SVX127D tests superbly

[Maciek_Cz]

@Jim L,

Of course you're right, variables such as ambient temperature and thermal stability are essential for this type of measurement.
A colleague Jeff from CN showed in one of his threads DPAC measurements performed during the optics' coming to a state of thermal equilibrium with the environment.
SA correction changes for all colors over time were significant!
Scott, who studied the first of the two SVX127D samples, says nothing about thermal stabilization time.
Moshen also makes no mention of it.
However, if it was about the lack of a fixed temperature, the correction in red would also be worse, which is not the case.
The position of a lens of this size doesn't matter at all. If this were the case, we would see astigmatism or coma depending
on the height above the horizon of the observed object. And that's not what happens. This would be a significant design flaw of the lens cell.

Now I will refer to the internal standards and the ZYGO test. As I wrote earlier, perfect tuning for the red light line does not guarantee
the same for the other lines (green and blue). With red only, they were able to eliminate SA for that color (red only) and coma, astigmatism, zones, and turned edges for all colors (red, green, and blue).

To sum up, the authors of the DPAC tests should be asked about the thermal stabilization time of the tested telescopes.

Each measurement of this type requires diligence, honesty, certain knowledge and significant time, above all, in the interpretation of the results.
I also don't like how excessive optimism and excitement about the topic affect the interpretation of the results.
I've often noticed this in some threads where AOS was used. However, anyone who has ronchigrams available
on the forum can repeat the analysis himself and check whether the author of the results has not suffered too much fantasy. I do just that.

[jetstream]

@Maciek_Cz I'm intrigued by your program actually. I'm not sure you ran the mentioned TEC160 through all three colours- can you do the green and red as well and post them for me?

@Sunshine got me the DPAC EP holders and now I'm searching for a good flat and hope get the camera lens sorted out -if it is even an issue, not sure yet.

I had previously expressed interest in a TEC 160FL hence my questions about it and potential sample to sample variation here as well. The fact that SV made that particularly good SVX127D to a level that beats this TEC 160 and many other triplets is amazing to me- and my feeling is it was no fluke.

That particular SVX127D would have better numbers than my TSA120 I bet.

In the end, the ability to take very high mag and not breakdown on the moon and planets is the real test IMHO.

@Maciek_Cz I appreciate your contributions in this thread and the knowledge you bring 👍

Gerry

[The60mmKid]

I appreciate this thread. I would place an order for one if it were not for the +20% VAT, cost of shipping overseas, and difficulty of addressing any issue that may arise since SV is located in the US. I wish there was a manufacturer in Europe who offered something comparable in terms of quality and price.

[Jim L]

8 hours ago, Maciek_Cz said:

@Jim L,

Of course you're right, variables such as ambient temperature and thermal stability are essential for this type of measurement.
A colleague Jeff from CN showed in one of his threads DPAC measurements performed during the optics' coming to a state of thermal equilibrium with the environment.
SA correction changes for all colors over time were significant!
Scott, who studied the first of the two SVX127D samples, says nothing about thermal stabilization time.
Moshen also makes no mention of it.
However, if it was about the lack of a fixed temperature, the correction in red would also be worse, which is not the case.
The position of a lens of this size doesn't matter at all. If this were the case, we would see astigmatism or coma depending
on the height above the horizon of the observed object. And that's not what happens. This would be a significant design flaw of the lens cell.

Now I will refer to the internal standards and the ZYGO test. As I wrote earlier, perfect tuning for the red light line does not guarantee
the same for the other lines (green and blue). With red only, they were able to eliminate SA for that color (red only) and coma, astigmatism, zones, and turned edges for all colors (red, green, and blue).

To sum up, the authors of the DPAC tests should be asked about the thermal stabilization time of the tested telescopes.

