71 replies to this topic

[noisejammer]

But his point was that the same can be accomplished with a single element of FPL53 and two crowns. 

 

It's the use of a large air space that provides the improvement in the Tak.

I get his point that you can achieve the same with flint-crown-flint that you can with crown-flint-crown. To a first approximation, this is true however the single ED performance has worse CA (as Vla's plot clearly demonstrates.)

 

My point is that the Tak arrangement outperforms either very considerably (also demonstrated by Vla's plot) and it appears this can't be equaled using a single ED slab (or it would be done.)

[Alan French]

I get his point that you can achieve the same with flint-crown-flint that you can with crown-flint-crown. To a first approximation, this is true however the single ED performance has worse CA (as Vla's plot clearly demonstrates.)

 

My point is that the Tak arrangement outperforms either very considerably (also demonstrated by Vla's plot) and it appears this can't be equaled using a single ED slab (or it would be done.)

I have not seen any triplet Crown-ED-Crown design posted here with a wide air-space to compare with the Tak design, so I have no idea what you have seen that leads to this conclusion.

 

The two closely spaced designs posted by Vlad look quite similar. 

 

Clear skies, Alan

[Alan French]

Here's a quick design, with a center element of FPL53 surrounded by two crowns and using a large airspace, Roland shared with me yesterday, with permission.

 

Clear skies, Alan

 

 

 

 

 

 

[Vla]

Alan, I'll take "quick" as a joke. Interesting part is that this shows that similar correction can be achieved with NPN arrangement too. Not nearly enough to make a final conclusion, but based on these samples looks like the PNP is still capable of better correction here, at least on paper (tolerances are super tight, even in the triplet context). I just couldn't reproduce those nearly straight up lines with the NPN, and don't see them in this example too. Here's the same PNP design from before, with optimized color correction (nearly identical error in F and C). But no one can tell, because the difference is really negligible, and we don't know is it the same glass pair, or not.

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[BillP]

With permission, here is what Roland Christen says about this...

 

"There is zero advantage to using 2 ED elements with mate in middle versus 2 mates with ED in middle. ZERO!"

 

The best debate here would be between RC and Tak's senior designer, not anyone here.  I'm sure the Tak designer would disagree and for a variety of reasons known to them, and not for reasons we can divine nor can RC.  There are plenty if A-list optical designers around the planet...not like only one of them has the best insight in all the world.  I think the Tak TOA performance speaks for itself and nothing more really needs to be said.

Edited by BillP, 14 October 2019 - 04:18 PM.

[Alan French]

The main point is that there is nothing magic about using two ED elements with a center crown. Similar results can be achieved with a single center ED element surrounded by two crowns. 

 

Here's another, more optimized design by Roland. He comments it was optimized for smallest spot size and the lines could be straighter, but at the expense of spot size.

 

 

Clear skies, Alan

 

 

[noisejammer]

Looks like everyone here is interested in the design of premium APO. For me this is really simple, good quality optics with decent price, I will buy it. [if it is] much more affordable than Stellarvue, ES and Skywatcher, not to mention Takahashi, TEC, AP or CFF. As long as the performance is close to 80-90%, I think it is worth the money. Most of the time, the image quality is limited by weather and other conditions, not just by a single scope.

Even as a TOA owner, I can't help feeling that technology has caught up over the past 10 years and there's very little justification for the exotics (assuming there ever was.)

 

I anticipate this scope will have a Strehl around 0.93-0.95 (unashamedly wild-assed guessing). If you compare this with an exotic at (perhaps) 0.98, the change is likely to be less than 5%. I have to wonder where the rest of the light will go - probably it results in a barely perceptible loss of contrast.

 

You might find the optics are excellent and decide to upgrade the focuser - even Tak owners do this routinely.

 

This doesn't mean I will dump my TOA - I'd still love to pass it down to a grandchild or maybe my alma mater - but I won't be buying another.

[Vla]

The main point is that there is nothing magic about using two ED elements with a center crown. Similar results can be achieved with a single center ED element surrounded by two crowns. 

 

Here's another, more optimized design by Roland. He comments it was optimized for smallest spot size and the lines could be straighter, but at the expense of spot size.

