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Paul_R
Carpal Tunnel
Reged: 04/05/05
Posts: 1648
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Looking for an eyepiece to complement my 20mm Binolite and 9mm Expanse on an Astroscan.
Would like something in-between, with a good 18mm+ eye relief (for eyeglasses), and with a reasonable fov, say 50-60 degrees. Light-weight preferred so as to not throw off the 'Scan's balance. Under $70 used would be good, too, as I'd like a throw-in-the-pocket, not to worry if the 'Scan drops it type of eyepiece.
The 20mm gives 22x; the 9mm about 50x. So probably looking at something in the 12-15mm range.
Any recommendations? Or, is this an impossible quest? 
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dothead
super member
Reged: 08/13/08
Posts: 138
Loc: Heidelberg, Germany
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Paul,
The Celestron X-Cel 12.5mm has 20mm eyerelief, 55 deg AFOV and costs $ 65.00 new.
Ralph
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Paul_R
Carpal Tunnel
Reged: 04/05/05
Posts: 1648
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Ralph, thanks! It's a definite possibility... I know from past experience that it also makes a great eyepiece for the PST!
One wrinkle... the 9 mm Expanse has an incredible 70-74 degree fov... which means it shows about 1.5 degrees of the sky... the same amount that the 12.5mm Xcel does! So, their fovs would be identical! (Maybe that doesn't matter...)
I might try another 14mm Orion Epic (similar), but the 3 I've tested have all had problems vs. the other ones in that series.
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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Hyperion?
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400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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Paul_R
Carpal Tunnel
Reged: 04/05/05
Posts: 1648
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I think they'd be much too heavy... the Astroscan is a roller ball design, without a set screw in the focuser. Too heavy an eyepiece and it can rotate and "spit" the eyepiece out! CRASH!
Anyone used one of those 15mm Superviews? I see that OPT (Starhunter), GSO, and others have them... probably poor sharpness across much of the fov because too wide fov for such a short f ratio.
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kaaikop
sage
Reged: 07/13/08
Posts: 468
Loc: Ste-Therese, Canada
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Just curious, what are the specs of the Astroscan?
This is the little red "portaball" thing right?
I saw someone using it at a star party, she was sitting at the picnic table all the time.
Talk about "grab & go"  you cant beat this!
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Benoit, RASC Montreal
-C 9.25XLT on EQ6 Pro / ED80SF on Portamount
-Plossls, Radians, Naglers, LVW's & Orthos.
-a pair of 7x50's
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Paul_R
Carpal Tunnel
Reged: 04/05/05
Posts: 1648
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Yes, it's the little red ball wonder!
The Astroscan is a 4 1/8" f/4.2 scope (445mm in focal length). It sits on a roller base that can be put on a table (as in your example with the picnic table) or it screws onto any 1/4-20 tripod... the Edmund tripod being a lightweight, collapsible, excellent product. The combo makes it easy to carry out a rich-field scope in one-- well two hands is smarter as the ball could bounce off the roller base if you stub a tripod leg on a door or snag it on a curtain! But with a few eyepieces in one's pocket, it makes for a real grab 'n' go set up.
The best part, though, is the roller ball action. One sits close to the scope and the motions are intuitive, fluid, and you feel connected with the scope and the heavens in a way that few other scopes can provide. It made me understand well why so many love their Portaballs-- someone once described dancin' with their 8"!
(It's too bad, though, that the Astroscan isn't a 5" f/5 because that would up the light grasp and reduce the coma dramatically. Add in a real focuser, with a set screw, and they'd have an even better design on their hands.)
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Jason B
Carpal Tunnel
Reged: 06/21/04
Posts: 2071
Loc: Mid-Michigan
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I use a 15mm Expanse all the time in a SCT. Never tried it in a fast scope but it works very well in the SCT and is very light weight. I have heard they are about average in a fast reflector but have never personally tried it.
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Jason
Discovery 12.5" F5 PDHQ
GSO 6" F5 Newt.
Vixen 80mm F8 APO (FL80S)
Vixen GP and Astro-Tech Voyager Mounts
MX 716 and Canon Rebel XT
Too many eyepieces and other accessories to list
Fox Park Observatory
16" and 2 x 12" LX200's
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KWB
Postmaster
Reged: 09/30/06
Posts: 7635
Loc: Westminster,Co Elev.1646Meters
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With that fast a scope I believe the 15 and 20mm Expanse eyepieces are going to feature a lot of off axis astigmatism and you won't have to go very far off axis to have it predominate your viewing. The 9mm even at F/4.7 is pretty severly tested IME,thought at F/5 and above is really a decent performing eyepiece for my purposes. IMO your tolerance for this optical defect is much higher than mine. Also we have different requirements in eyerelief as far as eyeglass useage is concerned. None of the Expanse line has near enough of it for me.
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Kenny
"When dealing with a mystery,choose the most unlikely of the likely possibilities"-Sherlock Holmes
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Paul_R
Carpal Tunnel
Reged: 04/05/05
Posts: 1648
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Yeah, the 20mm Expanse was a dog in the Astroscan (no offense to our canine buddies! :-)). The 15mm is supposed to have the least eye relief of the line...13mm or some such, way too little for eyeglasses. The 9mm and 6mm have just enough, and the 9mm does quite well even at f/4.2
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