Test and Comparison: Starfield 102mm F7 ED Doublet v Takahashi FC-100 DF f7.4 Doublet (Fluorite)

[JeremyS]

2 hours ago, John said:

And that particular DPAC tester had quite a long track record of knocking SV products .......

Don’t think that’s relevant John, or fair, considering this well documented, and unfortunate, saga.

His results clearly showed that SV methods were erroneous as they optimised lens performance in red, not in green - or even across a range of colours. Seems even SV admit that. The question that remains is whether this has affected smaller apertures than the one tested. Evidence from users is that they are fine.

[John]

3 hours ago, JeremyS said:

Don’t think that’s relevant John, or fair, considering this well documented, and unfortunate, saga.

His results clearly showed that SV methods were erroneous as they optimised lens performance in red, not in green - or even across a range of colours. Seems even SV admit that. The question that remains is whether this has affected smaller apertures than the one tested. Evidence from users is that they are fine.

Well it certainly is well documented 🙂

 

[900SL]

19 hours ago, JeremyS said:

Don’t think that’s relevant John, or fair, considering this well documented, and unfortunate, saga.

His results clearly showed that SV methods were erroneous as they optimised lens performance in red, not in green - or even across a range of colours. Seems even SV admit that. The question that remains is whether this has affected smaller apertures than the one tested. Evidence from users is that they are fine.

I had no argument with the initial test on the 180mm scope. It was the insufferable preening and beating a dead donkey that got my goat. There is clearly a partisan camp with an axe to grind over there. 

You can be both right, and an insufferable whistle at the same time ( not in reference to you Jeremy, I hasten to add 😂)

[Deadlake]

6 hours ago, JeremyS said:

Don’t think that’s relevant John, or fair, considering this well documented, and unfortunate, saga.

His results clearly showed that SV methods were erroneous as they optimised lens performance in red, not in green - or even across a range of colours. Seems even SV admit that. The question that remains is whether this has affected smaller apertures than the one tested. Evidence from users is that they are fine.

At the moment there really is not enough data on SV's line up to call this one way or the other.

Actually the only data points I see on this are for SV's with LZOS lens cells that are tested on the green line 😀.

See:

https://www.cloudynights.com/topic/868125-dpac-testing-repository-of-tests-performed-on-refractors/

Even what SV are going to do is not firmed up, originally they where going to move to testing in the green line and then that statement was removed from SV's site.

Note: I've had to have Nic remove around 2 pages of comments around SV on a thread I have on CN as went off on SV tangent.

Edited April 2, 2023 by Deadlake

[jetstream]

1 minute ago, Deadlake said:

At the moment there really is not enough data on SV's line up to call this one way or the other.

Even what SV are going to do is not firmed up, originally they where going to move to testing in the green line and then that statement was removed from SV's site.

It is very possible the rest of the line will be well corrected for green and blue despite being corrected best in red. Its also possible that the 180mm tested had some issues stemming from a slip through QC.IMHO.

To me, the DPAC test and others, take bias out of the equation optics wise. No doubt many scopes from many makers will do well in these tests and some will not.  Time will tell as more and more scopes are run through the test, unless owners are scared they wont test well and therefore affect resale value. IMHO.

I am very interested in further SV tests and also scopes like the Starfield. AT scopes seem to be testing well and it will be interesting to see sample to sample variation in them, if and when more scopes become available.

[Jim L]

12 hours ago, 900SL said:

I had no argument with the initial test on the 180mm scope. It was the insufferable preening and beating a dead donkey that got my goat. There is clearly a partisan camp with an axe to grind over there. 

You can be both right, and an insufferable s*** whistle at the same time ( not in reference to you Jeremy, I hasten to add 😂)

There is a small cohort of posters at CN that has apparently made damaging StellarVue and Vic Maris their mission in life. Though not a fan of StellarVue, Paul isn’t one of that bunch, and his bench test of a single 180 mm StellarVue triplet was made in good faith.

Paul found the scope was almost perfectly corrected in red, and less so in green and blue. StellarVue refunded the owner the full cost of the scope, including shipping, and I’m sure they’ll perform a detailed analysis to determine what went awry. One possibility is that one of the lens elements shifts in its cell, which is supported by the owners observation that sometimes he could see what looked like atmosphere dispersion, while other evenings he could not. That would seem to suggest atmospheric dispersion or a inconsistently located lens element.

