going to be able to get around that one.  So the question is a game I wouldn't play.  Nor would they.  

[gnowellsct]

taiwan, nice!!

 

as educated consumers with ethics, given a choice, always choose products made by the free

You can't really know just what Taiwan is sub contracting to the mainland these days.  The thought is nice though.

[gnowellsct]

As for not having developed any diseases from Chinese products yet, it's sobering to note that more than half of the population of Shanghai over 60 now dies of cancer, a disease nearly no one in that age bracket  died of 30 years ago.   (And for those of you at home thinking "yeah but did those statisticians account for x?", the short answer is yes to many, many variables.)  Personally, I'm not willing to risk my health on the benefit of the doubt any more.     

I agree with the fundamentals you are saying about production, and obviously the dog food incident and the Florida sheet rock incident are on the record for anyone to see.  And there are additional cases of that kind of fraud in goods produced for domestic consumption in China.  Let's not forget that the "capacitor plague" was generated by the Taiwanese all by themselves....

 

But on the cancer...China has the highest per capita smoking rate in the world, I think.  So tossing that one out (leaving us to infer that the cancer is due to esoteric chemicals--some might well be) to the crowd is going perhaps a bit too far.   No doubt a large part of the cancer is that as incomes have risen, more people can afford to smoke more.

 

Greg N 

[barbie]

I was just observing Mars,Jupiter and Saturn at 250x(I could have gone even higher but didn't have the eyepieces/barlow combination available to do so) this evening with my Orion 6"F8 dobsonian and had some incredibly sharp and detailed views of these  planets so I would say the Chinese optics are more than up to the task for serious astronomical observations where critical fine details are to be seen.  The clear sky chart for my area was indicating average seeing and transparency but I easily saw the Crepe ring of Saturn with Cassini's division sharply defined as well as multiple bands on the globe.  Mars also looked good, although still not prime due the remaining dust but Syrtis Major was seen as well as the SPC.  Jupiter featured numerous bands with festoons and the GRS.  Also viewed Epsilon Bootis(cleanly split), Mizar/Alcor, Alberio and M29 all from heavily light polluted and haze filled skies.  Not bad for an hour long session before bedtime!!

Edited by barbie, 12 August 2018 - 11:09 PM.

[Pinbout]

It's also true that I don't know how many come of the machine at 1/4 wave, 1/8 wave, etc., etc.

 

I can absolutely, without question, tell you this 10in f4.5 isn't even close to a 1/4~

 

Edited by Pinbout, 13 August 2018 - 05:10 PM.

[Pinbout]

 

figuring on a machine takes out the elbow grease, but it still takes lots of technique, lots of testing... lots of attention to parabolize a mirror.

 

its never ever set it and forget it.

 

 

Edited by Pinbout, 13 August 2018 - 05:15 PM.

[X3782]

Thanks for the interesting picture. I somehow imagined that the bigger company is machine-grinding parabolas in practically single-shot, at least for smaller diameter, large f-number mirrors, so there is in fact no explicit parabolization step (maybe in the program there might be?) in the traditional sense.... the manufacturing steps are actually quite simplified, relatively speaking. Also I thought they are not claiming any p-v or smoothness numbers to the customer.

 

The smaller more expensive company seems to be parabolizing (?) using closer to traditional techniques, and providing test data sheets. I got curious and bought one mirror, asking for a good sample! I am sure the quality is very good, especially compared to 35 years ago. All these products now are at a very high level.

 

I should stay silent, but I get nervous when small p-v numbers are quoted based on the readout of "quick-look" laser interferometers. This is really a device meant to control the uniformity of the product, it is also like the policeman or safety enforcer of the factory. If the marketing people try to use this one single number to appeal to the customers how precise the product is compared to the competition, then there can be a conflict-of-interest because I will tend to purchase the cheapest interferometer with the lowest spatial resolution or pixel count, and use the most relaxed settings to get the smallest p-v number possible. I might make subtle corrections to the mirror to get some instantaneously small value, even though the mirror changes shape with temperature. I think this number should not be used to compare products from different manufacturers.

 

If the customer is happy with the views through the telescope, then the optic has more than served its purpose, a normal customer would not know what to do with a p-v wavefront error number..... it gives a misleading impression that this one figure of merit will indicate how sharp the image will be, which is not exactly true for many reasons. In my country only a very few companies make Newtonian mirrors now and these are predominantly known opticians (e.g. used in Takahashi or large observatory telescopes), but years ago it was mass produced. I remember some companies claimed in magazine advertisements their implausibly small wavefront errors in large block letters. The most serious companies did not do this.

Edited by X3782, 13 August 2018 - 08:23 PM.

[Pinbout]

 

I should stay silent, but I get nervous when small p-v numbers are quoted based on the readout of "quick-look" laser interferometers

use many tests to develop a mirror profile.

 

never rely on one test only

[GShaffer]

Posts containing OFF topic geo-political and health discussion have been removed. As with most topics things tend to drift but still need to remain at least topical to astronomy. Lets keep it topical to the original discussion or it will be shut down.

[X3782]

There are (probably minority) people who prefer smaller aperture scopes of higher optical perfection for visual use. One of my associates swore that the "most beautiful" stars (in terms of "visually pleasing"; sharp, not bland, and not affected too much by the constantly-changing atmospheric seeing which some people find disturbing) can be seen through a carefully figured 60-80 mm "achromat" of f-ratio f>18-25 using more traditional flint/crown glasses which tend to allow better figure and smoother polish, a simple but precise coating with uniform thickness that does not mess up the figure. The next best thing is a long focal length Newtonian of around 3-4 inch aperture with a very carefully figured mirror, and a simple carefully applied reflective coating. A minimal-number-of-elements eyepiece should be used. The modern short-focal length apochromat using exotic glasses (he reasoned) emphasizes the reduction of chromatic aberration at the expense of other types of aberration. What is a bit interesting is that both of these telescope types are probably low cost.

 

Of course this is not the point of view for everyone, and newcomers to the hobby should take it with a grain of salt perhaps; many more people want to see more detail or brightness afforded by greater aperture. In any case, thank you this discussion was very informative!

Edited by X3782, 14 August 2018 - 07:56 AM.

[SandyHouTex]

 

figuring on a machine takes out the elbow grease, but it still takes lots of technique, lots of testing... lots of attention to parabolize a mirror.

 

its never ever set it and forget it.

 

 

Actually I think it is.  I own a lot of camera lenses with aspherics and I am virtually certain that no one at Nikon or Canon is setting at an optical bench somewhere aspherizing these elements.  It's all done by machine.  A parabola should be fairly easy.

[Pinbout]

Actually I think it is.  I own a lot of camera lenses with aspherics and I am virtually certain that no one at Nikon or Canon is setting at an optical bench somewhere aspherizing these elements.  It's all done by machine.  A parabola should be fairly easy.

they're not making lenses to 1/20~  -1 conics, 16" dia.

 

look at stellarvue - they do machine polishing...email vic