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Why specify glass type if you don't specify optical accuracy?

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#1 RichA

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Posted 11 January 2021 - 12:27 AM

Is it all marketing?  Deflecting a more important question?  Glass types obviously matter, you want to know that to know colour correction but no optical test means correction could be an issue.  I'd like to know that as much as glass type.


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#2 Mitrovarr

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Posted 11 January 2021 - 12:42 AM

Manufacturers hate to specify optical accuracy for a number of reasons. One of these is that they're afraid that people will send in scopes near the lower end of the tolerance range in hopes of 'rerolling' them for better optics. I.e. if the scope specifies a minimum strehl of 0.95 and most people get between 0.97-0.98, the guy who gets 0.955 is going to probably end up as a return.


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#3 alan.dang

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Posted 11 January 2021 - 12:49 AM

It’s definitely marketing in the present day where ED glass is readily available. I can see it being special in the old days were semi-APO glass was common and any type of unique dispersion was special.

Stellarvue and Questar optics can be purchased with test reports.

TEC will not give individual reports but have shared “batch averages” while Astro Physics just has a minimum specification that is very good.

One of the reasons why people respect Takahashi optics so much is that they have a high level of consistency with wait times in months not years. Even then, they do not offer individual test reports.
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#4 bobzeq25

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Posted 11 January 2021 - 01:39 AM

Marketing is the main reason.  But, still..

 

There's a strong correlation (not perfect) between glass type and optical quality.   People who make nice scopes tend to use good glass.

 

The real situation is that optical testing is rare.  Who would do it?  The Chinese factory that made the scope?  The vendor usually doesn't have the equipment or the expertise.  It would raise the price of inexpensive scopes "too much", and they'd get killed in the marketplace.

 

It should be noted that if you buy a scope from Karl Kloss, you can get a simple optical test of your specific scope.  Not perfect, good enough to provide some assurance you didn't get a bad one.  Why I bought my TS 130 F7 from him.

 

https://www.teleskop...8af911a1ce0bee6


Edited by bobzeq25, 11 January 2021 - 01:46 AM.


#5 db2005

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Posted 11 January 2021 - 01:41 AM

I would say specifying the glass type without stating the optical accuracy is primarily a marketing gimmick. Yet one could say exactly the same thing about specifying the glass type of one element without disclosing the glass type of the other element. And how about disclosing the different grades of optical glass? And how about the lens radii? We could go on, and we're probably now dealing with trade secrets which manufacturers have little interest in disclosing because of the risk of being copied.

 

The almost universal FPL-53 marketing hype that has been going on for the last 15-20 years may have led many unsuspecting prospective buyers to believe that all FPL-53 doublets are created equal (yes, I fell for that too, in case you are wondering), and that you need only to buy the cheapest optic with the FPL-53 tag to get world-glass optics. But comparing the views through a typical Synta ED doublet with a Vixen SD81S reveals that all FPL53-doublets are not created equal.


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#6 gwlee

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Posted 11 January 2021 - 04:08 AM

Is it all marketing?  Deflecting a more important question?  Glass types obviously matter, you want to know that to know colour correction but no optical test means correction could be an issue.  I'd like to know that as much as glass type.

Most consumers would. Manufacturers usually have internal optical accuracy specifications, but usually choose not to disclose them for various reasons, some high sounding. Things seem to be moving ever so slowly in the consumer’s direction, and only purchasing instruments from manufacturers that provide the information you want will accelerate that trend. 



#7 Simoes Pedro

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Posted 11 January 2021 - 04:26 AM

Marketing is the main reason.  But, still..

 

There's a strong correlation (not perfect) between glass type and optical quality.   People who make nice scopes tend to use good glass.

 

The real situation is that optical testing is rare.  Who would do it?  The Chinese factory that made the scope?  The vendor usually doesn't have the equipment or the expertise.  It would raise the price of inexpensive scopes "too much", and they'd get killed in the marketplace.

 

It should be noted that if you buy a scope from Karl Kloss, you can get a simple optical test of your specific scope.  Not perfect, good enough to provide some assurance you didn't get a bad one.  Why I bought my TS 130 F7 from him.

 

https://www.teleskop...8af911a1ce0bee6

Glass type and optical quality are very loosely correlated, at best. 


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#8 dan_1984

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Posted 11 January 2021 - 08:16 AM

Is it all marketing?  Deflecting a more important question?  Glass types obviously matter, you want to know that to know colour correction but no optical test means correction could be an issue.  I'd like to know that as much as glass type.

If you buy high end stuff, they send an optical test report



#9 junomike

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Posted 11 January 2021 - 08:50 AM

IMO very few manufacturers are going to "waste" premium glass on poor optical figure and/or quality.

Sure, some may be better then others, but overall they are usually all in the same league


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#10 LDW47

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Posted 11 January 2021 - 09:07 AM

It’s definitely marketing in the present day where ED glass is readily available. I can see it being special in the old days were semi-APO glass was common and any type of unique dispersion was special.

