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Best mount / tripod for Televue 85 or NP101

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#26 FirstSight

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Posted 13 February 2013 - 02:32 PM

This is not an APO OK, it does not deserve APO prices.


Actually, the TV85 does have apochromatic performance and uses the best fluorite substitute and matching glass currently available.


Historically, the TV-85 has always been considered an apochromat. Not all apochroamts are created equally. Roland Christen can probably find signs of chromatic aberration in any refractor...

Among the rest of us, it varies.

Jon


The reason for the ambiguity about the TV85 being an "apochromat" vs only a "semi-apochromat" (as in, not quite a true full-fledged APO) is because it's a doublet, rather than a triplet or Petzval (four-element) lens design. The argument for considering some of the higher-end doublets to sufficiently qualify for true APO status is because though two lenses still cannot as completely correct refractive differences in where different wavelengths of light focus as can high-quality triplets etc., nevertheless through use of the right glass and lens design it's possible to come close enough that the differences are near-vanishingly small to most people's eyes, or at least supposedly. So, to some extent it's in the eye of the beholder whether a doublet such as the TV-95 is a true apochromat or merely an almost, but not quite true apochromat. Nevertheless, it's not misleading marketing to describe a high-quality doublet like the TV-85 as an "apochromat", so long as the fact that it's a doublet is included in the description.

#27 Jon Isaacs

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Posted 13 February 2013 - 03:35 PM

The reason for the ambiguity about the TV85 being an "apochromat" vs only a "semi-apochromat" (as in, not quite a true full-fledged APO) is because it's a doublet, rather than a triplet or Petzval (four-element) lens design.


I am not sure that is the reason. There are many doublets that have long been considered apos, fir example, the TV-102, the various Takahashi's using fluorite and synthetic fluorite. Roland's article says that a doublet is capable of producing the necessary three color crossings but one is not in the visual.

I think the reason people question the TV-85 as an apo is that at 85mm F/7 with presumably an FPL-53 based objective, it's pushing the limit in terms of being color free visually.

Jon

#28 FirstSight

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Posted 13 February 2013 - 06:14 PM

The reason for the ambiguity about the TV85 being an "apochromat" vs only a "semi-apochromat" (as in, not quite a true full-fledged APO) is because it's a doublet, rather than a triplet or Petzval (four-element) lens design.


I am not sure that is the reason. There are many doublets that have long been considered apos, fir example, the TV-102, the various Takahashi's using fluorite and synthetic fluorite. Roland's article says that a doublet is capable of producing the necessary three color crossings but one is not in the visual.

I think the reason people question the TV-85 as an apo is that at 85mm F/7 with presumably an FPL-53 based objective, it's pushing the limit in terms of being color free visually.

Jon


I'm explaining the reasoning in many folks' minds when they question whether a doublet is a true APO, rather than the authoritative technical answer. I've come across the reference from Roland Christian you cited above.

I still think it's best practice to always be sure that when you refer to a given doublet scope as an "APO" that the audience understands that the scope is a doublet. That way, at worst some folks may regard the assertion as somewhat debatable, but none as misleading - and if applicable to the scope in question, you still have the Roland Christian trump card to pull out in response.

#29 tomchris

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Posted 13 February 2013 - 06:43 PM

I use my 85 on a Bogen/ Manfrotto tripod and it works very well. If I really want steadiness, I get out my DM-4 mount and tripod. I found the "apo" debate interesting. All I know is that the TV85 is very sharp and provides wonderful colorful views. However, $1600 is way too much to buy the 85 used!

#30 Jon Isaacs

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Posted 13 February 2013 - 06:59 PM

I'm explaining the reasoning in many folks' minds when they question whether a doublet is a true APO, rather than the authoritative technical answer. I've come across the reference from Roland Christian you cited above.

I still think it's best practice to always be sure that when you refer to a given doublet scope as an "APO" that the audience understands that the scope is a doublet. That way, at worst some folks may regard the assertion as somewhat debatable, but none as misleading - and if applicable to the scope in question, you still have the Roland Christian trump card to pull out in response.



This the way I look at it:

There are doublets that are not apos, there are doublets that are.

There are triplets that are not apos, there are triplets that are.

There are quadruplets that are not apos, there are quadruplets that are.

Generally one should specify whether a scope is a doublet, triplet, quadruplet and some designation of the color correction.

I think Thomas Back's discussion Defining Apochromatismhit's the nail right on the head.

" After designing, testing and selling many different apochromatic lenses I can state this: There is no "definite" line where a lens becomes "apochromatic" in the world of commercial apochromatic lenses.

