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Astro-Tech 102ED vs 102EDL

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#76 daquad

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Posted 06 April 2021 - 07:03 PM

 

I believe the importer is making a claim that the EDL is figured to a higher standard than his less expensive imported products, and justifying the higher price based, in part, on a higher figure. If in fact the EDL is figured to a higher standard, I think it’s reasonable to expect it to cost the manufacturer more, so I would expect to pay more to obtain it.

 

As evidence of higher figure, I believe the importer is relying on his own considerable experience as well citing the results of formal test protocols, none of which can be perfect, but each can be useful. Whether the incremental improvement is worth the incremental cost is a question the buyer must decide for himself.

Astronomics made no claim as to the higher figure of the EDL.  They simply guaranteed a minimum strehl of 0.95, a worthy accomplishment and if i were in the market for a relatively fast 4" APO, this would be the one I would buy as it represents an excellent value in a visual and AP scope.

 

However, you seem to be missing the point here.  I repeat my earlier post:  The higher cost is due to the better glass, better cell better focuser, not necessarily better figure.  Why would KUO not figure the ED to the same precision as the EDL?  The figuring process is the same for both lenses and I believe KUO and Astronomics would insist on the best figure the manufacturer could deliver.  The lower strehl of the ED (which was not advertised) is due to the higher dispersion glass, not to poorer figure.  Or to put it another way, the higher strehl of the EDL is due to the lower dispersion glass, not to better figure.  I'm done.

 

Dom Q.


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#77 Mitrovarr

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Posted 06 April 2021 - 07:07 PM

Eh, I do see a lot of elitism sometimes. People either say you need perfect top tier gear to do anything (astrophotographers love to do this) or they make the top end gear sound 10x better than the lesser gear when it's really like 95% perfect vs. 99% perfect.

 

I'm happy to hear about why a $2500 apo is better than a $600 one, but if the differences listed are anything other than "slightly better color correction", "possibly better figure so somewhat better on planets", "slightly better mechanics", or "better for astrophotography", I'm going to speak up.


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#78 GSBass

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Posted 06 April 2021 - 07:18 PM

I believe what Mike has actually paid for on the EDL scopes is a QA per scope, obviously any that don’t pass won’t be included in the Astro-tech line..... that’s most likely the only difference as far as that minimum strehl rating is concerned. Can’t really speculate on manufacture standards on the Regular ED but it’s obviously high but also pretty obvious that if you want QA to sign off on minimums then the vender has to pay. It’s my opinion that the manufacturer would not offer this option to the vender if they were not confident most of their optics in a particular production cycle would pass it.... I bet they are not tossing many

Astronomics made no claim as to the higher figure of the EDL.  They simply guaranteed a minimum strehl of 0.95, a worthy accomplishment and if i were in the market for a relatively fast 4" APO, this would be the one I would buy as it represents an excellent value in a visual and AP scope.

 

However, you seem to be missing the point here.  I repeat my earlier post:  The higher cost is due to the better glass, better cell better focuser, not necessarily better figure.  Why would KUO not figure the ED to the same precision as the EDL?  The figuring process is the same for both lenses and I believe KUO and Astronomics would insist on the best figure the manufacturer could deliver.  The lower strehl of the ED (which was not advertised) is due to the higher dispersion glass, not to poorer figure.  Or to put it another way, the higher strehl of the EDL is due to the lower dispersion glass, not to better figure.  I'm done.

 

Dom Q.


Edited by GSBass, 06 April 2021 - 07:19 PM.


#79 gwlee

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Posted 06 April 2021 - 07:33 PM

The average buyer has basically no way to confirm a Strehl claim, though.

 

The average buyer has basically no way to confirm a Strehl claim, though.

No, the average buyer probably won’t have an interferometer in his garage. I believe there are still independent labs that can provide this service, at least there were when I retired, but it’s probably still expensive. We shouldn’t expect results to be identical, but they should be reasonably similar.

 

The existence of independent test labs tends to keep most reputable manufacturers and importers on their toes, not that there aren’t spectacular exceptions. The recent VW emissions testing scandal for example. Also very reputable, top tier manufacturers have unintentional escapes. 
 

