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What if no manufacturer disclosed their lens glass?

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#1 25585

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Posted 10 January 2021 - 07:27 PM

Imagine... no fluorite, lanthanum, FPL#, FCD#, anything else to choose from. Just "apochromat" or "achromat" to go on, aperture, design & focal length. As in olden days.

 

Would you have bought differently, or less?  


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#2 wrvond

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Posted 10 January 2021 - 07:33 PM

No.  APO, aperture and focal length were the guiding factors.


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#3 Erik Bakker

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Posted 10 January 2021 - 07:34 PM

That would be paradise. Just evaluating a scope based on it’s performance under the stars, pure bliss.


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#4 JimP

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Posted 10 January 2021 - 08:28 PM

I would have purchased just as I did. I didn’t understand all the types of glass. Still don’t! Lol
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#5 Jon Isaacs

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Posted 10 January 2021 - 08:30 PM

That would be paradise. Just evaluating a scope based on it’s performance under the stars, pure bliss.

 

In the late 1990's Orion and others sold some ED Doublets based on FK-5. The TeleVue Pronto was called an ED scope and was based on FK-5 according to Roland Christen.  Technically this was ED glass but it provided achromatic performance. 

 

I bought a used Pronto in 2002 for $775.

 

I think people still buy used Prontos thinking they offer ED performance.

 

In 2003, Orion introduced the 80 mm F/7.5 refractor we know as the ED-80. Initially the particulars were unknown and many suspected it would be another FK-5 fake ED. The price certainly suggested it, $500. But then it was stated it was based on FPL-53 and the affordable apo/ED revolution began.

 

Optically, the Type of ED glass used is important in the color correction. Manufacturers like Kunming United and Long Perng often make two versions of the same scope, one based on FPL-51 class glass and one based on FPL-53 class glass. The cost difference can be quite large.

 

Scopes like these are commodities, and sellers buy them from the manufacturers and sell them under their label.  If I'm choosing between two 102 mm F/7 ED doublets,  there are two options, those based on ED glasses with Abbe numbers about 84 and those with Abbe numbers around 95.  The AT-102ED is an example of the former and costs $600, the AT-102EDL is an example of the latter and costs $1100.

 

You can read Roland's Abbe normal chart with annotations and see the longitudinal color errors of various combinations, you can look at Vlads polychromic Strehl pages, the differences in the color correction can be about a factor of two.

 

For someone shopping for a mid-level ED/apo, knowing what they're getting is an important part of the decision. Certainly there are other factors but the glass does make a big difference.  Without that information, how do you choose between vendor A selling a 102mm F/7 ED for $1100 and vendor B selling a 102 mm F/7 ED for $1100?

 

Who is selling you the AT-102ED and who is selling you the AT-102EDL?

 

How do you evaluate a scope under the stars if you have not yet purchased it?  How did people know the 2003 ED-80 was very likely to be far better than the 1990's 80 mm F/6.25 fake ED?

 

Some scopes have a well proven record. The NP-101 is not a commodity,  it's a complex dual ED design known to have excellent color correction. But when you're dealing with affordable ED refractors, the materials used are good to know. 

 

I've owned a number of affordable ED scopes, some with FPL-51 class ED, some with FPL-53.. there's a clear difference..

 

How many entry and mid level refractors have you owned???

 

Jon


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#6 junomike

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Posted 10 January 2021 - 08:36 PM

I think Jon hit on the topic as how can you determine what you're getting a paying for?

If that were the case I'd just buy the cheapest as there would be no guarantee for the more costlier item.

(I'm sure this wouldn't be the case with Tec, AP, CFF, Etc).


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#7 Stellar1

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Posted 10 January 2021 - 08:37 PM

John Lennon would be proud, i would have spent a lot less on an APO and, would have been just as happy.  Star parties would be a lot more interesting when we ask Tak owners how come their scopes cost so much more and they respond with "i have no idea, i just think the name is cool". 

 

Yes Tak owners, i'm aware of why they cost what they do, don't get all charged up lol.


Edited by Stellar1, 10 January 2021 - 08:43 PM.


