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Equipment Discussions >> Refractors

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Jon Isaacs
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Re: Televue 85 vs. Televue NP101 new [Re: skullpin]
      #5600351 - 01/01/13 09:18 PM

Keith:

As you point out, there are good reasons to purchase an 80mm-90mm apochromatic refractor. But if that is one's choice, I am not sure that a TV-85 is the wisest choice, you can get similar capability and quality for considerably less money from other vendors.

If someone were to ask me about whether they should buy a TV-85 or the NP-101 as a first scope, I would invite them over to my place and set up three scopes, my 80mm William Optics FD, my NP-101 and my 10 inch GSO Dob. Then I would point them all at Jupiter. After that, M42. After that, M35...

I do some birding with my NP-101 but then there are times when I do birding with my 12.5 inch Dobsonian.

Jon

Edited by Jon Isaacs (01/01/13 09:30 PM)


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BillP
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Re: Televue 85 vs. Televue NP101 new [Re: choran]
      #5600412 - 01/01/13 10:01 PM

Quote:

This will be for visual use only. ... love the wide field views. I'm interested in extreme ease of use, ... I wonder if I'd be giving up significant brightness and detail if I opt for the smaller 85.




OK...you really want ease of use...but you are having aperture fever which is obscuring things for you

Go back to your primary need...super easy. So smaller is better. I would consider the TMB 92. Splits the difference on aperture and is super small.


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Calypte
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Re: Televue 85 vs. Televue NP101 new [Re: Jon Isaacs]
      #5600606 - 01/02/13 12:52 AM

Quote:

Even an old codger like me can see 11th-12th magnitude galaxies in an 80mm if the skies are reasonably dark...

Jon



I confess that I've never seen a 12th mag galaxy in my NP101is.


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Jon Isaacs
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Re: Televue 85 vs. Televue NP101 new [Re: Calypte]
      #5600760 - 01/02/13 06:36 AM

Quote:

Quote:

Even an old codger like me can see 11th-12th magnitude galaxies in an 80mm if the skies are reasonably dark...

Jon



I confess that I've never seen a 12th mag galaxy in my NP101is.




J. Reynolds Freeman completed the Herschel 400 with a 55mm refractor... I am 64 years old and my eyes are not what they used to be, that is never going to happen.

I used 11th-12th magnitude because the magnitudes vary with the source. For example, the brightest Galaxy in Hickson 68 is NGC5350, Cartes du Ciel lists NGC-5350 as being magnitude 11.3 but Sky Tools lists it at 12.3. The Blue Flash Nebula NGC-6905 is listed by both as magnitude magnitude 12.0, I have observed the Blue Flash with my William Optics 80mm F/7 FD from our place in Boulevard.

Obviously a 3 or 4 inch refractor is not the ideal scope for such targets, they are much more easily seen in a larger scope. But sometimes I'll be observing and I get the hankering to see if I can find some favorite in a smaller scope. It is pretty amazing what can be seen in a small refractor.

Jon


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choran
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Re: Televue 85 vs. Televue NP101 new [Re: BillP]
      #5600956 - 01/02/13 10:26 AM

Bill, is the 92SS of similar build and visual quality?
Thanks,
Chuck


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Jim7728
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Re: Televue 85 vs. Televue NP101 new [Re: choran]
      #5601010 - 01/02/13 10:52 AM

I had the Genesis SDF and compared to the TV-85, the cool down time is significantly longer in the Petzval, than the TV-85.

Also of note: Field curvature is noticeable in the TV-85 when using a 21mm Ethos and most definitely in a 90mm f/5.5 ED doublet that I also own and would think the AT/ 92SS will have the same optical trait, depending how old your eyes are.

Quote:

I would dearly love to see Jupiter's moons resolve to disks, for example, and realize that a 3 or 4 inch scope is not likely to get me there. Still, those wide views..,




I personally need a 5" APO to start seeing Jupiter's moon's as disks in a light polluted location and to also have a wide view then it's a NP-127.


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Starman1
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Re: Televue 85 vs. Televue NP101 new [Re: Jim7728]
      #5601064 - 01/02/13 11:13 AM

Quote:

I would dearly love to see Jupiter's moons resolve to disks, for example, and realize that a 3 or 4 inch scope is not likely to get me there. Still, those wide views..,



That's the point, isn't it? Each type of scope has its own purpose.
A TeleVue NP101 will give you astounding, wide views. My 12.5" dob, at 456X, sees each Galilean moon a different color, making identification fairly easy, and at 608X, I thought I saw albedo markings on Ganymede in exceptionally stable seeing.


