87 replies to this topic

[Mike W]

Not any harder than finding & riding a unicorn.

[GGK]

Rather than a triplet, I'd like to see Tele Vue significantly reduce the physical length of their NP101is and their NP127is Petzval designs (to ~TV-85 length), increase the focuser size to at least 3", and have enough back focus for a 3" diagonal and eyepiece which should also enable Binoviewer use without a GPC or Barlow.  With proper adapter, this would also enable use of the A-P 0.75X focal reducer for an even faster scope and wider field.

 

I don't buy the NP127is today because it's too long and the focuser is too small to accept the A-P focal reducer.  I'd be a new scope buyer if they delivered on that design concept.

 

Gary

[Lagrange]

Rather than a triplet, I'd like to see Tele Vue significantly reduce the physical length of their NP101is and their NP127is Petzval designs (to ~TV-85 length), increase the focuser size to at least 3", and have enough back focus for a 3" diagonal and eyepiece which should also enable Binoviewer use without a GPC or Barlow.  With proper adapter, this would also enable use of the A-P 0.75X focal reducer for an even faster scope and wider field.

 

I don't buy the NP127is today because it's too long and the focuser is too small to accept the A-P focal reducer.  I'd be a new scope buyer if they delivered on that design concept.

 

Gary

That would require a radically different optical design since a consequence of the modified Petzval layout is that the physical length of the scope is longer than the focal length.

[GGK]

That would require a radically different optical design since a consequence of the modified Petzval layout is that the physical length of the scope is longer than the focal length.

Please explain why a longer physical length is a requirement for Tele Vue?  Can't the back two lenses be moved closer to the front two and sized appropriately for the larger light cone diameter at that point?  Trading f/11 length for f/5.4 length is more than a 2:1 reduction in physical length. And maybe the end focal ratio could also be reduced some as well.

 

Edit: see the diagram of the NP127 on Company7's website here: 

 

http://www.company7....opes/tv127.html

 

There's a lot of length between the front and rear lens pairs which keeps the rear lenses smaller.

 

Gary

Edited by GGK, 27 May 2025 - 09:55 AM.

[George N]

About 20 years ago, Tele Vue had an online chat (I forget exactly how it was done), and I inquired then about larger Tele Vue apo's other than the NP-127.  The Naglers made it clear that would never happen.

Two years ago at NEAF/NEAIC, David Nagler (who is the Prez and decision maker at TV now) told me "Nearly all our refractor customers are imagers now." Some of their most recent new optical products are re-designed correctors & focal reducers that (supposedly) improve their refractors' performance with full frame CMOS cameras. They were already good with full-frame, but the new (not cheap!!) correctors and reducers improve corner performance still more.

 

While David is more personally interested in imaging - Al Nagler has always wanted their refractors to provide a giant flat field for their Nagler and Ethos eyepieces. ( DavidN also told me he *only* uses Ethos himself, but in recent years I see Al with Delos mostly. ) For the past few years I see Al (who is really pretty physically frail now) only using a TV 76mm with NV device. For many years (25?) you could always see Al in public using TV's top-end refractor of the time - but at home or with his Rockland Club buddies, he mostly observed with a Dob based on his Stellafane-winning 12.5" primary.

 

Bottom line - I really doubt you will ever see any future refractor out of TV that is not a Nagler/Petzval. That design meets their goal of supporting their majority imager customers, and Al's vision that a visual refractor needs a huge flat field - and well-corrected eyepieces. I've heard Al also say that their eyepieces are best used on a telescope with a very large flat field "....like our refractors have......"

 

If you want an excellent visual APO and are not concerned about stars in the corners of a full-frame CMOS that might be a few pixels too big (if you blow the image up 1000%  ) - there are tons of them 'out there' right now - that TV could probably not compete with pricewise.

[balcon3]

Al first sought to be a game changer with his Prototype MPT, a 5” fast Petzval with a built in iris-diaphragm with user-selected F-stop setting. This evolved into the first 4” Genesis. His guiding strategy was to take the common-at-the-time long refractor and shorten it while preserving its optical integrity as best he could to make it more ergonomically friendly and more easily portable. This evolved into the Genesis SDF, then the TV101, then the NP101 (and 127), while throughout this evolution, continuing to improve the color correction and still offer a flat field. He has definitely accomplished this goal. IMO, that’s where his telescope legacy lies. I think that his smaller doublets (and the very briefly offered 102), were and are produced mostly to stay relevant in the marketplace by offering excellent optics and well-built mechanics, made in the USA. But it’s his Petzvals, since the first MPT to a current NP101 or 127, that show where his heart and mind really are.

