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Zambuto/Royce vs Synta/GSO

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#51 X3782

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Posted 05 August 2018 - 03:16 PM

>other than cost and bragging rights!

 

Precisely (not that I am bragging to anyone, but I have earned the right to by buying a premium optic). At work I am trying hard to always ask myself, what is reasonable, what is sensible, am I wasting resources somewhere? while looking hard at Microsoft Excel. Arguing with suppliers about cost performance and delivery times.

 

If I went for lowest bidder with my hobbies as well, there would really be no escape. I would spend my whole life being a cog in the big machine. bawling.gif

 

So I need my premium optics to make me feel better. lol.gif I'm not wasting money in any other pursuit.


Edited by X3782, 05 August 2018 - 03:46 PM.


#52 Chesterguy1

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Posted 05 August 2018 - 03:36 PM

I have had run of the mill 10" Newts and they were never close to a Zambuto.

I think one has to be careful about over generalizing about the optics on “run of the mill” scopes.  I had a 1998 10” Orion Deep Space Premium Explorer.  I can’t say for sure because I no longer have the scope, but I believe that Ostahowski made the primary.  If not, it was still a very good mirror.  I only got rid of the scope because the weight of the sonotube and base became tiresome.  In retrospect I would have been better served to have rehabbed the structure a la Jon Issacs although I don’t possess Jon’s skills.  It doesn’t have the cachet of my 8” Teeter with Zambuto primary and Antares secondary, but it was a fine performer (along with 2” more aperture).  The weaknesses in that scope were primarily mechanical :poorly made bearings, no fan, a really badly designed locking bolt system for the secondary.

 

Chesterguy


Edited by Chesterguy1, 05 August 2018 - 03:40 PM.

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#53 CHASLX200

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Posted 05 August 2018 - 05:58 PM

I think one has to be careful about over generalizing about the optics on “run of the mill” scopes.  I had a 1998 10” Orion Deep Space Premium Explorer.  I can’t say for sure because I no longer have the scope, but I believe that Ostahowski made the primary.  If not, it was still a very good mirror.  I only got rid of the scope because the weight of the sonotube and base became tiresome.  In retrospect I would have been better served to have rehabbed the structure a la Jon Issacs although I don’t possess Jon’s skills.  It doesn’t have the cachet of my 8” Teeter with Zambuto primary and Antares secondary, but it was a fine performer (along with 2” more aperture).  The weaknesses in that scope were primarily mechanical :poorly made bearings, no fan, a really badly designed locking bolt system for the secondary.

 

Chesterguy

The last run of the mill 10" i had was a 10" Celestron on the go-to AVX mount to flip since it came with a ton of Tele vue stuff.  The views were just lack luster at best.



#54 barbie

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Posted 05 August 2018 - 09:29 PM

That hasn't been my experience with 10" Newts.  Every one I've had was outstanding, albeit a bit too heavy so they were moved on to someone able to manage their weight better than I could.


Edited by barbie, 05 August 2018 - 09:30 PM.

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#55 X3782

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Posted 06 August 2018 - 12:44 AM

There is no question that computer-controlled optical grinding and correction/polishing machines have gotten better and better in the last 10 years, and cheaper. I don't test telescope mirrors, but for other types of optics the improvement in the accuracy is real. It's not just that labour costs are cheaper in the Far East where this type of mirror optic I think are almost exclusively made now (generally speaking in the recent 3-4 years average wages have increased very rapidly, in the next 10 years it will be more so as they become more affluent (is that correct English?)), it's also that there is technological progress in the companies worldwide that build these CNC machines that the telescope companies buy from. There is pricing pressure on the glass material side too, new suppliers have emerged that provide so-so acceptable raw material. If you want to buy an evaporation coating machine, it's getting cheaper too, also on the used market, I think there is a shift in the coating technology going on, though perhaps a bit more slowly than in the CNC side. The testing phase, laser interferometric devices are now cheaper too, so a technician who doesn't know how to make an optic or exactly how the testing device works can nevertheless put the optic on the testing rig on an assembly path, and point out on the PC display where the height of the optic is deviating from the theoretical one, and discard the optic or put it back on the route that leads again to the CNC polishing machine, at least if the person is paying attention. This kind of approach means you no longer need a specialist with 10+ years of experience on the fabrication line, you can almost use normal workers that are moderately trained for at least part or even most of the process, except the critical steps. It's great that they can give quality to a lot more of the general public at affordable prices. Nevertheless there are some things they aren't so good at.