Each measurement of this type requires diligence, honesty, certain knowledge and significant time, above all, in the interpretation of the results.
I also don't like how excessive optimism and excitement about the topic affect the interpretation of the results.
I've often noticed this in some threads where AOS was used. However, anyone who has ronchigrams available
on the forum can repeat the analysis himself and check whether the author of the results has not suffered too much fantasy. I do just that.

Greetings Maciek,

Interesting discussion and thank you for sharing your experience and knowledge.

Concerning orientation, you’re undoubtedly correct in that orientation will have no effect on what we see at the eyepiece. I’m less convinced that a sensitive test, such as laser interferometry, won’t respond to inclination. Our eye is a poor arbitrator of small errors in optical instruments, in most cases we’re unable to distinguish between 0.80 Strehl and 0.99 Strehl optics, and we probably shouldn’t rely on what our eye can or cannot detect as a basis for evaluating small differences if small differences are what we’re interested in. That our eye cannot detect the effect of orientation doesn’t mean that there is no effect or that it is undetectable. The question is whether a Zygo interferometer can detect the effect and whether that might result in a reported difference, say between 0.98 and 0.96 Strehl or greater. I don’t know the answer, but given the sensitivity of laser interferometry I’d be surprised if an optical element tested vertically and horizontally would yield the exact same Strehl number.

I’ve wandered into the weeds a bit to remind myself that while testing is an undoubtably important part of evaluating anything, testing without an understanding of its inherent weaknesses can be misleading, and that precision and accuracy are two entirely different things. If a manufacturer claims their instrument has a minimum manufactured Strehl of 0.98 and a careful independent tester finds it to have a value closer to 0.80, then Houston, we have a problem! If that same tester reports 0.94, one might reasonably wonder if the difference could be attributed to external variables related to differences in methodology.

[Maciek_Cz]

The orientation effect is probably there, but with a properly constructed cell and even pressure of the lens blocking ring, it is insignificant. In this case, the manufacturer is definitely the culprit of this state of affairs. Of course, SV lenses meet the SV specification. So a high Strehl for the red color. Unfortunately, the lack of control for the wider spectrum leaves the other colors with a rather random spherical aberration correction. This is clearly shown by the DPAC tests. The curvature of the Ronchi bands cannot be explained by anything other than the presence of excess SA. The DPAC for red shows a great SA correction for this line. Which immediately suggests that the tests were carried out very carefully, in thermal equilibrium conditions.

[jetstream]

2 hours ago, Jim L said:

I don’t know the answer, but given the sensitivity of laser interferometry I’d be surprised if an optical element tested vertically and horizontally would yield the exact same Strehl number.

They dont... vertical interferometry is preferred I believe. Getting different interferometers to agree totally is near impossible and even individual fringe pictures dont 100% agree with each other from the same interferometer- hence the need for many averaged pictures to get a complete "final picture" of the optic.

I believe you are right in the sense that properly set up interferometers will give close numbers so the relative differences show the direction the optic is going for the optician.

With regards to SV having random SA correction in the other colours- could it not be said of other brands too? Or is the mentioned TEC160 an anomaly? Or other brands including A-P or Skywatcher? and LZOS??

Is this an indication of a lack of control like SV is being accused of? Ive looked at many test reports over many years and if any of these test reports are to be believed most if not all brands show sample to sample variation. IMO this variation is normal, but should be constrained within certain bounds or the optic rejected.

I'm thinking after all the scrutiny that SV is receiving they will, in the end, put out some of the best, most consistent optics around, if they are not already doing so.

I sure wish someone would tell me if the camera taking DPAC pictures can influence the look of the bands lol

Gerry

 

 

[Maciek_Cz]

@jetstream

Here are the results for the TEC160ED f/8 (spherical aberration only):
green 1/12 - 0.97
red 1/10 - 0.96
blue   1/5 - 0.87

I am not talking about other brands here. For some, it's probably similar to what SV does.
We are talking about few tested specimens of SV telescopes.
We have SVX180T and one SVX127D that have this problem and on the other hand we have another SVX127D and SVR102T one excellent and one very good.

