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Televue 85 vs. Televue NP101

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#51 Jon Isaacs

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Posted 02 January 2013 - 08:38 PM

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..

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#52 cloud_cover

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Posted 03 January 2013 - 10:41 AM

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.

#53 Jon Isaacs

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Posted 03 January 2013 - 11:21 AM

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

#54 BillP

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Posted 03 January 2013 - 04:41 PM

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.

#55 Erik Bakker

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Posted 03 January 2013 - 05:06 PM

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


Very true Bill :bow:

#56 John Rhodes

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Posted 03 January 2013 - 11:25 PM

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.


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"

#57 Mark9473

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Posted 04 January 2013 - 06:46 AM

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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