This makes sense, but I don't necessarily think that the TV-60 and TV-76 are just to stay relevant. They also have gone through a series of refinements. I think one of the unifying themes in all the  TV telescopes is widefield views. At lower apertures, wide fields and good quality could be achieved with a doublet. Many have copied them but I think they started the trend, or at least were there in the beginning, At 100mm and higher, the Petzval was invoked to be able to get wide and also flat fields. Here, many fewer have followed. 

[George N]

......

 

Edit: see the diagram of the NP127 on Company7's website here: 

 

http://www.company7....opes/tv127.html

 

There's a lot of length between the front and rear lens pairs which keeps the rear lenses smaller.

 

Gary

Yes but - perhaps the main change in design for the current iteration of the 127mm was to make that 2nd pair larger in diameter - to reduce vignetting with large-chip cameras. It probably does nothing for most visual observers - except make the scope heavy and pricey.

[Jon Isaacs]

Please explain why a longer physical length is a requirement for Tele Vue?  Can't the back two lenses be moved closer to the front two and sized appropriately for the larger light cone diameter at that point?  Trading f/11 length for f/5.4 length is more than a 2:1 reduction in physical length. And maybe the end focal ratio could also be reduced some as well.

 

Edit: see the diagram of the NP127 on Company7's website here: 

 

http://www.company7....opes/tv127.html

 

There's a lot of length between the front and rear lens pairs which keeps the rear lenses smaller.

 

Gary

 

 

Yes but - perhaps the main change in design for the current iteration of the 127mm was to make that 2nd pair larger in diameter - to reduce vignetting with large-chip cameras. It probably does nothing for most visual observers - except make the scope heavy and pricey.

 

I suspect Gary want to use the 30 mm ES 100° with a TeleVue Petzval.

 

TeleVue makes telescopes for their eyepieces, let Explore Scientific build a modified Petzval for that single eyepiece.

 

I'm fine with the length and weight of the NP-101. It less than a pound heavier and less than an inch longer than my William Optics Zenithstar 103, F/6.9 despite having a second doublet. 

 

 

Jon

[peleuba]

Please explain why a longer physical length is a requirement for Tele Vue?  Can't the back two lenses be moved closer to the front two and sized appropriately for the larger light cone diameter at that point?  Trading f/11 length for f/5.4 length is more than a 2:1 reduction in physical length. And maybe the end focal ratio could also be reduced some as well.

 

Edit: see the diagram of the NP127 on Company7's website here: 

 

http://www.company7....opes/tv127.html

 

There's a lot of length between the front and rear lens pairs which keeps the rear lenses smaller.

 

 

I am sorry to be late to the discussion, and Petzvals, on paper, are terrific optical designs, but I'm a completely visual astronomer, so their primary benefits are less critical  on most of my observing targets.

 

As I understand it, Petzvals, as part of their optical design, require an OTA longer then the advertised focal length.  In other words the tube length is constant that's baked into the optical design.  I think the ratio of OTA length to native focal ratio is something like ~1.25x - ~1.5x (25%-50%) longer then the "advertised" focal ratio of the telescope.  I cannot recall the precise multiplier but do know that one cannot space their way (by reducing the distance between the elements groups) to a shorter OTA and have a working Petzval.  And, its not a matter of simple lens group placement so as to accept an unvignetted light cone.  As IIRC, the spacing is crucial to field flatness.  

 

Its my understanding that the intellectual property piece of the TeleVue "NP" patents are related to the "exotic" glass used to improve the color correction and spherochromatism that is inherent at such fast focal ratios.

 

If one prioritizes the benefit of a short OTA, its best to purchase a standard short focus triplet of which there are MANY. 

 

This exhausts my knowledge of the Petzval design.

 

 

 

***Edited multiple times for clarity - my thoughts don't always flow easily or logically!   

Edited by peleuba, 28 May 2025 - 11:11 AM.

