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Equipment Discussions >> Eyepieces

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Jeff Morgan
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Grava T]
      #5649644 - 01/29/13 02:23 AM

Quote:

I think most, if not all, Televue eyepieces are designed to be used with their own refractors or at least short focal length newtonians. Medium to high power eyepieces are more useful I would imagine. Hard to improve on the low power choices already offered by TV.




When I started the thread, I knew there would be no "answers", but was hopeful of a robust discussion and it has happened.

Not to be argumentative, put a few points stand out:

- As the old saying goes, "you don't know what you don't know". While it may be hard to imagine improvements in the longer focal length offerings, Tele Vue has a rather pronounced capability to surprise us. Before the first Nagler design, who could have guessed it could be that good?

- Many (some ) thought the Radian line could not be improved. Now we have Delos.

- Granted that for the most part long focal length eyepieces already have good eye relief, but even a simple weight reduction is a huge improvement for the owners of small scopes (like Tele Vue refractors) and even the medium ones (case study: 20mm Nagler Type 2 to Type 5). Perhaps another area for improvement would be Pincushion, one of the frequent knocks against the Panoptic line.

- There has been some who suggest the low power/long focal lengths are not so important for the faster focal ratio scopes of today. I would say that Tele Vue historically has been a player in the fast refractor market. At f/5 one still can productively use a 35mm eyepiece. Indeed, Al Nagler says that for refractors there is no effective upper limit on exit pupil. And f/5 is perhaps the most common focal ratio for reflectors too.

- I was wondering if I missed something in the timeline, and it appears no one caught an error. Point being, ten years is an exceptionally long period of time for a designer in the prime of his life to be absent from an important market segment. Granted Al Nagler has provided for the continuity of the company, but ten years is still a long time from a company perspective too.


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Jon Isaacs
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Jeff Morgan]
      #5649799 - 01/29/13 07:39 AM

Quote:


- There has been some who suggest the low power/long focal lengths are not so important for the faster focal ratio scopes of today. I would say that Tele Vue historically has been a player in the fast refractor market. At f/5 one still can productively use a 35mm eyepiece. Indeed, Al Nagler says that for refractors there is no effective upper limit on exit pupil. And f/5 is perhaps the most common focal ratio for reflectors too.




Consider this:

The 31mmm Nagler, the 35mm and 41mm Panoptics are good enough that the edge corrections issues are not the eyepiece but rather the telescope. The center sharpness issues are not the limitations of the eyepiece but rather the resolution of the observer's eye.

If you want that perfect sharp edge in a refractor, particularly around F/5, the eyepiece is not the problem, it's the telescope. Uncle Al has this one covered nicely, start with a NP-101 or NP-127, add the 31mm Nagler and it's about as close to heaven as we mortals will ever get.

The 42mm field stop of the 31mm Nagler means the best case scenario is an increase of 10% TFoV, not a lot.. If that last 10% is desired, there is the 41mm Panoptic.

Jon


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BillP
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: tomcody]
      #5649936 - 01/29/13 09:52 AM

Quote:



1. Is the 24mm Panoptic improvable (as TV's max TFOV 1.25" wide field eyepiece)? I would say easily yes! Eye relief is way too short on this eyepiece. Needs to be 20mm. So there's a much needed improvement.




That's only your opinion, I find 15mm eye relief to be Perfect! If you want 20mm? buy a Delos.
Rex




I disagree. There are many many posts of eyeglass wearers who feel the 24Pan is not quite sufficient and needs extended eye relief to be practical for them. So it very ddefinitely needs to be improved. Also, Tele Vue has no other offering of a 1.25" wide-field eyepiece which maximizes the TFOV capable from the barrel and also has eye relief sufficient for eyeglass wearers. The 24 Pan and 32 Plossl are their only two offerings that maximize the TFOV potential of the 1.25" barrel. Since the 32 Plossl is not a wide-field this leaves only the 24 Pan. The Delos is not an option since they offer no 1.25" Delos that maximizes the TFOV potential of the barrel.


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BillP
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: johnnyha]
      #5649939 - 01/29/13 09:54 AM

Quote:

...the 25 ES 100 is a knockoff that makes compromises as Don has pointed out, compromises that TV is unwilling to make.




What other 25mm 100 degree design is it knocking off?? The ES offering is an innovation for the consumer. One can't claim "knockoff" unless one has privy to the optical designs of both...which no one here has. FYI, all designs have compromises, including Tele Vue designs. It would not be logical to say that TV's compromises in a design are somehow not compromises and only compromises of other vendor are.

