11 replies to this topic

[peleuba]

I recently started a thread regarding the bench test output I gleaned from my TeleVue 76.  See here:  https://www.cloudyni...f-a-televue-76/

 

A couple of folks chimed in that the TAK FS78 is a superior telescope, with the "fluorite advantage" etc.  There is a website in the UK that directly compares the two OTA's (TV 76 and FS78) with nicely formatted graphs of the Strehl values of both scopes at various wavelengths.  The only problem is that data in misleading - it doesn't represent actual samples of either telescope.  So, why publish it?  I was born at night, but not last night and as a C-suite level manager who makes business-technology decisions everyday based on data, I'd would be foolish to make decisions based on mocked up data to push a narrative (Fluorite vs ED). 

 

At the end of the day, I am agnostic on the use of Fluorite, FPL-XX and for that matter FCD100.  I have owned terrific telescopes using all sorts of ED glass and Fluorite.  I liked them all.  Actually, I like most telescopes...  

 

I don't have a TAK Fluorite doublet, but I do have a Vixen Fluorite that I purchased new back in 2000 - the scope will be 20 years old this Summer.  It's spent several years with a local friend while I chased other refractors up/down the aperture ladder.  I was lucky enough to persuade my friend to sell it back to me a few years ago.

 

This Vixen Fluorite has been tested extensively but I never had a full set of DPAC images until last evening.

 

The Roddier analysis and star test images were captured several years back.  As you will see all the test methods agree.  This is an excellent lens.

Attached Thumbnails

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[peleuba]

White, Green, Blue, Red, Star Test, Roddier Analysis.

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[peleuba]

Overall, the spherical correction is really good; color correction is good, too.  Roland once commented to me that as good as it is, the VX102FL could be improved with a diff mating element that is no longer available.

 

The surface has some slight roughness that can be best seen in the white and green null images.  But, its not at the level of impacting the Strehl (~.980).  It's detail like this that demonstrates how sensitive DPAC can be at picking up stuff.  I don't think I could pick this level of roughness up in the outdoor star test on a typical night here in the mid-Atlantic.

 

Comment/Questions/Criticisms welcome.

Edited by peleuba, 07 February 2020 - 12:06 PM.

[Erik Bakker]

Paul, that FL102S of yours is of the quality people rave about. Thank you so much for sharing these DPAC results.

 

Many of the Vixen/Celestron/Orion fluorite doublets from yesteryear are that good and some even better. Similar quality is in the Takahashi fluorite f/7.4-f/8-f/9 doublets, though on an even more consistent level and generally slightly better. Having owned a few samples of both and observed with a few more, that's my personal experience with these under the stars.

 

The best samples of any of these fluorite doublets have unsurpassed visual quality, especially on delicate low contrast details and can be used at very high powers if seeing cooperates and the object at hand promotes that.

 

From my personal collection, the two top tiers were a black Celestron/Vixen FL 55 S f/8 and a Takahashi FS-102NSV f/8, besting even a sample of the FC-100 DL under the stars with regards to optical quality. Easily better than 1/10th wave P-V at the eyepiece. My own black Celestron/Vixen FL102 S f/8.8 was a bit less good, though still a very enjoyable instrument and I can say similar things about my white Vixen FL70 S.

 

When these fluorite doublets reach perfection at the sample level, you are treated with an unbelievable and very hard to equal let alone surpass experience at the eyepiece, which is often reflected in the comments observers write about these gems.

 

Per aperture, they are a visual observer's dream. Let's hope some manufactures will continue to make these instead of shifting production more to the short triplets that are in high demand these days.

[peleuba]

Paul, that FL102S of yours is of the quality people rave about. Thank you so much for sharing these DPAC results.

 

Many of the Vixen/Celestron/Orion fluorite doublets from yesteryear are that good and some even better. Similar quality is in the Takahashi fluorite f/7.4-f/8-f/9 doublets, though on an even more consistent level and generally slightly better. Having owned a few samples of both and observed with a few more, that's my personal experience with these under the stars.

 

 

Thanks...  This is the best one I have seen of the six I have first hand knowledge of and have worked on.  This includes one I had imported for me from Japan, 3  sold in the U.S. and were black Celestron branded F/8.8 models and one other one from Orion.  Its better on the bench then a friends TAK FS NSV-102.  The Vixen design has less color error and this sample has less "junk" floating around the in-focus star.  See image above of the infocus star - just an Airy disk with a single diffraction ring.   But, to be fair, I don't have a lot of experience with the ~100mm class TAK Fluorite doublets.

 

While DPAC is nice, Roddier fills in the blanks - 1/8 wave PtV, 1/47 wave RMS and .980 Strehl.

 

I am surprised that you are able to give a estimated wavefront rating based on the star test as spherochromatism in the NSV would tend to make the scope appear undercorrected in white star light.  I am speaking only for myself but do have a fair amount of experience as as star tester and I am not sure that I could give any sort of wave front estimate without weeks of star testing and even then I'd want to put it on the bench and use the artificial star and some filters to make sure.

 

Anyway, in Japan, when these were still sold, it was the Vixen Fluorites that were more highly sought after then the FS series.  Now, however, Takahashi is king.

[HARRISON SCOPES]

In that era the vixen fluorite always had the better colour correction over the equivalent Taks. I found the FS had the edge on contrast. Somehow planets looked colder and cleaner in the vixens and slightly warmer and richer in the taks.

I am currently hunting for another vixen fl90 or fl102 but getting hard to find here.

Personally I found the fl90 had superior optics but all were great.

