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Equipment Discussions >> Eyepieces

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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Starman1]
      #5653368 - 01/30/13 10:41 PM

Quote:

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.



Moving the field stop from 12mm above the top of the drawtube to 12mm below can increase the fully illuminated diameter by 5mm, with no change in field stop diameter or any other design change; this includes eyepieces that attempt to max out the use of a given diameter drawtube. This is an example of a design decision that can determine performance and where the line is drawn.


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johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: derangedhermit]
      #5653421 - 01/30/13 11:31 PM

Quote:

Quote:

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?



I'm surprised this post is still here. I got a nastygram for a similar statement.




Shhhhhh...


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careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: John F]
      #5653426 - 01/30/13 11:33 PM

Quote:

Jeff,

I've owned both the 22mm Pan and T4 Nagler in the past. Yes, the T4 has a larger and somewhat more immersive field than the Pan does.
...




Although AFOVs wider than the Panoptic's 68 degrees have their appeal, I find that an AFOV of roughly 65 degrees hits a sweet spot, since it matches the physiology of the eye which has a stationary FOV of about 60 degrees. Your eye is fully employed, and so is the EP's output.

Less than 60 degrees, and I am aware that I am looking into a narrower EP "view port", and must be conscious of where my eye is positioned. But 65-72 degree creates a feeling of a natural, filled FOV and I tend to gravitate toward using my Panoptic or Baader 68 degree EPs over my 82 degree Nagler or ES, or the 49-52 degree Plossls.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: johnnyha]
      #5653522 - 01/31/13 01:52 AM

Quote:

Quote:

What existing eyepiece design covers the full range of focal lengths with consistent ER and AFOV?



Pentax XW.



Alas, no longer true. The 30 and 40 have been discontinued, and the 20 does not have a field stop anywhere near the limit for a 1.25" eyepiece.


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johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Starman1]
      #5653541 - 01/31/13 02:22 AM

Oh right, i forgot they discontinued the 30 and 40. :

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cjc
sage


Reged: 10/15/10

Loc: Derbyshire, England
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: johnnyha]
      #5653568 - 01/31/13 03:15 AM

Quote:

What existing eyepiece design covers the full range of focal lengths with consistent ER and AFOV?




I did not get on with the 14mm but the Explore Scientific 82 series comes close. I note they now list the field stops.


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Paul G
Post Laureate
*****

Reged: 05/08/03

Loc: Freedonia
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: BillP]
      #5653861 - 01/31/13 09:05 AM

Quote:

Quote:

Lumping the Naglers together isn't appropriate. The type 4, 5, and 6 Naglers are three completely different designs, and none of them cover the full focal length range.




I disagree with that.




Seriously? You're saying the types 4, 5 and 6 are the same design?


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FirstSight
Duke of Deneb
*****

Reged: 12/26/05

Loc: Raleigh, NC
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: Paul G]
      #5653923 - 01/31/13 09:37 AM

Quote:

Quote:

Quote:

Lumping the Naglers together isn't appropriate. The type 4, 5, and 6 Naglers are three completely different designs, and none of them cover the full focal length range.




I disagree with that.




Seriously? You're saying the types 4, 5 and 6 are the same design?




The respective internal optical designs of the above types are different. However, from an END-USER PERSPECTIVE the vastly more important question is whether and how the viewing qualities produced differ across these various types. One difference that IS obvious between the T6s vs the T4s and T5s is strongly related to the significantly larger eyepiece lens size of tha latter: to me, it's MUCH easier to subjectively perceive the purportedly identical 82 deg AFOVs as generously expansive in the T4s and T5s than in the T6s. For example, I often find it takes a minute or two for my mind to "see" the AFOV in e.g. a 13mmT6 as equally expansive as in the 17mmT4 when I swap out the latter for the former, while by comparison, there is no such perceptual gap produced in switching from a 17mm Ethos to a 13mm Ethos (equal eye lens sizes). What's curious is that if I comparatively test the views through the raw eyepieces (no scope) against an illuminated sheet of white paper (i.e. an effectively "null" blank view), the perceptual gap produced by the difference in lens sizes between the 13T6 and 17T4 disappears in that I more or less instantly perceive the "sameness" of the 82 degree AFOVs.

Which brings us back to the larger question: what potential improvements could be made to the 31T5 Nagler, 41 Panoptic, or 21 Ethos, other than perhaps new versions thereof with expanded eye relief? What improvements would be sufficiently non-incremental to justify introduction of an additional eyepiece line or additional "type" for an existing line (e.g. T7 Naglers, or T2 Panoptics?) That is, enough of a difference that the re-labeling would be more than just marketing hype? Would you be more satisfied if Televue sold the improvement as "enhanced majesty factor" or if they sold it as "Ethos Type 2", or "3.7mm Ethos SX"...your choice for whatever the "SX" stands for (?)

Edited by FirstSight (01/31/13 10:51 AM)


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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: derangedhermit]
      #5653965 - 01/31/13 10:00 AM

Televue, Televue, whereforeartthou Televue....

Hey, Maybe I'll write a play........


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turtle86
Pooh-Bah Everywhere Else
*****

Reged: 10/09/06

Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: FirstSight]
      #5654202 - 01/31/13 12:01 PM

Quote:

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.




The ES 100 25mm is now out, sells for $600, and weighs in at 2 lbs, 10 oz., that is to say heavier than the 21mm Ethos but lighter than the 31mm Nagler. So, the weight is competitive and the price is competitive. The remaining question is how well it performs, or put another way whether is truly fills the void left by Televue not releasing a 25mm Ethos. The tidbits I've read about the 25mm ES 100 in other threads sound encouraging, but I don't know of any thorough reviews as of yet comparing it to other wide-field long focal length eyepieces, so it remains to be seen how it stacks up to the Ethos, Nagler or even other ES 100 eyepieces. I know I'd love to compare one to my 31mm Nagler...

I don't pretend to know enough about eyepiece design to speculate whether Televue should be able to make a 25mm Ethos that would perform as well as the rest of the line while weighing less than a bowling ball. It may well be that making one now isn't feasible for different reasons, but might be in the near future. I do see another problem for now--price. The 21mm Ethos is $900 and I'm almost afraid to ask what a 25mm Ethos would go for...


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Has Tele Vue Forsaken Long Focal Lengths? new [Re: FirstSight]
      #5655752 - 02/01/13 08:18 AM

Quote:

What improvements would be sufficiently non-incremental to justify introduction of an additional eyepiece line or additional "type" for an existing line (e.g. T7 Naglers, or T2 Panoptics?)






The issue of the need to update the coatings was mentioned. I believe TeleVue just does this as a matter of course, incremental improvements are made without renaming the line.

Jon


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