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Fluorite vs ED

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#1 snommisbor

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Posted 05 August 2015 - 03:49 PM

Been looking at TAK FSQ's and trying to decide if I want a Fluorite version or the new ED version. I have read advantages of both but I found an article on Takahashi's site and this is what it said.:

 

If you seek optical and mechanical perfection in a truly modern telescope, look no further. Takahashi is the answer. Other telescope manufacturers may claim that ED (Extra-low Dispersion) glass is the equivalent of fluorite or that their older designs will work as well. Unfortunately, they are not being honest. While ED and fluoro-crown lenses can achieve Abbe-coefficients approaching fluorite, they tend to absorb more light in the visible spectrum. This means that fluorite yields a brighter, higher contrast image. Leica, Zeiss, and Kowa have all gone to fluorite in their spotting scopes and telescopes to achieve the maximum performance levels their customers demand. Most of them previously used ED glass. Obviously, they know the difference between fluorite and ED. You will too. Takahashi pioneered the use of fluorite in astronomical telescopes and they are still the leader. Accept no substitute. Get the fluorite advantage. Get Takahashi!

 

Now I have heard that part of the reason they stopped using Fluorite is due to environmental reasons, but that can't be true, being TAK still produces Fluorite scopes. I am just curious if they actually found a better way with ED glass to where it truly is a better color correct glass. Not trying to bash the new Q's I am just wondering why if Fluorite was such a great glass and to read from TAK itself, why they would switch. Seems they are now not being "Honest". 

 

Never really found a good discussion about this online.

 

So let the debate begin. :grin:



#2 Peter in Reno

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Posted 05 August 2015 - 04:05 PM

I think Fluorite has better color correction than typical ED especially at low end of blue light spectrum. This prevents blue halos or bloats of brighter stars.

 

Fluorite is quite a bit harder to make lens than ED therefore quite a bit more expensive.

 

I looked up TAK latest FSQ-106ED at OPT web site and it turns out that it has four elements which may explain good color corrections but still pretty expensive ($5150).

 

TAK newest FSQ-130ED uses five elements which may produce even better color corrections. Costs a whopping $12.8K!!!!!

 

I believe the more elements the better color corrections. It may be cheaper this way than using Fluorite.

 

Peter



#3 tomcody

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Posted 05 August 2015 - 04:19 PM

Tak seems to build what the customers want, but it takes a few years to design and build that " new design" with all the customer's desires. So when Tak dsigned the "new Q" the customers were complaining the original Q was too heavy and too long for the big want items: a light airline portable scope with long back focus for binos, that would work with ASPC/ full frame chip dslrs and light to medium ccd cameras ( that were popular when the new Q was designed) and the trend in all other manufacturers was to go to ED glass so the flourite seemed like less of a selling point. The new Q does what it was designed for very well. 

But that does not answer your question, which is better? Both! it depends on your needs. For visual use on deep space nebula ( like M42) the flourite can bring out finer detail due to the high contrast of flourite, but the flourite scope has only 120mm of available backfocus so it is very hard (and a real pain) to make binos work or even limited sizes of   2" eyepieces, something the new Q ( with 178mm backfocus with the captian's wheel) can do with ease!

 

For photo work both are about equal to the camera,  but the flourite Q has a larger focuser that can handle the BIG  chip cameras without extensive mods that people do to the new Q focuser.

Which one to get? are you a visual person that does some ap and does not use binos or very large eyepieces? the original may be for you. Do you use binos? need airline portable? have a small light camera? the new Q is your best bet.

As always YMMV

Rex


Edited by tomcody, 05 August 2015 - 04:26 PM.


#4 Thomas A Davis

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Posted 05 August 2015 - 04:22 PM

It becomes a matter of mating glass and design. With a 4 element design, there should be no issue on this. Since the FSQs are designed for imaging, I seriously doubt Takahashi would produce a scope that had haloing on images. For one, they value their reputation, and to be sure, FP53 would be the fluorite replacement with mating glasses that correct CA to a very high degree for imaging. I'm sure the Takahashi designers have handled this quite well.