If the "issue" is that Tele Vue can't use their current Ethos design to get a good image at a 25mm Focal length, then the solution is not to throw up one's hands and say it can't be done...instead the solution is to create the design which can achieve 25mm at 100 degrees to their satisfaction. Many consumers obviously desire a 100 degree eyepiece which maximizes the TFOV capability of a 2" barrel. IMO, one can't claim "unwilling to compromise" as a reason. The real intent I am sure is that they are unwilling to utilize the Ethos design for a 25mm 100 degree eyepiece because the design can't maintain optical performance goals of the Ethos series. This is the more accurate statement and far from a statement saying it is not feasible. The solution for TV if the Ethos design can't handle 25mm acceptably is to create a new 100 degree design to handle the 25mm and longer focal lengths...so keeping with their past naming would be an Ethos Type-2.

Edited by BillP (01/29/13 11:54 AM)


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turtle86
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Starman1]
      #5649972 - 01/29/13 10:13 AM

Quote:

A 25 Ethos (not changing the internal design) would have poorer edge correction and significant vignetting, which TV won't do, not to mention being ridiculously expensive if the same glass types were used (not to mention weight). ES made a lot of compromises to introduce the 25 (it doesn't have the same internal design as the 20/14/9), and the market may say those compromises were justified and OK, but TeleVue has already said they won't. So you won't see a 25 Ethos.




This has me curious as to how well the ES 100 25mm performs in comparison to the other ES 100 eyepieces.

A 25mm Ethos would've been nice, but only if Televue had been able to maintain the image quality of the 21mm Ethos and 31mm Nagler. For my purposes, not really much point in springing for a 25mm Ethos if the image quality wouldn't have been as good as the 31mm Nagler. Sure, all eyepiece designs involve compromises, the tricky part is where to draw the line...


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FirstSight
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: turtle86]
      #5650047 - 01/29/13 10:58 AM

Quote:


A 25mm Ethos would've been nice, but only if Televue had been able to maintain the image quality of the 21mm Ethos and 31mm Nagler.




It's probably technically feasible to make a 25mm Ethos and satisfy all the same performance characteristics required of the rest of the line. What's probably not feasible is to do so without requiring an unacceptably bulky, heavy package size. It seems that for any given AFOV, past a certain focal length the required bulk and size begins to ramp up exponentially...consider how dramatically the 31T5 bulks up compared to the 26T5 or the 21E compared to the 17E. Would you buy and use a 25E only slightly smaller and lighter than a pony keg of beer? OK, so that hypothetical is a bit of an exaggeration in degree, but is correct in principle.


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Starman1
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: turtle86]
      #5650056 - 01/29/13 11:02 AM

Quote:


Sure, all eyepiece designs involve compromises, the tricky part is where to draw the line...



Indeed.

Take the issue of rectilinear distortion (usually pincushion). You cannot eliminate it in ultrawide field eyepieces without introducing significant angular magnification distortion, which is worse, visually. Add to the discussion that the human eye sees a certain percentage of RD as undistorted if looking sideways at the edge.

As an observer, I'd rather they left in the RD and eliminated AMD, which is pretty much what TeleVue has done (and other designers as well).

Those who cannot abide either form of distortion can achieve their goals of orthoscopy by sticking with narrow fields of view. But, as the field widens, you either get one form of distortion or the other, or both (many binoculars I've tested have some of both as a mistaken attempt to have each form be at as low a percentage as possible).

So as good an example of compromise as can be illustrated. Where does a designer draw the line?
Other areas of concern are weight (that's a big one), astigmatism, chromatic aberration, field curvature, spherical aberration, interaction with the optics, vignetting, light scatter, transmission, spectral balance, etc.--including PRICE. And ALL of those involve compromises.


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dcoyle
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Reged: 10/11/05

Loc: Turbulent but dark skies, N.M.
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Starman1]
      #5650137 - 01/29/13 11:48 AM

Someone commented something to the effect that the TV eyepieces are designed to be optimised for the TV refractors. I would point out that the widefield's ability to deal with the low ratios of relectors is not an accident.

In responding to questions about the original Paracorr, when I told him I was using it with a Coulter 13.1" f/4.5, Al Nagler said that he had designed the Paracorr to be optimised for that very setup.

I don't think reflectors are ignored at TV.

Dan


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Tom TAdministrator

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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5650409 - 01/29/13 02:06 PM

Quote:

Quote:

I am not sure there is room in the barrel for TeleVue to build an eyepiece 100 degree 25mm of sufficient quality to please Uncle Al.