[GGK]

 

 

The Petzval design has a slow initial focal ratio coming from the objective doublet lens set, and a faster focal ratio exiting the back correcting lens set, which also flattens the field and corrects for spherical and (I think) remaining chromatic aberration.  I'm not sure what else it does, but I've found the Petzval design to provide the best image for my wide field / rich field visual observing.

 

This picture shows the 100mm Pentax 4-lens Petzval beside the 101mm NP101is Petzval. Both dew shields are retracted.    

 

 

Compared to the Pentax, the NP design has a much longer distance between the 1st and 2nd pair of lenses.  I believe that the smaller second lens set in the NP is likely easier to manufacturer, reduces weight, and a reduces overall cost (smaller focuser and other back-end parts).  But are there any other reasons that a longer distance is needed between the front and back lens pairs?  

 

The Pentax refractor is an f/4 Petzval and has a ~3.3-inch focuser. It was designed for imaging, of course, but I use it as a wide field visual scope.  Unfortunately, it does not have enough back focus for anything larger than a 2" diagonal.

 

The NP101is is f/5.4 and has a 2.4-inch focuser.  A bigger focuser on the NP101is (or NP127is) would enable me to use the 2.7 inch Astro-Physics 0.75X, 55mm clear aperture photo-visual reducer for a wider field at f/4.

 

The NP101is is a great scope with an outstanding image as good as or better than the Pentax. But the Pentax goes wider and is more convenient to use - both features that have me grabbing the Pentax a lot more than the NP101is.  It's hard to beat the user convenience of the very short scope.  Eyepiece vertical movement is minimal, and since the eyepiece is so close to the mount axis, it's easy to keep the scope stationary even when removing the largest eyepieces.

 

I wouldn't buy a triplet just because Tele Vue made one, but I'd certainly replace my present scopes with a new Tele Vue Petzval like I described in my first reply.

 

Gary

[RichA]

I’m not sure about that….

 

Ed Ting, in a review of the Oracle, indicated that the TV76 had better optics.

I had two Oracles and a  76 side-by-side and it was almost impossible to tell the difference.  It certainly wasn't meaningful in any case.  I also compared the Oracle against a 70mm fluorite (old Celestron) and the Oracle produced a noticeably brighter image but with slightly less well-controlled colour.  However, neither had colour worth worrying about.

[sydney]

The Petzval design has a slow initial focal ratio coming from the objective doublet lens set, and a faster focal ratio exiting the back correcting lens set, which also flattens the field and corrects for spherical and (I think) remaining chromatic aberration.  I'm not sure what else it does, but I've found the Petzval design to provide the best image for my wide field / rich field visual observing.

 

This picture shows the 100mm Pentax 4-lens Petzval beside the 101mm NP101is Petzval. Both dew shields are retracted.    

 

Compared to the Pentax, the NP design has a much longer distance between the 1st and 2nd pair of lenses.  I believe that the smaller second lens set in the NP is likely easier to manufacturer, reduces weight, and a reduces overall cost (smaller focuser and other back-end parts).  But are there any other reasons that a longer distance is needed between the front and back lens pairs?  

 

The Pentax refractor is an f/4 Petzval and has a ~3.3-inch focuser. It was designed for imaging, of course, but I use it as a wide field visual scope.  Unfortunately, it does not have enough back focus for anything larger than a 2" diagonal.

 

The NP101is is f/5.4 and has a 2.4-inch focuser.  A bigger focuser on the NP101is (or NP127is) would enable me to use the 2.7 inch Astro-Physics 0.75X, 55mm clear aperture photo-visual reducer for a wider field at f/4.

 

The NP101is is a great scope with an outstanding image as good as or better than the Pentax. But the Pentax goes wider and is more convenient to use - both features that have me grabbing the Pentax a lot more than the NP101is.  It's hard to beat the user convenience of the very short scope.  Eyepiece vertical movement is minimal, and since the eyepiece is so close to the mount axis, it's easy to keep the scope stationary even when removing the largest eyepieces.

 

I wouldn't buy a triplet just because Tele Vue made one, but I'd certainly replace my present scopes with a new Tele Vue Petzval like I described in my first reply.

 

Gary

I love my stout Tak FSQ106 for visual compared to the TeleVue NP101is.  Less eyepiece swing, better balance, better focuser, and much more robust lens cell (no pinched optics in the cold).  

