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Tele Vue NP101

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#76 Mr.Jim

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Posted 14 September 2020 - 09:31 PM

I bought O'Meara's Messier Object book some years ago to complement my TV101. I was a little let down to find I probably needed a 5 or 6 inch to get the results he did from his wonderful observing site. Still love my 101 though.


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#77 RichA

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Posted 15 September 2020 - 01:11 AM

Is there any other 4 inch refractor that comes close to the NP 101 with regard to flat fields? We always hear that the Televue's main attribute are the glorious wide and flat fields so is there any competitor out there? Just curious.

Takahashi FSQ, Vixen's VSD, an acquired Pentax 100mm, though the Vixen price is much higher.  Most of the high-end apo makers offer field flatteners/reducers that accomplish the same thing as the TeleVue.  Borg makes a 125mm that goes to f/5.1 with reducer.



#78 laedco58

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Posted 15 September 2020 - 01:15 AM

I always thought of the 127-owners as the silent group that just enjoys their gear. smile.gif

 

 

I sure enjoy my NP127, I’ve read a number of times about how they are so much bigger and bulkier than the NP 101’s. The 101’s must be tiny! 


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#79 alan.dang

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Posted 15 September 2020 - 01:46 AM

The original Genesis, SDF and then the 101.

Aside from the Tak FSQ, nothing else in 4".


Don’t forget about the Vixen VSD100 if you are talking about photography. Visually, there is only enough back focus for Japanese style straight through viewing.

#80 Wildetelescope

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Posted 15 September 2020 - 06:14 AM

Terra:

 

If I could only keep two of your scopes, I would keep the Questar and the Telementor. I have neither one and I already have a 4 inch F/5.4 TeleVue.

 

But I suspect that I wouldn't be able to keep any of your scopes. smile.gif

 

(Hopefully this little bit of light-heartedness will make someone chuckle and smile.)

 

Jon

A friend of mine has a Telementor and a questar.  They are worthy companions to the tv101.  That telementor is a dandy little scope.  It pairs well with a good plossl or orthoscopic eyepiece.  

 

jmd



#81 Jon Isaacs

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Posted 15 September 2020 - 07:10 AM

Takahashi FSQ, Vixen's VSD, an acquired Pentax 100mm, though the Vixen price is much higher.  Most of the high-end apo makers offer field flatteners/reducers that accomplish the same thing as the TeleVue.  Borg makes a 125mm that goes to f/5.1 with reducer.

But most of the flatteners/reducers are not well suited for visual, often there is not enough back focus for a 2 inch diagonal.  The advantage of a modified Petzval is that the spacing is always correct.  With a flattener corrector, this is not the case.  

 

The Vixen VSD is an F/3.8 astrograph and doesn't have enough backfocus to use even a 1.25 inch diagonal.  From the looks of the Pentax, it appears that it is also an f/4 astrograph without sufficient backfocus for a diagonal.   

 

The NP-101 is primarily a visual scope and excels in that role.  

 

Jon


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#82 25585

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Posted 15 September 2020 - 07:48 AM

I'll have Terra's SDF Genesis! 


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#83 turtle86

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Posted 15 September 2020 - 02:05 PM

  

The NP-101 is primarily a visual scope and excels in that role.  

 

Jon

 

 

waytogo.gif  Yes it does.


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#84 Oscar56

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Posted 15 September 2020 - 07:41 PM

What is the going price on the used market for a NP101?



#85 Jeff Morgan

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Posted 15 September 2020 - 07:53 PM

But most of the flatteners/reducers are not well suited for visual, often there is not enough back focus for a 2 inch diagonal.  The advantage of a modified Petzval is that the spacing is always correct.  With a flattener corrector, this is not the case.  

 

The Teleskop Service TSFLAT2 is a 2" visual flattener that threads onto the front of of the diagonal. It can be used on many refractors, spacing rings optimize for focal length. It has no reduction, so magnification is unchanged.

 

I picked one up for a 80/480 scope I have. For conventional visual use it works well at all but the lowest powers. The clear aperture is 45mm, not 46mm. Unfortunately for my NV work with the Tele Vue 67 Plossl, there is some vignetting.


