43 replies to this topic

[RichA]

We've seen it or heard reports of quadruplet telescopes like TeleVue's and others with collimation issues.  Yet, how often do you hear about that when someone uses a conventional refractor with a reducer/field corrector in the focuser?  Not ever, as far as I've seen. And they are used in relatively loose-fitting tubes in the drawtube vs. fixed lenses in a quadruplet.   So what makes fitting the lens into the telescope body difficult when it comes to collimation, as is the case with quadruplets?

[bobzeq25]

We've seen it or heard reports of quadruplet telescopes like TeleVue's and others with collimation issues.  Yet, how often do you hear about that when someone uses a conventional refractor with a reducer/field corrector in the focuser?  Not ever, as far as I've seen. And they are used in relatively loose-fitting tubes in the drawtube vs. fixed lenses in a quadruplet.   So what makes fitting the lens into the telescope body difficult when it comes to collimation, as is the case with quadruplets?

You just have to pick the right quad.

My Stellarvue SV100Q came perfectly collimated. Which was guaranteed since they tested each scope individually.

It was a joy to use. A triplet with a permanently mounted flat field corrector. Slap a camera on (didn't have to space it precisely), focus, and you were done.

It's now sold by Teleskop Express, who also test.

https://www.teleskop...d-flatener-6478

Click on the mediocre CN thumbnail for a good version, and details.

Edited by bobzeq25, 09 April 2025 - 08:23 PM.

[ngc7319_20]

I think it is mostly a TeleVue design issue.  Most makers thread the tube and screw the objective on the end.  TeleVue slides the objective on the tube (slip fit), and sticks 3 bolts through the overlap.  Simple enough, but a good bump at either end of the tube, and the slip joint slides.  Maybe they have improved -- I haven't looked at one in a couple years.  OK, let me run and put on my flame-proof suit... I'll be right back...

 

What about Tak FSQ?  I've no experience there.  Anyone comment?

Edited by ngc7319_20, 10 April 2025 - 06:17 AM.

[Spikey131]

I have been shlepping my NP101 all over the Northeast for the past 8 years in search of wide, flat fields in dark places.  Lots of amazing views, with sharp stars from one edge to the other.  And one unforgettable view of the entire North America nebula with an O3 filter at Cherry Springs.

 

Still perfectly collimated.

[Mike W]

Televue does it that way so you don't mess with the collimation which is done at Televue with an MPT scope.

[Rasfahan]

We've seen it or heard reports of quadruplet telescopes like TeleVue's and others with collimation issues.  Yet, how often do you hear about that when someone uses a conventional refractor with a reducer/field corrector in the focuser?  Not ever, as far as I've seen. And they are used in relatively loose-fitting tubes in the drawtube vs. fixed lenses in a quadruplet.   So what makes fitting the lens into the telescope body difficult when it comes to collimation, as is the case with quadruplets?

I don‘t know where you got that impression. These doublet+corrector refractors are usually only suitable for imaging. Both imaging forums are full of reports of faults with them. It‘s generally called the „refractor lottery“.

[HydrogenAlpha]

I've owned 2 different FSQ85s, zero problems with them and by far the most reliable refractors I've ever had. It's plug and play and stars are *always* pinpoint to the corners. 

 

I can never get perfect round stars to the edges with anything else (especially with my full frame sensor and 3.76 micron pixels, which is anything but forgiving). This includes even high end triplets with matched flatteners or reducer/flatteners. I suspect it's because for quads, the lens elements are held within the OTA, and are farther away from where the sensor plane is. In contrast, for triplets + flatteners, the flatteners are on the focuser train which is more prone to misalignment/flex. 

 

Of course, quads all have vastly different designs. Even the FSQ85 and FSQ106 are not the same. Many quads are even just doublets with built-in 2-element flatteners. And there's the rabbit hole of adding more lens elements (sextuplets even), which doesn't seem to do much. Some are just triplets with built-in 3-element reducers/flatteners. 