But any lens, be it a doublet, triplet, quad, air-spaced or Petzval, that has a peak visual null (~5550A - the green-yellow) with a Strehl ratio of .95 or better, coma corrected and is diffraction limited from C (red) to F (blue) with 1/4 wave OPD spherical or better, has good control of the violet g wavelength with no more than 1/2 wave OPD P-V spherical and optical spot sizes that concentrate the maximum amount of photons within the diffraction limit -- a result of the low spherical aberration, which can be seen with modern optical design programs, as the "spot rays" will be seen concentrated in the center of the spot, not evenly or worse, concentrated outside the center -- will satisfy the modern definition of "Apochromatism.""

Jon

#31 tomchris

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Posted 14 February 2013 - 09:35 AM

Excellent. Thanks, Jon.

#32 KerryR

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Posted 14 February 2013 - 09:46 AM

I suspect that one of the reasons for the continuing debate about what makes an apo an apo has a lot to do with CCD cameras and their sensitivity to the blue end of the spectrum. A scope that a visual observer finds to have excellent color correction may produce a raw ccd image with heavy blue-end fringing. A "ccd apo" might be considered as having more stringent tolerances than a "visual apo" if the user wishes to avoid some post-process reduction of the fringing.

#33 Panotaker

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Posted 14 February 2013 - 10:04 AM

I have both a TV-85 and an NP-101. I bought my TV-85 used 10 years ago, so it is a pretty old one. I haven't looked through a late model TV-85 to compare to mine, but my TV-85 gives perfect color free views, that is the main reason I bought it. I have a Gibraltar V mount that I mount all kinds of scopes on, from my Questar Birder, to my AP-130. It doesn't have slow motion controls, but unless you are looking at the planets, you don't really need them. I have the digital setting circles on mine and they work excellent. There are better alt/az mounts out there, but I got mine pretty cheap, so I'm not upgrading any time soon. The nice thing about the mount, is that it looks fantastic, so you can leave it setup inside the house and it looks like a piece of furniture. You can't say that about most mounts.

#34 la200o

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Posted 14 February 2013 - 12:16 PM

I had my (f/6.3) TV 76 out last night and was once again impressed at how color-free it is. It is an APO.

I have it over-mounted on a Gibraltar, which I retired for awhile a few years ago after buying a Half-Hitch. When I got the TV 76, I brought the mount out of retirement and use it constantly with that scope and now and then with my 4" TV's. I have come to appreciate its virtues. Simple, steady, and, with proper adjustments, pretty smooth. You can pick them up inexpensively used (300--400 bucks and they are well worth the money IMO).

Bill

#35 KerryR

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Posted 14 February 2013 - 12:26 PM

I have a TV Telepod head that I used with my Pronto and Genesis. I believe it's the same as the Gibralter.(?)

Functional enough, but I prefer the PortaII head-- far easier to maintain position while switching ep's, and, of course, the slow motion controls add additional ease when tracking.

I now only use the Telepod with my PST.

#36 la200o

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Posted 14 February 2013 - 12:31 PM

Kerry, I've never used a PortaII; I believe what you say. For me, changing ep's w/the Gibraltar ain't so bad--a finger on the diagonal pretty much keeps the scope in place, and if it does move, it's generally strictly in the altitude axis, so it's pretty easy to recover the target. Now changing ep's with my HH--that's another story!

Bill

#37 Patrik Iver

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Posted 14 February 2013 - 02:52 PM

Actually, the TV85 does have apochromatic performance and uses the best fluorite substitute and matching glass currently available.


This is the first time I've seen someone "in the know" imply anything about the glass prescription of a TV doublet. So effectively you are saying that the ED-glass used is Ohara FPL53, as it can't very well be a Russian glass with similar properties?

Why the big secrecy about it? The scopes are doublets, and sold as such. Specifying the glass prescription (particularly if it is "the best fluorite substitute and matching glass currently available") should not be a bad thing? Just about anyone agrees anyway that your telescopes are very nice, both optically and mechanically.

#38 la200o

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Posted 14 February 2013 - 02:57 PM

Patrik,

I agree. I think the TV scopes are great, and I imagine they use FPL53. So why not tell us?

Bill

#39 johnnyha

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Posted 14 February 2013 - 03:15 PM

This is not an APO OK, it does not deserve APO prices.


OK OK, I officially withdraw my original post implying that the TV85 was not an APO. ;) :lol:

#40 Jon Isaacs

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Posted 14 February 2013 - 05:20 PM

Patrik,

I agree. I think the TV scopes are great, and I imagine they use FPL53. So why not tell us?

Bill


I think the "what glass is it" game started quite some time after TeleVue began making refractors. Many vendors play this game by telling you when they do use FPL-53 but choose more vague descriptions when they use something with a significantly lower Abbe index.