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#86 gnowellsct

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Posted 15 September 2020 - 08:01 PM

What is the going price on the used market for a NP101?

If you want one you should join Astromart.

 

The price is roughly $2k to $2.5k depending on whether it is older or recent vintage.  The most recent to be made (are they discontinued?) are the ones that command a bit more in price.  Price is always also dependent on whatever is included in the deal.  There's a new one for sale for $4k at B&H.

 

I'm surprised they don't command a higher price.  But all kinds of weird things going on in the markets these days.

 

Greg N


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#87 25585

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Posted 15 September 2020 - 11:06 PM

I have considered a pre-owned, but having read of people who have bought ine & found it was out of collimation, I shied away each time. Same for Tak FSQs.



#88 gnowellsct

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Posted 15 September 2020 - 11:12 PM

I have considered a pre-owned, but having read of people who have bought ine & found it was out of collimation, I shied away each time. Same for Tak FSQs.

It is a Petzval, and one of the reasons not to get those is four-lens collimation, two cells, each element in each cell must be lined up with each other, and then each pair lined up with the one down the tube.

 

This is an instance where you want some pretty fancy machining.  

 

Were I inclined to buy an NP101 (I am not) I wouldn't hesitate because of issues of collimation.  I would send it to Televue for that.  

 

Greg N


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#89 Oscar56

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Posted 15 September 2020 - 11:48 PM

What does The view through an out of collimation refractor look like?  Are TV refractors any more prone to collimating issues than other refractors?



#90 Tyson M

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Posted 16 September 2020 - 12:40 AM

What does The view through an out of collimation refractor look like?  Are TV refractors any more prone to collimating issues than other refractors?

Usually you get coma. Can't focus stars to a point, flares off to one side. And not all TV refractors (doublets are robust)  only quad element ones that get bought and sold and shipped around without proper packaging and mishandling by couriers.


Edited by Tyson M, 16 September 2020 - 12:40 AM.


#91 25585

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Posted 16 September 2020 - 03:32 AM

My TV doublets (85s, 102, Pronto) are all fine. Genesis is too, but its an original one bought new.

 

If I went for a NP, it too would be new or dealer warrantied. A Tak FSQ-85 as rich field must be the Petzval TV could have made maybe, short, portable, flat field, imagers's friend, telephoto lens, great when used with an extender. I would or may buy a pre-owned one.



#92 gnowellsct

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Posted 16 September 2020 - 07:02 AM

What does The view through an out of collimation refractor look like? Are TV refractors any more prone to collimating issues than other refractors?


Flares. And even double images if the lens is dislocated. The lens cell is more important than the glass, just like the mount is more important than the tube. This goes unremarked by the hoi polloi. A bad lens cell will shut you down good.

Petzvals are known finicky. It took chutzpah for Al to make one. There are few others on the market. You get to f/5 and the field is flat, but the tube is longer than f/5 as measured by a tape!

It makes more operational sense to make a shorter tube with a triplet in a good lens cell. The scope is more compact. Owners can put their own flatteners in at the focuser.

The Pentax 125mm was a four lens scope that priced for $7k over ten years ago. The price and four lenses kept me away, I bought an fs128 instead. Three extra millimeters at half the price. The 125 was not a true petzval but it was a similar idea.
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#93 Oscar56

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Posted 16 September 2020 - 09:10 AM

For visual purposes, what are the alternatives to the NP101?



#94 alan.dang

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Posted 16 September 2020 - 10:04 AM

For visual purposes, what are the alternatives to the NP101?

For flat field?  Probably nothing except for the FSQ-106EDX4 which is far better for imaging but has a lot of penalties for visual (weight/cost).   I think that's one of the reasons why the NP101 has been in continuous production for so long and is truly a unique instrument.  Pure visual may not sell as well since I believe you can only get the NP101is now.

 

If you don't need flatfield, but want 100mm+ aperture and wide field, the only ones I can think of are out of production

1. TEC APO 110FL f/5.6

2. Astro-Physics Traveler 105mm f/6


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#95 Jeff Morgan

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Posted 16 September 2020 - 10:12 AM

Usually you get coma. Can't focus stars to a point, flares off to one side. And not all TV refractors (doublets are robust)  only quad element ones that get bought and sold and shipped around without proper packaging and mishandling by couriers.