Now, as for the distortion of the lens of the camera taking the photo of the ronchigram, of course, a weak lens can deform the ronchigram, but then the whole would be stretched, not just the bands.
From what I've read in the DPAC threads on CN, they all use good lenses and cameras.
In general, all ronchigrams are as if stretched in a plane perpendicular to the lines of the Ronchi screen.
But this stretching is not caused by the optics of the camera but by the Talbot effect (diffraction on the Ronchi screen).
This does not cause distortion of the bands, but only their duplication, which does not interfere with the assessment of the curvature.

 

[nicoscy]

I could write a lot about why there is so much animosity against SV, but it would serve nothing as it is what it is for many reasons (had 3 SV scopes myself, but I am well aware of SV practices).

What IS important, is that SV accepted that part of the methodology and procedures they followed could be improved, and have committed to changing them. I am sure the new batches of SV scopes should all perform to the highest standards and this whole issue will not reflect badly on SV long term, but rather, will help them elevate their game and at some point, be at the level of TEC and AP if they wish.

 

[Jim L]

5 hours ago, nicoscy said:

…….
I am sure the new batches of SV scopes should all perform to the highest standards and this whole issue will not reflect badly on SV long term, but rather, will help them elevate their game and at some point, be at the level of TEC and AP if they wish.

 

It would seem that Moshen’s test of a SVX127D shows StellarVue already makes scopes that are as good or better than TEC and AP. Unless I’ve misunderstood Maciek’s post from that test thread, correction for spherical aberration in red, green, and blue was 0.994, 0.994, and 0.968, respectively.
 

I can’t recall any scope from AP or TEC or anyone else that’s tested that highly, and that those numbers came from a 127mm doublet is astonishing.  Almost as astonishing is that that sensibly perfect SVX127D cost it’s owner $3,000, while the AP 130GTX will cost it’s owner $8,000. It would be a very good 130GTX indeed, if it could match the SVX127D’s performance.

[nicoscy]

Consistency is key. Apparently Stellarvue is still struggling with this - churning out products at all apertures that would have the optical characteristics of this specific sample. The ability is there for sure.

[jetstream]

On 26/05/2023 at 21:21, nicoscy said:

Consistency is key.

I 100% agree.

I wonder if the other top makers have offered a very high level of consistency or is it taken for granted that they do? Is the TEC160 mentioned in this thread is an example of their consistency?

These DPAC tests are very revealing thats for sure and personally I love them. The tests will have all the makers on their toes IMHO. I'm pleasantly surprised at how well some SkyWatcher fracs tests actually. In their case the weak point might be the assembly of the scopes and the errors this can introduce like the example I have (120ED, gross focuser misalignment, fixed with a Moonlight).

Gerry

[nicoscy]

There are some other tests on the other side in a pinned topic. However, the sample is still low, although one can certainly get a feel for quality to some degree.

I have a feeling that the whole SVX180 bruhaha has been a wake up call for SV and that from now on, extra special care will be given on the optics. This may necessitate an increase in price by some %, but I would certainly pay a premium for this particular SVX127!!!!!

SW focuser for the ED series (81 and 120) are really something that one has to accept as in need to be replaced. Great scopes optically, let down by shoddy focusers. Still, an easy repair

[jetstream]

9 minutes ago, nicoscy said:

I have a feeling that the whole SVX180 bruhaha has been a wake up call for SV

Definitely and rightly so- that scope should have never left SV - multiple levels of QC should have caught this and prevented shipment. I think but dont know that certain lenses might not be able to be figured for the very high level of quality that we are talking about, and so would have to be rejected, a very costly proposition.

The fast f ratios that the market demands is a huge challenge for the makers IMHO, ie LZOS 130 f 6 vs the 130 f9.2 - Id take the slower scope any day for my visual planetary/lunar observing, the latter a very well known top performer. The TSA120 was chosen by me for the apparently consistent optics they have, eventhough most samples Ive seen test in the mid 90's Strehl wise, but with balanced colour correction and faster cooldown than the superb TOA130.