[Jon Isaacs]

I think it is mostly a TeleVue design issue.  Most makers thread the tube and screw the objective on the end.  TeleVue slides the objective on the tube (slip fit), and sticks 3 bolts through the overlap.  Simple enough, but a good bump at either end of the tube, and the slip joint slides.  Maybe they have improved -- I haven't looked at one in a couple years.  OK, let me run a put on my flame-proof suit... I'll be right back...

 

What about Tak FSQ?  I've no experience there.  Anyone comment?

 

I only know my personal experience and what I have read here.  I have read of FSQs with collimation issues.  I know of a few TeleVues that have collimation issues.  One thing to consider is that there are almost certainly more TeleVue Petzvals out there than the sum total of other designs.  They have building them for more than 40 years..  Mine is about 20 years old.

 

I purchased my NP-101 used in 2010 and the previous owner told me he had played with the collimation so I knew there might be an issue.  What I found was that with the 3.5 mm Nagler and a 2x Barlow, (310x), the diffraction rings were not perfectly centered, they were slightly offset. Someone doing astrophotography would never see it but I am a double star guy in a region known for it's excellent seeing so such things are visible.

 

Being a Dob guy and being a research engineer, I figured I would tackle this myself.  So, I built a collimation jig so I could dial in the collimation as I did with a Newtonian.  This that story:

 

 

 

https://www.cloudyni...g-my-tv-np-101/

 

That was about 15 years ago.  Since then the scope has ridden more than 15,000 miles in the back of a pickup truck and suffered one potential disaster..  I had set it outside and was rolling one of my Dobs out the garage door when I felt a gentle pressure in the middle of my back. I turned around to see the NP-101 and mount tumbling over with the objective end hitting the decomposed granite driveway, taking the brunt of the force.  As far as I could see, there was no damage except to the Telrad.  

 

The scope is still in what I consider to be perfect collimation. 

 

Others have copied my collimation design.  Not long ago someone sent me a PM telling me, they had built one of my collimation fixtures and had successfully collimated their scope.  They talked to TeleVue and apparently they do not have a collimation fixture and do it by hand.  

 

Jon

Edited by Jon Isaacs, 10 April 2025 - 07:50 AM.

[25585]

I have an original Genesis which is OK, but reviews of mis-collimated Petzvals have put me off wanting any more, triplets are my max lens limit, and mine have no negative reviews or scare stories AFAIK (TOA, TSA, LZOS).

[Jon Isaacs]

I have an original Genesis which is OK, but reviews of mis-collimated Petzvals have put me off wanting any more, triplets are my max lens limit, and mine have no negative reviews or scare stories AFAIK (TOA, TSA, LZOS).

 

It is my understanding that triplets are very sensitive to miscollimation, centering.  The tolerances on centering can be less than 10 microns.  They go back to the factory for that.. 

 

Jon

[andysea]

My fsq106 had to go back to Japan because the rear elements needed to be reset. They are not collimatable and they are set in place, not sure if they are cemented or how they are fixed.
I don’t think that the fsq is diffraction limited but after the trip to Japan I get excellent stars to the corners of the imx461.

[Rasfahan]

My first FSQ-85 came miscollimated from factory. I had the choice of it doing a round-trip to Japan or return. I returned it and got another. That one is perfect to full frame (6 um pixels - haven‘t tried it with 3.75um). It is paired with an Esatto 3“ focuser and is „set and forget“ for any image train I threw at it.

[Scott99]

We are conflating "quadruplet" with Petzval designs here.   To me the "XXXlet" refers to the number of lenses in the objective.  Petzval designs can be doublets or triplets, or quadruplets, with a flattener in the back end of the tube. 

[Terra Nova]

It is my understanding that triplets are very sensitive to miscollimation, centering.  The tolerances on centering can be less than 10 microns.  They go back to the factory for that.. 