Often buyers of sensibly perfect optics have enough experience with other more accessible test methods, and often have another sensibly perfect scope to use as a gold standard for comparison. For example, if views from a new scope aren’t up to expectations in good seeing, and a star test explains it, the Strehl results should show something is wrong too. If they don’t, the scope might have been dropped in transit, or the scope might be an escape for example. In any case, a reputable manufacturer will make it right.

 

Strehl testing is a useful tool that reputable, top tier manufacturers use to design and manufacture their products even if they don’t publish the results or make a minimum guarantee although some do, AP for instance.

 

Like any test procedure, Strehl testing is not perfect, it can be gamed, or poorly implemented, but I see no downside to receiving the results or a minimum guarantee. The manufacturer’s testing complements my own testing and should reinforce rather than contradict my test results. If it does, I am satisfied.


Edited by gwlee, 06 April 2021 - 09:25 PM.

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#80 Joe1950

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Posted 06 April 2021 - 07:56 PM

It’s nothing to do with being nasty. People get into the hobby, usually with modest equipment like myself. Then the government gives them a bunch of free money and they decide to upgrade some things. They can’t go to star parties to see how much better this scope or that eyepiece might be compared to what they currently have. They see a $600 4” Apo and a $2500 one, or a $35 eyepiece and a $500 one, and they want to legitimately know what the difference is. So people who have experience with expensive scopes and eyepieces share their experience about why one costs more and what you get for the price difference, so people can gauge how far up the ladder of diminishing marginal returns they want to go. And it seems like often some longer tenured users of modest equipment get offended by that. Ultimately if the $600 telescope was just as good as the $2500 one there wouldn’t be a $2500 one. People want to understand what the difference is so they can decide how much of an upgrade they want to commit to. We are just helping them understand so they can make an informed decision. Nobody is saying your $600 Apo is a bad scope or insulting you because you can’t afford anything better. We are just addressing the question posed by the OP. If you don’t want to hear about why a $2500 Apo is better than your $600 one, don’t read the thread.

People ask about this versus that comparisons all the time, especially in the eyepiece forum! We aren’t being rude or judgmental. We are using our experience to answer legitimate queries.

Scott

 

 

 

Now you’re being nasty Scott. wink.gif 

Scott, there is a right way and a wrong way to frame an answer to what is better and what is lesser. Some people do insult what others have and it isn’t right.

I was in a conversation about refractors and talking about the C-80ED that I happen to have. Another contributor chimed in that he had a C80ED and thought it was great, until he got a real telescope. Which happened to be a Tak.

Another thread on the usefulness of 80mm aperture scopes and one said they are only useful as finders!

​That kind of stuff along with an often elitist attitude crosses the line.

I responded to this thread just to let the OP know that as an experienced observer it is my opinion that the AT-102ED is an excellent scope that shows very good images of the moon, planets and doubles. That’s all. I don’t have an EDL and wouldn’t comment on how much better or not it is. Yet here we are at over 75 posts and many/most have been arguing which is the better overall deal, mostly based on a Strehl ratio.

It’s fine to give comparisons, but it can be done without making someone else feel belittled. And that is sometimes the message! You know as well as I do that much of the opinions are just that...opinions that are subjective. Same with eyepieces.

And Scott, don’t tell me that if I don’t want to hear....don’t read the thread. I have as much right to read and participate as you or anyone else. Maybe that kind of statement falls under the classification of what I’m talking about and objecting to.

Okay Scott?

 

 

Added:

 

We are using our experience to answer legitimate queries.

Sometimes. And sometimes contributors are using their opinions and biases to answer questions. The people asking don’t always know the difference. 


Edited by Joe1950, 06 April 2021 - 08:25 PM.

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#81 SeattleScott

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Posted 06 April 2021 - 08:14 PM

Eh, I do see a lot of elitism sometimes. People either say you need perfect top tier gear to do anything (astrophotographers love to do this) or they make the top end gear sound 10x better than the lesser gear when it's really like 95% perfect vs. 99% perfect.

I'm happy to hear about why a $2500 apo is better than a $600 one, but if the differences listed are anything other than "slightly better color correction", "possibly better figure so somewhat better on planets", "slightly better mechanics", or "better for astrophotography", I'm going to speak up.

Absolutely, generally the difference is subtle and should be represented as such. Usually it is but not always.

