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What if no manufacturer disclosed their lens glass?

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#26 25585

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Posted 11 January 2021 - 06:58 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

Mine go from Vixen & S-W ST80 achromats as entry scopes to the S-W Equinox FPL53 Schott Ohara range for mid level (80 Equinox not as good as the ED80).

 

Disregarding price, my TV-85s & TV-102 are mid-level optically, but like 100 & 120 Equinox, they are good mid. Really for the magnifications I use, those 4 would be enough. I found out recommendations were good from use, then that the glass was mainly why.

 

I bought a TV-85 on the strength of my original Genesis and having a TV mount already. I was sceptical about Chinese scopes, until the Equinoxes proved themselves good, but also consider myself lucky. This scepticism remains deep so...

 

..I bought a couple of Takahashi apo refractors. Always a fan of Japanese lenses dating back to the early 1980s camera systems from Canon, Minolta, Tamron and Vivitar. My eyepieces are 60% Japanese, all makes, binoculars 80%. No disappointments. I trust Japanese made optics & QC/QM, they have earned it.

 

Similar with then East German v West German optics (had both) in the Soviet era. 

 

Country of manufacture then/now has & continues influencing what and how much I buy from whom from 40 years as an optics consumer.   


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#27 Jon Isaacs

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Posted 12 January 2021 - 09:13 AM

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.

 

 

scratchhead2.gif

 

In my mind, an endorsement by a movie star has zero meaning. The David Levy Comet hunter is not of the quality of an Intes-Micro Mak-Newt. It's an Explore Scientic made to a pricepoint.

 

And Cadillac, they put out some real junk... just trading on their name. The days when a Cadillac was a Cadillac are long gone.

 

Celestron is now pointing out the white water glass correctors have better transmission than the older ones. The Starbright XLT has better coatings than the Starbright, about 10% better, and the Starbright were better than the early coatings, if they were coated at all.

 

In the 60s and 70s, there was no ED glass, there were no interferometers to test the optics, people weren't making thin quartz mirrors that were nearprice point. Today's scopes are much more sophisticated, much better, the buyer has to be more knowledgeable..

 

I'm an engineer/researcher by trade. Knowing about what I'm buying and knowing what I'm buying is important. Endorsements,  Sure, when Roland Christen said the Mike Lockwood mirror he tested had the finest figure he'd ever seen, that carried some weight.

 

David Levy endorsing the Comet Hunter.. not really.

 

Jon


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#28 RichA

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Posted 12 January 2021 - 09:58 AM

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

Not really.  No one would have a clue as to where to start.


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#29 mikeDnight

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Posted 12 January 2021 - 05:32 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?  

If that were the case, I think we'd quickly revert to how we were years ago, when owning any refractor gave the observer a quiet confidence. Nobody cared about glass types, they just knew that their refractor really delivered the goods way beyond its aperture class.

My observing buddy Derek, who was my mentor 40 years ago and who started me along the refractor route, told me a nice story. After attending a meeting at Manchester Astronomical Society in the 1960's, he got involved in the usual refractor vs reflector debate. But he noticed an elderly gent sat by himself puffing away on his pipe. Derek walked over to ask him why he wasn't getting involved in the debate. The elderly gent simply replied " Just leave em to it lad"! Derek being curious asked the man what scope he had. The man replied " I have a 6" Cooke refractor. Would you like to see it"? Derek immediately said yes and arranged to visit the man's observatory, somewhere in Cheshire England. He recalls walking down a garden path towards a beautiful Domed observatory. On entering, there before him was a gorgeous 6" F15 Cooke all in polished brass, and mounted on an equally gorgeous German equatorial. He was in awe!

 I don't smoke, but if I did I'd smoke a pipe just like that contented old man. He had no need to debate aperture or glass types, nor did he feel the need to defend his reasons for his scope choice. He owned a Cooke refractor, and back in the 1960's that almost gave him a god like status among amateurs.

 I think that if we didn't know glass types and debate the ins and outs of every detail, we'd simply get on with observing, completely content in the knowledge we have a great refractor that will often leave larger scopes standing.


