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Old 05-07-2011, 10:53 AM
solissydney (Ken)
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Coma Corrector

My images taken with my Canon 5D on my 12 inch F/5 Newt. shows very bad elongated stars all round the image. Would the 2 inch Baader MPCC coma corrector, in your opinion, be the best way helping solve the problem ?
Ken
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Last edited by solissydney; 05-07-2011 at 11:54 AM. Reason: Adding Image
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Old 05-07-2011, 09:18 PM
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Looks like coma to me. Either the MPCC or the Televue Universal Paracorr should improve things.
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Old 06-07-2011, 11:41 AM
solissydney (Ken)
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Coma

Thank you Peter.
My choice is the MPCC from Andrew's
Ken
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Old 06-07-2011, 01:16 PM
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Tandum (Robin)
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You might wanna check that the mpcc won't cause it to vignette.
The 5D has a full frame sensor so it has almost the same dimensions as an sbig STL-11000 chip and the mpcc is a t-thread device.

Last edited by Tandum; 06-07-2011 at 10:01 PM.
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Old 06-07-2011, 04:52 PM
solissydney (Ken)
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Glad you pointed out the possible problem of vignetting Robin.
After having bought the corrector and taken some images I shall let you know whether vignetting is a problem of any importance
Ken
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Old 06-07-2011, 06:37 PM
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multiweb (Marc)
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Quote:
Originally Posted by solissydney View Post
Thank you Peter.
My choice is the MPCC from Andrew's
Ken
Good choice with the MPCC. It's a good all rounder and you buy it once. Vignetting is very easily taken care of by flat-fielding so it's not really an issue.
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Old 07-08-2011, 06:23 PM
solissydney (Ken)
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Coma Corrector

The images shows an before and after image of the installation of my new Baader MPCC Coma Corrector on my 12 inch F/5 Newt. using my full frame Canon 5D.
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Last edited by solissydney; 07-08-2011 at 06:28 PM. Reason: adding image
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Old 08-08-2011, 11:20 AM
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Does flat fielding fix that black ring Ken?
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Old 08-08-2011, 11:35 AM
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They both still appear to show some coma? Which one is before? M8 or Eta Carinae? Could be the spacing between the camera sensor and MPCC - I know I had to add a spacer to my QSI583 to get it right, still think it's a little out.
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Old 08-08-2011, 12:58 PM
solissydney (Ken)
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Coma

Black ring Robin? Where, on which image. Do you mean the black in each corner in the M8?
The M8 came after the MPCC was installed.
Will look into the spacing Troy. Thanks for suggesting that.
Ken
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Old 08-08-2011, 01:07 PM
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Noticed you're using a 5D DSLR - I'm pretty sure the MPCC was designed, or by accident, to be the "right" spacing for a DSLR with EOS adapter etc. Think it's 56.5mm from memory. How've you got it mounted? EOS adapter straight into camera body, and that screwed directly into the MPCC's T thread?
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Old 08-08-2011, 06:15 PM
solissydney (Ken)
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Troy,
one end of the MPCC is screwed into the T-piece, the other end goes into the focuser.
that way the distance from the C-mos to the first surface of the MPCC is app 55mm.
I intend testing the gap 1 mm at a time.
What think you?
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Old 08-08-2011, 06:32 PM
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55mm - that's it. My brain was over-complicating it as usual
Sounds right, at least as I understand it, so not sure what's causing that bit of coma still in the corners. I'm getting a little bit still too on my 10", and need to test in 1mm increments as you're suggesting, so sounds like you're on the same path as me. Whether or not that's the right path is another issue...
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Old 08-08-2011, 07:29 PM
solissydney (Ken)
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Coma

I will have to wait for the sky to clear in order to take a few more images.
could take a few days.
Ken
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Old 08-08-2011, 08:06 PM
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The black ring is vignetting, and flats should correct it if you can get your flats right. I have 5d MKII and an 8" newt. I notice that with the full frame you can't get the coma corrected across the entire chip, or at least I couldn't. If you extend the mPcc out it gets worse, it's like it needs to be closer to the chip than you can get.

If you can find a solution I'd be all ears.


Thanks
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Old 08-08-2011, 10:52 PM
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Quote:
Originally Posted by solissydney View Post
Black ring Robin? Where, on which image. Do you mean the black in each corner in the M8?
The M8 came after the MPCC was installed.
Will look into the spacing Troy. Thanks for suggesting that.
Ken
Yes that one. Was wondering how well flats would work on it.
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Old 09-08-2011, 07:29 AM
solissydney (Ken)
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If the MPCC needs to get closer to the c-mos the only way to do that would be to either file or machine the t-ring to make it slimmer, which I am quite willing to try out.
Ken
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Old 09-08-2011, 10:23 AM
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Before you machine anything, might pay to check if WR's suggestion above is the problem. ie, is the MPCC designed for full frame sensors, or only crop APS-C sensor sizes etc? I'm not sure and haven't had a chance to check that out yet.
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Old 09-08-2011, 03:06 PM
solissydney (Ken)
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I wouldn't file it down without making sure I could return it to the original using some kind of washer. Actually, I would practice on another t-piece that I have, where it would not matter.
Thanks
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Old 09-08-2011, 08:32 PM
solissydney (Ken)
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Coma

Troy pointed out that the MPCC has a spacer ring. However , because the internal tread of the spacer ring has a bigger diameter, by removing it, it is not useful for minimizing the space.
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