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[GGK]

I love my stout Tak FSQ106 for visual compared to the TeleVue NP101is.  Less eyepiece swing, better balance, better focuser, and much more robust lens cell (no pinched optics in the cold).  

I didn't realize the FSQ-106 was that short.  

 

Gary

[sydney]

I didn't realize the FSQ-106 was that short.  

 

Gary

Like the Pentax, the Tak has large rear elements.  Both are great Petzvals.

 

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

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Edited by sydney, 27 May 2025 - 08:34 PM.

[sydney]

From Company 7 webpage on the TeleVue NP 101is:

 

http://www.company7..../tvnp101is.html

 

Notice the size and spacing of the rear elements compared to the Tak.

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Edited by sydney, 28 May 2025 - 12:50 PM.

[Jeff Morgan]

As Jon noted, it’s important to carve out your niche in a business and stick with it. APO triplets are a dime a dozen these days. If you want premium, look to AP, TEC or Tak among others. If you are willing to set pedigree aside, there are any number of options available by both Asian and European manufacturers. So many companies make the mistake of trying to be all things to all people. Regrettably this often leads to mediocrity and that to failure. To Uncle Al’s credit, he and Televue have done a pretty good job at discovering those niches and perfecting products that serve them. As a result, I can’t think of too many failures along the way. It seems that TV only discontinues a product when either they come up with a better replacement or it ultimately comes in competition with another of its own product lines (think eyepieces).

 

I think that is a solid analysis.

 

Tele Vue has a very dedicated fan base - for eyepieces, items generally under $1,000. Before the refractor market saturated they produced some nice (but not top end) refractors.

 

In telescopes, they clearly lack the cachet of an Astro-Physics, TEC, or Takahashi. Those top tier companies are quite serious about astronomy. So where does Tele Vue come in the market, and at what price point? Paying top tier prices for a Tele Vue refractor is a pretty big ask for that fan base.

 

The "low end" of the refractor market is a whole swamp full of alligators with very fast product cycles. Many of them already produce pretty good triplets and Petzvals. The trend of the Asian makers has been to move up-market, and up-aperture. Not a great landscape for a mid-market refractor company.

 

OTOH, the top eyepiece companies (with Japanese and German names) have very limited product lines/output. They aren't very serious about the astronomy market, effectively ceding the top to Tele Vue.

 

Things are much better for Tele Vue in eyepieces where they can concentrate on fending off the lower end of the market.

[Mike W]

"Not top end refractors" is a stupid statement.

[Jeff Morgan]

"Not top end refractors" is a stupid statement.

 

They are nice - but not comparable to AP, TEC, or Takahashi.

 

Cool your FanBoy rabies.

[25585]

Of the four TV scopes I have used, the 102 and 85 are my favourites. There are niches left like fluorite lenses, which Agema and TEC fill 120mm & up. For 100mm, only Takahashi and Borg. 
 

TV could get sales for a 4" fluoride, but it would be better to improve and strengthen internal lens cels for their NPs, so they stay collimated, and give them a longer warranty.

[bobhen]

I'll jump in the mix.

 

In his review of a TV 101, Roger Vine says...

 

"Cost aside, it is very hard to fault the NP101. Indeed, if someone were to put a gun to my head and force me to own just a single telescope, this would be high on the list, because it does everything. Not only does it perform well for visual or imaging use on all types of targets, astro’ and terrestrial, it is compact and highly portable: light, quick to cool and easy to mount. The icing on the cake is guaranteed quality and a huge range of Tele Vue accessories to go with it."

 

"A Takahashi FC-100D (or TSA-102, TMB 100-8 etc.) might well be just a tiny fraction sharper on planets at high power, but is typically less portable and lacks the wide, flat field for star-sweeping and imaging. So, is the NP101 the best do-everything small telescope currently available? I think it just might be: highly recommended."

 

IMO, if one lives at a dark sky location and one wants a single, high-end 4" refractor, it would be hard to fault the TV 101 because, as Roger says, it does everything really well. 

 

However, any telescope that does everything well can probably be bested by a telescope that does fewer things but does those few specific things better. Hence Roger's comment about Takahashi being slightly sharper at high power.

 

It might take two or three refractors to best the TV 101, in any incarnation, at what it does well; wide fields, high power and imaging. But for each of those disciplines, you can find refractors that are less expensive or refractors that are slightly better performers at a specific task. 

