John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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Hi,
Some may find this useful. It's a translation of the table in the German language Hyperion leaflet.
edited by popular demand to include AFoV
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
Edited by John Hoare (03/28/07 12:44 AM)
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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The 14 and 28mm extension rings (fine tuning extension rings is the direct translation) are intended for permanent or semi-permanent adjustment of an existing Hyperion to another desired focal length.
The point of being able to fit a 2" filter between the main body and the Smythe lens group/1.25" barrel is that if you have some you don't need to buy equivalent 1.25" filters.
The last pair of columns is the most interesting for me. It's probably not worth the effort of removing the Smyth lens group from the shorther focal lengths to use the main body as a 2" eyepiece if you also have the 21mm, but the 21mm itself converts to a 32.2mm Erfle, which is useful.
I have the full set and as far as I'm concerned they are keepers. Like all eyepieces (even the very best!) they have limitations but as wide field eyepieces with digiscoping and projection capability built in, bodies that can fit 2" or 1.25" clamps and covering a range of focal lengths from 3.5mm to 32.2mm they are certainly useful if (like me) you have a collection of scopes with a variety of focal lengths (400mm to 1325mm).
I may never buy another eyepiece (if you believe that I can hold to that I can get you some Irish air at a very reasonable price...).
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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rick rian
The Lockster
Reged: 08/03/04
Posts: 14724
Loc: The Tundra
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Thanks John, This is very helpful information.
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Rickster
NexStar 8i, TV85, Canon 15x50is
Time is precious, waste it wisely.
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Relativist
Post Laureate
Reged: 10/11/03
Posts: 3026
Loc: OC, CA, USA
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Any chance it also details what happens to the AFOV with those modifications?
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.......Curtis
20mm T2 Nagler, 10mm SW 82degrees, 5-8 SW Zoom:
All of the above replaced with WO Binoviewers!!!
Siebert OCA 1.25x-3.5x
10" OPT Starhunter (flocked & upgraded focuser)
10x50 & 15x70 Celestron Bino's
2" 2x GSO Barlow
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BigCaT
super member
Reged: 12/14/05
Posts: 136
Loc: Quebec, Canada
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Thanks john for this information. According to this table, when you use the 8mm eyepiece with the 28mm extension ring you turn your eyepiece at 5mm...but with a fiel stop larger (7.1) than the "real" 5mm which is 6.5. How this is can be possible... 
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Felix
Nexstar 8i SE
Antares 127mm F/6.45
30mm, 12.5mm, 10mm Celeston Ultimas
17mm Baader Hyperion
7.4mm TeleVue Plossl
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Bob W6PU
Carpal Tunnel
Reged: 12/23/04
Posts: 2191
Loc: Springer-N.E.NM
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Thank's for sharing this with us John!
I would love to try removing the lower lens/tube Assy. on my 21" Stratus, but unfortunately, my old 1956 Coast Inst.( U.S made) 10" Newt. has only a 1 1/4 inch focuser  , and I am hesitant to Mod. it as it is a classic scope, so I must make do with my 32mm, Vixen Plossl, for low power views, untill I upgrade to a larger modern Newt! 
Wiedersehen!
Bob
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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Quote:
Thanks john for this information. According to this table, when you use the 8mm eyepiece with the 28mm extension ring you turn your eyepiece at 5mm...but with a fiel stop larger (7.1) than the "real" 5mm which is 6.5. How this is can be possible...
Felix, I'm no optician but I think the overall effect is a result of having the Erfle-like top section in a 2" barrel and the Smythe lens group below in a 1.25" barrel. It's as if a 1.25" Barlow were successfully projecting an image into a 2" eyepiece. The unadjusted 5mm and 8mm Hyperions are made up of different upper and lower sections so while I can't explain it it seems feasible that there would be a difference in the diameter of the image being projected. Maybe one of the resident gearheads knows the answer?
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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Quote:
Any chance it also details what happens to the AFOV with those modifications?
Since you're effectively reducing the focal length and therefore increasing magnification won't all of the mods (except for removing the Smythe lens group) reduce the AFOV?
Do you know where to find or derive a formula that uses the field stop size and focal length to calculate FOV? Personally I'm more one for setting up the scope and looking at all the pretty things than for playing with numbers.
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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novbabies
Postmaster
Reged: 06/05/05
Posts: 15678
Loc: Northern Georgia!
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I'll add that the 21mm without the Smythe lens makes an admirable 32mm EP in my f/4.9 scope!!
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Good Seeing!
Mark
Orion 12" XTi f/4.9
VERY old Edmund 6" f/8 reflector
Assorted binoculars
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Jim Easterbrook
professor emeritus
Reged: 02/25/04
Posts: 562
Loc: Surrey, UK (N51.36 W0.25)
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Quote:
Do you know where to find or derive a formula that uses the field stop size and focal length to calculate FOV?
True field of view is derived from the field stop and the telescope focal length:
TFOV = (fs / flt) * (180 / π)
Apparent field of view is approximately the true field of view multiplied by the magnification. As the magnification is the ratio of the telescope and eyepiece focal lengths, we get:
AFOV ~= (fs / flt) * (180 / π) * (flt / fle) = (fs / fle) * (180 / π)
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Jim (N51.36 W0.25)
9¼" SCT & 4" Mak. 6" f/5 achro, 80mm f/7.5 apo & 66mm f/5.9 apo refractors.
EQ-6 SkyScan & NexStar 80 mounts. CoolPix 4500 & EOS 350d cameras.
