87 replies to this topic

[George N]

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, ......

 

Bob

....from Alan Dyer's review of the 101 in the May 2002 issue of Sky & Telescope -- "Great optics are easy to evaluate — the NP 101 showed no sign of any aberrations, period. End of review! ..."

[Terra Nova]

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. 

I didn't say exclusively, I said mostly. There are plenty of F7 to F9 ED doublets produced offshore, and have been for a long time. There is nothing unique in there design. The point I was trying to make is the unique contribution to telescope design accorded to the Nagler-Petzval, an instrument which affords flat-to-the-edge, well corrected views, perfectly matched and designed in concert with and made to take full advantage of Al's wide-field Nagler and Panoptic eyepieces. To me, that's the true Al Nagler/TeleVue legacy.

Edited by Terra Nova, 28 May 2025 - 10:41 AM.

[George N]

I didn't say exclusively, I said mostly. There are plenty of F7 to F9 ED doublets produced offshore, and have been for a long time. There is nothing unique in there design. The point I was trying to make is the unique contribution to telescope design accorded to the Nagler-Petzval, an instrument which affords flat-to-the-edge, well corrected views, perfectly matched and designed in concert with and made to take full advantage of Al's wide-field Nagler and Panoptic eyepieces. To me, that's the true Al Nagler/TeleVue legacy.

Plus, TV keeps working to improve them - again, I refer to the new (2 years old?) corrector lenses - one a flattener and the other a focal reducer - designed to improve outer-field performance when imaging with full-frame cameras - but might be of use to the visual observer (with a well-stocked check book).

 

I don't know but -- the TV-60 might just exist because Al Nagler likes to use one to photograph birds! ....and the TV-76 might just exist because its the only telescope Al can physically manage these days - with his Night Vision gizmo on it. A joint friend with a summer home on Tupper Lake NY (central Adirondacks) told me "When Al and Judy show up for a weekend, if it's on a clear night, he won't even come into the house! He heads straight down to the dock with that 76mm and NV gizmo and is out there until 3 AM or later!" 

[alnitak22]

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.

Uh…that schematic is for the original Renaissance scope with the cemented rear doublet clearly shown. It is absolutely incorrect and misleading to equate this picture to the np 101is.

[Terra Nova]

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

The LENGTH is just part of the design. Think of it as a sort of happy medium (not by accident but by design) between the actual focal length of the primary and the shorter/faster resultant Petzval focal length. It's just a fact of life. I LOVED my TV Genesis SDF right up to the day that I handed it off to it's new owner. I traded it in for my shorter F6 90mm triplet of the same f.l., (540mm) because I was getting older, not the telescope. I was simply needing something shorter and more manageable for my age. My AT90CFT fits the bill nicely. I still can get very wide FOV with low magnification and also have the capability of high magnifications >200X with a Vixen 2.5mm LV. In fact I use all the same eyepieces with the new scope and have the exact same range in magnification. But I never changed because of physical necessity or capability of the telescope but because of my own changing physical necessity and capability. I think the 4" Nagler-Petzval line has produced superb instruments over the years. In their regard, I wouldn't change a thing!

Edited by Terra Nova, 28 May 2025 - 11:55 AM.

[GGK]

The LENGTH is just part of the design. Think of it as a sort of happy medium (not by accident but by design) between the actual focal length of the primary and the shorter/faster resultant Petzval focal length. It's just a fact of life. I LOVED my TV Genesis SDF right up to the day that I handed it off to it's new owner. I traded it in for my shorter F6 90mm triplet of the same f.l., (540mm) because I was getting older, not the telescope. I was simply needing something shorter and more manageable for my age. My AT90CFT fits the bill nicely. I still can get very wide FOV with low magnification and also have the capability of high magnifications >200X with a Vixen 2.5mm LV. In fact I use all the same eyepieces with the new scope and have the exact same range in magnification. But I never changed because of physical necessity or capability of the telescope but because of my own changing physical necessity and capability. I think the 4" Nagler-Petzval line has produced superb instruments over the years. In their regard, I wouldn't change a thing!

I think the physical length of the scope could be shortened significantly by removing length between the lens pairs and adding back about half of it in the f/5.4 focuser end - if keeping the same focuser.  ~f/11 to f/5.4 is about a 2 to 1 ratio.  True that the correcting lens pair diameter must increase to accommodate the larger incoming light cone diameter and that would increase price and weight. See posts 35 and 37 for pics of the shorter Pentax SDUF and Tak FSQ106 4" class Petzval refractors.  I don't know why Tele Vue decided to make the scope long other than the reasons I suggested earlier.  The NP101is is a great scope either way, for sure.  It would be more convenient to use if it was the length of the TV-85, though.  

 

Gary

[sydney]

Uh…that schematic is for the original Renaissance scope with the cemented rear doublet clearly shown. It is absolutely incorrect and misleading to equate this picture to the np 101is. 

What is the size and spacing of rear elements in the NP101is?
This is the only picture I could find looking into the tube, but it is an NP101 and not an NP101is.

 

https://www.cloudyni...-101/?p=4381530

 

TeleVue should tell Company 7 to update the image.  Their diagram clearly labels this as an NP101is.

 

 

                                                 

Above: TeleVue "NP101is" telescope optical arrangement; 1. air spaced doublet objective, 2. mounting collar, 3. doublet lens, 4. 2" focuser,

5. "Everbrite" 2 inch mirror diagonal, 6. 2" to 1.25" reducer, 7. eyepiece (optional)

 

 

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

 

 

 

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[25585]

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.

The 30mm ES100 is a 3" eyepiece, TV focusers are not that large, though the 127 might take them.

 

Takahashi FSQ-106s have 4" focusers.

