HowardK
professor emeritus
Reged: 10/20/10
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straight line in FOV
#5326719 - 07/20/12 11:14 AM
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My Baader mk 5 's show a straight edge on a defocused star when i move the star to the edges of the FOV......it is a dead straight line as the star nears the edge of the viewing circle...is this normal and what causes it...is it the edge of the prism?
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: straight line in FOV
[Re: HowardK]
#5326804 - 07/20/12 12:12 PM
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Quote:
My Baader mk 5 's show a straight edge on a defocused star when i move the star to the edges of the FOV......it is a dead straight line as the star nears the edge of the viewing circle...is this normal and what causes it...is it the edge of the prism?
When a point focuses to a line, that is a sign of astigmatism probably combined with some field curvature. What happens when you try to focus that star?
Jon
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HowardK
professor emeritus
Reged: 10/20/10
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Re: straight line in FOV
[Re: Jon Isaacs]
#5326872 - 07/20/12 12:55 PM
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Jon
A focused star is fine
Also when i move the defocused star with its cut off straight edge towards the center of the fov it loses the straight edge and is perfectly circular
I use the sieberts lens system that gives me no extra magnification but allows me to come to focus in my planewave 12.5"......there is a lens in the front of the diagonal and a lens that screws into the nose of the binovue
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GlennLeDrew
Postmaster
Reged: 06/18/08
Loc: Ottawa, Ontario, Canada
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Re: straight line in FOV
[Re: HowardK]
#5327085 - 07/20/12 03:38 PM
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Have you tried moving the star toward other directions within the FOV, in order to see if this cutoff occurs at other positions? If so, does the cutoff have the same orientation and depth with respect to the field edge? Or is the cutoff apparent in one location only? Do you see the same thing in both eyepieces?
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johnnyha
Postmaster
Reged: 11/12/06
Loc: Sherman Oaks, CA
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Re: straight line in FOV
[Re: GlennLeDrew]
#5327115 - 07/20/12 03:56 PM
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Is this like a clipped edge? I wouldn't be surprised if it had something to do with the Siebert low mag catching the edge of the prism. Do you see anything when using say at least a 1.7X or 2X OCA?
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HowardK
professor emeritus
Reged: 10/20/10
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Re: straight line in FOV
[Re: johnnyha]
#5327244 - 07/20/12 05:46 PM
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Cloudy tonight
Will try with no Sieberts lw mag tomorrow and report
Thanku
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HowardK
professor emeritus
Reged: 10/20/10
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Re: straight line in FOV
[Re: GlennLeDrew]
#5327249 - 07/20/12 05:47 PM
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Glenn
The cutoff happens at all points around the fov
Will test out your other points next clear night
Thanku
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: straight line in FOV
[Re: HowardK]
#5327308 - 07/20/12 06:19 PM
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A focused star is fine
Also when i move the defocused star with its cut off straight edge towards the center of the fov it loses the straight edge and is perfectly circular
As Glenn and others have suggested, it is most likely something with the Binoviewer.
I was just wondering if it were off-axis astigmatism in the eyepiece. This can be seen by leaving the star at the edge and refocusing it.
Jon
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EdZ
Professor EdZ
Reged: 02/15/02
Loc: Cumberland, R I , USA42N71.4W
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Re: straight line in FOV
[Re: Jon Isaacs]
#5328001 - 07/21/12 10:14 AM
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If you are seeing a defocused star as an incomplete circular spot of light, having one edge showing up as a straight line chord on that ciruclar spot, then it may be induced by the edge of a prism. It can be that the light cone is being cut off inside the prism OR it can be that a prism does not completely span across the metal prism housing, leaving a slight gap of space exposed in the prism housing. That would cause a portion of the light cone to be missed by the prism edge and shows up as a straight line cord in a defocused circular image.
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johnnyha
Postmaster
Reged: 11/12/06
Loc: Sherman Oaks, CA
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Re: straight line in FOV
[Re: EdZ]
#5328312 - 07/21/12 01:40 PM
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I agree with Ed and the Siebert low mag would exacerbate that issue.
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HowardK
professor emeritus
Reged: 10/20/10
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Re: straight line in FOV
[Re: johnnyha]
#5328364 - 07/21/12 02:28 PM
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I dont think its a binovue thing as the exact same thing happens with a Televue binovue and a Baader Mk5.....
Will remove the Sieberts corrector replace with a 2x Powermate so i can find focus and see if this disappears
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johnnyha
Postmaster
Reged: 11/12/06
Loc: Sherman Oaks, CA
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Re: straight line in FOV
[Re: HowardK]
#5328488 - 07/21/12 03:58 PM
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Yeh I don't think it's the "fault" of the binos. I think it's what can happen when you use a low mag OCA or reducer with binoviewers.
That's why Roland at AP does not make one for instance when he came up with the Glasspath correctors for the Baader MkV. And the newtonian compensator is 1.7X and not less. The binos have a long light path with a 1" opening and there's only so much you can do. You can't expect a fast light cone coming in to not have some clipping or vignetting.
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HowardK
professor emeritus
Reged: 10/20/10
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Re: straight line in FOV
[Re: johnnyha]
#5331774 - 07/23/12 05:36 PM
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It is the Sieberts OCA system causing the clipping.
When removed there is no clipping.......but cannot reach focus with the Planewave 12.5" and binovue+powermate
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