I have heard that expressed before. However, another way of saying that is "I can't make a 25mm 100 degree eyepiece of sufficient quality." If they really can't make it then should they be considered a leader in the industry? Can't have it both ways...I'm a leader and I can't do stuff so let other innovate...but I'm the leader, etc. Contradictory.




Completely disagree.

It's easy to make a widefield eyepiece. Not so easy to make a *BLEEP* free widefield eyepiece.

Perhaps it simply isn't possible to make one to certain design specs.

Just because something can be done does not mean it should be done Bill. Leading the field in quality may involve realizing that if it's not possible to do it well, they don't want to do it at all. There is such a thing as maintaining standards.


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johnnyha
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Tom T]
      #5650492 - 01/29/13 02:55 PM

That's was my point too, surely TV can MAKE a 25mm 100 degree eyepiece - they can also make a 30mm 100 degree, or a 35mm 120 degree eyepiece - but how would they be an industry leader producing what they feel are sub-par eyepieces?

As far as the ES 100 line being a knockoff of Ethos, I though x-ray photos had long ago proven the obvious to be true?


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turtle86
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: dcoyle]
      #5650639 - 01/29/13 03:56 PM

Quote:

Someone commented something to the effect that the TV eyepieces are designed to be optimised for the TV refractors. I would point out that the widefield's ability to deal with the low ratios of relectors is not an accident.

In responding to questions about the original Paracorr, when I told him I was using it with a Coulter 13.1" f/4.5, Al Nagler said that he had designed the Paracorr to be optimised for that very setup.

I don't think reflectors are ignored at TV.

Dan




Totally agree. And with the Paracorr II, big Dobs that are sub-f/4 are now quite doable.


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turtle86
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Tom T]
      #5650645 - 01/29/13 04:06 PM

Quote:



Completely disagree.

It's easy to make a widefield eyepiece. Not so easy to make a *BLEEP* free widefield eyepiece.

Perhaps it simply isn't possible to make one to certain design specs.

Just because something can be done does not mean it should be done Bill. Leading the field in quality may involve realizing that if it's not possible to do it well, they don't want to do it at all. There is such a thing as maintaining standards.




Well said. Sometimes the best move is no move.


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BillP
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Tom T]
      #5650701 - 01/29/13 04:32 PM

Quote:

Just because something can be done does not mean it should be done Bill. Leading the field in quality may involve realizing that if it's not possible to do it well, they don't want to do it at all. There is such a thing as maintaining standards.




Well we are not talking about making atomic bombs here

Let's be clear that when one says "it's not possible to do it well" this is really saying "it's not possible for us to do it well". I whole-heartedly disagree that it is not feasible to make a 25mm 100 degree eyepiece "well". I also would not agree that every other eyepiece out there without the TV branding is not made "well" and does not perform "well". On the contrary, the performance differences between the TVs and other brandings is so small that it is a difference between one being B+ and B++. So many very much in the "well" category together.

If one company does not "choose" to make a 25mm 100 degree this does not mean it is not feasible, nor that other brands if they have them are not "well" as is being implied. That is brand-loyalty speaking and not objective treatments.

Like I tell my staff..."Easy for user, hard for us, and no such thing as can't." What people have been expressing on a 25mm 100 degree not being possible to do "well" is IMO just blind-speak. Anything is possible if you are innovative enough. Besides, many good reports on the ES 25 100 anyway. Certainly fits in the "well" category unless I have missed something recently. One man's vision of perfection is not anothers, nor should it ever be. One size does not fit all either. One way or the highway is also not a good motto to live by.

IMO, TV has not forsaken long focal lengths, they just have a peculiar mindset that if a specific design cannot extend all the way, they just stop it there and do not produce alternate designs to get to a full range of focal lengths. The Naglers were of course not like this as the T6 design for the shorter focal lengths, then the T5s for the rest and the T4 for longer ER. So they have abandoned it seems paying attention to a full range of focal lengths for a given class of eyepiece with the 72s (Delos) and 100s (Ethos). Sad IMO.


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Jeff Morgan
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5650790 - 01/29/13 05:29 PM

Quote:

IMO, TV has not forsaken long focal lengths, they just have a peculiar mindset that if a specific design cannot extend all the way, they just stop it there and do not produce alternate designs to get to a full range of focal lengths. The Naglers were of course not like this as the T6 design for the shorter focal lengths, then the T5s for the rest and the T4 for longer ER. So they have abandoned it seems paying attention to a full range of focal lengths for a given class of eyepiece with the 72s (Delos) and 100s (Ethos). Sad IMO.