Edited by mikeDnight, 12 January 2021 - 05:36 PM.

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#30 LDW47

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Posted 12 January 2021 - 07:16 PM

If that were the case, I think we'd quickly revert to how we were years ago, when owning any refractor gave the observer a quiet confidence. Nobody cared about glass types, they just knew that their refractor really delivered the goods way beyond its aperture class.

My observing buddy Derek, who was my mentor 40 years ago and who started me along the refractor route, told me a nice story. After attending a meeting at Manchester Astronomical Society in the 1960's, he got involved in the usual refractor vs reflector debate. But he noticed an elderly gent sat by himself puffing away on his pipe. Derek walked over to ask him why he wasn't getting involved in the debate. The elderly gent simply replied " Just leave em to it lad"! Derek being curious asked the man what scope he had. The man replied " I have a 6" Cooke refractor. Would you like to see it"? Derek immediately said yes and arranged to visit the man's observatory, somewhere in Cheshire England. He recalls walking down a garden path towards a beautiful Domed observatory. On entering, there before him was a gorgeous 6" F15 Cooke all in polished brass, and mounted on an equally gorgeous German equatorial. He was in awe!

 I don't smoke, but if I did I'd smoke a pipe just like that contented old man. He had no need to debate aperture or glass types, nor did he feel the need to defend his reasons for his scope choice. He owned a Cooke refractor, and back in the 1960's that almost gave him a god like status among amateurs.

 I think that if we didn't know glass types and debate the ins and outs of every detail, we'd simply get on with observing, completely content in the knowledge we have a great refractor that will often leave larger scopes standing.

Oh for those old days again ! In many things.


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#31 LDW47

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Posted 12 January 2021 - 07:18 PM

Not really.  No one would have a clue as to where to start.

They would just have to satisfy themselves with no explanations required !



#32 LDW47

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Posted 12 January 2021 - 07:27 PM

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.

Did Leonard ever really look through a telescope and understand what he was seeing ? Cadillacs are great cars until you have to repair them at double and triple the cost than a regular car just because of the name on the part which many times was the same part. The Eldorado for example, front wheel drive, air lift shocks etc were nice to drive but boy the costs to repair ! To use them as some sort of example, some sort of comparison may not ............ ?


Edited by LDW47, 12 January 2021 - 07:29 PM.


#33 LDW47

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Posted 12 January 2021 - 07:31 PM

Mine go from Vixen & S-W ST80 achromats as entry scopes to the S-W Equinox FPL53 Schott Ohara range for mid level (80 Equinox not as good as the ED80).

 

Disregarding price, my TV-85s & TV-102 are mid-level optically, but like 100 & 120 Equinox, they are good mid. Really for the magnifications I use, those 4 would be enough. I found out recommendations were good from use, then that the glass was mainly why.

 

I bought a TV-85 on the strength of my original Genesis and having a TV mount already. I was sceptical about Chinese scopes, until the Equinoxes proved themselves good, but also consider myself lucky. This scepticism remains deep so...

 

..I bought a couple of Takahashi apo refractors. Always a fan of Japanese lenses dating back to the early 1980s camera systems from Canon, Minolta, Tamron and Vivitar. My eyepieces are 60% Japanese, all makes, binoculars 80%. No disappointments. I trust Japanese made optics & QC/QM, they have earned it.

 

Similar with then East German v West German optics (had both) in the Soviet era. 

 

Country of manufacture then/now has & continues influencing what and how much I buy from whom from 40 years as an optics consumer.   

I think the 80 Equinox is better than the ED !



#34 25585

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Posted 13 January 2021 - 04:39 AM

I think the 80 Equinox is better than the ED !

Its a handier size and can be back packed easier. Nice rich field scope.



#35 Jon Isaacs

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Posted 13 January 2021 - 08:16 AM

If that were the case, I think we'd quickly revert to how we were years ago, when owning any refractor gave the observer a quiet confidence. Nobody cared about glass types, they just knew that their refractor really delivered the goods way beyond its aperture class.