 

I'm not an experienced astronomical observer, but I work with a lot of optics in my day job, the majority being CNC fabricated, the others being traditional custom. Considering a lot of things I would still buy from a traditional optician for my hobbies, and I do that. There are just things that happen when a person carefully works and examines each individual optic for the long weeks it takes to fabricate the optic, that you cannot quite do with fast industrial automation approaches. For example if there is a flaw (it is virtually impossible to avoid flaws in every optic, either in the material or in the fabrication chain, the level of precision needed is just too high), the human can compensate and find the best compromise based on experience, because the human specialist knows which of the unavoidable flaws are important and which are not, and the remedy. The machine will just run straight through, so what you get is a kind of multiplication of probabilities for each manufacturing step, sometimes you can even guess which machine slightly messed it up and how it propagated though the various steps. The only reason why the user can't see these flaws is because the user doesn't know how to. I don't want to buy something in a hobby and then look for the flaws that might or might not be there with admittedly lower probabilities as technology progresses. I want somebody really experienced to find the flaws and take care of them for me, according to the particular philosophy of that individual. This might be a bragging right.... but it's also peace of mind.


Edited by X3782, 06 August 2018 - 10:35 AM.

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#56 Chesterguy1

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Posted 06 August 2018 - 05:56 PM

The last run of the mill 10" i had was a 10" Celestron on the go-to AVX mount to flip since it came with a ton of Tele vue stuff.  The views were just lack luster at best.

We’ll agree that there are bound to be lackluster optics in mass-market newts.  However, I wouldn’t want new converts to the hobby to think that they can’t get a respectable or better mirror set.  It would be a poor 10” indeed that couldn’t outdo an 8”. Not everyone can afford premium.  My point was that you can get a very capable mirror without breaking the bank and that it’s often the mechanics of the M-M scopes that are the most problematic part of the purchase.  This is why there are numerous threads about improving on the standard (Zhummel, for example).  There are many, many positive reviews of the Z optics.  It’s the weight that turns me off, but that’s why skillful owners modify.

 

Chesterguy


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#57 barbie

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Posted 06 August 2018 - 10:45 PM

I've not encountered any problems with the mechanics on any of the mass produced dobs that I've owned, and I've owned many.  My current 6"F8 dob has an excellent focuser, mirror cell and spider/secondary holder.  I have not made any modifications to the scope nor do I plan to.


Edited by barbie, 06 August 2018 - 10:47 PM.


#58 X3782

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Posted 06 August 2018 - 11:22 PM

It's really impressive that they can sell a 10" Dob including eyepieces and free shipping for 499 USD, if one thinks about the cost breakdown and the packing, trucking, and ferrying of this bulky thing over the Pacific, the profit margin must really be thin. The primary mirror must be <50 USD to produce, the mount and OTA <100 USD?

 

I'm not sure how representative this is, but the top selling telescopes in Amazon US is a 70-80 mm refractor, a 5 to 6 inch Newtonian on a tripod, or a 5 to 8 inch SCT (because the commercialization of this is a US invention?) on a computerized goto mount. The first 8-inch Dob comes in at #32, it's cheaper than some of the instruments that came before it; the 10 inch Dob is at #76. On the OPT beginners telescopes list, number 1 is a GEM-mounted SCT for 2600 USD, only 1 Dob (Skywatcher 8 inch) in the top 10. Would it be safe to infer from this that only <5% of all telescope buys have an aperture of >8 inches?