[alnitak22]

Here’s an interesting article. For those wondering about the strength of the “is” scope focuser, scroll down to the section where it describes the focuser undergoing a sag test at 4 different angles using a 10lb weight, I think it safe to say that yes, it will handle the ES 30 Eyepiece. 
 

https://televue.com/...-build-secrets/

[RichA]

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.

the new 101 apparently incorporated a larger sub-diameter compressor lens than the original, but they were still smaller than the main objective.

[Jon Isaacs]

 

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.

 

It's worth thinking about that.

 

. Arguably, the NP-101 is the most versatile visual  4 inch refractor you can buy.  It does it all and it does everything just about as well as it can be done.

 

The one thing that 4 inch refractors do better than larger scopes are bright, low power, wide fields of view. 

 

The NP-101 excels at this while providing high quality views limited only by its aperture.

 

It does everything one can ask of a 4 inch refractor and does it just about as well as it can be done.

 

It is expensive and it does like well corrected eyepieces.. 

 

Jon

Edited by Jon Isaacs, 28 May 2025 - 03:40 PM.

[Jon Isaacs]

 

It would be more convenient to use if it was the length of the TV-85, though.

 

According to the specs, the TV-85 is 21.5 inches in length, the NP-101, 25.5 inches. 4 inches.. the big difference is the weight.

 

I think the 106 FSQ is the scope you want. 4 inch focuser, pretty short. The OTA does weigh 15 lbs.

 

Jon

[GGK]

What is the size and spacing of rear elements in the NP101is?
 

This is from Tele Vue's website under Tele Vue APO Design and Build “Secrets” here:

 

https://televue.com/...-build-secrets/

 

 

The NP127is graphic looks about the same.

 

Gary

[alnitak22]

This is from Tele Vue's website under Tele Vue APO Design and Build “Secrets” here:

 

https://televue.com/...-build-secrets/

 

IMG_1018.jpg

 

The NP127is graphic looks about the same.

 

Gary

I posted the link in post #59 above

[Jon Isaacs]

Since this discussion involves the NP-101, a few years ago I used my laser fixture to measure the effective aperture of the NP-101. I measured it between 101 mm and 102 mm. 

 

I contacted TeleVue and was told it's actually a full 4 inches, 101.6 mm.

 

Jon

[GGK]

I posted the link in post #59 above

Sorry about that.  I read the post, but missed the link.

 

Gary

[alnitak22]

Sorry about that.  I read the post, but missed the link.

 

Gary

Please…no worries!

[GGK]

According to the specs, the TV-85 is 21.5 inches in length, the NP-101, 25.5 inches. 4 inches.. the big difference is the weight.

 

I think the 106 FSQ is the scope you want. 4 inch focuser, pretty short. The OTA does weigh 15 lbs.

 

Jon

 

The TV-85 measures about 18.5 inches without the diagonal compared to the 25.5 inches for the NP101is.

 

 

 

I actually browsed the classifieds today to see what FSQ106 scopes are available.

 

But I already use the 100mm f/4 Pentax SDUF Petzval refractor which weighs 8.4 pounds and is only 13 inches long without the diagonal.  It's very stable on my small mounts.  The Tak would need a larger mount, which I have, but I don't gain anything on the wide field observing end vs. the Pentax, even if I add the 0.75X focal reducer to the Tak.

 

 

What I've really been looking for (opened a topic on it a while back), is a shorter (than the NP127is) 5" Petzval, but there aren't many 5-inch Petzval refractor options. I trust Tele Vue quality, so I know the NP127is would be a great scope within its size and specs.  I simply wish it was shorter.

 

And for those who mentioned Tele Vue's NP reducer in earlier posts, I've looked at that, but the back focus is only 68mm, so not enough for a diagonal.

 

Gary

[GGK]

Since this discussion involves the NP-101, a few years ago I used my laser fixture to measure the effective aperture of the NP-101. I measured it between 101 mm and 102 mm. 

 

I contacted TeleVue and was told it's actually a full 4 inches, 101.6 mm.

 

Jon

I believe in another post that you said they named it NP101 so it wasn't confused with the TV102. Fun story 

[GGK]

The 30mm ES100 is a 3" eyepiece, TV focusers are not that large, though the 127 might take them.

 

Takahashi FSQ-106s have 4" focusers.

What I've read says that the NP127is has a 2.4 inch focuser like the NP101is, but I don't know for certain.

 

The Agena Astro website says the FSQ106 has Generous 178 mm back focus allows the user to attach a variety of imaging cameras and accessories, 2 inch diagonals, and many other visual devices including bino viewers.

 

I honestly don't know if that's enough back focus for a 3" diagonal and eyepiece.

 

Gary

[scotsman328i]

Well, after reading so many comments on the Televue refractors, I figured I could melt my TV102 and TV76 together and it should give me a TV101. 

 
(p.s. yes…rabid Televue FanBoy here. Have been for over 25 years. )

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Edited by scotsman328i, 28 May 2025 - 09:12 PM.

[AnakChan]

[Mod Hat On]
Folks, let's keep the topic about Company 7 outside of this thread - this is about Tele Vue instead.
[/Mod Hat Off]

[Jon Isaacs]

[Mod Hat On]
Folks, let's keep the topic about Company 7 outside of this thread - this is about Tele Vue instead.
[/Mod Hat Off]

 

 

Jon

[areyoukiddingme]

I'm glad Televue makes Petzvals rather than triplets. My only complaint is that they can't make them for less money.

 

On the other hand, they are bargains used, depreciating a good bit more than similar aperture offerings from AP and Takahashi. 

 

I assume that price drop reflects issues with collimation, higher availability on the market, and perhaps some quality variance.

[The Ardent]

I don’t care what they make , as long as the average user can collimate it easily. 
I don’t see that happening.