 

Jon

I’ve had no problems whatsoever with my two AT triplets. They came perfectly collimated and the views are textbook perfect. They replaced my two Petzvals (TV Genesis SDF and Vixen 120S). I had no problems with either of them either. But I’ve never dropped them either! All four have/had handles.

[Jan-S]

We are conflating "quadruplet" with Petzval designs here. To me the "XXXlet" refers to the number of lenses in the objective. Petzval designs can be doublets or triplets, or quadruplets, with a flattener in the back end of the tube.

Yes, I think that’s an important distinction. If not made, any number of optical trains could be labeled quadruplet, quintuplet, … and talking about them as a single type of product/scope gets confusing.

True quadruplet onjectives have reportedly been made by Zeiss and also by Lichtenknecker, many decades ago. They may be revived by APQ, though those have not been seen in the wild yet as far as I can tell.

Edited by Jan-S, 10 April 2025 - 01:49 PM.

[RichA]

We are conflating "quadruplet" with Petzval designs here.   To me the "XXXlet" refers to the number of lenses in the objective.  Petzval designs can be doublets or triplets, or quadruplets, with a flattener in the back end of the tube. 

I don't like Petzval used for  telescopes at all, considering they were f2.0 camera lenses or relatively short focal length originally.  There have been scopes with single element lenses down the tube (Vixen) and more, TeleVue, etc.

Edited by RichA, 10 April 2025 - 02:03 PM.

[Jon Isaacs]

We are conflating "quadruplet" with Petzval designs here.   To me the "XXXlet" refers to the number of lenses in the objective.  Petzval designs can be doublets or triplets, or quadruplets, with a flattener in the back end of the tube. 

 

If you read the first post, it's clear the original poster is referring to Petzvals.. the reference to TeleVue makes that clear 

 

The TeleVue NP series stands for Nagler-Petzval. According to Company 7, the NP-101 is more complicated than an ED doublet with an ED doublet flattener/reducer.  The objective cannot be used alone...

 

For those who believe scopes like the NP series cannot be used for visiable, Mr. Yoshida's group of planetary observers ranked the NP-101 near the top of the list of 4 inch refractors.

 

(69 points）Zeiss APQ100/1000
(68 points）William Optics10cmF8
(67 points) TV NP101
(67 points）Takahashi TSA-102
(66 points）Zeiss APQ100/640
(66 points）TAKAHASH FSQ-106ED
(66 points）NIKON 10cmED
(66 points）William Optics FLT110
(65 points) Vixen FL102
(65 points）Takahashi FSQ-106
(64 points) TV TV101
(63 points) TV TV102
(63 points）Takahashi FS-102
(63 points）PENTAX 105SD
(62 points）UO　WHITEY DOB 15cmF8
(61 points) TV SDF
(61 points）PENTAX 105SDP

 

The ED doublet "objective" of the NP-101 is F/11.5.. 

 

Jon

[Jon Isaacs]

I don't like Petzval used for  telescopes at all, considering they were f2.0 camera lenses or relatively short focal length originally.  There have been scopes with single element lenses down the tube (Vixen) and more, TeleVue, etc.

 

Just be clear.. they are "modified" Petzvals. Highly modified..

 

Jon

[turtle86]

I’ve had no problems whatsoever with my two AT triplets. They came perfectly collimated and the views are textbook perfect. They replaced my two Petzvals (TV Genesis SDF and Vixen 120S). I had no problems with either of them either. But I’ve never dropped them either! All four have/had handles.

 

I make it a point to put handles on most of the expensive scopes I have owned over the years--NP 101, AP 130 GT, and Stowaway.  A handle is cheap insurance and also makes mounting and dismounting a lot easier for me.

[turtle86]

If you read the first post, it's clear the original poster is referring to Petzvals.. the reference to TeleVue makes that clear 

 

The TeleVue NP series stands for Nagler-Petzval. According to Company 7, the NP-101 is more complicated than an ED doublet with an ED doublet flattener/reducer.  The objective cannot be used alone...