Tom

#5 Raginar

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Posted 06 August 2015 - 01:04 AM

I don't know much about the differences between the two.  But, I can say my FSQ106n is very well corrected and the focuser is well built for imaging.  I'm glad I purchased it.  The only thing I kind of wish I could do is use the reducer so I could get it down to 350mm for some really wide field images.



#6 Sky Muse

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Posted 06 August 2015 - 02:40 AM

Now I have heard that part of the reason they stopped using Fluorite is due to environmental reasons, but that can't be true, being TAK still produces Fluorite scopes.

 

I've read that the FS series was discontinued around 2005 due to the toxicity of their rear mating elements.  I had also read that fluorite had become prohibitively-expensive in sizes 4" and larger.  Then began a seven-year hiatus until a 4" fluorite was reintroduced in 2012; but nothing larger we've seen, and for the common marketplace.  And all the while, at least their 60mm fluorites have remained in production, unabated; not to mention their special-order 8" fluorite refractors, and larger even, if you've got the cash.  So no, fluorite has never been considered toxic.

 

Who knows what goes on behind Takahashi's doors, but Takahashi itself. 



#7 Paul G

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Posted 06 August 2015 - 06:59 AM

Been looking at TAK FSQ's and trying to decide if I want a Fluorite version or the new ED version. I have read advantages of both but I found an article on Takahashi's site and this is what it said.:

 

If you seek optical and mechanical perfection in a truly modern telescope, look no further. Takahashi is the answer. Other telescope manufacturers may claim that ED (Extra-low Dispersion) glass is the equivalent of fluorite or that their older designs will work as well. Unfortunately, they are not being honest. While ED and fluoro-crown lenses can achieve Abbe-coefficients approaching fluorite, they tend to absorb more light in the visible spectrum. This means that fluorite yields a brighter, higher contrast image. Leica, Zeiss, and Kowa have all gone to fluorite in their spotting scopes and telescopes to achieve the maximum performance levels their customers demand. Most of them previously used ED glass. Obviously, they know the difference between fluorite and ED. You will too. Takahashi pioneered the use of fluorite in astronomical telescopes and they are still the leader. Accept no substitute. Get the fluorite advantage. Get Takahashi!

 

Now I have heard that part of the reason they stopped using Fluorite is due to environmental reasons, but that can't be true, being TAK still produces Fluorite scopes. I am just curious if they actually found a better way with ED glass to where it truly is a better color correct glass. Not trying to bash the new Q's I am just wondering why if Fluorite was such a great glass and to read from TAK itself, why they would switch. Seems they are now not being "Honest". 

 

Never really found a good discussion about this online.

 

So let the debate begin. :grin:

 

Not much to debate. That's the old "fluorite advantage" sales pitch they used when FS and FCT scopes were their bread and butter. Even Tak doesn't believe that stuff any more. And the statement about Zeiss and Leica spotting scopes is blatantly false. They use "fluoride glass" which is ED glass like FPL53 (which has fluorite as an ingredient), not fluorite. Sorry, no magic.



#8 BillP

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Posted 06 August 2015 - 08:38 AM

I am just curious if they actually found a better way with ED glass to where it truly is a better color correct glass. Not trying to bash the new Q's I am just wondering why if Fluorite was such a great glass and to read from TAK itself, why they would switch. Seems they are now not being "Honest". 

 

As has been said many times, there is nothing about a single element that leads to better color correction...it is only in the mating of 2 elements that one gets more advantage.

 

As to the Fluorite Advantage, it is the same as to advantages that Astro-Physics makes about their wares, or that Tele Vue makes about their wares, or that TEC makes about their wares...it's all just Sales & Marketing speak :lol:   Better determination will come from field observers IMO.  In that realm, to me seems to be a mixed bag with some folks saying they see an advantage in less scatter, and others not.  Unfortunately I have not viewed through Fluorite anything :bawling: 
 


Edited by BillP, 06 August 2015 - 08:41 AM.


