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Peter in Reno
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Reged: 07/15/08

Loc: Reno, NV
Re: Analysis...How can I further improve? new [Re: korborh]
      #5564397 - 12/10/12 03:41 PM

Hi Sal,

I am saying is if you can guide tight and focus well to get low FWHM of stars, then I do not see an issue of imaging at less than 0.5" if the seeing allows it. I don't like to image under bad seeing even if the image scale is between 1" and 2" because the results would be mediocore. It's a personal preference. Dave lives where there's very little to no light pollution and the seeing is normally good which is why I think he should stick to 0.46" image scale.

Peter


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Peter in Reno
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Re: Analysis...How can I further improve? new [Re: korborh]
      #5564800 - 12/10/12 08:02 PM

Quote:

Your FWHM is 2.67" which is good, however I would try to bring it under 2", given your location. That would be a significant step in added resolution, assuming seeing allows it.

What is the FWHM of your focus stars? It will tell you if your collimation and focus is optimized as best as possible. If it is much smaller than 2.67", then you know its in the tracking or other factors like focus shift, flexure etc. limiting your long exposure FWHM/resolution.




Dave,

In your original post, you said FWHM is 5.8 pixels. I and maybe others thought it was in arcsecs. To convert to arcsecs based on your image scale is closer to 2.67 arcsecs which is pretty good despite bad seeing. That's better than my typical images in my area. FWHM in arcsecs is usually more meaningful than in pixels.

Do not discard your Luminance images since the FWHM of the stars are very good. I am curious what's your typical FWHM of the stars in excellent seeing condition?

Peter


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SGT500
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Re: Analysis...How can I further improve? new [Re: Peter in Reno]
      #5564802 - 12/10/12 08:03 PM

Quote:

Hi Sal,

I am saying is if you can guide tight and focus well to get low FWHM of stars, then I do not see an issue of imaging at less than 0.5" if the seeing allows it. I don't like to image under bad seeing even if the image scale is between 1" and 2" because the results would be mediocore. It's a personal preference. Dave lives where there's very little to no light pollution and the seeing is normally good which is why I think he should stick to 0.46" image scale.

Peter




I agree fully, i think in good seeing he will be able to get away with 1x1 binning and make some really nice images.


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SL63 AMG
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Reged: 12/21/09

Loc: Williamson, Arizona
Re: Analysis...How can I further improve? new [Re: David Ault]
      #5566956 - 12/12/12 03:47 AM

Quote:

Dave,

You might take a look at Starizona's guides. They have one on Nyquist Sampling and how it relates to CCD astrophography that might help explain the concept better. It certainly explains it better than I could.
http://starizona.com/acb/ccd/advtheorynyq.aspx

Regards,
David




David,

Thank you. This was helpful for me to understand under and over sampling. It makes sense now and after reading the article and also reading the help files for CCDInspector to learn what is meant by aspect ratio and curvature with respect to the over all measurements taken across each sub I can now better understand the numbers.

Comparing subs from each night as the seeing has progressively improved I am obtaining better aspect ratios and lower curvature numbers for each sub. It was important to understand how CCDInspector averages these values across the entire image. Incidentally, my FWHM's are lower tonight also.

Current Conditions
==================
Cloud Cover: None
Transparency: Above average
Seeing: Average to Good

Measurements
============
FWHM 3.3px or 3.05"
Aspect ratio 6
Contrast ratio 33.36
Air mass 1.31
Curvature 10.4
Scale 0.46 "/px
Tilt in X -0.0"
Tilt in Y -0.0"

3D Curvature Chart
==================
Min FWHM 3.07px
Max FWHM 3.24px
Curvature 11.4%
Total Tilt 1%
Collimation 2.6px
Stars Used 121


Considering all that I have learned, I guess I am pretty happy with the data I am getting out of this system. I have always been pleased with the results of my ASA N10 astrograph but I was skeptical about this AT12RC.

For anyone considering an AT12RC for imaging I highly recommend that you consider an FLI Atlas focuser. It has made a huge difference in the stability of the system with regard to flexure and stable collimation.

I am currently gathering RGB data binned 2x2 at 10.8 micron pixel sizes for NGC2403 and the results look awesome!

Thanks for all the feedback folks. I really appreciate your insight as I continue to gain more knowledge in my pursuit of capturing excellent data.



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