 

In Germany refractors are the most popular (historically they almost practically invented the commercial achro and apo....), then it's 6-8 in reflectors mounted on tripods. In Japan in the biggest discount electronics outlet, top 10 include 60-80 mm refractors or 4-to-6 inch reflectors on tripods; the 3 biggest telescope companies do not produce Dobsonians. One website says Dobs skip a lot of the features of proper telescopes to extremely reduce the price. A dedicated amateur might own a Tak or a Vixen on a GEM (one claims to have invented the commercial fluoride apo), there may not be enough realization what a Dob can do, because not a lot of people ever used one. Even in the mainland Chinese Hangzhou (Skywatcher) website, the recommended telescopes for beginners are mostly tripod-mounted, refractors, Maks, equatorial reflectors. 1 Dob (collapsible) on the list in the 8 inch range. In one Chinese website, the selling point of Dobs is said to be the low price, good for beginners on a budget.

 

Tripods, GOTO computerization, compactness, lightness would seem to sell; aperture not so much (majority are happy with <=6 inches) and the profit margin of a 499 USD, 10 inch Dob may be very slim compared to the warehousing and shipment costs. If I were the CEO of a telescope company, spending R&D money on improving the optics or mounts of such a product wouldn't have a high priority because that is not where I am making most of my profits, so I am impressed with the willingness to invest in new manufacturing equipment, it shows that they care about astronomy, as the CEO says. Now if the labor costs are increasing, this product no longer makes sense at this price point; an 8-inch SCT would seem to have greater sales volume and profit.

 

Only dedicated amateurs would know that there is even a product called a premium Dob, and these are predominantly manufactured in the United States because that is your important culture (in fact the lineage can be traced directly to the first invention of the Dob, i.e., the "hand made by individuals" aspect), that would be my perspective as a foreigner...... almost all the important innovations of Dobs were made by small companies or individuals. There are some high-end opticians outside the US, mostly in Europe and a very few in Japan, Australia, Taiwan, etc. but there might not be enough demand to keep such a field innovating if the leading US market decides that they cannot see the value..... Commercial low-cost Dobs in factories I guess appeared in the 1970's and 80's? and these were from the very beginning manufactured mostly overseas in the Far East (?), it's a class of product that can only exist with cheap labor, and I would say probably even for these companies they aren't very attractive to manufacture, they would want to move higher end.


Edited by X3782, 07 August 2018 - 02:20 AM.

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#59 bvillebob

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Posted 07 August 2018 - 12:21 AM

Given the year-long wait from order to delivery for a premium mirror from some of the top makers these days I don't think there's much danger of the market not being able to see the value.

 

I've had scopes of all sizes up to 16", from most of the manufacturers, and they've all served me pretty well.  The GSO mirrors did a good job, but they always left me wanting more.  I got a couple of mirrors from Hubble Optics and there were a solid step up in performance from the GSO (12" and 16"), very noticeable improvement.

 

I finally decided to try a "premium" mirror and ordered a 12.5" f/5.5 quartz mirror from ZOC.  After observing with it all year it's clearly performing much better than the HO, which were better than the GSO.  All of them gave good images, at times very good images, but each step up in quality has been noticeable at the eyepiece.  One thing that really has struck me with the ZOC mirror is that there is exactly one spot where it is in focus.  With the other mirrors I was always hunting back and forth slightly trying to find the best focus, with the ZOC there's a point where all the fine detail just snaps into focus, indicating to me, a lack of spherical aberration.  

 

At the end of the week I'm headed to the central Oregon desert for week of dark sky observing, I'll be taking my 16" Hubble Optics homebrew dob.  It's a very good mirror and the much larger size makes up for the difference in quality for deep sky work.

 

ALL of these mirrors have their place, it's not a matter of one OR the other, just like there's more than one brand and model of car.  The GSO / Synta are great for their low cost.  At some point of involvement in the hobby some people want better and the market is there to answer, whether it's a premium mirror or a Feathertouch focuser.  The mass market mirrors are getting better and better, and that's a good thing, but my experience and the experience of many others is that they're still not equal to one made by a master craftsman and probably will never be.  The difference between them is getting smaller, but it's real.  The bottom line is use and enjoy whatever you have and don't worry about what others choose to do.