Stellarvue and Questar optics can be purchased with test reports.

TEC will not give individual reports but have shared “batch averages” while Astro Physics just has a minimum specification that is very good.

One of the reasons why people respect Takahashi optics so much is that they have a high level of consistency with wait times in months not years. Even then, they do not offer individual test reports.

And you pay big bucks for that perceived consistency with little gain for the majority of astronomers with average eyes under average-good skize ! And then you say they still don’t offer individual reports ??



#11 bobhen

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Posted 11 January 2021 - 09:36 AM

Test reports from the manufacturer who made the optics are in many cases also part of marketing. There are many ways to fudge or manipulate those reports that make them look better than the optic might be. A minimum optical quality guarantee is all that is required. Synta offers diffraction limited, Astro-Physics offers 98% Sterhl. That’s all you need to know as far as optical quality is concerned.

 

It is also important to know the glass used, especially for imagers, as speed and a high level of color correction are desired. Color crossing diagrams and spot diagrams would be nice to see from manufacturers in place of ad copy fluff.

 

The bottom line is: a high level of optical figure and high quality glass used means a manufacture can and should charge more. The problem is when marking is used with false test reports or ad copy exaggerations etc. to charge more “instead” of using high quality glass and delivering high optical quality. Then the consumer is not getting what he or she paid for.

 

In some cases no glass is ever defined and the only optical guarantee is diffraction limited.  And yet people still pay thousands for those refractors. The consumer should demand more, even if the price is low. And if the price is high, the consumer should demand “outside certification and verification” of that high quality that they are paying more for.

 

Some manufacturers have been around for almost half a century and their optics have been reviewed and tested many times. New manufactures offering new products should be more accountable to the consumer.

 

Bob


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#12 Jon Isaacs

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Posted 11 January 2021 - 10:22 AM

Mike of Astronomics said he paid a premium to have the manufacturer of the AT-102EDL guaranty the Strehl was at least 0.95. 

 

https://www.astronom...-7-doublet.html

 

The glass types are also specified as being FCD-100 with a Lanthinum mating element.

 

I'd buy one.

 

Jon


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#13 RichA

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Posted 11 January 2021 - 10:34 AM

Marketing is the main reason.  But, still..

 

There's a strong correlation (not perfect) between glass type and optical quality.   People who make nice scopes tend to use good glass.

 

The real situation is that optical testing is rare.  Who would do it?  The Chinese factory that made the scope?  The vendor usually doesn't have the equipment or the expertise.  It would raise the price of inexpensive scopes "too much", and they'd get killed in the marketplace.

 

It should be noted that if you buy a scope from Karl Kloss, you can get a simple optical test of your specific scope.  Not perfect, good enough to provide some assurance you didn't get a bad one.  Why I bought my TS 130 F7 from him.

 

https://www.teleskop...8af911a1ce0bee6

I think a couple retail companies offered actual guarantees of tested optics for SCT's a while back, but then so was Celestron themselves.



#14 SandyHouTex

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Posted 11 January 2021 - 10:51 AM

Telling what glass is used will tell you how good the scope can be.  I don’t know of any manufacturer, including the Chinese, that doesn’t guarantee at least “diffraction limited” which means 1/4 wave or better at the focal plane.  I have star tested every scope I’ve bought, and returned a few with astigmatism or that didn’t meet the 1/4 wave of spherical aberration test.  None of the vendors have quibbled about replacing them.


Edited by SandyHouTex, 11 January 2021 - 10:52 AM.

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#15 LDW47

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Posted 11 January 2021 - 12:17 PM

Test reports from the manufacturer who made the optics are in many cases also part of marketing. There are many ways to fudge or manipulate those reports that make them look better than the optic might be. A minimum optical quality guarantee is all that is required. Synta offers diffraction limited, Astro-Physics offers 98% Sterhl. That’s all you need to know as far as optical quality is concerned.

 

It is also important to know the glass used, especially for imagers, as speed and a high level of color correction are desired. Color crossing diagrams and spot diagrams would be nice to see from manufacturers in place of ad copy fluff.

 

The bottom line is: a high level of optical figure and high quality glass used means a manufacture can and should charge more. The problem is when marking is used with false test reports or ad copy exaggerations etc. to charge more “instead” of using high quality glass and delivering high optical quality. Then the consumer is not getting what he or she paid for.

 

In some cases no glass is ever defined and the only optical guarantee is diffraction limited.  And yet people still pay thousands for those refractors. The consumer should demand more, even if the price is low. And if the price is high, the consumer should demand “outside certification and verification” of that high quality that they are paying more for.

 

Some manufacturers have been around for almost half a century and their optics have been reviewed and tested many times. New manufactures offering new products should be more accountable to the consumer.

 

Bob

Even the long timers can stretch their statements because they know 99.9% of the time they will be forgiven if they are found out, no one is absolutely perfect in most eyes until you get the bill for the price of the scope ! Its not just in telescopes, lol !