 

WideAirspacedSuperApo-1 SM.jpg

 

Clear skies, Alan

Hard to tell based on what we have here, because we can really compare only two OG's that use the same glasses. I can't go down to f/6.5 with FPL53/BSL7 in the NPN arrangement, but have no problem if it's PNP, gives nice straight lines all the way up (well, almost). If I use Ohara BSM81 instead, it works in the NPN at even faster ratio (f/6.33). In fact, it's similar to Roland's before computer optimization, only with even less spherochromatism.

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Edited by Vla, 15 October 2019 - 10:28 AM.

[Alan French]

We don't know specifics of the Tak design. Although we can assume they had reasons for using two ED elements, we can only guess what they were. (I was also thinking that, although it is the more expensive choice, many serious astrophotographers seem willing to spend significant sums on equipment.) Perception can certainly enter into the marketing end of things. 

 

Are we talking about differences that would be significant in terms of performance?

 

I'm unlikely to buy another telescope, so this is just a matter of curiosity for me.

 

Clear skies, Alan

Edited by Alan French, 15 October 2019 - 10:47 AM.

[Vla]

How fast it can go is definitely part of performance. That's all that triplets are about. There are differences between PNP and NPN, and from what I see they can be significant. It's still to little to generalize, but I see Roland's "zero difference" as relating to some narrower context. What exactly made Tak go PNP is anyone's guess. But one thing already mentioned is that the spaced  design has significantly tighter tolerances, so everything else equal, it will be farther away from its design optimum. How much, and where that exactly puts it vs. standard triplets may be in that movie that we'll never see.

[BillP]

Are we talking about differences that would be significant in terms of performance?

 

I'm unlikely to buy another telescope, so this is just a matter of curiosity for me.

 

I would say yes.  The reason is that even some very subtle nuance-level differences are important for some people.  So just depends on what is important for you as an individual.  So even a single, very subtle, nuance of a difference in the right area, can make all the difference in the world for an observer and thereby it makes it significant in terms of performance for them!  At the eyepiece, the designers opinion is fairly meaningless and the wants and needs of the particular observer become the most authoritative opinion.

[Michaeljhogan]

With permission, here is what Roland Christen says about this...

 

"There is zero advantage to using 2 ED elements with mate in middle versus 2 mates with ED in middle. ZERO!"

 

Roland pointed out that a triplet is simply two doublets combined. With the middle elements of the same glass, they can just be merged into a single element, creating a triplet.

 

So you can have a Crown-ED + ED-Crown becoming a Crown-EDED-Crown and thus Crown-ED-Crown (Steinheil + Fraunhofer).

 

Or an ED-Crown + Crown-ED becoming an ED-CrownCrown-ED and thus ED-Crown-ED (Fraunhofer + Steinheil).

 

Two f/15 doublets, with the same glasses adjoining and allowed to fuse together, form an f/7.5 triplet.

 

Whether you create an Crown-ED-Crown triplet or a ED-Crown-ED triplet. "the result is almost exactly the same - no change in color correction or any of the Seidel aberrations." - Roland Christen

 

Clear skies, Alan

And what do you think would be the result if Roland said yes their is an advantage with Takahashi using 2 FPL-53 or FPL-55 elements

where do you think the costumer would go ??? and they dont have to wait 3-5 years to get it of course Roland wouldnt tell a lie to sell

his Apo,s never and stop you from contacting Takahashi.   All Hail the Great Lord Roland

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Edited by Michaeljhogan, 15 October 2019 - 07:35 PM.

[noisejammer]

And what do you think would be the result if Roland said yes their is an advantage with Takahashi using 2 FPL-53 or FPL-55 elements

where do you think the costumer would go ??? and they dont have to wait 3-5 years to get it of course Roland wouldnt tell a lie to sell

his Apo,s never and stop you from contacting Takahashi.   All Hail the Great Lord Roland

That's quite unfair. A month after the 140EDF was offered, I wanted to order one. Marj suggested I buy a Tak because I'd be very lucky to ever receive the 140. So I did. Roland & Marj didn't loose a sale - they sell everything they can make at a price that suits them.

[Michaeljhogan]

That's quite unfair. A month after the 140EDF was offered, I wanted to order one. Marj suggested I buy a Tak because I'd be very lucky to ever receive the 140. So I did. Roland & Marj didn't loose a sale - they sell everything they can make at a price that suits them.

