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Declining Quality of Premium Optical Glass

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#1 10gauge

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Posted 19 November 2012 - 09:08 PM

There seems to be an alarming trend in securing premium optical glass for us refractorphiles. Summarizing from a few threads in the Yahoo TEC Group, Yuri has seen an increase in the rejection ratios of premium glass. It appears that the quality of CaF2 and FPL53 premium glass is not what it was 10 years ago. He is having to send lenses back to Ohara for visible striae in artificial star tests. In another thread he stated that he is not taking any new orders for the APO 160FL at this time. He feels that the quality of large lenses are in decline, even to the point of shifting production to reflectors if the situation does not improve. That would be a sad day. How do people feel about the future trends, philosophy, and quality of optical glass?...

http://tech.dir.grou...s/message/22839

I also noticed that the TEC 140 is now $5,700, up from $5,500. I ordered my TEC 140 a year ago, and I still haven't received it yet. Yuri said it would be done in 6 months as there were 50 people ahead of me. I am getting a little nervous... I am crossing my fingers, hoping I don't get the bottom batch of glass.

#2 Sky Muse

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Posted 19 November 2012 - 09:34 PM

Within this review of the Takahashi FS-78, about a third of the way down, there is a very interesting read about calcium fluorite crystal...

http://scopeviews.co..._Takahashi_FS78

I read it just today, and it finally confirmed my suspicion as to why Takahashi practically abandoned calcium fluorite for its objectives.

Alan

#3 Danno2006

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Posted 19 November 2012 - 09:59 PM

I owned a TEC140, bought a C14 and the TEC140 stayed in its case until I sold it. I moved away from a quality refractor and have not looked back. Given glass availability, LZOS may be the last manufacturer remaining making larger than 150mm premium quality, triplet refractors. I can't wait to see what kind of quality and aperature that Yuri can put into a compound mirror scope at the price point of a TEC180. Just noticed a 30" Starmaster dob at another site at the same price as the TEC180 tube - and the dob is mounted. The writing is on the wall, the king is dead, long live the new king.

#4 Sky Muse

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Posted 19 November 2012 - 10:30 PM

"The writing is on the wall, the king is dead, long live the new king."

Might one suggest, analogously, the abandonment of a succinct novel in favour of comics.

Alan

#5 BillP

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Posted 19 November 2012 - 10:37 PM

Hopefully the Tak glass will stay high quality as I believe their lenses are made for them by Canon and Canon pours its own glass.

#6 vahe

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Posted 19 November 2012 - 10:39 PM

It appears that the quality of CaF2 and FPL53 premium glass is not what it was 10 years ago. He is having to send lenses back to Ohara for visible striae in artificial star tests. In another thread he stated that he is not taking any new orders for the APO 160FL at this time. He feels that the quality of large lenses are in decline, even to the point of shifting production to reflectors if the situation does not improve.



When the word got around that TEC was not producing larger apos I asked Yuri if fluorite quality was the reason, he said that the reason was the quality of mating elements and not the fluorite. Fluorite is available in larger sizes with the problem being the price which is astronomical.
FPL-53 has always been a problem with nominal 6” being its practical limit.

In another thread Yuri indicated that one of the reasons for not producing Maksutovs, again, is the glass quality needed for the meniscus. Using premium quality glass, which by the way is available, would increase the price of his 10” Mak to near 180FL price level.

Vahe

#7 Sky Muse

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Posted 19 November 2012 - 11:54 PM

Canon made the calcium fluorite lens of my FS-102.

#8 chboss

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Posted 19 November 2012 - 11:58 PM

Canon-Optron to be precise:
http://www.canon-optron.co.jp/english/

best regards
Chris

#9 Sky Muse

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Posted 20 November 2012 - 11:53 AM

When I purchased my apochromat in 2003, the A-P "Traveler" was out of the question given its limited availability and higher cost, and the TeleVue offerings with their "warm" views were never even considered. The FS-102 was on sale for $1899 at the time, and from Texas Nautical Repair...how could I resist? No matter, for while I might've strived towards purchasing the "Traveler", and in all probability, successfully, I had chanced upon this prior to making my decision...

http://www.scopereviews.com/aptak.html

I knew that it was special, but until recent light, I never knew just how special, and unique compared to the vast majority of all other apochromats.

And to think that so many owners of the FS series have sold and are presently selling off these true fluorite gems, for even less than what they paid when new, and for whatever reason, is nothing short of tragic.

