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Lightweight 5" Fluorite doublet

beginner dso optics refractor
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#1 ratnamaravind

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Posted 21 April 2017 - 12:32 PM

Why isn't there a compelling lightweight 5" fluorite doublet offering in the market??

 

Is it because:

1. The demand side: Not enough people want 5" fluorite doublets
(that argument doesn't pass the smell test for me- since 5" seems to be the refractor sweet-spot between portability, cool down, enough aperture for brighter DSOs and knockout views on planets, moon and popular objects)

 

2. The supply side: Good lightweight ones are very expensive to produce
(AFAIK nothing comparable to Tak FS128 and the Borg 125SD or some rarity like the FC125)

 

3. Some other emotional/legacy reason?

 

...just out of curiosity.

 

I would be VERY interested if there was a well corrected f/7 - f/8ish 5" fluorite with the latest coatings.


Edited by ratnamaravind, 21 April 2017 - 12:41 PM.

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#2 glend

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Posted 21 April 2017 - 12:48 PM

Demand side, the market has quickly passed it by. The obsession with APOs, and flat field APOs, mean ED doublets do not sell as well, regardless of glass they are not seen as premium scopes (in that size) any more. They are regarded as a yesterday design. Niche demand continues for some, like the APM 140 ED Doublet, which has its fans,  but it is bigger of course. Many folks aspire to 130 -152mm APOs, where more competition has improved pricing.

Simple 127mm EDs do not impress at Star Parties, dark site gatherings, NEAF, etc anymore. Imho


Edited by glend, 21 April 2017 - 12:55 PM.


#3 BillP

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Posted 21 April 2017 - 01:39 PM

Takahashi is certainly moving that way.  The 76 fluorite doublets, then the 100 fluorite doublets and stopping production of the TSA-102.  I would bet that they will continue and come out with a fluorite doublet in the 120-125mm, then retire the TSA-120. 


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#4 balu01

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Posted 21 April 2017 - 01:47 PM

Takahashi is certainly moving that way.  The 76 fluorite doublets, then the 100 fluorite doublets and stopping production of the TSA-102.  I would bet that they will continue and come out with a fluorite doublet in the 120-125mm, then retire the TSA-120. 

Bill this is exactly what I am waiting for too, say a reincarnation of the FS128 or similar, I was hoping to see TAK releasing something like that this year I was sort of disappointed seeing the FC100DL re-enter as a new offering. The DL is an amazing scope , frankly it is my favorite right now, exactly for it's light weight and impeccable views. It's like taking a toy ( feather ) scope out in the field to have your socks blown off when you look through it.

 

If there was such thing released I would be all over it too.  I suggest we start a sign up sheet and send it to TAK maybe we can talk some sense into those guys bounce.gif


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#5 BillP

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Posted 21 April 2017 - 01:53 PM

I consider the 100DL as a good sign...obvious that there is sufficient interest to make more.  The more the 100mm class is successful, the greater chance they will make a larger one.  I personally think they will go with 125mm as a throwback to the old FC125.  If they do offer one...I will have to sell a kidney or something I suppose.


Edited by BillP, 21 April 2017 - 01:54 PM.


#6 balu01

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Posted 21 April 2017 - 01:59 PM

Start looking for a buyer for my kidney too Bill


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#7 bob midiri

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Posted 21 April 2017 - 02:13 PM

You may think I'm nuts but th SW- Ed 120, though a tad short of 5" is a compelling choice. The FPL-53 ED glass makes it a very strong candidate , in this aperture range


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#8 rml63

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Posted 21 April 2017 - 02:16 PM

Start looking for a buyer for my kidney too Bill

Sold :)

 

Mike


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#9 Phillip Creed

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Posted 21 April 2017 - 02:52 PM

Why isn't there a compelling lightweight 5" fluorite doublet offering in the market??

Because nobody wants to take out a HELOC just for a 5"-doublet.

 

And why would they if you can pick up a used SW120-ED for only $1,000?

 

Clear Skies,

Phil


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#10 JCAZ

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Posted 21 April 2017 - 02:53 PM

Takahashi is certainly moving that way.  The 76 fluorite doublets, then the 100 fluorite doublets and stopping production of the TSA-102.  I would bet that they will continue and come out with a fluorite doublet in the 120-125mm, then retire the TSA-120. 