Sharpstar are the Takahashi and AP of Chinese Apo refractors they are the number one ultra high end company thats now geared toward

imaging they now also make ultra high end Newtonian reflectors just in the last eight years they have just kept growing.

 

In Europe they have a great name many of their scopes are sold under a different name like TS in Germany now that is ending its

well known that Roland admitted back just a few years ago that the market was flooded with cheap Chinese from 3 to 5 inch Apo refractors

this is why Takahashi and AP stopped making the FS TSA-102 Traveller 92 and 105 their getting better every year.

 

Yes their not as good but they are very close just look at the focusers on Chinese apos today from back in 2011 now with Sharpstar

im willing to bet less and less people are willing to spend the extra 3-4 thousand i would say their is little difference between my TSA-120

and the Sharpstar 140PH Apo every year the gap closes thats why Sharpstar are usually the more expensive of Chinese Apo 

 

PS ask Roland about his 92mm F5.5 Stowaway im sure he will agree with me

 

http://www.sharpstar...en/product.html

[noisejammer]

Your comment was

And what do you think would be the result if Roland said yes their is an advantage with Takahashi using 2 FPL-53 or FPL-55 elements where do you think the costumer would go ??? ...

I find this is objectionable. It implies deceit.

 

There's no doubt that some Chinese makers are delivering good scopes.

 

I have no inside knowledge of why Tak stopped the TSA102 (do you?) but they are excellent scopes. While it's plausible that competition undermined it; absent privileged information, statements to this effect are speculation. Ditto for why the Stowaway lines were stopped and then restarted.

 

I have no doubt that A-P is doing quite nicely from the current run of Stowaways.

[Heywood]

Sharpstar are the Takahashi and AP of Chinese Apo refractors they are the number one ultra high end company thats now geared toward
imaging they now also make ultra high end Newtonian reflectors just in the last eight years they have just kept growing.

In Europe they have a great name many of their scopes are sold under a different name like TS in Germany now that is ending its
well known that Roland admitted back just a few years ago that the market was flooded with cheap Chinese from 3 to 5 inch Apo refractors
this is why Takahashi and AP stopped making the FS TSA-102 Traveller 92 and 105 their getting better every year.

Yes their not as good but they are very close just look at the focusers on Chinese apos today from back in 2011 now with Sharpstar
im willing to bet less and less people are willing to spend the extra 3-4 thousand i would say their is little difference between my TSA-120
and the Sharpstar 140PH Apo every year the gap closes thats why Sharpstar are usually the more expensive of Chinese Apo

PS ask Roland about his 92mm F5.5 Stowaway im sure he will agree with me

http://www.sharpstar...en/product.html

Are Sharpstar scopes sold in the USA? If so, by whom? I would like to learn more about them.

Thank you.

[syxbach]

You can contact their manager Michael Fong from the website about details. You can also get them from US vendors such as astronomics or agena. Sometimes their products are rebranded (just like discontinued Astro-Tech EDQ65). Now I guess they can be sold as their brand. 

 

Are Sharpstar scopes sold in the USA? If so, by whom? I would like to learn more about them.

Thank you.

Edited by syxbach, 16 October 2019 - 04:00 PM.

[Jared]

I’m sure there was a good reason Tak chose to put two ED elements in the TOA, not just marketing.  I’m also sure it’s a mistake to simply extrapolate that to mean more ED elements make a telescope better.  What makes a telescope better is a well though out design that has been well executed—whatever the materials chosen for the glass.  Just using the “best” materials is not enough, any more than the “best” ingredients are enough when cooking. Trust me, I can make a really lousy meal with really good ingredients.  Do it all the time. The glass is one component.  If the design is a good one (well suited for the purpose with achievable tolerances).  If the materials are good.  If the machining is accurate.  If the multi-coatings are good.  If the figure is good.  If the polishing is good.  If the assembly is good and the optics are properly spaced and aligned.  If all this happens, you get a good scope.  
 

We tend to obsess over the choice of glass because it is something that shows up in a spec sheet.  We can evaluate it.  The other factors?  We can’t judge them except by buying, using, and evaluating the scope.  So we fight over glass.

