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Is the FC100DZ the best DOUBLET ever made?

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#51 RobM

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Posted 06 February 2021 - 02:55 PM

I would say that the object glasses made by Alvan Clark are the best doublets ever made- in crown and flint.

 

I don't know about these new-fangled fluorite doublets but discounting the glass types used, I don't think Alvan Clark et al have ever been surpassed with regard to optical figure.

Hi Steve,

 

I think, given the long focal lengths Mssr. Clark was working with, spurious CA would have been present, but at a really minimal level.

 

He was an optical genius, the Thomas Back of his time. waytogo.gif



#52 laedco58

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Posted 09 February 2021 - 09:11 PM

Interesting thread. I did a lot of reading about the different configurations of the FC100 D's, when i decided i wanted to get one. General consensus by highly knowledgeable individuals, with considerable experience with theses scopes, seemed to agree at that time that the visual performance of the different models was close enough that picking the configuration that fit your observing criteria was more important to your satisfaction with the scope. My original interest was in the DL as i wanted to try a longer focal length. Both runs were sold out, and the DZ was just being released. DC's and DF's were very popular with the individuals concerned with compact setups for travel or easy deployment. I decided to step back and watch the used market for a bit to see if a good deal popped up, and after a few months I scored a second run DL at what I feel was a good price with a clam shell ring, dovetail plate, finder scope and bracket included. Had a comparable deal on a DC or DF came my way first, I'm sure I would be just as pleased.

 

Larry


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#53 Howard Gao

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Posted 17 February 2021 - 07:01 PM

The best just arrived. lol.gif

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Edited by Howard Gao, 17 February 2021 - 07:02 PM.

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#54 blakestree

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Posted 17 February 2021 - 07:30 PM

I believe the DZ is the optically best 4” doublet in the world.

 

At the moment ........

 

Until the SVX102D ships.


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#55 Tyson M

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Posted 17 February 2021 - 09:46 PM

Until the SVX102D ships.

I am very excited for these scopes.  The SVX127 and this 1SVX02D. 

 

I LOVE Stellarvue build mechanics and these will be binoviewing friendly. 



#56 gwlee

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Posted 18 February 2021 - 02:16 AM

Looking at the attached info and considering other great 4" refractors that are, or have been available, is there any doublet that's better than the DZ?

 

attachicon.giffc-100dz-strehlratio.jpg.jpg

 

attachicon.giffc-100dz-aberration.jpg.jpg

Better for what? The graphs are nice, but telescopes are used by different people, at different sites, and for different purposes. The answer to your question depends on who’s using it, where they are using it, and for what purpose. 


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#57 25585

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Posted 18 February 2021 - 04:44 AM

Choosing between a DL & DZ, if the former was still made, and I was buying for the first time, would be hard.

 

Shallowly, the DZ's sliding dewshield might be its a deal maker (had DC or DF been given one as the TSA-102 was, I may have bought one of those). But that 100mm extra FL of the DL, as I like using longer FL eyepieces, is a big pro in its favour. 

 

MikeDnight, had you bought a DL, not the DC, as your 1st modern Tak, would you have changed to a DZ?



#58 ScottW

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Posted 18 February 2021 - 09:53 AM

Hi,,

Could all of this be moot?  I noticed that the spot diagrams diameters are extremely small, how small can the human eye see?  If you can't see things that small what is the minimum diameter of a spot that you can?  Wouldn't that be a limit for any scope?  It seems to me passing that limit would not produce any visual advantage.

 

Scott


Edited by ScottW, 18 February 2021 - 01:25 PM.

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#59 mikeDnight

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Posted 18 February 2021 - 10:02 AM

Choosing between a DL & DZ, if the former was still made, and I was buying for the first time, would be hard.

 

Shallowly, the DZ's sliding dewshield might be its a deal maker (had DC or DF been given one as the TSA-102 was, I may have bought one of those). But that 100mm extra FL of the DL, as I like using longer FL eyepieces, is a big pro in its favour. 

 

MikeDnight, had you bought a DL, not the DC, as your 1st modern Tak, would you have changed to a DZ?

   I had three opportunities to change to a DL but loved my DC so much that I just couldn't let go. I think the issue for me was the extra physical length of the DL. Having used two of them on my GP,  I noticed it was a stretch to reach the manual controls without having to use flexi drive cables. With the DC I could reach everything without any issue.  Then when the DZ came onto the scene, I knew there would be very little difference in physical length. So I thought it would be nice to have a short scope that behaved like the longer DL. 

   As regards the sliding dewshield. I really wish Tak offered a fixed option. I find the sliding shade pretty pointless, as it only moves 80mm due to the beautiful lens cell occupying much of the dew shield. With the DC/DF & DL you can just remove the shade anyway, so its not really much of an issue for travel.