That would be great - I wish they would get on with it!  Instead they release a 60mm scope. confused1.gif


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#11 HARRISON SCOPES

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Posted 21 April 2017 - 03:00 PM

As Markus (APM) has said this comes up on CN a fair bit - the perceived demand for a perfect mid sized long f ratio mainly visual Apo is high on forums but never relates to actual sales. Maybe those of us (myself included) are loud voices on here wanting such a scope but in sales we are a small percentage. A prime example is the APM / LZOS 130 at f6 outsold the f9 variant by 10 to 1!

The odd special appears now and again but priced high - the Goto 125/1200 is a great option.

Maybe we will see a Chinese model nearer what we demand, but yes a Tak FC120 or FC125 would be on my wish list. There is some magic to the concept of an f8 or longer fluorite doublet actually breaking the 100mm aperture barrier in recent years. There are a few manufacturers who could do this technically but the most likely is of course Takahashi.


Edited by HARRISON SCOPES, 21 April 2017 - 03:20 PM.

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#12 ratnamaravind

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Posted 21 April 2017 - 03:30 PM

 

Takahashi is certainly moving that way.  The 76 fluorite doublets, then the 100 fluorite doublets and stopping production of the TSA-102.  I would bet that they will continue and come out with a fluorite doublet in the 120-125mm, then retire the TSA-120. 

Bill this is exactly what I am waiting for too, say a reincarnation of the FS128 or similar, I was hoping to see TAK releasing something like that this year I was sort of disappointed seeing the FC100DL re-enter as a new offering. The DL is an amazing scope , frankly it is my favorite right now, exactly for it's light weight and impeccable views. It's like taking a toy ( feather ) scope out in the field to have your socks blown off when you look through it.

 

If there was such thing released I would be all over it too.  I suggest we start a sign up sheet and send it to TAK maybe we can talk some sense into those guys bounce.gif

 

+2 here smile.gif

 

 

You may think I'm nuts but th SW- Ed 120, though a tad short of 5" is a compelling choice. The FPL-53 ED glass makes it a very strong candidate , in this aperture range

I want Fluorite.

 

 

Takahashi is certainly moving that way.  The 76 fluorite doublets, then the 100 fluorite doublets and stopping production of the TSA-102.  I would bet that they will continue and come out with a fluorite doublet in the 120-125mm, then retire the TSA-120. 

That would be great - I wish they would get on with it!  Instead they release a 60mm scope. confused1.gif

 

I do see the allure of tiny color-free refractor giving nice views. Look up what the Nikon 65mm f/12 (not tiny in length!) can do on doubles. At the end of the day it's prioritization and it sounds like 5" is low on the list.

 

Can't wait for BillP's prediction to come true- I am more of a DSO guy so need the 5" (I'm THIS close to buying an 4" FC-100DF but something is holding me back).

 

My Oberwerk tripod is waiting and I'll pick up an Ayo DIGI in anticipation maybe smile.gif

 

 

As Markus (APM) has said this comes up on CN a fair bit - the perceived demand for a perfect mid sized long f ratio mainly visual Apo is high on forums but never relates to actual sales. Maybe those of us (myself included) are loud voices on here wanting such a scope but in sales we are a small percentage. A prime example is the APM / LZOS 130 at f6 outsold the f9 variant by 10 to 1!

The odd special appears now and again but priced high - the Goto 125/1200 is a great option.

Maybe we will see a Chinese model nearer what we demand, but yes a Tak FC120 or FC125 would be on my wish list. There is some magic to the concept of an f8 or longer fluorite doublet actually breaking the 100mm aperture barrier in recent years. There are a few manufacturers who could do this technically but the most likely is of course Takahashi.

 

As Markus (APM) has said this comes up on CN a fair bit - the perceived demand for a perfect mid sized long f ratio mainly visual Apo is high on forums but never relates to actual sales. Maybe those of us (myself included) are loud voices on here wanting such a scope but in sales we are a small percentage. A prime example is the APM / LZOS 130 at f6 outsold the f9 variant by 10 to 1!

The odd special appears now and again but priced high - the Goto 125/1200 is a great option.

Maybe we will see a Chinese model nearer what we demand, but yes a Tak FC120 or FC125 would be on my wish list. There is some magic to the concept of an f8 or longer fluorite doublet actually breaking the 100mm aperture barrier in recent years. There are a few manufacturers who could do this technically but the most likely is of course Takahashi.