Scott
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#82 gwlee

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Posted 06 April 2021 - 09:22 PM

Astronomics made no claim as to the higher figure of the EDL.  They simply guaranteed a minimum strehl of 0.95, a worthy accomplishment and if i were in the market for a relatively fast 4" APO, this would be the one I would buy as it represents an excellent value in a visual and AP scope.

 

However, you seem to be missing the point here.  I repeat my earlier post:  The higher cost is due to the better glass, better cell better focuser, not necessarily better figure.  Why would KUO not figure the ED to the same precision as the EDL?  The figuring process is the same for both lenses and I believe KUO and Astronomics would insist on the best figure the manufacturer could deliver.  The lower strehl of the ED (which was not advertised) is due to the higher dispersion glass, not to poorer figure.  Or to put it another way, the higher strehl of the EDL is due to the lower dispersion glass, not to better figure.  I'm done.

 

Dom Q.

It’s probably a safe assumption that better glass, a better focuser, and a better cell contribute to increased cost.

 

I am not familiar with the details of KUO’s manufacturing process, which I assume is a trade secret. If KUOs standard figuring process is held to a sufficiently high standard, it seems possible that they might achieve a .95 minimum Strehl for the EDL without any figuring improvement or cost that goes with it. Do you know enough about KUO’s manufacturing processes to know whether this is the case? 

 

Why wouldn’t it be the case? Because figuring all products to the highest possible standard would increase the cost of all products, including the products that are intended to be “low cost” products, limiting there appeal to more cost-conscious consumers, and a slightly lower figuring standard might go unnoticed and unappreciated by these customers. 

 

All I know for sure is that the importer claims a .95 Strehl for the EDL, doesn’t for the lower cost product, and both figure and chromatic aberration effect the Strehl calculation, so it’s also possible that the figuring standard of the EDL is taken up a notch in addition to the glass, cell, and focuser. 
 


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#83 gwlee

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Posted 06 April 2021 - 10:43 PM

there is a right way and a wrong way to frame an answer to what is better and what is lesser. Some people do insult what others have and it isn’t right.

I was in a conversation about refractors and talking about the C-80ED that I happen to have. Another contributor chimed in that he had a C80ED and thought it was great, until he got a real telescope. Which happened to be a Tak.

Another thread on the usefulness of 80mm aperture scopes and one said they are only useful as finders!
 

I frequently here similar comments about my AT72ED2 and my XT8. Although there are better instruments, these are both inexpensive, good quality instruments that have proven very useful to me and many others. So, I consider these statements hyperbole, intentional exaggeration for literary effect, that’s not intended to be insulting although it can be if taken personally. 

 

I doubt anyone really thinks an 80mm refractor is only useful as a finder, or thinks the C80ED isn’t a real telescope. These enthusiasts have probably discovered something that works a little better for them that they like a lot better, at least for the moment, and it probably costs more too. 


Edited by gwlee, 06 April 2021 - 11:09 PM.

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#84 Joe1950

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Posted 06 April 2021 - 11:30 PM

You’re right, gwlee. I shouldn’t let those things bother me.

Very good observation! Thanks.



#85 nicknacknock

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Posted 07 April 2021 - 05:27 AM

Eh, I do see a lot of elitism sometimes. People either say you need perfect top tier gear to do anything (astrophotographers love to do this) or they make the top end gear sound 10x better than the lesser gear when it's really like 95% perfect vs. 99% perfect.

 

I'm happy to hear about why a $2500 apo is better than a $600 one, but if the differences listed are anything other than "slightly better color correction", "possibly better figure so somewhat better on planets", "slightly better mechanics", or "better for astrophotography", I'm going to speak up.

Better color rendition, higher contrast of views, negligible CA (if any visible to the eye), ability to soak up magnification to ridiculous extremes, which despite not providing more resolution, provides a closer view, better built quality, higher value in the second hand market, feel-good factor, aesthetic form, satisfaction that "it's as good as it really gets so let's stop and enjoy it now, with no worries".

 

So many things wrapped up in that price difference, some qualitative, some measurable, some relating to personal circumstances. Not judging, not taking sides, just my personal thoughts on the matter and since it is a supply and demand driven market, it appears that many people gravitate towards expensive scopes as well as towards not so expensive. There is a market for every type of scope and every configuration.