Regards,

Alan

#10 jrbarnett

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Posted 20 November 2012 - 12:48 PM

Fluorite optical glass is in reasonable supply and quality remains high. In fact, for large blanks this is the only reliable way to go unless you make your own ED glass as LZOS does.

I like the FS-series scopes, and have one now, and have had a couple of others. However, above 4" I don't find them to be particularly well color corrected visually. Even at 4" I can coax in-focus false color that is just detectable on very bright targets like Vega, Venus and Sirius. The 3" remains visually color free, but that's simply a function of the constant f/8 focal ratio for the line and the declining aperture.

That said, color correction isn't the do all to end all anyway. I find the figure quality on the FS scopes to be quite good, and the simple doublet design using extremely homogeneous fluorite scatters very little compared to harder glass doublets and triplets.

They're nice scopes. But even when they were being cleared out, they were relatively expensive given that they were totally "ala carte" and Tak accesories (clamshells, finders, etc.) are ridiculously expensive.

I also agree that folks selling them now are nuts. Hang on to them. The fluorite doublet is not coming back. As doublets go, these are about the ultimate iteration of the concept; the pinnacle of doublet refractor evolution.

Regards,

Jim

#11 Sky Muse

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Posted 20 November 2012 - 01:36 PM

This morning I was mindful of the overlooked rear element within mine, as I understand it's well-matched to the fluorite, its high quality necessary even to that of the front element's performance, and in tandem to the doublet overall, so I've read, but I'm still unaware of its type.

Regards,

Alan

#12 Paul G

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Posted 20 November 2012 - 01:58 PM

Fluorite optical glass is in reasonable supply and quality remains high. In fact, for large blanks this is the only reliable way to go unless you make your own ED glass as LZOS does.

I like the FS-series scopes, and have one now, and have had a couple of others. However, above 4" I don't find them to be particularly well color corrected visually. Even at 4" I can coax in-focus false color that is just detectable on very bright targets like Vega, Venus and Sirius. The 3" remains visually color free, but that's simply a function of the constant f/8 focal ratio for the line and the declining aperture.

That said, color correction isn't the do all to end all anyway. I find the figure quality on the FS scopes to be quite good, and the simple doublet design using extremely homogeneous fluorite scatters very little compared to harder glass doublets and triplets.

They're nice scopes. But even when they were being cleared out, they were relatively expensive given that they were totally "ala carte" and Tak accesories (clamshells, finders, etc.) are ridiculously expensive.

I also agree that folks selling them now are nuts. Hang on to them. The fluorite doublet is not coming back. As doublets go, these are about the ultimate iteration of the concept; the pinnacle of doublet refractor evolution.

Regards,

Jim


I agree, they are very nice scopes. I had an FS128 and enjoyed using it. As you noted the false color is there if you know where to look, particularly if you have a color free scope to side by side with it. It also contributes to the "warm" tone the image has in the FS (blue is out of focus). If I had not been offered an AP 130 EDF I would not have sold the FS.

#13 RodgerHouTex

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Posted 20 November 2012 - 02:51 PM

I intend to be buried with my FS-152!

#14 TG

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Posted 20 November 2012 - 03:39 PM

... He feels that the quality of large lenses are in decline, even to the point of shifting production to reflectors if the situation does not improve. That would be a sad day. How do people feel about the future trends, philosophy, and quality of optical glass?...


The real sad day for me was when I found out that TEC was no longer making their Maks. So you're saying there is hope yet! :jump:

Tanveer.

#15 Jarno

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Posted 20 November 2012 - 05:00 PM

I also agree that folks selling them now are nuts. Hang on to them. The fluorite doublet is not coming back.


A couple of years ago I bought a Vixen FL102 which uses the same Canon/Optron optics. If you ever see my scope for sale you'll know I'm either six feet under or own its Tak half-brother. 'Nuff said.

#16 Sky Muse

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Posted 20 November 2012 - 05:23 PM

I second that!

Alan

#17 M13 Observer

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Posted 20 November 2012 - 05:36 PM

... He feels that the quality of large lenses are in decline, even to the point of shifting production to reflectors if the situation does not improve. That would be a sad day. How do people feel about the future trends, philosophy, and quality of optical glass?...


The real sad day for me was when I found out that TEC was no longer making their Maks. So you're saying there is hope yet! :jump:

Tanveer.


I think Yuri said that the glass for the miniscus was getting incredibly expensive and he did not feel that there was a sufficient interest in an expensive Mak. He was thinking about making shorter focal length reflectors with near focus refractive corrector type systems instead, or something to that effect. One never knows until it is actually produced though.