The Goto 125/1200 is 1) heavy 2) not fluorite and 3) VERY expensive for what it offers- the APM 140mm ED FPL-53 might be a better deal. Even the TEC-140, which is a triplet but is oil-spaced so will cool faster, will be a better deal.

 

Either way, I'm looking to stay under 15 lb. Even 12 lb.

 

Why can't someone just  replicate the 125SD's great virtues (btw for imaging, the 125SD is supposed to be superior in almost every respect than the holy grail FSQ106ED when you reduce it to f/3.9- and I'm not even an imager)?


Edited by ratnamaravind, 21 April 2017 - 03:39 PM.


#13 tomecz

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Posted 21 April 2017 - 03:33 PM

both LZOS are heave so why not buy shorter.

there is no light 5" on the market as there is fc100d in 4" area. I have a feeling tak will fill the gap and discontinue tsa120

#14 carlcat

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Posted 21 April 2017 - 03:45 PM

Explorescientic makes a 128 triplet with FCD-100 glass (fpl-53 comparable glass) which sells for 2 grand. I would imagine they could make a similar doublet and sell it a little less than 2 grand. It would be lighter and cheaper and probably perform similar or almost as good as the FS-128.



#15 SandyHouTex

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Posted 21 April 2017 - 03:54 PM

I'm in!



#16 BWAZ

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Posted 21 April 2017 - 04:36 PM

The upcoming Stellarvue SV125 f7.8 doublet would get you what you're looking for as close as it can. 

 

http://www.stellarvu...ctor-telescope/


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#17 Eric H

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Posted 21 April 2017 - 04:49 PM

There's this one:

http://www.agemaopti...s/agema-130-sd/


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#18 ratnamaravind

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Posted 21 April 2017 - 05:50 PM

BWAZ- I said it twice before and I'll say it again- I need Fluorite.

Eric- Agema is an option but isn't great value at that weight and cost. If they can shave 7 lb and price it closer to $4K, they have a winner.
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#19 BillP

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Posted 21 April 2017 - 06:08 PM

As Markus (APM) has said this comes up on CN a fair bit - the perceived demand for a perfect mid sized long f ratio mainly visual Apo is high on forums but never relates to actual sales. Maybe those of us (myself included) are loud voices on here wanting such a scope but in sales we are a small percentage.

 

This is very true.  So for scopes like the SV mentioned, which looks fantastic btw, it will probably be an uphill battle.  However, for brandings which have large loyal followings, and when they put out a new scope that rekindles the past from that branding, then more folks will come to the trough.  So all that people inflicted with takitis will certainly start salivating if an updated version of the venerable FC125 comes out again.  And since Tak is now taking a tactic of limited runs of 100, it is IMO more likely to happen.


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#20 sctchun

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Posted 21 April 2017 - 06:22 PM

The Borg 125SD was something on my list, but if my memory serves me correctly.  One it was F6 and two it wasn't Fluorite though the lens was made by Pentax.

 

There is the Borg 107FL which is a Fluorite doublet and extremely portable and light, but it's F5.6.

 

Steven



#21 LewisM

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Posted 21 April 2017 - 09:06 PM

Fluorite - just check my signature line. It's why I stick with Tak.

 

Tak took the TOA design with ED glass, went back to the drawing board and put in fluorite (not as simple as that, but you get the gist) and made the FOA-60. As a famous movie line says "Big things have small beginnings" - well, we can hope so - as many have said, bring on the FOA-102, 128 etc.

 

I have owned many ED glass scopes. They don't grab me like a fluorite does. A Mate claims I drool fluorite like the hound of the Baskervilles...perhaps he is right.


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#22 Phillip Creed

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Posted 21 April 2017 - 09:54 PM

"Fluorite -- everything else is just glass."

 

I'm not trying to knock the decision or desire for a fluorite refractor, but I'm admittedly among the uninitiated and puzzled considering the economics involved here.  What EXACTLY is it about fluorite that makes it desirable enough to spend FAR in excess of a comparably-sized FPL-53 doublet or triplet?

 

And if it's "fluorite or nothing", why settle for merely a fluorite objective?  Why not have a top-notch 2"-fluorite prism diagonal + fluorite-lensed eyepieces?  Aren't those components made out of g---...gl....that...OTHER material?

 

Clear Skies,

Phil


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#23 LewisM

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Posted 21 April 2017 - 10:23 PM

"Fluorite -- everything else is just glass."