All in all I think we are in the glory days with regards to telescope choices- a lot of the makers are getting long in the tooth however and who knows how long some of them will be around, this in reference to dobs as well.

I'm really glad all those guys are doing DPAC tests, I like looking at the results- the very long banter not so much, but it is my choice to read or not lol

Gerry

[nicoscy]

Gerry, I would agree re doublets and long focal ratios, but triplets can afford well corrected optics at shorter focal lengths.

Between a 130F6 and 130f9 triplets, I would definitely go for the f9 as it is easier to figure and you can ramp up magnification much easier than the f6 in terms of eyepieces + barlows used. After all, most DOS fit in under 0.5° TFOV and if I want wide fields, that's why we have those lovely 60mm f6 ED scopes (dual mounting anyone?). Slap the TS 2" flattener on a diagonal and you also have a flat field to boot with the 60mm. In terms of imagers, a few points off in Strehl as long as spherochromatism is well controlled, makes no difference and it is usually the skill of the person processing the image that determines the outcome IMHO.

In terms of QC, SV is more expensive than resellers, but cheaper than say TEC and AP for example. If they want to step up their game, they would need to perhaps reject more, or test rigorously so that they can correct figuring as it happens. Both add to cost. It is up to SV to decide what segment of the market they wish to occupy. It's a matter of deciding on quality of optics. Judging by the steps they announced, I do think they will up their games and I personally welcome that.

If I was not "across the pond" so to speak, I would consider one of the new SVs to roll the assembly line. However, unless the USD crashes against the Euro, 19% VAT and 4.3% optics tax make importing stuff from the US prohibitive...

[jetstream]

3 minutes ago, nicoscy said:

Gerry, I would agree re doublets and long focal ratios, but triplets can afford well corrected optics at shorter focal lengths.

For sure and at some point fast and larger aperture triplet figuring gets much harder I think which of course makes the lenses deadly expensive. I'm still considering a TEC 160, but like you, my exchange rate is not that great. With regards to f ratio, my own preference is around f7.5-f8 for a frac, triplet or otherwise. My new DM6 is fantastic, very easy to carry, great in use and can handle a largish frac, plus Tom Peters is great to deal with. Who knows what other frac I'll end up with on it, but I know this- if I drop a wad of cash I want the scope to be right up there optically.

There should be zero question about optical quality at these high prices from any maker.

[John]

3 hours ago, jetstream said:

.... LZOS 130 f 6 vs the 130 f9.2 - Id take the slower scope any day for my visual planetary/lunar observing, the latter a very well known top performer....

It sure is 🙂

https://stargazerslounge.com/topic/385898-what-did-you-see-tonight/?do=findComment&comment=4384203

 

[Jim L]

I doubt there’s a manufacturer that tests their scopes more thoroughly or watches quality control more carefully than StellarVue. So what happened to that SVX180? I had a lengthy conversation with Vic Maris in which he thought that scope may have had an optical element rocking in its cell. He didn’t know for sure since at that time he hadn’t received the scope back, but he said that as tested by a Paul it was far below their standard.

One variable not mentioned are the perils of shipping from the West Coast to the East, which has no doubt been the downfall of many a fine instrument. Having the luxury of living only 90 miles from StellarVue I drove to their shop to pick up my own scope so that I could be assured that it’s optics would arrive in the condition in which it was certified. Perhaps the SVX180 had gotten more of its share of wacks courtesy of FedX; who knows?

On the possibility that the issue was caused at his end, however, Vic said he was returning to first principals and examining his entire operation from start to finish, including calling in a technician from Zygo to examine their interferometer. The end result, I expect, will be very positive for both StellarVue and its customers.
 

As to other manufacturers, I don’t know the lengths to which they go to manufacture and deliver quality scopes, but the comprehensive AiryLab test results provide a window into what is in the hands of some of their owners.