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johnnyha
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Re: Televue 85 vs. Televue NP101 new [Re: Starman1]
      #5601159 - 01/02/13 12:22 PM

Quote:

I would dearly love to see Jupiter's moons resolve to disks, for example, and realize that a 3 or 4 inch scope is not likely to get me there. Still, those wide views..,




My 4" FS102NSV when I had it, easily resolved the moons of Jupiter as discs, each an individual size and color, and I could easily see them cross the face of the planet. Shadow transits looked like fresh bulletholes.


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t.r.
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Re: Televue 85 vs. Televue NP101 new [Re: johnnyha]
      #5601196 - 01/02/13 12:44 PM

Just for clarification on resolving Jupiters moons read the quote by EdZ from a previous post on the topic titled "Jupiter's Moons"...

" What affect does scope diameter have?
Scope size determines the smallest object that can be resolved. The smaller the scope, the larger the object needs to be for it to be resolved. A 6" scope can resolve down to about 0.8 arcseconds, enough to see all the moons resolved. A 5" scope would see the smallest moons only as the visible disk within Airy disks. These are not resolved. A 3" scope has an Airy disk so large that it would would bloat the smallest moons to nearly double their resolved size. A 3" scope would bloat even the largest moons to a visible disk that does not represent a resolved disk. Sure they would look like resolved disks, but actually they are large visible disks within the Airy disks."

" How big are the moon's
Well that varies with the distance to Jupiter.
Jupiter is 88,700miles in diameter. At 5AU its disk would appear 39.3 arcsec.
The sizes (at 5AU) and the magnitudes of Jupiter's moons are:
Ganymede 3,270 = 1.45 arcsec, mag 4.6
Callisto 2,980 = 1.32 arcsec, mag 5.6
Io 2,260 = 1.00 arcsec, mag 5.0
Europa 1,940 = 0.86 arcsec, mag 5.3 "

" Except perhaps when Jupiter is at it's very closest, and only then for Ganymede, none of Jupiter's moons can be resolved with a 80mm scope. But even in an 80mm scope variations in magnitude can make one moon look larger than another. None-the-less, that is not resolved.
Ganymede and Callisto can probably both be resolved in a 100mm scope, and potentially, for the most eagle-eyed, at powers as low as 100x, but probably for most people closer to 125x-150x.
To resolve the smallest moon, you'd be safe in your expectations by using a 6" or larger scope at 160x to 200x"

Most people with smaller scopes are really reporting seeing the airy disk created by the moon and not a true resolved disk.


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Calypte
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Re: Televue 85 vs. Televue NP101 new [Re: Jon Isaacs]
      #5601724 - 01/02/13 06:39 PM

Quote:

J. Reynolds Freeman completed the Herschel 400 with a 55mm refractor... I am 64 years old and my eyes are not what they used to be, that is never going to happen.



I'm 68. I once was proud of my ability to see faint DSOs. I considered the Horsehead "easy" in my 12.5-inch f/5 Newt and "there" in my 8-inch f/6. This was from sites like Blair Valley in Anza-Borrego Desert State Park, which I know you're familiar with, Jon. A day came when I went to show the Horsehead to a skeptic, and it wasn't there for me. That's when I threw in the towel and turned to imaging. But I have to say that I considered mag 12 galaxies (the unlabeled ones in Atlas Coeli 1950.0) to be about my absolute limit with the 8-inch. Maybe I gave up too easily on fainter ones simply because no atlas I owned showed them.


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Jon Isaacs
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Re: Televue 85 vs. Televue NP101 new [Re: Calypte]
      #5601917 - 01/02/13 08:38 PM

Quote:

But I have to say that I considered mag 12 galaxies (the unlabeled ones in Atlas Coeli 1950.0) to be about my absolute limit with the 8-inch. Maybe I gave up too easily on fainter ones simply because no atlas I owned showed them.




I am not saying I can see every 11th or 12th magnitude nebula or galaxy but there are some I can see... But I start with ones I know already in a larger scope.

At 64, I am afraid my eyes are not what they once were, that's one reason I hunt these things down, it gives me a little reassurance that there is still some gas left in the tank..

Jon


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cloud_cover
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Re: Televue 85 vs. Televue NP101 new [Re: choran]
      #5602707 - 01/03/13 10:41 AM

Quote:

I would dearly love to see Jupiter's moons resolve to disks, for example, and realize that a 3 or 4 inch scope is not likely to get me there. Still, those wide views..,



I use the NP-101 with an Ethos SX 3.7mm. Adding Jon's 2x GSO barlow lens (without the extension) gives about 220x. I see Jupiter's moons clearly as nice round discs, not points
Personally, I think unless portability is an issue, go with the NP-101. It does fabulously wide views (I don't think there's any scope out there than can match it for widest-sharpest-field ) If cash is an issue, then truly other scopes would be better than the TV-85.