My observing buddy Derek, who was my mentor 40 years ago and who started me along the refractor route, told me a nice story. After attending a meeting at Manchester Astronomical Society in the 1960's, he got involved in the usual refractor vs reflector debate. But he noticed an elderly gent sat by himself puffing away on his pipe. Derek walked over to ask him why he wasn't getting involved in the debate. The elderly gent simply replied " Just leave em to it lad"! Derek being curious asked the man what scope he had. The man replied " I have a 6" Cooke refractor. Would you like to see it"? Derek immediately said yes and arranged to visit the man's observatory, somewhere in Cheshire England. He recalls walking down a garden path towards a beautiful Domed observatory. On entering, there before him was a gorgeous 6" F15 Cooke all in polished brass, and mounted on an equally gorgeous German equatorial. He was in awe!

 I don't smoke, but if I did I'd smoke a pipe just like that contented old man. He had no need to debate aperture or glass types, nor did he feel the need to defend his reasons for his scope choice. He owned a Cooke refractor, and back in the 1960's that almost gave him a god like status among amateurs.

 I think that if we didn't know glass types and debate the ins and outs of every detail, we'd simply get on with observing, completely content in the knowledge we have a great refractor that will often leave larger scopes standing.

Well..

 

Realistically, today's scopes are much better than they were 40 years ago. 

 

Nobody knew the glass types because they were all achromats except for a very few.. And those you did know. Zeiss apos, maybe something from Japan with Fluorite..

 

Refractors don't deliver the goods befond their aperture, a top refractor performs as its aperture should.

 

Is ignorance bliss?

 

Jon


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#36 wrvond

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Posted 13 January 2021 - 08:24 AM

Well..

 

Realistically, today's scopes are much better than they were 40 years ago. 

 

Nobody knew the glass types because they were all achromats except for a very few.. And those you did know. Zeiss apos, maybe something from Japan with Fluorite..

 

Refractors don't deliver the goods befond their aperture, a top refractor performs as its aperture should.

 

Is ignorance bliss?

 

Jon

In some respects yes, ignorance is bliss.

I've never looked through a Takahashi. My Sky-Watcher 120 ED APO is the highest quality I've used.

In my ignorance I'm perfectly happy with it, but probably wouldn't be if I spent time with a truly high end scope.


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#37 bobhen

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Posted 13 January 2021 - 08:25 AM

Back in 1989 I bought an AP 152 F9 triplet. I don’t believe the glass used was disclosed, or if it was it didn’t mean much to me at the time. However, AP supplied color-crossing diagrams that showed CA to be equal to a Tak FS 152 Fluorite doublet. At the time, the AP 152 was about $7,000 less than the Tak! So I could save 7K and get the same color correction as the Tak. This made for an easy decision.

 

Bob


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#38 John Huntley

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Posted 13 January 2021 - 09:48 AM

In some respects yes, ignorance is bliss.

I've never looked through a Takahashi. My Sky-Watcher 120 ED APO is the highest quality I've used.

In my ignorance I'm perfectly happy with it, but probably wouldn't be if I spent time with a truly high end scope.

You might be pleasantly surprised by the ED120.

 

I have one and also a Takahashi FC100-DL and a TMB/LZOS 130 F/9.2 triplet. The ED120 holds its head up well in performance terms. There are differences but not as marked as I thought they might be. The ED120 is a very good refractor.


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#39 LDW47

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Posted 13 January 2021 - 09:54 AM

In some respects yes, ignorance is bliss.

I've never looked through a Takahashi. My Sky-Watcher 120 ED APO is the highest quality I've used.

In my ignorance I'm perfectly happy with it, but probably wouldn't be if I spent time with a truly high end scope.

Or maybe you might still be happy afterwards ??


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#40 25585

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Posted 13 January 2021 - 10:14 AM

I can vouch for the ED120 as well. Its better than the ED100 choosing between both and the 120 is closer to my Tak DL. Bit warmer, but suits Mars, Jupiter & for G to C spectral class stars.


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#41 SandyHouTex

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Posted 13 January 2021 - 07:44 PM

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

I accept the vendors word unless there have been truth issues before.


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