#9 Niklo

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Posted 06 August 2015 - 09:58 AM

Hello,

as far as I remember I read that the advantage of Fluorite is or was to find a good partner glass for a two lens APO to do a good correction of CA and spherical aberration. For FPL53 it's or was harder to find a good partner glass to do both good colour correction and good correction of spherical aberration. A good optic designer will find a way to get a very good ED, too. For a triplet APO it is no problem to use ED glass instead of fluorite glass.

Fluorite glass is very expensive and hard to work so today it's avoided.

Clear sky,

  Roland


Edited by Niklo, 06 August 2015 - 10:02 AM.


#10 ed_turco

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Posted 06 August 2015 - 10:10 AM

Fluorite wins every time.  All these special "crowns" that come out are all wannabes.  Nothing comes close to Fluorite for color correction.  I still remember the guy who made an apo and brought it to Stellafane.  It was, believe it or not, a fluorite/Bk7 combination, the Bk7 element being the "flint' in this case.  And it was pretty good, to say the least.  Tried that one myself years later and it still was a whole lot better than the ED combinations out way back when.

 

I've repeatedly told the story of my religious experience when I looked through Roland Christen's apo.  It was that good.  Remember though that his was a three element job.  With two elements, fluorite is all you need.

 

 

ed



#11 snommisbor

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Posted 06 August 2015 - 11:39 AM

I do know the old FSQ's have two fluorite elements one in the front doublet and one in the rear doublet. I am pretty sure the front one is on the outside but not sure where the back fluorite is, I would assume it is on the inside keeping the same lens configuration all the way through. Think I am going to try the Fuorite one. Ive always wanted to get a fluorite scope, figure if I don't like it could resale for what I paid more than likely or lose very little.



#12 t.r.

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Posted 06 August 2015 - 11:56 AM

I still like Fluorite...the laser test confirms for me that like Mr. "Winter Warlock", there is still a little magic left in it. ;)

Attached Thumbnails

  • images.jpg

Edited by t.r., 06 August 2015 - 11:57 AM.


#13 Eddgie

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Posted 06 August 2015 - 02:12 PM

Fluorite might be an excellent glass but it is still a refractive medium and in the thicknesses used in telescope lenses, the absorption can be completely dismissed as a concern.

 

(Either that, or the refractor forum has a serious problem that the most perfect telescope design ever known to man has a serious problem with transmission.  LOL)

 

 

Anyway, or friend Vladimer has done us the great favor of plotting out many different designs, and this info comes from his must excellent web site.

 

 

A 100mm  doublet at f/7  with CaF2 with a mating element of K5 has a polychromatic Strehl of .93.  That is not so great..

 

By comparison, a 140mm f/7 triplet with K10, FPL53, and BK7 has a polychromatic Strehl of .955.

 

Now, you could make the 140mm f/7 with K7, CaF2 and K7 and get a whopping improvement to .965, which is a difference sooooooooo minute that only the marketing people at Takahashi probably have the ability to see when they look at the balance sheet.

 

But it gets better!!!!  If you have the money, you can build a 140mm F/7 with ZKN7, FPL 53, and ZKN7 and get a blistering .970 polychromatic Strehl.

 

Not only was Fluorite expensive to make, it was dangerous to the people that were involved in manufacture.

 

Fluorite is good when you want to make a doublet, but the modern triplet LED is as good, and given that you can make a triplet with less exotic glass that performs better than a much slower doublet would have to be, the handwriting was on the wall.

 

All of these plots can be seen here in table 12:  http://telescope-opt...po_examples.htm

 

And anyone that suggests that the transmission in Flourite is so much better as to make a difference needs to be drummed off of the refractor forum for condemning the refractor as in inferior design.  I mean we have been told repeatedly how much better transmission is in refractors, but OMG if it has to be a Fluorite refractor, well that puts the rest of you non Fluorite owners in big trouble, running around with your vastly inferior triplets.

 

 Hard to beat a modern ED triplet, and while you can (oh so very very very slightly if your goal is to make as much profit as possible), the question is simply is it worth it.  

 

Answer is no.  If cost is not object, you can beat a Fluorite with FPL 53 sandwhiched between ZKN7

 

Maybe in very small spotting scopes the tradeoff to a doublet Fluorite to an ED doublet makes sense, but in telescope size instruments, probably cheaper to go with a triplet and get better performance to boot.  


