29 replies to this topic

[peleuba]

This thread highlights the results I’ve gleaned from a second sample of the popular TeleVue 76.  You can read about the testing of the first sample here:  https://www.cloudyni...f-a-televue-76/

 

I’ve had quite a long relationship with TeleVue products owning complete sets of T4, T5, T6 Naglers, Delos, Delites Radians and Plossls.  I love these eyepieces and don’t ever see a need to look elsewhere.  I’ve also been lucky enough to own, use and test a handful of TV OTA’s – everything except a TV140, NP127 and TV60.  I’ve always admired the build quality and how all the accessories work well together. To me, this is the overarching reason to buy TeleVue because, when you do, you enter into an ecosystem where everything just works and the support is legendary.

 

Recently, Jon Issacs (longtime CN contributor beloved by me and a lot of others) and I were discussing, via PM, how terrific all the TeleVue accessories (finders, diagonals, storage cases etc.) are and how well they integrate into an “observing system”.  Jon said it best:  “It just seems to me the fact that Al was an amateur astronomer first and a lens designer second means TeleVue understands what matters to the amateur.”    I concluded long ago that a well accessorized TeleVue OTA is a stout observing package at any aperture. 

 

But, as I’ve often said, I’ve found the optical quality to be variable between samples.  I don’t say this lightly, but I come by it honestly having tested a fair number of scopes.   Back in 2004 I purchased a new NP101 that was dead-nutz perfect.  My second (and third) were middling.  I have seen examples of this in all the models that I have used and its always annoyed me.  Sample to sample variability is nothing new to our hobby.  But, IMO, one should not experience it much (if at all) at the high end. 

 

The aperture of these sub 100mm OTA’s is limited.  It makes no sense produce a telescope that is not superb because at this aperture every millimeter counts.  Unless, of course, you’re an astrophotographer where optical quality is not an absolute necessity.  One can sample, stack, sharpen and stretch the data to achieve a decent result.  Unfortunately, us visual guys cannot stack or stretch anything - once the light hits the retina its gone.

 

Anyway, so I wanted a white TeleVue 76/85 to keep at our condo in West Palm Beach, FL.  About 18 months ago, I purchased a green one as that was the only color available.  It was optically pretty good but not terrific - maybe a little better than a ¼ wave in green light.  I included a link to the thread on this scope in the first paragraph.

 

Ultimately, I decided that a green slightly better then diffraction limited TeleVue 76 was not the scope I wanted to use in Florida.  Fast-forward to a few weeks back and I lucked into and purchased a white, mint, nearly new, TeleVue 76 that was for sale locally and was purchased by the original owner new from my local dealer – Company 7.  Its never been shipped.  These are the results of the bench test for this scope.  In a word, it’s terrific and noticeably better than the first sample.

 

Questions, Comments and Criticisms are welcome.  Have a safe Labor Day.

 

Best Regards.

 

Paul Leuba

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Edited by peleuba, 01 September 2022 - 07:24 PM.

[peleuba]

Green and White  Click on image for a larger view

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Edited by peleuba, 01 September 2022 - 01:41 PM.

[peleuba]

Blue

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[peleuba]

Red

 

 

 

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[peleuba]

The Star Test.

 

This is a single frame unretouched.  The camera is sensitive to color, any color.  The image is not this colorful when star testing with one's eye.  But, it does go to show that short focal ratio ED doublets are not color free.  Not even close.  Its also the quintessentially perfect example of why a green filter will help in deciphering the star test.  If possible, I like to stack a green and yellow filter.

 

The image has not been processed at all except to convert the RAW image to JPG so it could be small enough for posting.  Again, a single frame - no stacking.  I could have stacked the image to lower the signal-to-noise ratio but I thought this was pretty good without doing that.    

 

Overall its a very nice lens.

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Edited by peleuba, 01 September 2022 - 03:02 PM.

[alnitak22]

Looks great…enjoy!  And doubtful the color error will bother you at all for visual use.