OK. I'm ready for the Panoptic Type 2, Type 3, and Type 4's. The focal plane of each variant is matched to the focal plane curvature of refractors, reflectors, and Schmidt-Casses respectively for the tightest possible star images across the entire field.

Of course some of use would have to buy two (or three) copies of each variant ...


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bdcmd
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5651019 - 01/29/13 07:42 PM

Quote:

Anything is possible if you are innovative enough.

IMO, TV has not forsaken long focal lengths, they just have a peculiar mindset that if a specific design cannot extend all the way, they just stop it there and do not produce alternate designs to get to a full range of focal lengths. So they have abandoned it seems paying attention to a full range of focal lengths for a given class of eyepiece with the 72s (Delos) and 100s (Ethos). Sad IMO.



I wonder what the R&D budget for a completely new design 25mm/100° eyepiece would be? And would it be feasible for a small company like Televue to develop something like that for a rather limited market? Probably similar considerations for 2" versions of the Delos at longer focal lengths, although I would think the market for a replacement for the Panoptics would be greater. Difficult to raise that R&D money and justify spending it if the ability to recoup that investment is limited by having a very short time period before reverse engineered, B+ quality competitive products hit the street at substantially lower prices. Still, it wouldn't surprise me if TV comes out with new developments on their latest designs at some point. But, I suspect they will do it on THEIR time, at THEIR standards, for a price THEY can live with. In the meantime, we will just have to struggle on with what we have. Sad, IMO.


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Lt 26
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: bdcmd]
      #5651051 - 01/29/13 07:58 PM

I heard they already developed a 25E but it keeps snapping everbrights.

Dereck


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Scanning4Comets
Markus
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Lt 26]
      #5651089 - 01/29/13 08:20 PM

http://www.televue.com/Pdf/Astronomy_TVO_Article.pdf

Not 100 degrees, but TV ALMOST made a 25mm, (Top left corner on page #2)


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Tom TAdministrator

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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5651243 - 01/29/13 09:56 PM

Quote:

Quote:

Just because something can be done does not mean it should be done Bill. Leading the field in quality may involve realizing that if it's not possible to do it well, they don't want to do it at all. There is such a thing as maintaining standards.




Well we are not talking about making atomic bombs here




No we're talking optics.

A FAR more explosive field.

AHHH - The internet. Where everyone can be an expert. Every amateur on the planet has an opinion here. With an a-bomb, it'd be far simpler: we'd just have to agree if it exploded or not (maybe a discussion or two on yield...)

Back to the eyepiece. Question: Have you made one? If so, I'd love to see it. If not, then show me it can be done and (here's the kicker) for a reasonable cost with good quality and performance. Otherwise, with respect sir - you ain't got nuttin.

TV (or really *any* other company out there) aren't idiots. If they could make one that would turn them a profit (and not dilute their brand) - they would. It's as simple as that. Who knows? Maybe ones coming...

(And BTW - Brand loyalty? Seriously? You can do better than that... )


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Jon Isaacs
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5651436 - 01/30/13 12:11 AM

Quote:


Let's be clear that when one says "it's not possible to do it well" this is really saying "it's not possible for us to do it well". I whole-heartedly disagree that it is not feasible to make a 25mm 100 degree eyepiece "well".




Neither of us are optical designers so we are only guessing.

As an engineer, I do know that sometimes there are design constraints that really do limit what is possible. For example, a 38mm field stop will not fit in a 1.25 inch barrel.

These are negative-positive eyepieces and a good part of the optics have to fit inside the 2 inch diameter barrel. It's also clear that the positive section of these eyepieces must have quite long focal lengths, lenses that are significantly greater in diameter than 2 inches and the actual field stop is quite large. It is my understanding that the constraints of the 2 inch barrel size limit the 82 degree eyepieces to an effective 42mm field stop, I suspect that the 100 degree AFoV path requirements place a constraint that is even greater.

Jon


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Starman1
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Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Jon Isaacs]
      #5651446 - 01/30/13 12:20 AM

There are 1.25" eyepieces with 29mm field stops, a diameter larger than the inside diameter of the bottom barrel. How? Accept lower illumination of the edge that would be the case in a 1.25" eyepiece with a 27-27.5mm field stop.
As was said earlier--it's all about compromises and where one draws the line.


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