[starman876]

So nice to see folks posting DPAC test results.  That is a beautiful lens.  Let's hope someday all lenses will test like that.  Will be a lot of happy scope owners.  

[SeattleScott]

So nice to see folks posting DPAC test results. That is a beautiful lens. Let's hope someday all lenses will test like that. Will be a lot of happy scope owners.

For the right price they will. SV is claiming even higher. The technology is there. Ideally yeah it sure would be nice if the technology was cheap enough to hit these marks on $700 Apos. Not sure if that is realistic though.

Scott

[jeffmac]

In that era the vixen fluorite always had the better colour correction over the equivalent Taks. I found the FS had the edge on contrast. Somehow planets looked colder and cleaner in the vixens and slightly warmer and richer in the taks.

I am currently hunting for another vixen fl90 or fl102 but getting hard to find here.

Personally I found the fl90 had superior optics but all were great.

 

Maybe, but remember, the Taks were f8 scopes and the Vixens and Celestron C102F were f9ish. I think this is the reason the Vixen made scopes had the better color correction. BTW, that's my experience with these scopes. I own a vintage FC100 and a C102F. The color error seems to be slightly better in the latter. The better inside/outside focal patterns belong to the Tak.

[Jeff B]

I recently started a thread regarding the bench test output I gleaned from my TeleVue 76.  See here:  https://www.cloudyni...f-a-televue-76/

 

A couple of folks chimed in that the TAK FS78 is a superior telescope, with the "fluorite advantage" etc.  There is a website in the UK that directly compares the two OTA's (TV 76 and FS78) with nicely formatted graphs of the Strehl values of both scopes at various wavelengths.  The only problem is that data in misleading - it doesn't represent actual samples of either telescope.  So, why publish it?  I was born at night, but not last night and as a C-suite level manager who makes business-technology decisions everyday based on data, I'd would be foolish to make decisions based on mocked up data to push a narrative (Fluorite vs ED). 

 

At the end of the day, I am agnostic on the use of Fluorite, FPL-XX and for that matter FCD100.  I have owned terrific telescopes using all sorts of ED glass and Fluorite.  I liked them all.  Actually, I like most telescopes...  

 

I don't have a TAK Fluorite doublet, but I do have a Vixen Fluorite that I purchased new back in 2000 - the scope will be 20 years old this Summer.  It's spent several years with a local friend while I chased other refractors up/down the aperture ladder.  I was lucky enough to persuade my friend to sell it back to me a few years ago.

 

This Vixen Fluorite has been tested extensively but I never had a full set of DPAC images until last evening.

 

The Roddier analysis and star test images were captured several years back.  As you will see all the test methods agree.  This is an excellent lens.

 

Amen and me too Paul! 

 

There seems to me to be a certain snobbery and arm chair pontificating that goes on here relative to glass type this or that, when I've learned by direct experience that what really matters is how well the objective is made. 

 

Some of my most satisfying refractors have no ED glass at all, can even be achromats, but have exceptional figures in the bulk of the visual spectrum.  Now imagers are in a different universe and their requirements are a bit different when it comes to the ends of the red and blue spectrum, but for visual use.... well there are a lot of excellent scopes out there that people just ignore because they don't have FPL or FL this or that.   

 

And that limiting of one's horizons due to non experience based prejudices is too bad IMO.  

 

Keep up the great work sensi Paul.

 

Jeff

[Chesterguy1]

Yes, thanks Paul.

 

The V90 was my first true telescope. I have used it many, many times over the last 22 years. It's my go-to travel scope even at f/9. The only complaint I have ever had about it was the focuser. It came with a single speed, which was generally fine for f/9, but I found I was always trying to tweak the focuser--it just never was quite as smooth as I would like. Last year I replaced the stock Vixen focuser with a Moonlite and it's like the telescope was reborn, just so much more satisfying. I won't go into the gory details about getting the old seized focuser out of the tube, but it did require some significant tube reconditioning (and prayer).

 

It has always been a champ on the planets, moon and tight doubles and works closer to its theoretical resolving limits than my bigger scopes because of typically average seeing at best. Even with the Moonlite it weighs less than 9 pounds and thus is easily mounted on my UA deluxe and probably would work fine on a Bogen tripod. It does all one could expect visually of a 90mm refractor.

 

Chesterguy

 

[mikeDnight]

I'm from a time when a 4" refractor was thought of as a SERIOUS scope to own, and the owner a very lucky person. And although I've owned some very desirable high end refractors that were larger, at heart all I ever really wanted was a good 4" refractor.

My first serious refractor was a Vixen 102mm F13 achromat which was amazing, even on deep sky targets. I foolishly sold it and ended up in a no man's land for several years, until I bought a 120mm Chinese achro, then a 150mm achro. They were good, but not in the same league as the Vixen FL102 that was donated to my local astro club. That scope showed Saturn in more detail than I'd ever seen in any telescope irrespective of aperture.

I saved like crazy to buy one for myself, but here in the UK the sole importer couldn't get hold of one for months. Meanwhile, many of you will remember that TeleVue had started importing them into the US. The advert in S&T simply stated VIXEN -Your Ship Has Come In.  Anyone who bought a Vixen fluorite back then and who still has it , has a truly top class refractor that will be hard to beat.

I never did get a Vixen of my own, so I've had to rough it with three different Takahashi scopes. And although I loved my Tak's and still do, I've never forgot how that superlative Vixen FL changed my life. I'm also still a bit sore about not being able to buy a brand new FL 102 at the start.