#8 John Huntley

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Posted 10 January 2021 - 09:10 PM

I don't think it would have changed my purchasing decisions. I was more influenced by reports on how the scopes performed for other owners.


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#9 markb

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Posted 10 January 2021 - 09:11 PM

Not bliss, just a return to less information and unexpected disappointments.

 

Information and knowledge, as always, empower.

 

I am not a fan of Vegas-style astro purchasing.

 

Barring the fat wallet needed to buy and sell on if not satisfactory, or membership in a large, diverse astro user club, many users would end up 'eating' substandard or not-what-I-thought-it-was scopes.

 

It happened to me, when I bought a first 'real' scope a B&L 6000. Little did I know I would be a victim of the awful Dynamax tooling and cheap and or unsuitable corrector glass selection.

 

Who thought B&L could not be relied upon 

 

I am sure 'Halley Era' SCT clunker purchasers were unhappy too.

 

It lived in the closet for 35 years once I learned how to read a Ronchi test.

 

I then bought, and eventually sold, a large number of scopes to find what I liked and to learn what was good and not so good.

 

When I made my next full-retail, new, 'real' scope before retirement, glass type, combined with a trusted seller and APO, ED and now SD (wish I waited 8 months!) descriptions made all the difference in purchase confidence. Knowing rhe glass type used was important in setting CA expectations.

 

And I had no unpleasant surprises.

 

Even knowing the specific glass types is a major plus, allowing one to avoid the semi APOs that barely outperform achromats. Of course build quality, optical figures and polishing separate the mundane from the excellent.

 

Sure folks buy the most expensive, without research or knowledge, but buying a top brand has always been a safer way to avoid disappointment. Too bad we all can't do that.


Edited by markb, 10 January 2021 - 10:20 PM.

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#10 RedzoneMN

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Posted 10 January 2021 - 09:21 PM

It is the bane of this hobby that when starting out, most astronomy purchases are not the right ones and eventually you acquire the costly wisdom to know otherwise. 


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#11 Scott in NC

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Posted 10 January 2021 - 09:37 PM

It is the bane of this hobby that when starting out, most astronomy purchases are not the right ones and eventually you acquire the costly wisdom to know otherwise. 

Fortunately, the ability to take advantage of the shared experiences from this community has helped me to make many more “right” purchase decisions than I was able to make before I found CN.  Before then it was much more trial-and-error.  


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#12 SandyHouTex

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Posted 10 January 2021 - 10:03 PM

I don’t buy anything unless I know what it’s made of.  I don’t buy “ultra-wide”, “super-wide”, etc., etc., eyepieces just for that reason.  Same with refractors.  If you don’t tell me what glass you use, I look elsewhere and you lose the sale.


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#13 Bomber Bob

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Posted 10 January 2021 - 10:26 PM

Imagine... no fluorite, lanthanum, FPL#, FCD#, anything else to choose from. Just "apochromat" or "achromat" to go on, aperture, design & focal length. As in olden days.

 

Would you have bought differently, or less?  

Nope.  I base my buying decisions more on threads, posts, reviews, etc. on CN & other sources; my intended uses for the scope; and, cost (total, including mount & accessories).

 

If NONE of the makers disclosed the glasses used, that would encourage posting Lab Reports (individually, or typical for the model / series).  Personally, I'd rather see that information.

 

Thanks to the Internet, CN, and personal DPAC rigs, us buyers can quickly assess the quality of our new scopes; and, send the duds back.  We can get the word out.  Knowing that Scope X uses FPL-53 isn't as critical as knowing Scope X was ground & polished on a pottery wheel; or, has zone(s) deep enough for a finger-bowl...


Edited by Bomber Bob, 10 January 2021 - 10:37 PM.

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#14 teashea

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Posted 10 January 2021 - 10:32 PM

I would have purchased based on the reviews, test reports, reputation of the manufacturer and my personal preferences.  For me that mean just about any telescope that Takahashi makes.  The precise composition and design of the lens is extremely important.  I believe that the lens designers at the top manufacturing companies know more that I could conceivably know (there is an understatement). 

 

The precise manner in which they design their lenses is something for them to decide.  I will enjoy the fruits of their hard and intelligent work.  