TeleVue may be somewhat unique in that they don't broadcast exactly which glasses they use but then they are unique in a number of ways.

One aspect that is interesting is that Roland C. is well known for pointing out that it's not only the ED glass used but also the mating element. I am as guilty as anyone else of referring to the ED glass only.

I would like to know what glasses the NP-101 uses, that the focal ratio of the objective is... Don't think I will be finding out.

Jon

#41 la200o

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Posted 14 February 2013 - 06:10 PM

Jon,

Alas, I fear you are right. We will never unravel this mystery.

Regards,
Bill

#42 Jon Isaacs

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Posted 14 February 2013 - 06:46 PM

Jon,

Alas, I fear you are right. We will never unravel this mystery.

Regards,
Bill


Bill:

If I knew, it wouldn't affect the views one iota nor would I actually understand anything more.

Jon

#43 FirstSight

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Posted 14 February 2013 - 10:08 PM

Patrik,

I agree. I think the TV scopes are great, and I imagine they use FPL53. So why not tell us?

Bill


Televue is perfectly willing to patiently tell you what you know, in as much detail as you want to know, while the cement block slowly hardens around your legs, out by a boat-dock on a very deep lake.

:grin:

#44 Keith-in-Texas

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Posted 15 February 2013 - 09:21 PM

Here's what I did when looking for a lightweight yet sturdy and high quality mount for my Stellarvue SV90TBV.

I purchase a "like new" Vixen Super Polaris mount (non go-to) with excellent slow motion controls. This mount can be use in either GEM or Alt-Az configuration.

Best thing is they can be picked up used for $150 - $250 depending on condition and options.

Good luck in your search for the optimum mount that meets your needs.

Best regards,

Keith

#45 John Rhodes

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Posted 15 February 2013 - 11:57 PM

I have a TV Telepod head that I used with my Pronto and Genesis. I believe it's the same as the Gibralter.(?)


They are the same head for all the tripods Tele Pod, Panoramic and the Gibraltar, only the Gibraltar 5 is different being wide enough to hold the 127is scope.

#46 chaoscosmos

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Posted 24 February 2013 - 01:55 PM

"I used it three times. Tried tried tired to love love love it for simplicty and beauty, but as a working mount for anything but fixed low power sweepting, found it miserable."

Well, as some may know, I was able to pick up a used NP-101 and at the same time was convinced on a used Gibraltor mount and tripod. At this point, unless I'm just not handling it correctly, I'm having the same reaction to the Gibraltar mount as Eddgie did in his quote above. I've used it on three successive nights, rebalanced the OTA a couple of times, and still find it a pain to use at even moderately high magnification. Has a serious case of the jiggles focusing at even 60X and damping time seems too long. I could add a Feather Touch focuser, which should help focusing some. The tripod seems rock solid, I just think it's the mount that's lacking. Mine says 'Gibraltar', not 'Gibraltar 5' ~ not sure if there's a difference. But in any case, I'm looking at Discmount and wondering if I'm going to be sinking into a money pit here, especially since I don't know if another mount would be worthwhile either.

I know that suspending a 10 lb tube in space and expecting it to be rock solid and yet easily moveable is a formidable task, but I expected a $4K set-up to have none of the weak characteristics of my 60mm Sears refractor alt/azimuth mount I had as a kid. Although it's 500% better, to my surprise, there are still some similarities.

#47 Mark9473

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Posted 24 February 2013 - 04:10 PM

I know that suspending a 10 lb tube in space and expecting it to be rock solid and yet easily moveable is a formidable task

Not for a DiscMount.

#48 chaoscosmos

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Posted 25 February 2013 - 05:15 AM

Oh my, I'm a little embarrassed now. The Gibraltar seemed so bad I began thinking something must be broken on it, and in effect, it was. I took the OTA off to get a good look at the mount and within a few seconds realized the plastic tighten down nut underneath the center of the tripod wasn't tightened. Since this was a used mount and tripod, everything was already put together and I assumed it was all good to go. Now it is and I'll be able to get a reasonable idea of how much I like the mount. One thing is clear- the jiggling has almost completely disappeared, so the scope stops dead when you want it to stop. What a relief.

Sorry Televue, my fault, operator error was the culprit!

#49 Jim7728

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Posted 25 February 2013 - 08:01 AM

I used Genesis SDF(old NP-101) on a Telepod with an Oberwerk wooden tripod and thought the setup worked fine. I did have a Focusmate fine focus attached to the R&P, which is a must have for such a fast telescope. Also some dampening pads for the tripod legs which are effective when viewing at high magnification.

One other accessory nice to have is the Televue Equalizer Brass 1.25" to 2" adapter which eliminates the need to re-balance when going from a heavy 2" eyepiece to a light 1.25".






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