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  #21  
Old 14-08-2016, 09:04 AM
Sat5
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Hi Glen any progress with this project?
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  #22  
Old 14-08-2016, 10:18 AM
glend (Glen)
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I have had some problems with the field flattener. Many tries but can't get the spacing right to achieve good focus, i suspect the rear mounted Petzval correct is affecting the focus through the flattener and simply i cannot get a good focus diffraction pattern (this is through a Ha filter). I am going to sell the flattener i think and try without it and rely on cropping as the field was not that bad before.
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  #23  
Old 14-08-2016, 01:00 PM
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Slawomir (Suavi)
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The Ha image looks pretty good

However, the real test will be combining a tri-colour narrowband image - fingers crossed it will be at least as good as the Ha one!
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  #24  
Old 26-08-2016, 10:33 AM
glend (Glen)
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Got sick of waiting for some clear nights to finish my M16 narrowband test. I have gone ahead with the little data i have available and created a bi-colour image (Ha 6x300" and Oiii 10x300"). They are far enough apart on the spectrum to test for any issues caused by slightly different focal lengths, which i think the rear corrector manages to sort out. That was my testing intent, to see if they register and stack without fringe offset, and i think it looks ok.
I have a concern about what appears to be a few vertical diffraction spikes on some brightest stars but it maybe that i left a focus mask on during one sub and that could cause it. I have to go through the subs individually to check for focus mask diffraction.
The main issue is still field curvature, and my attempts to flatten it with a Hotech fast refractor flattener failed, actually made the situation much worse. Given the design, with the rear corrector, i may not be able to flatten the field. So cropping seems to be the inevitable solution on this scope; and frankly to be expected in that it is optically designed for visual use.
I have posted the image to my Astrobin gallery, see the link below.
Don't expect a masterpiece, its a test image, and it is cropped.
Comments welcome as long as you don't suggest buying an APO.

http://www.astrobin.com/261164/

Last edited by glend; 26-08-2016 at 02:39 PM.
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