Author Topic: SFS: Subs taken through cloud vs clear, dark sky?  (Read 214 times)

Offline Terry Danks

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SFS: Subs taken through cloud vs clear, dark sky?
« on: 2019 February 28 05:57:02 »
Last night I know there was thin, high cirrus cloud about. When I checked the subs against those taken another night, when it was clear, I expected to see figures in the SFS that would allow me to distinguish "bad" subs, i.e., those taken through the cloud, from the "good" subs, taken in a clear sky.
I saw nothing in the FWHM, Ecc, or SNR figures that pointed to the "cloudy subs" being better, or worse than the "clear" subs.
This does not seem logical and I am puzzled.
Comments?

Offline John_Gill

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Re: SFS: Subs taken through cloud vs clear, dark sky?
« Reply #1 on: 2019 February 28 07:17:26 »
Hi,

I have had subs that have had similar SNR, Eccentricity, FWHM, etc. etc. Except one sub that has a large spike in the SNR.  When looking carefully at that sub I found that it was "brighter" because of thin cloud hence the SNR spike. Perhaps the seeing conditions and the clouds even things out.  ;)

space is not black
John

APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline mschuster

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Re: SFS: Subs taken through cloud vs clear, dark sky?
« Reply #2 on: 2019 February 28 07:57:46 »
Yes, things like clouds, gradients, and dew sometimes cause excessively large "signal" measurements. Can you place one "good" and one "bad" sub in DropBox? I will take a look. Also, as a workaround, you might try an integration with no weighting, no output normalization, and no rejection normalization. Although this may not sound like a good idea, and the results may not look like your reference sub, the integrated results from an SNR perspectively often will be excellent.

Mike