[Polyphemos]

Thank you, Paul, for this informative and interesting thread.  We need more of these objective reviews and analyses.

 

Jim

[Jeff B]

As usual, great stuff Paul.  I like your straight forward honesty.

 

Yes a much better sample indeed.

 

I took the liberty of manipulating your star test image.  Who needs filters when I have software.    Seems to high lite that mild under correction in green.

 

Nice scope.

 

Jeff 

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[stevew]

Paul, do you think there is variation in the TV eyepieces as well?

But, as I’ve often said, I’ve found the optical quality to be variable between samples.  I don’t say this lightly, but I come by it honestly having tested a fair number of scopes.   Back in 2004 I purchased a new NP101 that was dead-nutz perfect.  My second (and third) were middling.  I have seen examples of this in all the models that I have used and its always annoyed me.  Sample to sample variability is nothing new to our hobby.  But, IMO, one should not experience it much (if at all) at the high end. 

 

Paul Leuba

[peleuba]

 

Paul, do you think there is variation in the TV eyepieces as well?

 

I use TeleVue eyepieces exclusively except for a a set of rarely used KK orthos.  And, I have only ever had a problem with one eyepiece...  It was years ago and it was a 3mm TeleVue Radian.  As luck would have it, I was observing with Al Nagler at the time at Cherry Springs using my excellent NP101.  I mentioned it, and he took a look and noticed it too, and swapped it out on-the-spot with his 3mm Radian.  I did say the service is legendary.

 

I know this does not answer your question specifically.  But, one does hear, anecdotally, of complaints with coating issues and a lack of lens blackening etc.  But you never hear of a "truly" defective TeleVue eyepiece; meaning that the view provided through such an eyepiece is so aberrated that the eyepiece is deemed defective.   I think TeleVue does a good job weeding these out.  So the "true" defect rate must be quite low.  Small spherical lenses are VERY easy to manufacture; even small aspheres are easy to make.  Its a completely automated process done on high speed polishers.  The real art to manufacturing multi element eyepieces is in the assembly.  

 

Refractor objective lenses are another story - they are large and expensive.  And while TeleVue has these lenses polished and figured to their spec, they perform the final assembly (matching, spacing etc.) an Q/A inhouse.  I doubt that any sort of quantitative assessment is utilized such as interferometry.  At one time the indoor star test was used but I don't know what they do today...  And, who knows how they handle rejects/defects?  I am sure they try to have as few as possible which means they probably have a wide range of what is considered acceptable for an objective lens.  My experience over the last 25 years as a consumer has borne this out.

 

Anyway, long story short…  my sense is that the TeleVue probably does not have the sample to sample variability within the eyepiece line that I’ve experienced in the refractor line. 

Edited by peleuba, 02 September 2022 - 05:38 AM.

[aztrodog]

Bought a 17mm Ethos from B&H some years back that was horrible. My observing buddy Sergio Figuera and I could not believe how bad the views were. No rattling noises, but perhaps de-centered elements. Sent it back the next day. The replacement was perfect and continues to be one of my most used eyepiece. Then again, it was a UPS ground delivery which might explain things.

 

I have owned a TV Genesis for many years, awesome scope. Color correction is not perfect, but as sharp as any top shelf triplet I’ve used. There’s been some less than complementary reports on the Genesis line over the years, so I guess I lucked out.

 

Paul, I wrote this post primarily to thank you for the effort you put into documenting and sharing these tests with us. I’ve learned quite a bit from your postings over the years. Enjoy your new scope!

 

Angel

[ion]

I’ve found the optical quality to be variable between samples.

Do you have any thoughts on the cause of the variations? I've had to send a couple
of scopes back to the mothership for collimation and they always return in perfect
optical condition. I've heard they will replace bad glass that somehow got through
the quality control process too. Thanks for the objective review!

[Tyson M]

Thanks for sharing Paul, looks like a nice lens!