Edited by Eddgie, 06 August 2015 - 02:26 PM.


#14 Eddgie

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Posted 06 August 2015 - 02:20 PM

Another one from the table referenced above.

 

100mm f/10--- 7KN7 and FPL53.   Polychromatic Strhel of .99.   

 

CaF2 and K5..  .984..   

 

And yet another one... 

 

Here is a glass most people would throw up on vs FPL53.   Another 100mm f/7 triplet   It is a ZNK7, FK51, ZNK7  with a polychromatic Strehl of .97.

 

Man, people tend to dismiss the magic of a triplet.  Even using non ED glass, a triplet can come very close to a Fluorite doublet.

 

Even an FK51 triplet can give outstanding performance in a 4" instrument.    Only the marketing and sales people at Tak would see a real difference in performance, and it would all be in the ledger.

 

This last one is perhaps a rant at the 120ED.  People think it is better than the ES because it uses FPL 53..

 

But a doublet is a doublet, and adding an extra piece of glass to the ED formula makes it possible to get superior color correction over what you can get with Fluorite or FPL 53 in a doublet.   Three pieces of glass rule...   To suggest that the 120ED has better color correction than the ES 127 because it uses FPL 53 instead of the FPL51 equivalent used in the ES ignores the awesome benefit of adding a third element.


Edited by Eddgie, 06 August 2015 - 02:26 PM.


#15 edif300

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Posted 06 August 2015 - 03:05 PM

The improvement of the FSQ-106ED over FSQ-106N comes basically by improved the optical design. Not as easy as using ED or Fluorite. Takahashi had explained this point well in 2007.

 

On the FSQ-106ED they increased the size of G3 lens about 50% and also positioned nearest to G2. This improves field illumination over sensor and improves color correction because now works similarly to a TOA.

 

FSQ-106ED and FSQ-106N are different optical design.

 

FSQ-106N -> G1 and G3 are Fluorite.



#16 Niklo

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Posted 06 August 2015 - 03:11 PM

Hi Eddgie,

yes that is similar to what I read somewhere. For doublet like the old 102/920 fluorite is good but for triplets it does not make sense.

There should be a good partner glass for fluorite that should be fine doublets to have very little CA and very little spherical aberration, too while the normal FPL53 doublet has a very good correction of CA but more problems with spherical aberration. I tried to find the text but I currently cannot find it any more. Maybe I remember wrong. At least I seem to remember correctly that for triplets Fluorite does not improve things.

Clear skies,

  Roland



#17 Lance1234

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Posted 06 August 2015 - 03:18 PM

[color=#800080][i]Man, people tend to dismiss the magic of a triplet. ]

Just a couple of other considerations...

And how much longer does said triplet take to reach thermal equilibrium prior to observing?
And if said triplet somehow gets out of alignment?

Perfect optics aren't necessarily the only consideration.

Edited by Lance1234, 06 August 2015 - 03:21 PM.


#18 Markab

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Posted 06 August 2015 - 03:25 PM

More to life than just simply color correction. No doubt that an FPL-53 triplet will outperform a fluorite doublet here. I've seen it everytime between my Tak fluorite doublets and AP triplets.

 

However, despite this, I also felt that my Tak fluorites produced better contrast and color saturation compared to the triplets for critical planetary observation. This may or may not have anything to do with the fluorite specifically or may or may not have to do with the doublet versus triplet design. However, from an intuitive level, it makes sense that a well-corrected doublet should produce slightly better contrast than a triplet, all else being equal (which, of course, it never is).



#19 BillP

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Posted 06 August 2015 - 03:35 PM

Just a couple of other considerations...

And how much longer does said triplet take to reach thermal equilibrium prior to observing?
And if said triplet somehow gets out of alignment?

Perfect optics aren't necessarily the only consideration.

 

 

:waytogo:   Excellent point.  What makes a scope "good" involves a whole lot more than a Strehl difference of .05 and perfection in color correction.  Thermal behavior, scatter, and other things all are working in the system that are of different levels of importance to different observers.