#18 TG

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Posted 20 November 2012 - 06:14 PM

I think Yuri said that the glass for the miniscus was getting incredibly expensive and he did not feel that there was a sufficient interest in an expensive Mak.


The first part doesn't seem right as the meniscus is just BK7, the cheapest optical glass on the planet.

The second part I can agree with as Maks appeal to a limited segment except when it's the A-P Mak in which case everybody wants one.

Tanveer.

#19 vahe

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Posted 20 November 2012 - 06:53 PM

The first part doesn't seem right as the meniscus is just BK7, the cheapest optical glass on the planet.



Check out post #19837 on tec-ug.

Vahe

#20 10gauge

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Posted 20 November 2012 - 11:40 PM

Why are prices for premium glass expanding faster than the universe? The chemistry hasn't changed much, contrary to the fact that production techniques have improved and should have become cheaper over the years. Is it demand, labor, raw materials, facilities, or is it simply because that people will pay for such premium glass?

#21 Eddgie

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Posted 21 November 2012 - 12:40 AM

These kinds of questions come up from time to time, and without being in the business, you may never know the facts.

That means that I get to guess.

First, it isn't just the amount of something that is available (someone said BK7 is plentyful), but rather the amount of something that is suitable for the desired purpose.

And most people don't need 200mm x 80mm thick blocks of optical quality BK7.

And when no one is in line to buy a couple of thousand blanks of optical quality BK7, you take your giant furnace that costs tens of thoushands of dollars a month in energy to keep hot and you make stuff that people order by the pallate.

In business, it is always about profit and even if you get several hundred to several thousand dollars for a blank, these days, you will struggle to pay the energy bill if someone only want 20 of them.

But if you can make 10,000 small blanks for use in lenses and other small optics, then even though you don't make as much profit on each one, you make more money because of the volume.

While we can't know the exact reason, you can bet that it is the economics of it.

But if you place an order for 10,000 large BK7 blanks, I bet someone will make them for you.

But not a couple of dozen that a botique telescope maker might consume in a year.

Any time you see a question like this, remind yourself that big refractors are a very specialized and tiny market. No one is going to cater to it if they can make more money running their giant glass melting facilities to fill giant orders for other kinds of glass.

#22 vahe

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Posted 21 November 2012 - 07:32 AM

Why are prices for premium glass expanding faster than the universe? The chemistry hasn't changed much,



Chemistry is in fact one of the main reasons, environmental rules and restrictions play a major role in availability, what was once an easy solution is no longer permitted.

Vahe

#23 M13 Observer

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Posted 21 November 2012 - 10:38 AM

Why are prices for premium glass expanding faster than the universe? The chemistry hasn't changed much, contrary to the fact that production techniques have improved and should have become cheaper over the years. Is it demand, labor, raw materials, facilities, or is it simply because that people will pay for such premium glass?


As Vahe said:

Check out post #19837 on tec-ug.

If you can't read it, the succinct summary is that Yuri has quite a number of what initially "look" to be excellent pieces of said glass in sizes up to 12.5" sitting on a shelf. They are all useless for anything other than paperweights. This is due to the changes in the way said glass is made, changing to "environmentally friendly processes".

If you want more info, read his original post.

#24 TG

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Posted 21 November 2012 - 02:28 PM

Why are prices for premium glass expanding faster than the universe? The chemistry hasn't changed much, contrary to the fact that production techniques have improved and should have become cheaper over the years. Is it demand, labor, raw materials, facilities, or is it simply because that people will pay for such premium glass?


As Vahe said:

Check out post #19837 on tec-ug.

If you can't read it, the succinct summary is that Yuri has quite a number of what initially "look" to be excellent pieces of said glass in sizes up to 12.5" sitting on a shelf. They are all useless for anything other than paperweights. This is due to the changes in the way said glass is made, changing to "environmentally friendly processes".

If you want more info, read his original post.


Interesting but funny how Roland has never complained about BK7 (he's complained enough about FPL53). A-P currently sells a large scope with a large corrector which I suspect is BK7 and possibly the primary mirror as well is some BK7-like glass, being a Mangin mirror. I'm guessing about BK7 being the glass used in the A-P scope but most designs for the R-H astrograph I've seen here in the ATM group are BK7 based so I think my guess is probably correct. I wonder if Yuri's problem is particular to his glass supplier. In any case, it's a shame if that's what's stopping Yuri from building Maks. Maybe a corrected D-K would be more to his liking (and to mine if it's optimized for visual).

Tanveer.

#25 dscarpa

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Posted 21 November 2012 - 02:38 PM

SAs the owner of a IM-715D and mak fan in general I'm with you on that. David






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