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#60 dweller25

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Posted 18 February 2021 - 02:09 PM

DC, DF, DL, DZ - hmmm which one and why ?

 

Well we are all different, the DL was too long for me.

 

I was torn between the lightweight DF and the slightly heavier DZ, but for me the DZ on paper has the best optical performance, has a sliding dew shield and the focuser knobs are metal - so that swung it lol.gif

 

No regrets, it’s a great scope.


Edited by dweller25, 18 February 2021 - 02:14 PM.

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#61 25585

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Posted 18 February 2021 - 05:25 PM

Unscrewing & back any scope's dewshield, delicate fine aluminium threads, will wear them out IMO. 


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#62 dweller25

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Posted 18 February 2021 - 06:05 PM

Unscrewing & back any scope's dewshield, delicate fine aluminium threads, will wear them out IMO. 

Candle wax helps


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#63 John Huntley

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Posted 19 February 2021 - 08:10 PM

I bought the DL because I already had a nice Vixen ED102SS F/6.5 so the F/7.4 DC or DF would be rather close to that and the DZ had not been launched back in 2016.

 

If I was buying now ...... it would probably be the DZ because the DL is out of production and does not come up too often on the pre-owned market.

 

I could probably not tell the difference between any of them anyway ! smirk.gif


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#64 balu01

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Posted 20 February 2021 - 01:11 AM

i had both the DL and DZ , I have not been able to tell a difference where the DZ is claimed to be better , and funny as it seems phot wise the DL beats the DZ regarding field. It illuminates full frame lovely at .85.

.66 is not acceptable on either one to me regardless of claimed 43 mm image circle. While it might be you better make nice flats and still have south. / north spikes on stars.

With that said. I sold the DZ , might be more attached to the DL , to me it is better looking sleeker just as light and a truly amazing scope that is simply hard to match. Not to say the DZ isn’t , but to me it is just not where the DL is.
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#65 teashea

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Posted 20 February 2021 - 01:00 PM

 The best doublet is the Takahashi FOA60Q.  Just compare the test results.  


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#66 blakestree

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Posted 20 February 2021 - 01:03 PM

 The best doublet is the Takahashi FOA60Q.  Just compare the test results.  

Toy scopes don't count. tongue2.gif

 

J/K


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#67 StarAlert

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Posted 20 February 2021 - 02:00 PM

 The best doublet is the Takahashi FOA60Q.  Just compare the test results.  

What test results? I’m confident my DL and DZ will do everything the FOA60Q can do... and more. 

 

 

Edit: Except for fitting in a smaller travel case. grin.gif


Edited by StarAlert, 20 February 2021 - 03:01 PM.

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#68 mikeDnight

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Posted 20 February 2021 - 03:08 PM

 The best doublet is the Takahashi FOA60Q.  Just compare the test results.  

Ah, but doesn't this version use an extender-Q, which would technically bar it from the best doublet competition? question.gif


Edited by mikeDnight, 20 February 2021 - 03:08 PM.

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#69 teashea

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Posted 20 February 2021 - 06:24 PM

What test results? I’m confident my DL and DZ will do everything the FOA60Q can do... and more. 

 

 

Edit: Except for fitting in a smaller travel case. grin.gif

Takahashi itself declared that the FOA60Q is the finest optical quality telescope they ever produced.  Do some research.  



#70 teashea

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Posted 20 February 2021 - 06:26 PM

Ah, but doesn't this version use an extender-Q, which would technically bar it from the best doublet competition? question.gif

Even the FOA60 without the Q is the finest optical quality telescope.   Look at the test results.  



#71 teashea

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Posted 20 February 2021 - 06:28 PM

What test results? I’m confident my DL and DZ will do everything the FOA60Q can do... and more. 

 

 

Edit: Except for fitting in a smaller travel case. grin.gif

Do some research.  Here on Cloudy Nights.  There are at least five posts with the results.  The FC 100's are terrific and I have two of them myself.  But the FOA60, Q or non Q are optically superior.  



#72 25585

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Posted 20 February 2021 - 06:34 PM

Not much known about are Agema SD doublets

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#73 25585

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Posted 20 February 2021 - 06:38 PM

FOA & DZ

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#74 teashea

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Posted 20 February 2021 - 06:40 PM

http://www.scopeview...k/TakFOA-60.htm



#75 25585

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Posted 20 February 2021 - 06:47 PM

OK. Size can matter. DZ is arguably the best 100mm, FOA the best 60mm. But also arguably, as lens size increases, it probably gets harder to attain perfection with 2 lenses.

 

So which is the better achievement? 


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