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#60 Astrojedi

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Posted 07 August 2018 - 01:35 AM

The right answer will depend on individual preferences. For me the answer is very simple... 10”. No 6” scope, even a premium refractor will show more than a 10”. A 10” of even average quality optics will do everything better. Period.
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#61 barbie

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Posted 07 August 2018 - 10:58 AM

A 10" is much heavier and more difficult to manage for some, myself included.  That's why I settled on a 6" because it's plenty of aperture, enough to show a lifetime's worth of DSO's and still manageable for me. That's MY bottom line!!

A 10" may dig deeper, but what good is it if it doesn't get used due to weight and size issues? That's exactly what I encountered when I had my 10" newts and won't repeat that mistake again!!  That ship sailed long ago!


Edited by barbie, 07 August 2018 - 11:04 AM.

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#62 dscarpa

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Posted 07 August 2018 - 04:38 PM

 If I couldn't have the mass produced mirror re-figured I'd keep the 6" but F8 if you please. I used to have one with 1/8 wave optics that was pretty much coma free and  was very nice for  lunar planets and DSOs. I'm so bad at collimating at this point that a truss dob would be  exasperating.  David


Edited by dscarpa, 07 August 2018 - 04:39 PM.

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#63 tommy10

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Posted 07 August 2018 - 05:56 PM

Premium mirrors are a marketing device, people buy them for bragging rights or piece of mind, or feel  they deserve such luxuries,but the views they produce are only marginally better on some objects , about the same on most objects. Other variables ,especially seeing conditions, collimation,tube currents, eyepieces, stray light, local thermal issues, secondary, exc, etc, are far more important then the alleged smoothness of the premium ,gourmet mirror.Folks that purchase such stuff, probably also buy paracors,premium hand grenade eyepieces,top shelf collimation aides,fans, etc, they usually although not necessarily are better at controlling the variables I mentioned and thus get the more from their scopes then the average mass market guy, and hence better views that they will attribute to their magic mirrors.


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#64 jjgodard

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Posted 07 August 2018 - 07:04 PM

Premium mirrors are a marketing device, people buy them for bragging rights or piece of mind, or feel  they deserve such luxuries,but the views they produce are only marginally better on some objects , about the same on most objects. Other variables ,especially seeing conditions, collimation,tube currents, eyepieces, stray light, local thermal issues, secondary, exc, etc, are far more important then the alleged smoothness of the premium ,gourmet mirror.Folks that purchase such stuff, probably also buy paracors,premium hand grenade eyepieces,top shelf collimation aides,fans, etc, they usually although not necessarily are better at controlling the variables I mentioned and thus get the more from their scopes then the average mass market guy, and hence better views that they will attribute to their magic mirrors.

 

The law of diminishing returns can be applied.

 

Imagine a perfect mirror being rated 100%, knowing it doesn't exist.

But you can get 50% of the way there for $.

75% - $$$

85% - $$$$$

90% - $$$$$$$$

At some point, lets say above 90% of perfection, the ability to get better becomes cost prohibitive,

92.5% - $$$$$$$$$$$$$$$$$

94% - $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

95% - $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

and eventually improvement is impossible with current technology.

 

When it comes to deciding on cost to value, opinions vary. 

 

For me, if I want to drastically improve my primary mirror, I clean it.


Edited by jjgodard, 07 August 2018 - 07:19 PM.

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#65 Astrojedi

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Posted 07 August 2018 - 07:53 PM

A 10" is much heavier and more difficult to manage for some, myself included.  That's why I settled on a 6" because it's plenty of aperture, enough to show a lifetime's worth of DSO's and still manageable for me. That's MY bottom line!!

A 10" may dig deeper, but what good is it if it doesn't get used due to weight and size issues? That's exactly what I encountered when I had my 10" newts and won't repeat that mistake again!!  That ship sailed long ago!

