#1  
Old 14-03-2012, 05:59 PM
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tilbrook@rbe.ne (Justin Tilbrook)
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Coma corrector problems ??

Hi,

Has anybody got any idea's on what i might be doing wrong?

I have a 2" BINTEL coma corrector apparently bases on a GSO deisign according to BINTEL.
They say to space it 53 to 55mm from the chip, this point is marked on the canon 1100D.
The image below is a spacing of 54mm, as you can see there's still coma. Iv'e tried other spacings, but it only makes it worse.

Any idea's.

Tips appreciated.
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  #2  
Old 15-03-2012, 12:37 PM
Ken
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The coma seems worse than no corrector, sure it is not on backwards?.
Clear skies Ken.
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Old 15-03-2012, 01:21 PM
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troypiggo (Troy)
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You've just got the DSLR connected to EOS adapter and straight to the coma corrector? Pretty sure the 55mm nominal spacing takes the 10mm or so of the EOS adapter into account, so that's all you should need.
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Old 15-03-2012, 01:29 PM
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Tandum (Robin)
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I have an baader mpcc here at the moment. If I hold it and look through it in daylight, it is obviously in focus in the center and obviously out of focus around the outside. Does that GSO one look like that?
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Old 15-03-2012, 01:35 PM
bratislav (Bratislav)
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Justin,

this coma corrector looks like the same as AstroTech model (designed by Roger Ceragioli). That one was designed to have much longer BFL distance (so an off axis pick-up prism style guiders, AO units and like could be used).
If that is true (and I'm pretty sure it is), the distance you should be shooting for is more like 75mm.
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Old 15-03-2012, 05:44 PM
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tilbrook@rbe.ne (Justin Tilbrook)
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Hi all,

Thanks for the tips.

Ken, I tried reversing the corrector, definitely wasn't that.

Troy, certainly that's what Iv'e been told but it won't work at 55mm spacing.

Robin, it does look out of focus toward the edges but not much.

Bratislav, Haven't tried at a 75mm spacing, I'll give that a go tonight if the weather holds.

Cheers,

Justin.
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Old 15-03-2012, 06:38 PM
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If it's this one: http://www.bintel.com.au/Astrophotog...oductview.aspx have you unscrewed the extension part so the EOS adapter screws straight to the glass piece in this photo: http://agenaastro.com/catalog/produc...36/image/5604/

The agenaastro site does mention 70mm back focus. http://agenaastro.com/gso-2-coma-corrector.html
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Old 15-03-2012, 07:05 PM
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tilbrook@rbe.ne (Justin Tilbrook)
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Quote:
Originally Posted by troypiggo View Post
If it's this one: http://www.bintel.com.au/Astrophotog...oductview.aspx have you unscrewed the extension part so the EOS adapter screws straight to the glass piece in this photo: http://agenaastro.com/catalog/produc...36/image/5604/

The agenaastro site does mention 70mm back focus. http://agenaastro.com/gso-2-coma-corrector.html
Thanks Troy,

Yep removed the eyepiece extension.

Cheers,

Justin.
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