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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
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I dunno, that's one of my hot buttons - I really don't like a field stop that is not in focus. In fact I often can judge the quality of an eyepiece by examining the field stop - for both sharpness and lack of color fringing. My 15mm Plossl, same as Greg's, has a starkly defined and colorless field stop, so I'm sure he's got a defective one.
-drl
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starrancher
professor emeritus
Reged: 06/09/09
Posts: 596
Loc: Northern Arizona
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I have two 15mm Meade 4000 Plossls & the field stop is as sharp as a razor on both of them .
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LXD75 AR5
LXD75 SN8
Series 4000 Plossls
Misc. other stuff
Fort Rock , Az .
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TonyTowe
member
Reged: 07/21/09
Posts: 35
Loc: North Georgia, USA
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I decided to call Televue, and I spoke to one of their designers. He tells me that the vignetting will occur with their plossls with slow f-ratio telescopes, but their computer models suggest that this should start at f/16. Again, mine is f/13, so I guess I am at the threshold of where this begins. I am glad Televue confirmed what I am seeing, but it is also a little disappointing as I too prefer a well defined field stop like I see with my Meades.
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Tony T.
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3939
Loc: "Metrowest" Boston
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Quote:
but their computer models suggest that this should start at f/16
That's probably in a refractor or a Newtonian. Vignetting will be slightly worse when in a catadioptric telescope with a negatively powered secondary for the same reason as it is worse with Barlows.
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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TonyTowe
member
Reged: 07/21/09
Posts: 35
Loc: North Georgia, USA
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I think I may take a hard look at the UO HDs for this scope.
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Tony T.
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