 

Fair enough. But note there is no "right" or "wrong" answer here. As I said it boils down to personal preference. If I had only one scope I would pick a 10". For me a 6" just does not have enough light gathering ability and I never find the views satisfying. Also I find a 10" absolutely no issue to use and not heavy at all. I know many observers who feel the same way. But I also know many observers who just don't care for weight of a 10" for a variety of personal reasons and stick with smaller scopes.

 

But there are ways around the weight issue. For example an Alkaid 10" F5 dob weighs only 26lb fully assembled. Even if I had issues with weight I would take that any day over a 6". There is simply no comparison in the views even with a 6" premium mirror.



#66 Adun

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Posted 07 August 2018 - 09:23 PM

The law of diminishing returns can be applied.

 

95% - $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

and eventually improvement is impossible with current technology.

 

Then there's adaptive optics and space telescopes.

 

Have you seen that picture of Neptune rivaling Hubble? It's almost unbelievable that was taken from Chile. Even the perfect 100% mirror couldn't take that picture from earth. Those adaptive optics are real magic, but probably very expensive and out of budget for even the most lavish amateur. Maybe one day...


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#67 barbie

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Posted 07 August 2018 - 09:33 PM

Fair enough. But note there is no "right" or "wrong" answer here. As I said it boils down to personal preference. If I had only one scope I would pick a 10". For me a 6" just does not have enough light gathering ability and I never find the views satisfying. Also I find a 10" absolutely no issue to use and not heavy at all. I know many observers who feel the same way. But I also know many observers who just don't care for weight of a 10" for a variety of personal reasons and stick with smaller scopes.

 

But there are ways around the weight issue. For example an Alkaid 10" F5 dob weighs only 26lb fully assembled. Even if I had issues with weight I would take that any day over a 6". There is simply no comparison in the views even with a 6" premium mirror.

As you said, there is no right or wrong but I would still take the 6 inch because it is easier to transport as well.  Truss tube dobs just don't cut the mustard for me so that's why I like traditional solid tube reflectors.  I was observing with someone who had an 18" Obsession and it took him quite a while to get it set up.  In that time frame, I had already observed several DSO's.  I also don't drive big vehicles so a 10' f5 would be more difficult to transport and set up.  Besides that, faint fuzzies all begin to look the same even with a 10 inch scope. A 10 inch may be better for YOU, but it isn't for me and I should know as I've had three of them in the last 20 years, from f5 to f8 focal ratios. To each their own!grin.gif


Edited by barbie, 07 August 2018 - 09:58 PM.


#68 Astrojedi

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Posted 07 August 2018 - 10:01 PM

As you said, there is no right or wrong but I would still take the 6 inch because it is easier to transport as well.  Truss tube dobs just don't cut the mustard for me so that's why I like traditional solid tube reflectors.  I was observing with someone who had an 18" Obsession and it took him quite a while to get it set up.  In that time frame, I had already observed several DSO's.  I also don't drive big vehicles so a 10' f5 would be more difficult to transport and set up.  Besides that, faint fuzzies all begin to look the same even with a 10 inch scope. A 10 inch may be better for YOU, but it isn't for me and I should know as I've had three of them in the last 20 years, from f5 to f8 focal ratios. To each their own!grin.gif

I usually setup my truss tube 14” when there is still light. Plenty of time smile.gif



#69 jjgodard

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Posted 07 August 2018 - 10:02 PM

Then there's adaptive optics and space telescopes.

 

Have you seen that picture of Neptune rivaling Hubble? It's almost unbelievable that was taken from Chile. Even the perfect 100% mirror couldn't take that picture from earth. Those adaptive optics are real magic, but probably very expensive and out of budget for even the most lavish amateur. Maybe one day...

I was speaking in the context of amateur astronomers. 



#70 X3782

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Posted 07 August 2018 - 11:05 PM

Premium mirrors are a marketing device, people buy them for bragging rights or piece of mind, or feel  they deserve such luxuries,but the views they produce are only marginally better on some objects , about the same on most objects. Other variables ,especially seeing conditions, collimation,tube currents, eyepieces, stray light, local thermal issues, secondary, exc, etc, are far more important then the alleged smoothness of the premium ,gourmet mirror.Folks that purchase such stuff, probably also buy paracors,premium hand grenade eyepieces,top shelf collimation aides,fans, etc, they usually although not necessarily are better at controlling the variables I mentioned and thus get the more from their scopes then the average mass market guy, and hence better views that they will attribute to their magic mirrors.