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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Hi Jim,
The meaning of "n" escapes me. Can you please define it?
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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Relativist
Post Laureate
Reged: 10/11/03
Posts: 3026
Loc: OC, CA, USA
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Or is that pi? Yes, I believe it is, he's just converting to degrees from radians with 180/pi.
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.......Curtis
20mm T2 Nagler, 10mm SW 82degrees, 5-8 SW Zoom:
All of the above replaced with WO Binoviewers!!!
Siebert OCA 1.25x-3.5x
10" OPT Starhunter (flocked & upgraded focuser)
10x50 & 15x70 Celestron Bino's
2" 2x GSO Barlow
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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OK. Now you know why I don't wear this pair of eyeglasses for observing!
But the really key point in Jim's post is that we can't give AFOV/TFOV in a table of information that's about the eyepiece only, because you must have the focal length of the specific telescope to calculate them.
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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rtomw77
sage
Reged: 10/06/04
Posts: 463
Loc: Deer Valley, AZ
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When do you use your extension rings? Do you add/change them while observing, or do you adjust your EP's before hand based on what you want to observe? Just curious.
Tom
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Celestron 8" Nexstar GPS XLT
Meade 8" f/6 newtonian on GEM-New GSO Mirror
StarBlast 4.5" Dob
XT12 IntelliScope Dob with COL
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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I don't use any extension rings. I have the full Hyperion set and a selection of small telescopes with focal lengths from 400m to 1325mm - the biggest physically being a 152mm Newt with an fl of 762mm. So far I haven't needed to consider 'fine-tuning'.
Where the extension rings would come in useful is if you had a small number of Hyperions and switched from using a telescope with a longer focal length to a shorter one, or if you got one second hand at a good price and wanted to reduce its focal length to suit a spot in your eyepiece set.
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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novbabies
Postmaster
Reged: 06/05/05
Posts: 15678
Loc: Northern Georgia!
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Auf einem Seemannsgrab,
da blühen keine Rosen
I got a translation of this ("On a seaman's grave, no roses flower") but am not sure of the "full meaning". I am quite curious now; can you explain it a bit further?
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Good Seeing!
Mark
Orion 12" XTi f/4.9
VERY old Edmund 6" f/8 reflector
Assorted binoculars
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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It's an traditional German sea shanty, the title of which is those two lines of the refrain. During WWII a version became known as Der U-bootsfahrer Leid (The U-boatman's Song) but the original is much older than that. Perhaps the most poignant historical references to the song are the eyewitness accounts of it being sung by the surviving crew of the Kreigsmarine ship Scharnhorst after she was sunk in action in the North Sea, as they waited either for rescue or for hypothermia to take them. The accounts tell of the song being taken up by many voices at first, and of the chorus fading as they succumbed one by one until the last handful of survivors stopped because they realised that the sea had taken their comrades. Be it in war or peace a watery grave where no roses bloom is one possible fate faced by all seafarers regardless of their flag.
The reason I put it in my signature is that just after Christmas the seas around the coast of Ireland were particularly treacherous, some fishing crews lost their lives in the storms and were never found. As a former member of the seafaring community I thought it the most apt quote out of all the relevant songs and poems that I know.
This is not Off Topic, so let's get back on track  we don't want folks crying on their eyepieces.
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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boren
super member
Reged: 01/17/07
Posts: 192
Loc: Northern Indiana
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Quote:
When do you use your extension rings? Do you add/change them while observing, or do you adjust your EP's before hand based on what you want to observe? Just curious.
Tom
They _can_ be changed in the field. It's pretty much like putting a filter on. That said, it has to be a clean environment since cleaning the internal two lenses is going to be very hard. I have done it in the field to see how it works since I'm lens poor. It's also not very dirty/dusty where I observe. I own a 13mm and I plan to keep the either the 28mm or 14mm installed to give me a 11 or 9mm eyepiece. Not sure which yet.
I have a 17mm and 13mm. The next time I'm out I'm going to add in a tuning ring to convert the 17mm down to 13mm and I will compare the two in the field.
Do be warned the eyerelief seems to reduce when you add in the fine tuning rings. The 17mm with the 28+14mm seems to have about 10 maybe 12mm of eye relief. I think.
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Orion xt10i
Rodenstein Model II 60mm f/11
Hyperion: 17mm, 13mm, 5mm. WO UWAN 28mm. Orion Shorty Plus barlow.
Geek.Farm.Life Podcast
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neoweb
Pooh-Bah
Reged: 12/10/06
Posts: 1482
Loc: UK
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Quote:
Do you know where to find or derive a formula that uses the field stop size and focal length to calculate FOV?
True field of view = eyepiece field stop diameter / telescope focal length x 57.3
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Celestron StarHopper 8" f/6 Dob
38mm Burgess 2" SWA | 30mm Ultima | 20mm Omni
17mm Hyperion | 12.5mm Baader Ortho
8mm TV Plossl | 6mm TMB/BO Planetary
Orion Shorty Plus barlow
15 X 70mm Skymasters
Saturn-like: desktop image
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John Hoare
seantoir
Reged: 04/25/04
Posts: 8873
Loc: Area 14, Kildare, Ireland
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57.3 being a sufficient approximation of 180/pi. (see Jim Easterbrook's version above)
It's certainly easier if you don't have a calculator with a pi button to hand.
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John
Watery Glebe
Puddlestown
Co. Kildare
Chaos is the rule of nature
Order is the dream of man
Henry Brooks Adams
IFAS
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