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#86 daquad

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Posted 07 April 2021 - 08:28 AM

I believe what Mike has actually paid for on the EDL scopes is a QA per scope, obviously any that don’t pass won’t be included in the Astro-tech line..... that’s most likely the only difference as far as that minimum strehl rating is concerned. 

Well, I guess I'm not done.  Don't you think Astronomics would insist on the same QA for the ED's even though the color correction is not as good?  Especially given the claims in the description of the ED's.

 

Dom Q.


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#87 Joe1950

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Posted 07 April 2021 - 08:50 AM

Agreed, Dom. I’m done.

Ciao all.



#88 daquad

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Posted 07 April 2021 - 10:10 AM

Agreed, Dom. I’m done.

Ciao all.

Ciao.  This time I mean it.


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#89 SeattleScott

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Posted 07 April 2021 - 10:44 AM

I frequently here similar comments about my AT72ED2 and my XT8. Although there are better instruments, these are both inexpensive, good quality instruments that have proven very useful to me and many others. So, I consider these statements hyperbole, intentional exaggeration for literary effect, that’s not intended to be insulting although it can be if taken personally.

I doubt anyone really thinks an 80mm refractor is only useful as a finder, or thinks the C80ED isn’t a real telescope. These enthusiasts have probably discovered something that works a little better for them that they like a lot better, at least for the moment, and it probably costs more too.

I seem to remember one report of a C80ED holding up well against an AP. The report was met with initial skepticism but eventually confirmed. So it seems it is possible for a “budget “ Apo to perform similarly to the top brands. Granted I doubt all C80’s are that good, but apparently some are. As for whether an 80mm is a real telescope versus a finder, I think that depends a lot on your level of light pollution.

FWIW, regarding AT specifically, I have only heard good things. I have never owned one but a buddy has one he is happy with, and I spent an evening with a fabulous AT111 once. Granted the AT111 wasn’t exactly a budget Apo, but I suppose it was a budget Apo compared to a Tak. So it would seem confidence in Astronomics to deliver high quality at affordable price is justified, at least from my limited experience and reading reviews.

Now whether the optical figure in the EDL is typically better than the ED, that I have no idea.

Scott

Edited by SeattleScott, 07 April 2021 - 10:53 AM.

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#90 Cpk133

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Posted 07 April 2021 - 11:09 AM

I thought the 102ed listed minimum strehl of .92 at one time.  It's too bad I live in MI where a 4" column of air has a strehl of .5 on most nights.  Maybe a 60mm with .99 strehl is the ticket?  


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#91 gwlee

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Posted 07 April 2021 - 06:26 PM

Don't you think Astronomics would insist on the same QA for the ED's even though the color correction is not as good?  Especially given the claims in the description of the ED's.

 

Dom Q.

Dom,

 

No, my educated guess is still different than your educated guess, but I think either is possible. Hopefully, Mike will come along and enlighten us. 

 

Gary
 

 

 

Gary



#92 GSBass

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Posted 07 April 2021 - 06:43 PM

It’s not how it works, the factory has it as an option on the vendors order form. It cost the vendor extra which makes the scope cost more.... it unknown whether the factory offered the option on the ED scope, but if they did and astrotech had paid then the scope would have cost more than 599 .... it’s not quite as cryptic as everyone makes it out to be

Well, I guess I'm not done.  Don't you think Astronomics would insist on the same QA for the ED's even though the color correction is not as good?  Especially given the claims in the description of the ED's.

 

Dom Q.



#93 TNmike

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Posted 07 April 2021 - 06:56 PM

I look at it this way. Astronomics has sold, what, hundreds of AT102ED's? Every now and then a new version comes out which is slightly better than the previous versions in some respect. I don't know that I have read one serious complaint about the AT102ED. Everyone seems to feel their telescope met or exceeded their expectations, and felt that at that price point it was a good to great deal. The bottom line is we have a substantial baseline in place with the AT102ED.

 

Now with Mike introducing the AT102EDL, at a $500 higher price, with better glass, a strehl guarantee, and perhaps a little better mechanicals, he has no place to hide. We are not comparing two scopes from two different vendors, it's himself against himself. I believe Mike has full confidence that this new scope will be received as well as its sibling, and worth the extra $500. Like I say, he has hundreds of AT102ED's out there for the AT102EDL to be compared to and see if it is $500 better. So, in the months ahead we'll see how it turns out.