 

Fair enough. But at the risk of being offensive, often these "premium" mirror manufacturers are say serious 2 people operations (the marketing department also does production, finance, R&D, customer support, and raw material purchasing) making I assume <100 mirrors per year. The 1-year waits aren't necessarily because of huge demand, it's time-consuming per optic if you insist to examine everything carefully yourself. They represent how some part of the field "used" to operate for 100+ years, until not so long ago. The mass market, cheap machined mirrors are a relatively new development, the computer and CNC technology wasn't advanced enough until recently, and these factories never existed in the US, the first ones were made by Far East companies.

 

You can't compete with a mid-ranged value product in terms of price (say 50 dollars) against a machine and cheap labor. The raw glass material alone in US might be more than 50 dollars. If I'm not mistaken, there aren't any US-owned large telescope manufacturers left. In my home country too, many telescope manufacturers closed or shifted to other fields in the late 1980's and 90's.

 

I'm far from rich lol.gif , I don't own a car nor home, and shop at the grocery store carefully, but I respect this history so spend what I think is fair for a mirror, I personally contributed to the US economy in this way smile.gif  Not to comment on anybody else's decisions. Also for eyepieces...... until my home country started mass production based on then-cheap labor (average wages were 5x different) 60-70 years ago, even simple eyepieces cost like the hand grenade or Paracorr, relatively speaking. When the cheap exports dropped the price,  the traditional companies positioned themselves as upscale or innovative to justify the price difference.

 

In this sense it's not gourmet or luxurious (yesterday it was sandwiches all day long, though it's supposed to be vacation time), it's just how things used to be until the price was slashed lol.gif, manufacturing and R&D jobs in developed countries just have to aim for high end. There used to be an age before my time when people would buy a camera worth 2 months of salary and try to use it for 20 years, now it's not eccentric for people to rebuy in 6 months. I read that the median household income in US is 58000 USD, that's 38% more than in my country lol.gif, 10 times more than in some populous Far East countries where the optics are made..... but as they catch up in income and operational overhead, it won't be possible to manufacture a high-quality mirror for 50 USD, but say closer to 300-500 USD. US domestic mirror manufacturers aren't charging hefty unfair margins, it's more that they look "premium" compared to countries where the average wages are factor 5-10 less, and automation and technology are used to compensate for the deficit in experience and manufacturing history. I'll go out on a limb and claim, as far as I know there was hardly a time in the last 200 years when a US, German, or British-manufactured commercial astronomical telescope including eyepieces and mount could be had for say <1000 USD equivalent.


Edited by X3782, 08 August 2018 - 08:49 AM.

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#71 Mike Lockwood

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Posted 08 August 2018 - 10:10 AM

Fair enough. But at the risk of being offensive, often these "premium" mirror manufacturers are say serious 2 people operations (the marketing department also does production, finance, R&D, customer support, and raw material purchasing) making I assume <100 mirrors per year. The 1-year waits aren't necessarily because of huge demand, it's time-consuming per optic if you insist to examine everything carefully yourself. They represent how some part of the field "used" to operate for 100+ years, until not so long ago.

Your 1-year wait figure is not accurate for all optical shops, and it's not good to generalize.  Wait time also depends on mirror size, material availability, etc.
 

The mass market, cheap machined mirrors are a relatively new development, the computer and CNC technology wasn't advanced enough until recently, and these factories never existed in the US, the first ones were made by Far East companies.

I think you are quite wrong in your assumption that the optics for mass-market telescopes are made with "CNC technology".  Those machines are quite expensive and slow and are generally used for smaller work.  The larger machines are used for more challenging projects where a sufficient hourly rate can be charged to help justify the cost of the machine.  Of course we may be arguing about the definition of CNC, but that is out of the scope of this thread.