 

I do find it very interesting to read and study about lens design.  It is a fascinating subject to me.  So, I am glad that there is at least some information regarding how they design the lenses and what glass they use.

 

I note that even within the lineup of one manufacturer, say Takahashi, there is a wide variety of lens designs.  I have recently purchased a TSA 120, FC100DC, FC76DS and FS60Q.  Each has a different design philosophy and approach.  But, each is successful, in my opinion.  

 

 

 

Tom


Edited by teashea, 10 January 2021 - 10:33 PM.

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#15 havasman

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Posted 10 January 2021 - 10:36 PM

I don't know what glass is in my refractor and I don't care. So it wouldn't change anything. I like my refractor because it works for me very nicely. All that fuss over glass, well they won't print what I think of it but it's not what you want to step in in the pasture if you're barefooted.


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#16 teashea

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Posted 10 January 2021 - 10:36 PM

Fortunately, the ability to take advantage of the shared experiences from this community has helped me to make many more “right” purchase decisions than I was able to make before I found CN.  Before then it was much more trial-and-error.  

I am also grateful to have CN as a resource.  It is full of excellent information by some very knowledgeable people.  Without it, it would be much more difficult to determine what to buy and what to leave alone.  



#17 teashea

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Posted 10 January 2021 - 10:43 PM

In the late 1990's Orion and others sold some ED Doublets based on FK-5. The TeleVue Pronto was called an ED scope and was based on FK-5 according to Roland Christen.  Technically this was ED glass but it provided achromatic performance. 

 

I bought a used Pronto in 2002 for $775.

 

I think people still buy used Prontos thinking they offer ED performance.

 

In 2003, Orion introduced the 80 mm F/7.5 refractor we know as the ED-80. Initially the particulars were unknown and many suspected it would be another FK-5 fake ED. The price certainly suggested it, $500. But then it was stated it was based on FPL-53 and the affordable apo/ED revolution began.

 

Optically, the Type of ED glass used is important in the color correction. Manufacturers like Kunming United and Long Perng often make two versions of the same scope, one based on FPL-51 class glass and one based on FPL-53 class glass. The cost difference can be quite large.

 

Scopes like these are commodities, and sellers buy them from the manufacturers and sell them under their label.  If I'm choosing between two 102 mm F/7 ED doublets,  there are two options, those based on ED glasses with Abbe numbers about 84 and those with Abbe numbers around 95.  The AT-102ED is an example of the former and costs $600, the AT-102EDL is an example of the latter and costs $1100.

 

You can read Roland's Abbe normal chart with annotations and see the longitudinal color errors of various combinations, you can look at Vlads polychromic Strehl pages, the differences in the color correction can be about a factor of two.

 

For someone shopping for a mid-level ED/apo, knowing what they're getting is an important part of the decision. Certainly there are other factors but the glass does make a big difference.  Without that information, how do you choose between vendor A selling a 102mm F/7 ED for $1100 and vendor B selling a 102 mm F/7 ED for $1100?

 

Who is selling you the AT-102ED and who is selling you the AT-102EDL?

 

How do you evaluate a scope under the stars if you have not yet purchased it?  How did people know the 2003 ED-80 was very likely to be far better than the 1990's 80 mm F/6.25 fake ED?

 

Some scopes have a well proven record. The NP-101 is not a commodity,  it's a complex dual ED design known to have excellent color correction. But when you're dealing with affordable ED refractors, the materials used are good to know. 

 

I've owned a number of affordable ED scopes, some with FPL-51 class ED, some with FPL-53.. there's a clear difference..

 

How many entry and mid level refractors have you owned???

 

Jon

Jon, very intelligent and articulate.  The glass does make a difference.  



#18 teashea

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Posted 10 January 2021 - 10:45 PM

John Lennon would be proud, i would have spent a lot less on an APO and, would have been just as happy.  Star parties would be a lot more interesting when we ask Tak owners how come their scopes cost so much more and they respond with "i have no idea, i just think the name is cool". 

 

Yes Tak owners, i'm aware of why they cost what they do, don't get all charged up lol.

I chose Takahashi telescopes because of their performance and quality.