#94 GSBass

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Posted 07 April 2021 - 07:14 PM

Yeah I don’t really see what the discussion is about, the ED is a great scope, the EDL is a great scope, I see post daily of someone dropping 400 on a new focuser, not trying to compare the edl focuser to those but it is a substantial upgrade from what I’ve read. I suppose the next question is will the edl out perform a Tak.... the one I’m getting most certainly will haha

I look at it this way. Astronomics has sold, what, hundreds of AT102ED's? Every now and then a new version comes out which is slightly better than the previous versions in some respect. I don't know that I have read one serious complaint about the AT102ED. Everyone seems to feel their telescope met or exceeded their expectations, and felt that at that price point it was a good to great deal. The bottom line is we have a substantial baseline in place with the AT102ED.

 

Now with Mike introducing the AT102EDL, at a $500 higher price, with better glass, a strehl guarantee, and perhaps a little better mechanicals, he has no place to hide. We are not comparing two scopes from two different vendors, it's himself against himself. I believe Mike has full confidence that this new scope will be received as well as its sibling, and worth the extra $500. Like I say, he has hundreds of AT102ED's out there for the AT102EDL to be compared to and see if it is $500 better. So, in the months ahead we'll see how it turns out.


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#95 Mitrovarr

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Posted 07 April 2021 - 07:55 PM

I'd be curious which is better, the EDL or the EDT, for those sizes where they both exist.



#96 GSBass

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Posted 07 April 2021 - 08:21 PM

In general it’s best not to get in to a doublet/triplet comparison, kind of a different animal and although the lower end ones are close in price they use cheaper glass to become close to what the doublet achieves with more expensive glass. It’s a given though that a triplet that uses expensive glass will out perform both.

——

in general, a low end triplet will be comparable to a high end doublet though if that helps any

 

I'd be curious which is better, the EDL or the EDT, for those sizes where they both exist.


Edited by GSBass, 07 April 2021 - 08:27 PM.


#97 Mitrovarr

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Posted 07 April 2021 - 08:31 PM

In general it’s best not to get in to a doublet/triplet comparison, kind of a different animal and although the lower end ones are close in price they use cheaper glass to become close to what the doublet achieves with more expensive glass. It’s a given though that a triplet that uses expensive glass will out perform both.

It seems like a sensible comparison to make given that the cost is very similar and the focal length is also really close. People interested in those sizes would probably actually need to make that comparison.

 

For example the 80EDT and 80EDL are $50 apart, and only differ in focal ratio from F/6 to F/7. So it's going to be a tough decision for anyone wanting one or the other.



#98 GSBass

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Posted 07 April 2021 - 08:49 PM

I guess it’s a difficult decision, but after you research the pros and cons of each it gets easier, people choose doublets because they are lighter, have less colmination problems or are primarily visual observers. People are attracted to triplets because they are well corrected in color for astrophotography. Most doublets will show some color in photographs... a few, the edl being one of them are corrected well enough to not be an issue.

It seems like a sensible comparison to make given that the cost is very similar and the focal length is also really close. People interested in those sizes would probably actually need to make that comparison.

 

For example the 80EDT and 80EDL are $50 apart, and only differ in focal ratio from F/6 to F/7. So it's going to be a tough decision for anyone wanting one or the other.



#99 Joe1950

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Posted 07 April 2021 - 09:13 PM

Some interesting facts about the Strehl ratio:

 

  • The minimum standard for high quality performance for an optical system, that being to perform to the ‘Rayleigh Limit’ or to be considered  ‘Diffraction Limited’ is a Strehl ratio of 0.82, equivalent to a wavefront error of 1/4 λ, P-V.
  • A Newtonian reflector that has perfect optics for both the primary and secondary mirrors and having a central obstruction of 25% will have a system Strehl ratio no greater than 0.90.
  • A SCT or MCT that has perfect optics for the primary, secondary and corrector and having a typical central obstruction of 34% will have a system Strehl factor no greater than 0.81. Just at the Rayleigh Limit, or to be considered Diffraction Limited, with a system wavefront error of 1/4 λ. Again with perfect optics!

