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kfred
Carpal Tunnel
Reged: 11/11/03
Posts: 2000
Loc: Dayton, Ohio
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You got me, I saw the title first.
Fred
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River Cam - Cambridge England
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Fireball
sage
Reged: 03/24/06
Posts: 265
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I knew you are pulling our leg a little bit 
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20x90 Bino
12" Lightbridge
Selection of ultra wides from Meade, Televue and Pentax.
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10920
Loc: Los Angeles
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Quote:
One other factoid, a 27mm field stop in the 82 degree AFoV results in about a 20mm eyepiece, which no ultra-wide manufacturer makes.
Now.
But they did.
There was a Japanese eyepiece called the Widescan III that had a 20mm focal length and a (claimed) 84 degree apparent field.
And if partial edge-of-field illumination is accepted, field stops can be larger than 27-27.4mm in a 1.25" eyepiece.
The 35mm 5-element "Plossl" sold by Orion, Parks, Antares, etc. has a 28.5-29mm field stop which is above the 1.25" barrel. Obviously, edge-of-field illumination isn't 100% (it rarely is), but the eyepiece works quite well.
So it is possible (assuming you can accept the large amount of infocusing necessary) to make an eyepiece with a field stop larger than the I.D. of the barrel.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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Skywatchr
Carpal Tunnel
Reged: 06/03/06
Posts: 1549
Loc: North-Central Pa.
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Too bad the Ethos can't be "scaled". That is according to Al Nagler. Each of the 2 Ethos we have now are actually uniquely designed. They are not "scaled" versions of each other.
Jeff
Quote:
Since the title implied a discussion on yet-to-exist long-focal-length Ethos (Ethi? Ethus? What is the plural of "Ethos" anyway?), I thought I'd throw some speculation in!
I can't wait for the 20mm Ethos 
Why 20mm? Well, 3 reasons. 1) The 13mm is roughly 1.6x the focal length of the 8mm 2) 20mm is roughly 1.6x times the 13mm 3) 2" barrels are roughly 1.6x the diameter of a 1.25" barrel, meaning a perfectly scaled Ethos to 2" barrel would be about 20mm.
Of course, this would yield a very heavy eyepiece with somewhere around 24mm of eye relief. Obviously it would require careful redesign (much like the T5s allowed Naglers to be made in longer than 22mm focal lengths).
One other interesting factoid: The 8mm ethos is about 1.6x the focal length of a 5mm ethos. A 5mm ethos is 1.6x a 3mm ethos. The "1.6x" is a nice multiplier, not only the 13/8 ratio, but also the 2"/1.25" ratio. If TV decides to make Ethos in 1.6x increments, we'd end up with 20mm, 13mm, 8mm, and 5mm (and possibly 3mm). That would make a good starter set, and depending on demand, more could be made to fill in between.
Thoughts?
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18" F/5 Home-Built Dob. with Mike Dudley Mirror
Highly Modified Meade DS-16 in Roll Off Roof
6" F/15 Brass w/ D&G Lens on DS-16 Mount
DS-10 10" F/4.5 Newtonian
LXD650, LX200 Classic
Orange Tube C11
DayStar 0.45 with multiple ERFs
Vixen ED80sf
11x80 Meade, 20x80 Celestron binocs (Japan Made).
Lots of Naglers and 8mm and 13mm Ethos.
Gadgets and parts everywhere.
And a Wife that loves it as much as me!
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hoof
Pooh-Bah
Reged: 04/07/05
Posts: 1421
Loc: Irvine, CA
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Quote:
Too bad the Ethos can't be "scaled". That is according to Al Nagler. Each of the 2 Ethos we have now are actually uniquely designed. They are not "scaled" versions of each other.
Jeff
Sure they can. However, scaling has other issues (e.g. a lens element could get to thin, scaling up results in rapid weight gain, changing scale affects eye relief and eye lens size). TeleVue has scaled eyepieces in the past (the T5 series is the same design scaled to 16/20/26/31mm), and the original Nagler series was also scaled (which is why the 4.8mm Nagler has such short eye relief).
However, like the T6 Nagler series, I can see why they redid the design for the 8mm. If you're interested in maintaining the eye lens size (so that you can, for example, use the astigmatism corrector, or maintain a fixed eye relief), then you have no choice but to redesign. The T6's maintain eye relief, from 13mm down to 3.5mm, by having a custom design for each one.
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Jonathan Hoof
15" F/4.14 Discovery Truss
8" F/5.9 Orion XT8i
6" F/6 Intes-Micro MN66
4.5" F/4 Orion Starblast
80mm F/7.5 Orion 80ED
18x50 IS Canon binoculars
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Oly Olson
super member
Reged: 02/17/08
Posts: 154
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I agree that the views through the 31mm Axiom are stunning but I must say that between the 31mm Nagler and the 41mm Panoptic I prefer the Panoptic on my 11" SCT. Perhaps it's the higher focal length of the scope that leads me to feel this way but I often prefer the absolute widest field I can get.
Best,
Oly
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