 

Hopefully the manufacturer of this 140 will do a good job on all the aspects I mentioned (and probably several others I didn’t think of) and the telescopes will be right up there with AP, Tak, TEC, LZOS, and others.  Only the experiences of owners will tell us.  A spec sheet won’t.  Spot diagrams won’t.  They can tell you whether the design, if well executed, is suitable for the purpose.  That’s about it.  This scope is clearly aimed at imagers.  The specifications look fine.  Don’t worry about the glass.  Don’t worry about whether one ED element is better than two.  Ultimately, the care taken in manufacturing is much more important.

Edited by Jared, 16 October 2019 - 05:00 PM.

[syxbach]

Totally agree! I may take the first step to buy and test it when I get extra savings . Hope it will have good performances.

 

I’m sure there was a good reason Tak chose to put two ED elements in the TOA, not just marketing.  I’m also sure it’s a mistake to simply extrapolate that to mean more ED elements make a telescope better.  What makes a telescope better is a well though out design that has been well executed—whatever the materials chosen for the glass.  Just using the “best” materials is not enough, any more than the “best” ingredients are enough when cooking. Trust me, I can make a really lousy meal with really good ingredients.  Do it all the time. The glass is one component.  If the design is a good one (well suited for the purpose with achievable tolerances).  If the materials are good.  If the machining is accurate.  If the multi-coatings are good.  If the figure is good.  If the polishing is good.  If the assembly is good and the optics are properly spaced and aligned.  If all this happens, you get a good scope.  
 

We tend to obsess over the choice of glass because it is something that shows up in a spec sheet.  We can evaluate it.  The other factors?  We can’t judge them except by buying, using, and evaluating the scope.  So we fight over glass.

 

Hopefully the manufacturer of this 140 will do a good job on all the aspects I mentioned (and probably several others I didn’t think of) and the telescopes will be right up there with AP, Tak, TEC, LZOS, and others.  Only the experiences of owners will tell us.  A spec sheet won’t.  Spot diagrams won’t.  They can tell you whether the design, if well executed, is suitable for the purpose.  That’s about it.  This scope is clearly aimed at imagers.  The specifications look fine.  Don’t worry about the glass.  Don’t worry about whether one ED element is better than two.  Ultimately, the care taken in manufacturing is much more important.

[Vla]

A few things could be said based on the published LA graph. The error in the violet g-line is about 0.44mm, which gives about 0.37 wave p-v wavefront error (from W=L/64F^2 in mm for the longitudinal error L in mm, for primary and secondary SA, for the mixed, curled back forms good approximation). That's pretty good, but comes at a price of compromised green and red (plots leaning to the left), where error in the red is still only about half as large, but in the green it's about 1/6-1/7 wave, and could be less than 1/10 if minimized. This implies that objective is kind of compromise between best visual and best photo correction (and the plot looks better too). Can't tell how close the actual units will remain to it, but indicates what they are aiming at.

[Heywood]

You can contact their manager Michael Fong from the website about details. You can also get them from US vendors such as astronomics or agena. Sometimes their products are rebranded (just like discontinued Astro-Tech EDQ65). Now I guess they can be sold as their brand. 

Well, Astronomics and Agena Astro, according to their websites, sell only a few of the Sharpstar telescopes, none of them "large" refractors.  

Edited by Heywood, 16 October 2019 - 07:53 PM.

[25585]

Your comment was

I find this is objectionable. It implies deceit.

 

There's no doubt that some Chinese makers are delivering good scopes.

 

I have no inside knowledge of why Tak stopped the TSA102 (do you?) but they are excellent scopes. While it's plausible that competition undermined it; absent privileged information, statements to this effect are speculation. Ditto for why the Stowaway lines were stopped and then restarted.

 

I have no doubt that A-P is doing quite nicely from the current run of Stowaways.

I hope the TSA120 continues. But if Takahashi introduce a FC125DZ, the TSA will be on borrowed time.

[noisejammer]

I hope the TSA120 continues. But if Takahashi introduce a FC125DZ, the TSA will be on borrowed time.

Indeed, but the Chinese makers are rapidly approaching the same level of performance. This is a problem inherent to chasing people's disposable income.

 

I expect that the true exotics will be safe for a while but to stay in business, Tak has to keep sales bubbling along. One way is to offer equal performance at lower cost.

[Don Allen]

Having owned one of Vic’s dual OK-4 scopes I can attest to the beautiful images it gave. Is it better than his current SVX series? I would enjoy the time spent at the EPs determining that but my bank account wouldn’t survive.

[calypsob]

what is the asking cost?