 

I once saw a photographic presentation of Jupiter that was intentionally blurred to show an interpretation of system wavefront errors. The sharpest photo represented a perfect optical system.

 

The difference between a system having a 1/2 λ wavefront error and that of one having a 1/4 λ wavefront error was significant. The 1/2 λ was very blurry, but the 1/4 λ optic was rather sharp.

 

The samples were for 1/2 λ, 1/4 λ, 1/8 λ, 1/10 λ and 1/20 λ. And also perfect. The difference, as I said going from 1/2 λ to 1/4 λ was obvious. Going from 1/4 λ to 1/8 λ the difference was minuscule! Going from 1/8 λ to 1/20 λ was barely perceptible. You had to look really hard to see it. 

 

So, aside from CA, telling the difference between a Strehl factor of 0.95 or more for the EDL, and whatever the Strehl is for the ED, is likely very difficult to see, IMO. Add that seeing is rarely perfect and that the ED shows an obvious high level of contrast and color dynamic indicating at least a very good figure and high polish, I would have to say, again IMO, the optical difference is very little, if noticeable at all.

 

Not saying the EDL is not a better scope for many reasons. It certainly is. Better lens elements for controlling CA, a better build with an upgraded focuser and objective cell and a guaranteed optical standard.

 

Again, IMO, out under the stars the difference in views would be minimal. You just can’t fault the optical performance of either scope, the ED or EDL.

 

With that, the defense rests.  lol.gif  Or at least retires to chambers. 

 

All opinions counter to these these findings are welcomed, will be reviewed, considered and duly filed for historical significance.

 

2E9D14E7-0B75-4E44-B656-59F6B4D83E76.gif

c.  Joe1950

 

 


Edited by Joe1950, 08 April 2021 - 10:47 AM.

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#100 GSBass

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Posted 07 April 2021 - 09:58 PM

Sounds good to me 

Some interesting facts about the Strehl ratio:

 

  • The minimum standard for high quality performance for an optical system, that being to perform to the ‘Rayleigh Limit’ or to be considered  ‘Diffraction Limited’ is a Strehl ratio of 0.82, equivalent to a wavefront error of 1/4 λ, P-V.
  • A Newtonian reflector that has perfect optics for both the primary and secondary mirrors and having a central obstruction of 25% will have a system Strehl ratio no greater than 0.90.
  • A SCT or MCT that has perfect optics for the primary, secondary and corrector and having a typical central obstruction of 34% will have a system Strehl factor no greater than 0.81. Just at the Rayleigh Limit, or to be considered Diffraction Limited, with a system wavefront error of 1/4 λ. Again with perfect optics!

 

I once saw a photographic presentation of Jupiter that was intentionally blurred to show an interpretation of system wavefront errors. The sharpest photo represented a perfect optical system.

 

The difference between a system having a 1/2 λ wavefront error and that of one having a 1/4 λ wavefront error was significant. The 1/2 λ was very blurry, but the 1/4 λ optic was rather sharp.

 

The samples were for 1/2 λ, 1/4 λ, 1/8 λ, 1/10 λ and 1/20 λ. And also perfect. The difference, as I said going from 1/2 λ to 1/4 λ was obvious. Going from 1/4 λ to 1/8 λ the difference was minuscule! Going from 1/8 λ to 1/20 λ was barely perceptible. You had to look really hard to see it. 

 

So, aside from CA, telling the difference between a Strehl factor of 0.95 or more for the EDL, and whatever the Strehl is for the ED, is likely very difficult to see, IMO. Add that seeing is rarely perfect and that the ED shows an obvious high level of contrast and color dynamic indicating at least a very good figure and high polish, I would have to, again IMO, the optical difference is very little, if noticeable at all.

 

Not saying the EDL is not a better scope for many reasons. It certainly is. Better lens elements for controlling CA, a better build with an upgraded focuser and objective cell and a guaranteed optical standard.

 

Again, IMO, out under the stars the difference in views would be minimal. You just can’t fault the optical performance of either scope, the ED or EDL.

 

With that, the defense rests.  lol.gif  Or at least retires to chambers. 

 

All opinions counter to these these findings are welcomed, will be reviewed, considered and duly filed for historical significance.

 

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c.  Joe1950


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