 

I'm not trying to knock the decision or desire for a fluorite refractor, but I'm admittedly among the uninitiated and puzzled considering the economics involved here.  What EXACTLY is it about fluorite that makes it desirable enough to spend FAR in excess of a comparably-sized FPL-53 doublet or triplet?

 

And if it's "fluorite or nothing", why settle for merely a fluorite objective?  Why not have a top-notch 2"-fluorite prism diagonal + fluorite-lensed eyepieces?  Aren't those components made out of g---...gl....that...OTHER material?

 

Clear Skies,

Phil

There is a special finesse and technique in "pushing"/figuring fluorite - Roland Christen describes it aptly in various articles. The Chinese don't seem to have this finesse - yet - hence don't seem interested in making fluorite scopes, rather sticking to easier to figure glasses. Tak doesn't even make their lenses - Canon-Optron does. Tak rejects MANY - hence also why the price is higher. GENUINE QC costs. TEC also still do fluorite, as does, I believe Agema (seeing their optician is former-TEC, that is no surprise).

 

The differences between fluorite and ED is noticeable to many, but not to others. Some see the "fluorite magic", others can't. I certainly think I do, after owning many fluorite scopes, so my decision is made. ED glasses to me seem pallid. Some say fluorite is a more vivid, but flase colour. I don't think so. ED is COLD.

 

It's more what you prefer. Takahashi obviously sees the benefits of fluorite not only in a marketing way but seemingly in an optical way. They went to "Eco-glass" ED, but now are switching back to fluorites. Why? Ask them :)

 

As to the SW120, they CAN be good, they CAN be mediocre. I've looked through a couple good ones and several so-so. You roll the dice. With Tak, I don't have to.


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#24 SeattleScott

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Posted 22 April 2017 - 01:31 AM

I brought up the issue of other optical components being glass awhile ago and the best explanation I got was that the primary fluorite lens is the thickest lens in the optical system, so it can make a detectable difference even if there are half a dozen glass lenses in the mated objective lens, prism, and ortho eyepiece. But it was also clear that not nearly everyone is sold on fluorite being superior.

 

That being said, onto the question of no 5" fluorite doublets in the market place. For one, price. I believe the price of fluorite goes up faster as you increase aperture than FPL53. But to me it is also a weight issue. Probably the biggest benefit of a doublet is lower weight than a triplet. Ok faster cool down too. So a 4" doublet can be a good grab and go on a light alt az mount. Not saying a 4" triplet can't be grab and go, but for most people, a doublet is already pushing the boundaries of portability. Of course we were talking 5'. To me a 5" doublet is kind of a tweener. I see value in a 4" doublet (fluorite or otherwise) as being the largest grab and go refractor. And I see value in the APM140 as being the largest Apo that is well suited for a medium duty eq mount like a CG5 or LXD75. But why a 5" doublet? I know people buy the SW120 like hot cakes, but if I am gonna pull out a CG5 type mount, why not get a 20lb 5" triplet to go on it? A 5" doublet is too heavy for GNG and too light to max out a CG5. At the price of the SW120 it presents a compelling alternative to a 5" triplet. But a fluorite model would not be so compelling. I strongly suspect a 5" fluorite doublet would be more expensive than a 5" FPL53 triplet. If you are going to put either one on the same mount, shaving a couple pounds off the OTA just isn't gonna matter much. You would have to REALLY want fluorite. Bottom line is this: there are more of us who prefer money than fluorite.

 

Scott 


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#25 Far Star

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Posted 22 April 2017 - 02:15 AM

lightweight 125 mm Takahashi fluorite doublet would be my absolute dream scope.

 

Some years ago, I had a Tak FS-128. But even the FS-128 is unnecessarily heavy (weight of OTA: 7.5 kg). You can see this when you compare the OTA weight of the FS-102 with the weight of the FC-100D:

 

FS-102: 5.3 kg
FC-100DC: 2.8 kg
FC-100DF: 3.2 kg

 

Therefore, it is no problem at all to make a 125 mm f/8 or f/9 fluorite doublet with an OTA weight of less than 6 kg. If Takahashi would offer an FC-125D, I would immediately buy it and sell my heavy and front-heavy APM-LZOS 130 mm f/6 triplet.


Edited by Far Star, 22 April 2017 - 02:29 AM.

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