 

It's also interesting to note that when Roger went looking for and purchased a 4" apo, he found and selected an Astro-Physics Traveler. When I wanted a 4" apo, I selected a Takahashi because I don't need the 101's wide fields but I wanted high power sharpness. As with most things astro, it depends on what the user is after.

 

Bob

Edited by bobhen, 28 May 2025 - 01:39 PM.

[alnitak22]

They are nice - but not comparable to AP, TEC, or Takahashi.

 

Cool your FanBoy rabies.

The NP scopes are comparable to ANY other scopes. No need to resort to trite fanboi BS.

[Mike W]

Of the four TV scopes I have used, the 102 and 85 are my favourites. There are niches left like fluorite lenses, which Agema and TEC fill 120mm & up. For 100mm, only Takahashi and Borg. 
 

TV could get sales for a 4" fluoride, but it would be better to improve and strengthen internal lens cels for their NPs, so they stay collimated, and give them a longer warranty.

Your Genesis is what, 35 years old, even A/P that old have issues.

[Jon Isaacs]

 

Compared to the Pentax, the NP design has a much longer distance between the 1st and 2nd pair of lenses.

 

The Vixen is a camera.  How does it do at 200x on the planets, 300x on doubles?

 

The beauty of the NP-101 is that it provides those wonderful flat fields while providing excellent color correction and optical performance at the highest magnifications.

 

The NP-101 has an F/11.5 objective. What focal ratio do you think the Vixen is?

 

Jon

Edited by Jon Isaacs, 28 May 2025 - 10:09 AM.

[Jon Isaacs]

The NP scopes are comparable to ANY other scopes. No need to resort to trite fanboi BS.

 

I have heard a lot about this and that. I know that no other 4 inch combined the capabilities of the NP-101 but I thought maybe there's a compromise in the Petzval design.

 

Then I see this thread about a group of Japanese planetary observers headed by Mr. Yosida who ranked the planetary performance of a wide range of telescopes. 

 

Among the 4 inch scopes, a Zeiss 100mm x 1000 mm. Next a WO 102 F/8, probably a Lomo triplet. Next, an NP-101. Various Tak doublets and a triplet were ranked. 

 

TeleVue need not take a back seat to anyone ..

 

Jon

[George N]

 

I suspect Gary want to use the 30 mm ES 100° with a TeleVue Petzval.

 

TeleVue makes telescopes for their eyepieces, let Explore Scientific build a modified Petzval for that single eyepiece.

 

I'm fine with the length and weight of the NP-101. It less than a pound heavier and less than an inch longer than my William Optics Zenithstar 103, F/6.9 despite having a second doublet. 

 

 

 

Jon

 

I'd *really* like to see a TV 101 with an ES 30mm 100 stuck on the tail - and the mount that would handle it! The only ES30 100 I've used even unbalanced a 36" Dob - and required a hefty counterweight added to the big Dob's tail-end. But now you got me thinking -- what would the view thru a TV-101is be with that ES 30mm 100 *and* TV's recently improved reducer lens? The reducer lens supposedly provides full correction to the corners for a full-frame chip - so might work will with the ES 30mm 100. Might be worth the few minutes to do some calculations.  

 

I once saw a guy with a TV-101 'stuck' on the side of his Obsession 25 -- he had made a triangular shape plywood gizmo that clamped onto two of the truss poles to hold the refractor - add some extra stuff like a bino-viewer to the UTA, and a big tail to hold a laptop and -- that 25-inch was always chewing up its StellarCat az drive board!  

 

When considering the current 101 or 127 (versus the OP's proposed TV triplet) - it may be important to consider the improved performance claimed by TV when using their new-ish flattener or reducer lenses (price of either is in the same league as a good TV eyepiece - and very hard to find in stock).

 

I think TV knows who their future refractor customers are - or at least they always have a joint booth with FLI the camera company at NEAIC every year. To the extent that a visual observer might buy one - they push low power wide-field sweeping with a flat field -- or NV use. I do note here that Al Nagler has said he could spend *hours* observing the M-24 star cloud thru one of his refractors. As the OP probably implies - the TV refractors are really specialty instruments and not really for the visual observer wanting a fine general-use APO refractor.