 

Ive always wanted to try a small TV76. I did had a TV60 which was an interesting experiment.  

 

The TV85 I probably shouldnt havent sold.  Nothing wrong with it at all, a nice aperture in a small package. I really liked that scope.

 

The 127 I had took a bit to cool and felt a bit unwieldy at times in and out of its hard case but views were amazing. Widefields from that scope can be quite addicting.  Like you said, with its system of everbrite diagonal and 31N, its just sublime under dark skies. Roger Vine describes the NP127 perfectly in his review. It just does everything well.

 

I too found Tele Vue overall outstanding (all things considered) and of extremely nice build quality. 

[desertlens]

Thanks again Paul. The phrase "meets expectations" comes to mind. If "three inches" is your game, It's hard to beat the TV-76.

 

Edited by desertlens, 01 September 2022 - 11:34 PM.

[alnitak22]

Thanks again Paul. The phrase "meets expectations" comes to mind. If "three inches" is your game, It's hard to beat the TV-76.

 

TV76tp.jpg

Gorgeous setup!

[peleuba]

Do you have any thoughts on the cause of the variations? I've had to send a couple
of scopes back to the mothership for collimation and they always return in perfect
optical condition. 

 

 

Yes, lots of thoughts.  These are all my own and have no inside knowledge of the TeleVue specific process. 

 

A point of clarification - clean and collimated is not the same as "perfect optical condition".  These are certainly part of it, but you'd need a bench test to be able to state this.  Picking nits?  Maybe.  But I just want to make sure we're on the same page...  

 

There are two primary modes where defects can cause variation in the final product: 

 

(1) Lens manufacturing.  Cconsisting of the polishing/figuring and coating of the individual lens elements.

 

(2) Assembly of the loose coated lenses into a telescope objective.  This includes the spacing, rotation and tweaking of each lens stack into an optimal configuration so the aberrations in each piece of glass cancel each other out.

 

For #1 TeleVue depends upon their supplier to do the heavy lifting of quality assurance.  For #2 TeleVue depends upon local highly skilled employees who assemble the telescopes and do the final QA check.  My sense is that once TeleVue gets the loose coated lenses from the supplier they are assumed to be good.  And, every effort is made by TeleVue to use every single piece of glass in a lens for a refractor.  Rejects cost money.

 

 

I've heard they will replace bad glass that somehow got through
the quality control process too.

 

I think the average amateur astronomer would have a very difficult time convincing TeleVue that there is something wrong with the glass - either a figuring error or an internal stain/striae issue.   Every time I have talked to anyone related to TeleVue, they are supremely confident in the "100% QA" almost to the point of being over-confident.  To this end, I think its a high bar to overcome and actually convince TeleVue that something is amiss with one of their telescopes.  Secondly, its only an issue for TeleVue if a lens does not meet the minimum requirement.   The problem is that no one knows (outside of TeleVue) what that minimum quality level is.

 

Make no mistake, TeleVue is a great company who's strength is multi faceted:

• They make good products that integrate well into a turnkey "observing system".
• They make, IMO, the best eyepieces for the amateur astronomer.
• They have great relationship with the amateur astronomers cultivated tirelessly by Al over the years.
• They are relentless in eyepiece innovation.  They operate in a competitive environment where their intellectual property (eyepiece designs) is reverse engineered and incorporated into competing offerings.  Yet TeleVue still remains on top.   

Anyway, just my .02; hope it was worth it!  

[Daniel Mounsey]

The Star Test.

 

This is a single frame unretouched.  The camera is sensitive to color, any color.  The image is not this colorful when star testing with one's eye.  But, it does go to show that short focal ratio ED doublets are not color free.  Not even close.  Its also the quintessentially perfect example of why a green filter will help in deciphering the star test.  If possible, I like to stack a green and yellow filter.

 

The image has not been processed at all except to convert the RAW image to JPG so it could be small enough for posting.  Again, a single frame - no stacking.  I could have stacked the image to lower the signal-to-noise ratio but I thought this was pretty good without doing that.    