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#19 Wildetelescope

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Posted 10 January 2021 - 11:39 PM

In the late 1990's Orion and others sold some ED Doublets based on FK-5. The TeleVue Pronto was called an ED scope and was based on FK-5 according to Roland Christen.  Technically this was ED glass but it provided achromatic performance. 

 

I bought a used Pronto in 2002 for $775.

 

I think people still buy used Prontos thinking they offer ED performance.

 

In 2003, Orion introduced the 80 mm F/7.5 refractor we know as the ED-80. Initially the particulars were unknown and many suspected it would be another FK-5 fake ED. The price certainly suggested it, $500. But then it was stated it was based on FPL-53 and the affordable apo/ED revolution began.

 

Optically, the Type of ED glass used is important in the color correction. Manufacturers like Kunming United and Long Perng often make two versions of the same scope, one based on FPL-51 class glass and one based on FPL-53 class glass. The cost difference can be quite large.

 

Scopes like these are commodities, and sellers buy them from the manufacturers and sell them under their label.  If I'm choosing between two 102 mm F/7 ED doublets,  there are two options, those based on ED glasses with Abbe numbers about 84 and those with Abbe numbers around 95.  The AT-102ED is an example of the former and costs $600, the AT-102EDL is an example of the latter and costs $1100.

 

You can read Roland's Abbe normal chart with annotations and see the longitudinal color errors of various combinations, you can look at Vlads polychromic Strehl pages, the differences in the color correction can be about a factor of two.

 

For someone shopping for a mid-level ED/apo, knowing what they're getting is an important part of the decision. Certainly there are other factors but the glass does make a big difference.  Without that information, how do you choose between vendor A selling a 102mm F/7 ED for $1100 and vendor B selling a 102 mm F/7 ED for $1100?

 

Who is selling you the AT-102ED and who is selling you the AT-102EDL?

 

How do you evaluate a scope under the stars if you have not yet purchased it?  How did people know the 2003 ED-80 was very likely to be far better than the 1990's 80 mm F/6.25 fake ED?

 

Some scopes have a well proven record. The NP-101 is not a commodity,  it's a complex dual ED design known to have excellent color correction. But when you're dealing with affordable ED refractors, the materials used are good to know. 

 

I've owned a number of affordable ED scopes, some with FPL-51 class ED, some with FPL-53.. there's a clear difference..

 

How many entry and mid level refractors have you owned???

 

Jon

Hi Jon,

     The mid to late 90’s pre-date my awareness of such things as apo vs achromat.  Out of curiosity, what was out there to compete with the Pronto and the Orion scopes that could be considered even closely apochromatic in their price range.   Also, how did the Pronto perform relative to achromat s with the same focal ratio?   Just curious about the context of what was available when these scopes were introduced.  

 

Cheers!

 

JMD


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#20 Wildetelescope

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Posted 11 January 2021 - 12:03 AM

Imagine... no fluorite, lanthanum, FPL#, FCD#, anything else to choose from. Just "apochromat" or "achromat" to go on, aperture, design & focal length. As in olden days.

 

Would you have bought differently, or less?  

If one understands the appropriate context, then knowledge of the glass type can be helpful.  The challenge is that a telescope is a system.   A while back I got a chance to look through a synta 100 mm ED owned by an acquaintance.  The target was the Pleiades.  Try as I might, I could not get the stars to sharpen up with focus.  The view through my son’s f11 60 mm achromat was MUCH sharper,  as was the view through my vintage 127mm AP non-ed  triplet.  The comparison was made at an outreach event  There could have been many reasons for this, including the economy eyepiece that was used in the 100mm ED.   My point is that there are many things that go into what you see through the eyepiece and that the telescope and eyepiece must be considered as a system.  Assuming all other factors are equal, glass type can be a fair indication of the level of control of CA.  But that IS a big assumption.  I do not consider ANY of my refractors as truly apochromatic.  But I enjoy all of them.   The level of color that I do see on occasion is trivial to my eyes.  Other peoples eyes might come to a different conclusion:-). As they say, YMMV!

 

Cheers!

 

JMD


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#21 Mitrovarr

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Posted 11 January 2021 - 12:19 AM

Imagine... no fluorite, lanthanum, FPL#, FCD#, anything else to choose from. Just "apochromat" or "achromat" to go on, aperture, design & focal length. As in olden days.