#16 LDW47

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Posted 11 January 2021 - 12:18 PM

Telling what glass is used will tell you how good the scope can be.  I don’t know of any manufacturer, including the Chinese, that doesn’t guarantee at least “diffraction limited” which means 1/4 wave or better at the focal plane.  I have star tested every scope I’ve bought, and returned a few with astigmatism or that didn’t meet the 1/4 wave of spherical aberration test.  None of the vendors have quibbled about replacing them.

They must be happy to get your phone call, lol !



#17 LDW47

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Posted 11 January 2021 - 12:21 PM

Mike of Astronomics said he paid a premium to have the manufacturer of the AT-102EDL guaranty the Strehl was at least 0.95. 

 

https://www.astronom...-7-doublet.html

 

The glass types are also specified as being FCD-100 with a Lanthinum mating element.

 

I'd buy one.

 

Jon

And on those dark, clear nites what do you see different for the $’s ? Hopefully more than just a feeling of satisfaction ?



#18 bobhen

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Posted 11 January 2021 - 12:55 PM

Even the long timers can stretch their statements because they know 99.9% of the time they will be forgiven if they are found out, no one is absolutely perfect in most eyes until you get the bill for the price of the scope ! Its not just in telescopes, lol !

With the internet, false advertising or not delivering what is promised or "guaranteed" can really damage a reputation and turn-off potential buyers.

 

Bob 


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#19 junomike

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Posted 11 January 2021 - 01:05 PM

And on those dark, clear nites what do you see different for the $’s ? Hopefully more than just a feeling of satisfaction ?

Does one see a difference in getting to the mall in a $250,000 Porche' or $20,000 sedan?

Both arrive around the same time (realistically)?

 

Bottom line is "value" is in the eye(piece) of the beholder......



#20 LDW47

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Posted 11 January 2021 - 01:26 PM

With the internet, false advertising or not delivering what is promised or "guaranteed" can really damage a reputation and turn-off potential buyers.

 

Bob 

But not all, with some buyers will just look right over their misdemeanours ! They only look at the name but ........ ?


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#21 LDW47

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Posted 11 January 2021 - 01:36 PM

Does one see a difference in getting to the mall in a $250,000 Porche' or $20,000 sedan?

Both arrive around the same time (realistically)?

 

Bottom line is "value" is in the eye(piece) of the beholder......

In this case only when they are looking up on a clear, star filled nite ! With a Porche, with a Volkswagen Beetle, with a ........ its rain or shine, night or day ! The values are kind of different, the logic is kind of different so let me ask again. What do you see different using the Porche of telescopes vs the Volkswagen of telescopes that amazes more than the other after all is said and done ? Just a question, I am curious ? PS: The greater value has to provide something tangible in the eye(piece) of the beholder, hopefully ?



#22 bobhen

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Posted 11 January 2021 - 04:22 PM

But not all, with some buyers will just look right over their misdemeanours ! They only look at the name but ........ ?

Some buyers will buy anything. But “some” is not enough. Companies won’t stay in business long if they get a reputation for not delivering on their quality promise or guarantee. Those companies can’t just rely on the few buyers who don’t care to sustain their business.

 

Bob


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#23 LDW47

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Posted 11 January 2021 - 04:38 PM

Some buyers will buy anything. But “some” is not enough. Companies won’t stay in business long if they get a reputation for not delivering on their quality promise or guarantee. Those companies can’t just rely on the few buyers who don’t care to sustain their business.

 

Bob

But if they don’t give you some sort of test results, some sort of confirmed verification or if you don’t have some sort of third party retesting how do you really know what you have ? Do you go strictly by the name of this company, or that company or ........  ? I mean what a way to handle your big $’s and every purchaser of these renowned scopes are in the same way ! Thats sure not the way I would do business not for that kind of $’s, lol !


Edited by LDW47, 11 January 2021 - 05:18 PM.


#24 sg6

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Posted 11 January 2021 - 05:12 PM

Just marketting, within reason. Suppose the idea is that if it has FPL-53 then at least you likely have the best glass generally available.

 

Works the same on reflectors - They are specified by diameter and no mention of the optical accuracy. Same thing. Ever read anyone asking "Do I buy a good 8" newtonian or a mediocre 10" newtonian?"



#25 LDW47

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Posted 11 January 2021 - 05:23 PM

Just marketting, within reason. Suppose the idea is that if it has FPL-53 then at least you likely have the best glass generally available.

 

Works the same on reflectors - They are specified by diameter and no mention of the optical accuracy. Same thing. Ever read anyone asking "Do I buy a good 8" newtonian or a mediocre 10" newtonian?"

Marketing within reason ? Do you realize what cost we are talking, these aren’t $500 scopes ! The ability to buy one or not buy one isn’t the issue, its a simple what are you really getting for that $ ? Just a name ? Its very important !


Edited by LDW47, 11 January 2021 - 05:23 PM.



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