 

One of my observing buddies had this happen. I would have called it "reverse coma".

 

Definitely not usable until re-collimated, which he had done.

 

In all fairness, it does not seem to happen very often. 



#96 gnowellsct

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Posted 16 September 2020 - 11:32 AM

Maybe somebody can help me out here. I thought that coma referred specifically to an aberration that is baked into the structure of a mirror or other optic and can't be removed other than by an alternative design, especially a longer focal ratio, or some kind of corrective lens. But a couple of times in this thread I have seen it referred to as the aberration one sees on something which which has minimal or no coma inherently but has been misaligned either due to a severe shock to the lens cell or some other accident.

You get these kinds of stars in an SCT when the secondary mirror is tilted way too far.But what we SCT users will say is that the scope is out of collimation. I've never really heard someone say the scope is exhibiting severe coma.

Edited by gnowellsct, 16 September 2020 - 11:33 AM.


#97 Jeff Morgan

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Posted 16 September 2020 - 01:15 PM

Maybe somebody can help me out here. I thought that coma referred specifically to an aberration that is baked into the structure of a mirror or other optic and can't be removed other than by an alternative design, especially a longer focal ratio, or some kind of corrective lens. But a couple of times in this thread I have seen it referred to as the aberration one sees on something which which has minimal or no coma inherently but has been misaligned either due to a severe shock to the lens cell or some other accident.

You get these kinds of stars in an SCT when the secondary mirror is tilted way too far.But what we SCT users will say is that the scope is out of collimation. I've never really heard someone say the scope is exhibiting severe coma.

 

I was describing the visual impression. What it resembled.

 

The exact nature of the aberration is is not too material, the key point is the scope was unusable without re-alignment.

 

Edit - there are types of refractors that do have coma which was minimized by spacing. Might have been the Cooke achromat design, I can't recall.


Edited by Jeff Morgan, 16 September 2020 - 01:18 PM.

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#98 213Cobra

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Posted 16 September 2020 - 08:31 PM

For flat field?  Probably nothing except for the FSQ-106EDX4 which is far better for imaging but has a lot of penalties for visual (weight/cost).   I think that's one of the reasons why the NP101 has been in continuous production for so long and is truly a unique instrument.  Pure visual may not sell as well since I believe you can only get the NP101is now.

 

If you don't need flatfield, but want 100mm+ aperture and wide field, the only ones I can think of are out of production

1. TEC APO 110FL f/5.6

2. Astro-Physics Traveler 105mm f/6

If one can afford a used FSQ, either 106 or 85, both are highly viable for visual. I own both and use both exclusively for visual. For planets, their respective Tak Extenders are essentially invisible (i.e. no deleterious effects to get more FL). Both of my FSQs were shipped robustly packed and arrived in fine shape. I see no collimation risk if reasonable precautions are taken when rumbling to a dark site. A Stellarview M2 can handle either of them. A Sergio Bonilla mount on a Gitzo 5 CF tripod handles either or both just fine. That's what I use when I'm not hauling out the DM6/Berlebach Planet. Of course, THAT can handle the FSQ-106ED wrapped in lead sheeting.

 

The TSFlat2 works really well visually on my LOMO 80/480 and 80/600 (though it's almost not needed with the latter).

 

A used Stellarvue SVQ-100 and TS has 86 and 100 quads. Flat field scopes are my go-to for visual.

 

Phil


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#99 Oscar56

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Posted 17 September 2020 - 11:20 AM

Does anyone have the specs on the 4" clam-shell ring mount?  What are the bolt spacings and the bolt sizes required for a Vixen-style mounting plate.  I don't see those specifics on the Tele Vue website.



#100 Oscar56

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Posted 21 September 2020 - 03:44 PM

Does anyone have the specs on the 4" clam-shell ring mount?  What are the bolt spacings and the bolt sizes required for a Vixen-style mounting plate.  I don't see those specifics on the Tele Vue website.

oops.. That question was answered in the first few posts of this thread.




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