 

Would you have bought differently, or less?  

No, not the one "apochromat" I have. That manufacturer didn't disclose the glass and I wasn't under the impression it would be perfectly color free.

 

I will say it would make other purchases harder, particularly for telescopes that might be used for AP. With ED doublet pairs you really need to know what the glass is, as a FPL-53/FCD-100 based scope is mostly color free and suitable for basic AP at least, and a FPL-51 based scope has a fair bit and is mostly good for visual use. When you get into triplets and stuff it gets hard to parse out glass types from other aspects of the design and you probably just need to go to reviews.


Edited by Mitrovarr, 11 January 2021 - 12:19 AM.


#22 Jon Isaacs

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Posted 11 January 2021 - 03:05 AM

Nope.  I base my buying decisions more on threads, posts, reviews, etc. on CN & other sources; my intended uses for the scope; and, cost (total, including mount & accessories).

 

If NONE of the makers disclosed the glasses used, that would encourage posting Lab Reports (individually, or typical for the model / series).  Personally, I'd rather see that information.

 

Thanks to the Internet, CN, and personal DPAC rigs, us buyers can quickly assess the quality of our new scopes; and, send the duds back.  We can get the word out.  Knowing that Scope X uses FPL-53 isn't as critical as knowing Scope X was ground & polished on a pottery wheel; or, has zone(s) deep enough for a finger-bowl...

 

Realistically, they're all made by just a few companies and theyre all quite decent. 

 

None of them are ground and polished poorly.. 

 

One thought:  if you're going to make a quality refractor, part of that starts with using the best materials.  In this case materials make real differences. Vlads page on Polychromatic Strehl is down but it shows the differences. 

 

Jon


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#23 Chuck2

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Posted 11 January 2021 - 03:12 AM

I think everyone missed the OPs question...

 

What if the type of glass was never known, never became a marketing selling point, was never disclosed by any manufacturer? How would you know what scope was best to buy?

 

Obviously word of mouth, recommendations by friends, sponsored ads by scientific community or demonstrations by local astronomy clubs would become important.

 

Think back to the 50's and 60's when endorsement by a respected organization, corporation or movie star was 'proof' of quality. Even Leonard  Nimoy and David Levy have promoted commercial scopes. Would we ever deny their judgement and credibility?

 

Brand name recognition would also dominate. People bought Cadillacs just because they were Cadillacs. Even the word 'Cadillac' became associated with the best.  People associated Unitron refractors and Cave reflectors as the Cadillacs of the 60's and 70's yet I never saw an ad stating the glass used in a Unitron.

 

Just as Rolls Royce became synonymous for quality, so did Celestron in the 70's. Everyone wanted a C-8, and I can't recall that the glass used to produce the mirrors or correctors was ever placed in their ads. Nonetheless, everyone bought and enjoyed their C-8 and Celestron grew to an industry giant.

 

Yes, the industry has grown to associate glass type with quality, but in the 50's, 60's and 70's we never had that info, and yet we still enjoyed the hobby and some fine equipment.

 

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Edited by Chuck2, 11 January 2021 - 03:19 AM.

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#24 John Huntley

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Posted 11 January 2021 - 12:58 PM

I don’t buy anything unless I know what it’s made of.  I don’t buy “ultra-wide”, “super-wide”, etc., etc., eyepieces just for that reason.  Same with refractors.  If you don’t tell me what glass you use, I look elsewhere and you lose the sale.

When told, do you accept the manufacturer / vendors word or do you have the materials tested yourself to be sure ?



#25 rexowner

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Posted 11 January 2021 - 01:43 PM

Imagine... no fluorite, lanthanum, FPL#, FCD#, anything else to choose from. Just "apochromat" or "achromat" to go on, aperture, design & focal length. As in olden days.

 

Would you have bought differently, or less?

Tele Vue doesn't disclose the glass, and my main scopes are a TV-85 and NP-127is, so I guess I wouldn't have

done anything differently.

 

It's true that with a good design, it's possible to get a better dispersion curve with certain glasses over others,

but unless you're an optical designer, it's the compound result that counts IMO


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