#20 roadi

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Posted 06 August 2015 - 03:47 PM

Take a look at Mr.Rohr's test results of both Fluorit and ED doublet's. 

Easy to see which has the best color correction, judge for your self..

One test with a TMB 100/800 and a Tak FS102/820 shows both having about equal W-index number (Apo index) The Tak has the blue slightly out and the TMB the red slight out, both reaching about same w-index.

Tak FS W=0.21

TMB W=0.24

 

W =  < 1 = Apo

W = 1-2 = Semiapo

W = > 2 = Achroma



#21 Astrojensen

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Posted 06 August 2015 - 03:52 PM

From what I have read and understand, the reason for choosing fluorite is today not so much the color correction that can be achieved, but the much lower scatter. Fluorite can be exceptionally pure and will basically scatter no light at all. A famous test is to shine a green laser through the objective and the beam is invisible where it passes through the fluorite, while it is easily visible where it passes through normal glass.

 

 

Clear skies!
Thomas, Denmark



#22 roadi

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Posted 06 August 2015 - 03:59 PM

BillP, with your visulal acuity I think it would be interesting to see your judgement on fluorite vs ED in a comparo, both scopes well made of course  :)


Edited by roadi, 06 August 2015 - 04:00 PM.


#23 GJJim

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Posted 06 August 2015 - 04:04 PM

For a given f-ratio, fluorite allows for surfaces with slightly longer radii and this reduces higher-order aberrations. It also reduces or eliminates the need for aspherical surfaces.



#24 sydney

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Posted 06 August 2015 - 04:40 PM

The improvement of the FSQ-106ED over FSQ-106N comes basically by improved the optical design. Not as easy as using ED or Fluorite. Takahashi had explained this point well in 2007.

 

On the FSQ-106ED they increased the size of G3 lens about 50% and also positioned nearest to G2. This improves field illumination over sensor and improves color correction because now works similarly to a TOA.

 

FSQ-106ED and FSQ-106N are different optical design.

 

FSQ-106N -> G1 and G3 are Fluorite.

 

Yes, Tak's design specs show improved correction of the FSQ106ED over the older fluorite FSQ106N. 

 

There is lots of good info on Tak Q scopes here:

http://www.astrosurf...Q-106ED/FSQ.htm

 

Rohr's test of the FSQ106ED also shows exceptional performance when using the 1.6X extender:

http://www.microsoft...34374#post34374



#25 Eddgie

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Posted 06 August 2015 - 04:46 PM

For a given f-ratio, fluorite allows for surfaces with slightly longer radii and this reduces higher-order aberrations. It also reduces or eliminates the need for aspherical surfaces.

 

 

Spherochromatism is indeed a serious issue and one that the refractor forum tends to totally discount (as it does the horrible damage done by Chromatic Aberration in fast acrhromats while thoroughly slamming the damage done by even the smallest of central obstructions which do far less damage).

 

The thing though is that spherochromatism is a much different kind of error, and while the damage is real, it really only shows up when imaging with fairly large or fairly fast refractors.

 

The 120ED and 127ED is a case in point.  I would estimage by similar designs that the 127ED has better chromatic aberration correction (defocus( than the 120ED doublet.    The fringing people see (in both cases actually) is probably more to do with the spherical aberration of the blue/violet diverted to the diffraction rings because of the spherical aberration of those colors than from the defocus.

 

In other words, the defocus on these is almost nil.    With either design, the crossover is so close that for visual use, it would be hard to see the defocused colors.

 

But not the fringing caused by the spherical aberration of the blue/violet light, because this means the Airy Disk in these colors is slightly larger than in the green and red lines (at least this is the way I understand it).

This can actually be seen in the plots in figure 149 on the above referenced page.   A lot of these designs suffer from almost zero defocus.   When the scope gets big and fast though, the spherochromatism will start to show visually, and if it is really big and really fast, it will show dramatically in a long exposure CCD image.

 

And that is why Roland Christen does apherize his objectives.

But hardly anyone else in the business does this.




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