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Jon Isaacs
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Re: Televue 85 vs. Televue NP101 new [Re: cloud_cover]
      #5602769 - 01/03/13 11:21 AM

Quote:

Quote:

I would dearly love to see Jupiter's moons resolve to disks, for example, and realize that a 3 or 4 inch scope is not likely to get me there. Still, those wide views..,



I use the NP-101 with an Ethos SX 3.7mm. Adding Jon's 2x GSO barlow lens (without the extension) gives about 220x. I see Jupiter's moons clearly as nice round discs, not points





The difficulty is that stars do not resolve to points but rather round disks and this can be clearly seen in a 4 inch scope at 220x. The Raleigh Criteria for a 4 inch scope is 1.36 arc-seconds, about the size of Jupiter's largest moon. The additional difficulty is that the size of the disk depends on the brightness of the object. Consider an unequal double star like Castor, both the primary and the secondary are points sources but the secondary is about 1.4 magnitudes dimmer and when magnified, the Airy disk appears smaller.

In a 4 inch scope, a point source like a star resolves to a disk about the size of Jupiter's largest moon, a moon is seen as something larger than this, but it is dependent on the brightness. Thus, seeing disks of varying size is not sufficient to "resolve" the moons of Jupiter.

Jon


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BillP
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Re: Televue 85 vs. Televue NP101 new [Re: choran]
      #5603345 - 01/03/13 04:41 PM

Quote:

Bill, is the 92SS of similar build and visual quality?
Thanks,
Chuck




Would put its build quality a notch lower than the TV as TVs are built like tanks. But the build is still excellent on the TMB. Optically I would say they are all very good. TV85 is a doublet and some folks report they can coax a very little color out of now and then. NP101 essentially color-free. TMB had a little color as it is a super-fast triplet. NP would be a more complicated re-collimation given it's dual doublet design, other two perhaps a bit simpler if needed (TMB is meant for user collimation, TVs are built for it to be done at factory).

NP is really in a class of its own and should IMO be considered as such due to its optical design - Petzval. It produces a flat field whereas doublets and triplets do not. You might gets some field curvature visible at the eyepiece for low power ultrawides with the TMB, not with the NP. If optical performance were the ONLY deciding factor then would go with the NP as it has the unique flat field, very fast focal ratio. But since portability and simplicity are prominent goals for you, and aperture as well to some degree, the others come into the mix. For me, if just a choice between the 85 and the 92, I would go with the 92 because smaller and wider field and more aperture...simply more versatile than the 85. Plus the TMB92 (not the L version) has Starlight focuser which puts most focusers to shame, and still $350 less than the 85. If you go with the L version then $850 less than the 85. So could get the 92L with a battery of fine eyepieces and have more TFOV and more aperture than just the 85. To me, the choice is between the 92SS and the NP101. If I was going to make the refractor I buy my only largest refractor, then would probably opt for the NP101 if could afford. If I anticipated getting a 120mm or 130mm APO in the future, then that would steer me directly to the 92 as would never need an 80mm for travel since the 92 is so very small and a 101 is IMO just too big to keep with a 120 or 130 APO also. It is s always more about other things than purely optics.

Edited by BillP (01/03/13 04:49 PM)


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Erik Bakker
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Re: Televue 85 vs. Televue NP101 new [Re: BillP]
      #5603384 - 01/03/13 05:06 PM

Quote:

It is s always more about other things than purely optics.




Very true Bill


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John Rhodes
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Re: Televue 85 vs. Televue NP101 [Re: BillP]
      #5603889 - 01/03/13 11:25 PM

Quote:

NP would be a more complicated re-collimation given it's dual doublet design,



Tele Vue scopes only need tilting of the front cell to collimate... like most scopes, the rear elements cannot move in their cell.


Quote:

if just a choice between the 85 and the 92, I would go with the 92 because smaller and wider field and more aperture...simply more versatile than the 85. Plus the TMB92 (not the L version) has Starlight focuser which puts most focusers to shame, and still $350 less than the 85.




All Tele Vue scopes come with custom Starlight Feathertouch 10:1 Rack & Pinion focus assemblies... except the TV 60 "is"


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Mark9473
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Re: Televue 85 vs. Televue NP101 new [Re: Jon Isaacs]
      #5604145 - 01/04/13 06:46 AM

Quote:

In a 4 inch scope, a point source like a star resolves to a disk about the size of Jupiter's largest moon, a moon is seen as something larger than this, but it is dependent on the brightness. Thus, seeing disks of varying size is not sufficient to "resolve" the moons of Jupiter.




Well as long as I'm seeing dimmer Callisto as a larger dot than the brighter Io and Europa, you're not convincing me that I'm not seeing the size differences between the jovian moons. Did this in a 90mm achromat many years ago, and more recently in my 107mm apo. But it helps to be close to opposition, when the moons are just a bit larger.


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