 

For those who believe scopes like the NP series cannot be used for visiable, Mr. Yoshida's group of planetary observers ranked the NP-101 near the top of the list of 4 inch refractors.

 

(69 points）Zeiss APQ100/1000
(68 points）William Optics10cmF8
(67 points) TV NP101
(67 points）Takahashi TSA-102
(66 points）Zeiss APQ100/640
(66 points）TAKAHASH FSQ-106ED
(66 points）NIKON 10cmED
(66 points）William Optics FLT110
(65 points) Vixen FL102
(65 points）Takahashi FSQ-106
(64 points) TV TV101
(63 points) TV TV102
(63 points）Takahashi FS-102
(63 points）PENTAX 105SD
(62 points）UO　WHITEY DOB 15cmF8
(61 points) TV SDF
(61 points）PENTAX 105SDP

 

The ED doublet "objective" of the NP-101 is F/11.5.. 

 

Jon

 

Not surprised at all. My old NP 101 gave excellent planetary views.

[HydrogenAlpha]

If you read the first post, it's clear the original poster is referring to Petzvals.. the reference to TeleVue makes that clear 

 

The TeleVue NP series stands for Nagler-Petzval. According to Company 7, the NP-101 is more complicated than an ED doublet with an ED doublet flattener/reducer.  The objective cannot be used alone...

 

For those who believe scopes like the NP series cannot be used for visiable, Mr. Yoshida's group of planetary observers ranked the NP-101 near the top of the list of 4 inch refractors.

 

(69 points）Zeiss APQ100/1000
(68 points）William Optics10cmF8
(67 points) TV NP101
(67 points）Takahashi TSA-102
(66 points）Zeiss APQ100/640
(66 points）TAKAHASH FSQ-106ED
(66 points）NIKON 10cmED
(66 points）William Optics FLT110
(65 points) Vixen FL102
(65 points）Takahashi FSQ-106
(64 points) TV TV101
(63 points) TV TV102
(63 points）Takahashi FS-102
(63 points）PENTAX 105SD
(62 points）UO　WHITEY DOB 15cmF8
(61 points) TV SDF
(61 points）PENTAX 105SDP

 

The ED doublet "objective" of the NP-101 is F/11.5.. 

 

Jon

I consider the Televue NP series as visual scopes. I don't see them used often in imaging

[RichA]

If you read the first post, it's clear the original poster is referring to Petzvals.. the reference to TeleVue makes that clear 

 

The TeleVue NP series stands for Nagler-Petzval. According to Company 7, the NP-101 is more complicated than an ED doublet with an ED doublet flattener/reducer.  The objective cannot be used alone...

 

Are we 100% sure of that, or has anyone ever tried it?

[RichA]

Just be clear.. they are "modified" Petzvals. Highly modified..

 

Jon

There comes a point where what it is bears little resemblance to what it was supposed to be.  Does this description of the Petzval design sound like a TeleVue scope?

wiki:

 

Optical DesignThe lens consisted of two doublet lenses with an aperture stop in between. The front lens is well corrected for spherical aberrations but introduces coma. The second doublet corrects for this and the position of the stop corrects most of the astigmatism. However, this results in additional field curvature and vignetting.

[Jon Isaacs]

There comes a point where what it is bears little resemblance to what it was supposed to be.  Does this description of the Petzval design sound like a TeleVue scope?

wiki:

 

Optical DesignThe lens consisted of two doublet lenses with an aperture stop in between. The front lens is well corrected for spherical aberrations but introduces coma. The second doublet corrects for this and the position of the stop corrects most of the astigmatism. However, this results in additional field curvature and vignetting.

 

You better talk to Al Nagler about that.  

 

Jon

[25585]

It is my understanding that triplets are very sensitive to miscollimation, centering.  The tolerances on centering can be less than 10 microns.  They go back to the factory for that.. 

 

Jon

 
My 3 are OK. The TOA and LZOS have big heavy cels (making OTAs heavy), so I feel they will stay good.