 

Based on what I have seen, I can pretty much guarantee that for low-cost optical manufacturing, there are a handful of workers tending a myriad of machines, and they are just executing a particular routine/recipe to come close to the desired result.  It's not hard to come up with the recipe if you make enough mirrors.  This accounts for the significant variation in quality, because there are variables that are difficult to control without paying individual attention to an optic.

 

Also, to apply "CNC technology" to the poorly annealed glass or non-annealed glass that mass market telescopes seem to feature these days would be profoundly stupid and a massive waste of capability.  It would also be quite difficult to do if one was attempting to close the loop on a test and work cycle, because the glass will deform unpredictably as it cools off after work.



#72 Astrojedi

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Posted 08 August 2018 - 10:37 AM

There seem to be generalizations flying both ways and neither are fully accurate.

 

The premium mirror makers are not fly-by-night operators. They are folks who have established solid reputations over the years by producing quality optics. And for many observers these mirrors are very much worth it even with a little wait time. To me for example an excellent/premium optical figure is immediately obvious but I am still very satisfied observing with other scopes. Many here are not.

 

On the other hand Commercial mirrors receive more Q&A than folks here are lead to believe. Manufacturing technology and overall processes have come a long way in the past decade have improved in leaps and bounds. These days based on the sample set of very recent 20-25 Celestron and Sky-Watcher as well as GSOs that I have looked through the mirrors have been very good - almost 95%+ are diffraction limited. Most harmful issues actually arise from other factors in the scope - alignment, cooling, collimation, baffling etc. This is why differentiation for the premium mirror makers is now shifting to larger mirrors and/or faster focal ratios where the commercial operations are yet to catch up (and they may never go there).

 

To me the Op's question is a matter of personal preference as much as it is of performance.


Edited by Astrojedi, 08 August 2018 - 10:39 AM.


#73 X3782

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Posted 08 August 2018 - 11:16 AM

I apologize if I have offended, I do not want to generalize.

Also I do not want to contradict world experts that we all have the highest opinion of.

 

For me "CNC" (computer numerical control) is anything that runs on G-Code including

specific-task machines, with or without sensory feedback to control its movements. 

I am not speaking about the general-use devices that machine arbitrary aspherical surfaces

to 100 nanometer precision, which I agree would be too inefficient and would normally need

annealed materials to achieve the advertised specifications.

 

I have not gone to the factories in question myself, all I have are hearsay from various sources

on my side of the pond. Mastering automation technology means the ability to build machines

that can do the specific tasks, with all the quality control steps of that particular job, and this

leads to increases in productivity and quality which no longer will be affected quite so much

by variations in the skills of the workers involved, and which also allows a wide variety of

optical products to be released simultaneously and in volume. No one doubts that this has

been mastered already, to higher and higher levels of proficiency.

 

The quality of the glass material is improving in my opinion. Also that would match the opinions I

have heard from the glass manufacturers who compete in that part of the world. There are even very

specific types of optical crystals where the samples that I have purchased are unequaled anywhere else

in the world, one must note the long history and tradition of, e.g., jade and glass that certain countries have,

this is improvement that I have seen over the last 15-20 years. But I do not want to contradict anything,

since experts can see much more than we can by looking at samples of the shipped products.

 

But I repeat, I completely agree that the high-quality US mirrors that I own myself have

higher levels of performance. This is also a generalization, but what can I do about it.


Edited by X3782, 08 August 2018 - 11:59 AM.


#74 jjgodard

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Posted 08 August 2018 - 11:38 AM

Your 1-year wait figure is not accurate for all optical shops, and it's not good to generalize.  Wait time also depends on mirror size, material availability, etc.
 

I think you are quite wrong in your assumption that the optics for mass-market telescopes are made with "CNC technology".  Those machines are quite expensive and slow and are generally used for smaller work.  The larger machines are used for more challenging projects where a sufficient hourly rate can be charged to help justify the cost of the machine.  Of course we may be arguing about the definition of CNC, but that is out of the scope of this thread.