The owner of the tested scope observed that the belts in Saturn were more apparent and easier to see in the StellarVue than in his 6” IZOS refractor or his 10” Zambuto reflector, that the Cassini Division was a wide, etched, division, and that in the thinnest part of the rings the division remained very apparent as a thin line. The owner made similar favorable observations of Jupiter, Mars, and Sirius and its companion. I’m not an imager, but photos I’ve seen taken through a SVX180T look very nice to me. The large majority of StellarVue’s sales is to imagers.

Concerning the use of a Zygo interferometer set up in red, I know little about it, other than it doesn’t necessarily have to be problematic as long as green and blue follow along for the ride, and that at least some optics made for the aerospace and defense industries must be certified in red by contract. StellarVue uses their interferometer as a tool to identify and map areas on a lenses for further figuring.

Where does that leave us?  Beyond the abundant nonsense from the CN test thread, including a ludicrous bit concerning whether “another venue” referred to the law courts or to FaceBook, one has to decide whether a group of posters who have never made a telescope, much less one for sale to the public, that on the basis of one test of one scope that may have a faulty lens cell, have somehow caught a very successful company that has sold telescopes for two decades and has hand figured their own optics for the past ten years in a mistake of such magnitude that the company can’t and won’t survive. William of Ockham might have thought the number of assumptions required to come to that conclusion excessive.

My own take is that there’s a distinct possibility that the lens cell from the tested scope may be faulty and allow one or more elements to shift. We may hear back from StellarVue in a couple of months after they’ve returned from NEAF, or we may never know. As to Vic Maris and the rest of the crew at StellarVue, I suspect they are capable of designing and building a telescope that performs well and to the expectations of their customers as evidenced by their long history doing so.

Whatever the outcome of the StellarVue drama one thing is certain, there is a partisan camp of insufferable whistles with an ax to grind against Vic Maris and StellarVue and in a way that seems antithetical to the spirit of amateur astronomy. The pity is that there is an even larger audience that without much in the way of reason or reflection are all too happy to tag along for the ride. It’s probably best they stay over there.

[Deadlake]

4 minutes ago, jetstream said:

It is very possible the rest of the line will be well corrected for green and blue despite being corrected best in red. Its also possible that the 180mm tested had some issues stemming from a slip through QC.IMHO.

To me, the DPAC test and others, take bias out of the equation optics wise. No doubt many scopes from many makers will do well in these tests and some will not.  Time will tell as more and more scopes are run through the test, unless owners are scared they wont test well and therefore affect resale value. IMHO.

I am very interested in further SV tests and also scopes like the Starfield. AT scopes seem to be testing well and it will be interesting to see sample to sample variation in them, if and when more scopes become available.

I think the reason for little data is the hit on resale value, a theory but a reasonable one.

With regards to red line testing, I think the current theory is that the blue line will be more optimised than testing in the green and the green line will also not be as high.

Obviously eyes and CCD are more sensitive to the green line wavelength.
 
At the same time if SV are forced to optimise in the green and red line then the produced lens will be made similar to how AP and LZOS produce their respective lens by testing with multiple wavelengths with an interferometer. 

Which is good for the quality on the lens, however will make them more expensive to produce.
 

[Franklin]

@Mr Spock started a great thread comparing a couple of fine refractors. I've just returned to read on and tbh I'm a little lost, which is the best scope again? The Starfield or the Tak?😁

[John]

11 minutes ago, Franklin said:

@Mr Spock started a great thread comparing a couple of fine refractors. I've just returned to read on and tbh I'm a little lost, which is the best scope again? The Starfield or the Tak?😁

Very nearly a dead heat. 

Until some bright spark DPAC tests a Starfield and shows that it can't be 😜

[Mr Spock]

Now now, let's be sensible. The Tak was the better scope optically, but only be a few percent. Something you wouldn't notice in general use, and not by 3 times (the price).

I don't care much for testing. Just like speakers - because they test well doesn't mean they are going to sound good 

[Peter Drew]

I could buy a 4" Tak tomorrow if one is available, but I won't and probably never will.  Not that I doubt whether the Tak is one of the best available but because I already have a good 4" Vixen Fluorite.  Given my age and the conditions I "observe" in, there would not be the difference in performance to me that would justify the price.  As it happens, I very rarely use the Vixen, why?, because to use it I have to take a tripod, mount and the Vixen outside and set it up to do so.  By contrast I can just switch on a dome mounted 16" SCT which carries a SW 150ED as a finder/alternative view telescope.   🙂

[mikeDnight]

*

Edited April 5, 2023 by mikeDnight

[jetstream]

1 hour ago, Deadlake said:

With regards to red line testing, I think the current theory is that the blue line will be more optimised than testing in the green and the green line will also not be as high.