Here are the five Astro Physics StarFire130 AiryLabs has published:

https://www.airylab.com/contenu/mesures/astro/rapport 2011-05002-public.pdf
 

https://www.airylab.com/contenu/mesures/astro/rapport 2011-05003-public.pdf
 

https://www.airylab.com/contenu/mesures/astro/rapport 2013-15001-a.pdf
 

https://www.airylab.com/contenu/mesures/astro/rapport 2012-46001-a.pdf
 

https://www.airylab.com/contenu/mesures/astro/rapport 2014-09002-a.pdf
 

TEC is often discussed here, so here are the two TEC 110FC results published by AiryLab:

https://www.airylab.com/contenu/mesures/astro/rapport 2014-33001-a.pdf
 

https://www.airylab.com/contenu/mesures/astro/rapport 2014-33001-a.pdf

I’m not sure what to say about those results except that perhaps their owner’s delivery service is even worse than ours here in the States. Significantly, astronomically, worse. Here’s a visual from one of the TEC tests:

For those readers who don’t wish to go through the trouble of reviewing the tests I don’t expect you would find many of the results of optical quality either superior or consistent, and your assumptions about the performance of some of your favorite scope makers might be challenged.

There are dozens of additional test results published by AiryLab on their website, but be advised that if the test link doesn’t work you will have to replace “net” in the link with “com” after “airylab.” Here’s a link to AiryLab:

https://airylab.com/astronomy-test-reports/

Some of the published test results are quite good, others much less so, but it’s difficult to find any sign of consistency. The difference, it appears, is that when a StellarVue scope tests poorly they’re flayed before being tied to a stake and burned, and when a scope from another top maker tests equally poorly or worse, the subject is swept under the carpet to be ignored until forgotten. Then StellarVue is damned with faint praise as the maker that is almost as good, and can be as good if they just try harder, but that are not quite there yet. StellarVue is every bit as good right now, I expect they will try harder, and if the test results linked are any indication perhaps other makers should try harder as well.

One lesson that’s finally sinked in over my 67 years is that when I’m resolutely positive that someone who absolutely should know better has screwed up majestically, when my thoughts go to, “what could they possibly have been thinking…. ”, a deeper examination of the facts almost always shows that it was I who did not adequately understand the subject. I think a bit of that trap creeps into every discussion about StellarVue scopes. Mark Twain’s observation that, “What gets us into trouble is not what we don’t know. It’s what we know for sure that just ain’t so.” should probably be kept in mind in any discussion about StellarVue.

[jetstream]

@Jim L I read a lot of those reports a good while back and others and yeah its an eye opener... IMHO.

[nicoscy]

Jim,

Well said on all fronts! I have had 3 SV scopes, one I will call average, one really good and one sublime. I should never have sold the SV80T but I stupidly did!

If it wasn’t for taxes and shipping, if I were looking for another scope, SV scopes would definitely be on the list - a key driver being the SVX180 thread believe it or not. SV have taken steps to ensure consistency in quality and this has / will definitely filter down to the quality of scopes leaving their facilities from now on.

I will never like SV marketing language, and I so wish Vic Maris would do something about it, but apparently this is the way he prefers it. Too much Kool Aid for my taste, but I like the product line and that’s enough for me. I can separate the two.

”The other site” is frequented by many who dislike SV marketing over the years (and some mistakes by SV over the years) and are the first to attack SV. Your links to scope tests do indicate something which is indeed a bit sad: many choose to forget the mistakes made in the past by other premium manufacturers. I think SV is just going through some growing pains at the moment and so is Vic Maris as an owner. 

SV was not helpful initially when they insisted that testing in red is better. However - and this is the key take - they changed their position and will be doing in-house DPAC as well to verify the optics. Also, since scrutiny is now high, they will ensure that they manage expectations. In the end, this is a win win. SV keeps improving, we have more alternatives for high end scopes in the market.