 

Based on what I have seen, I can pretty much guarantee that for low-cost optical manufacturing, there are a handful of workers tending a myriad of machines, and they are just executing a particular routine/recipe to come close to the desired result.  It's not hard to come up with the recipe if you make enough mirrors.  This accounts for the significant variation in quality, because there are variables that are difficult to control without paying individual attention to an optic.

 

Also, to apply "CNC technology" to the poorly annealed glass or non-annealed glass that mass market telescopes seem to feature these days would be profoundly stupid and a massive waste of capability.  It would also be quite difficult to do if one was attempting to close the loop on a test and work cycle, because the glass will deform unpredictably as it cools off after work.

I've said this before, I'm glad that folks are producing premium, American-made optics, even if I don't own one, it's nice to know I could.



#75 X3782

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Posted 08 August 2018 - 06:34 PM

These are photos of the largest amateur telescope factory (sorry about the language....) that we are maybe speaking about.

 

http://tentai.asablo...5/07/10/7704715

 

Quote, "For (telescope) reflective mirrors, many manufacturers have developed the technology to polish precise paraboloid surfaces using numerical control" In this language, numerical control = NC or CNC. "The precision of objective lenses and reflective mirrors are inspected using (laser) interferometers". Another description of this company elsewhere mentions "many Zygo interferometers".

 

It's hard to see from the small photos, but I do recognize some CNC devices, computer controlled injection molding devices....... The many mirrors shown in one of the photos are said to be 200 mm = 8 inch Newtonian, there are  "even low temperature evaporation machines" that "hardly exist in Japan by comparison".  Last photo is a 20 inch primary mirror. This would square with the info I get from other sources........

 

I assumed that since they have such a big building, expensive evaporation chambers, rows of CNC injection molding devices, and hundreds of employees etc. they must easily have capital to buy something like this CNC grinding machine attached below (running cost in my home country for a smaller older model that grinds up to 12 inch optics is said to be like 100 USD/hour meaning that is what they can charge me for grinding some piece even if I haggle, minus labour costs minus the programming and setup jig costs, but maybe it gets cheaper if it's moved to another country? and since it is grinding, rather than traditionally abrasively polishing, to obtain the mirror surface I assumed it will be fast enough "Large reduction in machining time compared to conventional aspherical surface machining time", I have watched a similar machine working before, but I have never programmed nor operated one myself. Also I have heard comments that none of the astronomical telescope companies in my country can afford this kind of investment, even the largest company has less than 200 employees, so only our neighbor next door has the size scale to buy it, also I think their government endorses this and even provides loans and financial support, so it is a bit different from our completely market-driven economies in terms of judging when is it financially viable to install some high-tech device).

 

You are right I do not know which specific machine they are using, only that it is "CNC". But this product advertisement specifically mentions "astronomical telescopes" as an application, and there are no other telescope companies of this size in the world. The device supports "on-the-machine surface form measurement..... by mounting an optical interferometer", so I guess the measure-work-measure-work loop efficiency is not reduced. One of the options include a "super precision ambient temperature control system 'nanoenvior' which supposedly control deformation of the workpieces, I have no experience with such a device. The larger models could polish a 20 inch mirror too. So maybe the technical objections stated above are solved here? Again I caution I do not know the specific device.

 

http://www.nagase-i....product_14.html

 

This is a very industrial approach to building telescopes, using a lot of capital, manpower, and technology, and as the article notes, all the production of the telescope parts under one roof. This visit was from 2015 but I guess there can be further advances in 2018. Yet what for me has value is that an optician produces a superior mirror compared to this kind of tremendous automation technology, so I am happy to spend the money.

 

I am trying to be careful when I make a categorical statement, or a qualifier when I am not that sure, or guess if it's speculation. Some of the engineering universities that can in principle supply technicians and engineers to these kinds of industries seem to have "form fabrication" devices maybe for education and training purposes, so clearly there are enough workers with the relevant skills too.....

 

https://www.youtube....h?v=SPl2cgm0Q-Y

 

Video (guess there might be copyright issues but....). The situation of >10 years ago.


Edited by X3782, 09 August 2018 - 07:32 AM.



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