I understand this and also more than some might think regarding optics. It puzzles me when people think they can tell the difference between .90 strehl and .95 strehl when the mags they use are under 200x usually indicating seeing issues.  A good, smooth diffraction limited scope ie .80 strehl will give great views . The better the optics the higher the mag they can go.

If any scope including SV, Starfield, Tak, Tec A-P can get the colour lines all at .90 strehl and above the view will be very very good.

I never doubted for a minute the tester of the 180SV. I would guess this particular scope had issues and I would also guess the rest do not. Given the close results by @Mr Spock I would like to see a DPAC test of the 2 scopes- they are probably very similar and would be interesting to correlate the results to the visual through both.

[Franklin]

21 minutes ago, Peter Drew said:

As it happens, I very rarely use the Vixen, why?, because to use it I have to take a tripod, mount and the Vixen outside and set it up to do so.

You could stick it on the other side of the 16"SCT to help balance the SW150ED😁.

[RobertI]

This thread has generated some really interesting discussion. There were a couple of comments that nearly made me start separate a thread on the subject of “Can people choose to believe something?” (eg: can someone choose to believe that Tasco make the best telescopes) and another thread on “The psychology of why people buy premium gear”……… but I thought it was best not to poke this hornet’s nest any further! 🙂

Edited April 2, 2023 by RobertI

[Franklin]

6 minutes ago, RobertI said:

(eg: can someone choose to believe that Tasco make the best telescopes

Tasco used offer good scopes, back in the days when Vixen made them for them!😁

[RobertI]

3 minutes ago, Franklin said:

Tasco used offer good scopes, back in the days when Vixen made them for them!😁

Yeah, but Vixen are rubbish. 😆

[Ratlet]

I'm going to have to get to a star party to have a look through some refractors.  I've got an ST80- but it is sitting unloved and unused in a box as the few clear nights have been dominated by the Dob.

I'd quite like to see what the fuss is about.

[F15Rules]

Having just revisited this thread this evening and reading some of the rather combative and rambling posts which have nothing to do with the original topic, I was sadly reminded of the reasons I rarely visit the "other site" these days..🥴

I do hope this isn't a sign of things to come over here.

Dave

[bosun21]

2 hours ago, Franklin said:

Tasco used offer good scopes, back in the days when Vixen made them for them!😁

I think I can remember them, were they little red refractors?

[Franklin]

6 hours ago, bosun21 said:

were they little red refractors?

Yes they were but they weren't DPAC'd, just red😁.

[Stu]

8 hours ago, Ratlet said:

I'm going to have to get to a star party to have a look through some refractors.  I've got an ST80- but it is sitting unloved and unused in a box as the few clear nights have been dominated by the Dob.

I'd quite like to see what the fuss is about.

Try it, you might be pleasantly surprised. I was when I tried mine recently.

Perhaps I’ll do a side by side with my FC-76DC, might help its resale value if I come to sell it.

[Mr Spock]

10 hours ago, F15Rules said:

Having just revisited this thread this evening and reading some of the rather combative and rambling posts which have nothing to do with the original topic, I was sadly reminded of the reasons I rarely visit the "other site" these days..🥴

I do hope this isn't a sign of things to come over here.

Unfortunately is does detract from the thread somewhat, and I agree - that along with some individuals' jibes and childish sarcasm are letting the site down. Let's hope they put the best interests of SGL first. There's nothing I can do about it, but I do know Admin are watching 

[Littleguy80]

I found the review helpful. For me, the takeaway is that the Tak has the edge in performance but at a cost. How much of a difference we see comes down to a lot of factors and whether that difference is worth the cost is down to the individual. DPAC testing certainly sounds like it could be the answer to giving a quantifiable value to the difference between scopes.

[Mr Spock]

30 minutes ago, Littleguy80 said:

I found the review helpful. For me, the takeaway is that the Tak has the edge in performance but at a cost.

Thank you. It does have the edge, though some see reviews like this as some kind of marketing ploy!