I will also post something here, where I don’t expect to be crucified by AP fanbois: I had a second run AP Stowaway 92. I have had many scopes in that aperture so I feel I can make a fair estimate of its abilities. To bottom-line it, nothing special at all and a bit underwhelming actually. It went the way of the dodo quite fast. A second reason for its sale was the behavior or many fanbois on AP group badly disparaging people “on the other site” and Roland not asking that they keep it civil, when he could have. So, a lot can be said about characters….

I’d gladly buy a SV scope again. And I may do so in the future! Not AP thought.

 

 

Edited May 31, 2023 by nicoscy

[Jim L]

1 hour ago, nicoscy said:

Jim,

Well said on all fronts! I have had 3 SV scopes, one I will call average, one really good and one sublime. I should never have sold the SV80T but I stupidly did!

If it wasn’t for taxes and shipping, if I were looking for another scope, SV scopes would definitely be on the list - a key driver being the SVX180 thread believe it or not. SV have taken steps to ensure consistency in quality and this has / will definitely filter down to the quality of scopes leaving their facilities from now on.

I will never like SV marketing language, and I so wish Vic Maris would do something about it, but apparently this is the way he prefers it. Too much Kool Aid for my taste, but I like the product line and that’s enough for me. I can separate the two.

”The other site” is frequented by many who dislike SV marketing over the years (and some mistakes by SV over the years) and are the first to attack SV. Your links to scope tests do indicate something which is indeed a bit sad: many choose to forget the mistakes made in the past by other premium manufacturers. I think SV is just going through some growing pains at the moment and so is Vic Maris as an owner. 

SV was not helpful initially when they insisted that testing in red is better. However - and this is the key take - they changed their position and will be doing in-house DPAC as well to verify the optics. Also, since scrutiny is now high, they will ensure that they manage expectations. In the end, this is a win win. SV keeps improving, we have more alternatives for high end scopes in the market.

I will also post something here, where I don’t expect to be crucified by AP fanbois: I had a second run AP Stowaway 92. I have had many scopes in that aperture so I feel I can make a fair estimate of its abilities. To bottom-line it, nothing special at all and a bit underwhelming actually. It went the way of the dodo quite fast. A second reason for its sale was the behavior or many fanbois on AP group badly disparaging people “on the other side” and Roland not asking that they keep it civil, when he could have. So, a lot can be said about characters….

I’d gladly buy a SV scope again. And I may do so in the future! Not AP thought.

 

 

Nicos, I’m glad we see eye to eye on the things that matter, and here’s to more sublime scopes in our future, wherever they may come from.

[jetstream]

9 hours ago, nicoscy said:

I will also post something here, where I don’t expect to be crucified by AP fanbois: I had a second run AP Stowaway 92. I have had many scopes in that aperture so I feel I can make a fair estimate of its abilities. To bottom-line it, nothing special at all and a bit underwhelming actually

Many kudos to you Nicos !

Calling it like it is regardless of brand, I do the same.

Years ago I reported sub par performance in a SW120ED, eyebrows raised. After a long while I fixed it (with advice here) and it gives great views. It was then a side by side was done between it and the TSA120- the TSA120 showed contrast detail the 120ED did not- again eyebrows raised.

IMO, the only way to sort things out is from testing and real world reviews... honest, non biased reviews.I brought the TEC160 up in this thread for two reasons- to illustrate a recently made scope from a top maker that could be said to be sub par in blue and also to illustrate the hesitation for criticism of certain brands...which by default illustrates the willingness to criticize a particular one.

If SV puts out a bunch of sub par scopes or bs's their numbers I'll be in line to first report it should I have experience with it believe me.

We are all winners here IMHO, all the makers will ensure better consistency now that scopes can easily be called out through DPAC which is hard to argue with when done properly and with reasonable equipment. My next high end refractor will be DPAC'd no question.

Gerry