 

Overall its a very nice lens.

Nice work Paul. 

[Daniel Mounsey]

I've always liked Televue refractors. They've always made beautiful scopes and I love their focusers. 

[ion]

A point of clarification - clean and collimated is not the same as "perfect optical condition".  These are certainly part of it, but you'd need a bench test to be able to state this.  Picking nits?  Maybe.  But I just want to make sure we're on the same page...  
 
There are two primary modes where defects can cause variation in the final product: 
 
(1) Lens manufacturing.  Cconsisting of the polishing/figuring and coating of the individual lens elements.
 
(2) Assembly of the loose coated lenses into a telescope objective.  This includes the spacing, rotation and tweaking of each lens stack into an optimal configuration so the aberrations in each piece of glass cancel each other out.

Very good point, thanks for the clarification. All
I can say for sure is that I've had unimpressive
Tele Vue scopes come back from service delivering
the expected high photovisual performance. Each
time support informed me that the cause was lens
alignment errors measured in microns!

[Old_Yharnam_Astronomer]

Hey Paul! Nice work as always.

 

If you don't mind me asking -- how did the test bench difference between your excellent and middling np101s manifest at the eyepiece?

[Polyphemos]

Hey Paul! Nice work as always.

 

If you don't mind me asking -- how did the test bench difference between your excellent and middling np101s manifest at the eyepiece?

That is an excellent question!

[Castor]

Paul,

 

Congratulations on your new Tele Vue 76 refractor and thanks for sharing your objective bench test report, great job!

 

P.S.  I hope the scope can fulfill all your expectations for the purpose that you bought it!  I’m very happy with mine!

[peleuba]

P.S.  I hope the scope can fulfill all your expectations for the purpose that you bought it!  I’m very happy with mine!

Thanks!   I wish it were larger!  

[peleuba]

Hey Paul! Nice work as always.

 

If you don't mind me asking -- how did the test bench difference between your excellent and middling np101s manifest at the eyepiece?

 

Thanks.   Don't mind at all.  I have written about here on CN before but not in the last 5 years or so...

 

I've had three NP101's...  The first, was truly excellent in every way.  Optically it was one of the best 4" telescopes I have ever seen.  Near prefect star test, no color, just a terrific telescope.  I had upgraded to it from a TeleVue 102 so it was a nice upgrade and well worth the premium price.  in 2004, I sold it to a gentleman in San Diego, who has since moved, but still in California.  I email him every couple of years asking to buy it back.   We've not been able to agree to a deal.   Its a early model with a serial number in the 1050's.  

 

The second was purchased from a formerly very active astronomer in the Phoenix area.  This one was probably the worst of the three.  It had a somewhat prominent zone at the ~50% radius that wrecked the star test.  It was doffraction limited, but probably not much better and certainly nothing like the my original.

 

The third was purchased new from a vendor during their "TeleVue day".  This one had a central zone as well as some spherical.  Collimation was also out - not a deal breaker, but it was not a great lens anyway and to get it recollimated, I would have had to pay for shipping to TeleVue and then back to me.  To much of an expense and hassle for a middling lens.  So I returned to retailer for a refund, minus the restocking fee.  It was probably resold to some unsuspecting amateur.  

 

So, the difference was that the first, was nearly perfect in every way.  The second and third had aberrations in which I was not comfortable living with in a high performing/high cost telescope.

 

 

===

***EDIT***    So its from this experience that partially drives my belief that there is some inconsistency within the TeleVue refractor lineup.   I know its not popular to say this, but I call it as I see it.

===

 

 

That is an excellent question!

 

I hope you found the answer to be equally excellent.   

Edited by peleuba, 03 September 2022 - 08:13 PM.

[Castor]

Thanks!   I wish it were larger!  

 

You’re welcome!

 

Ok, now you lost me!   Larger as in a TV-85?