Sunday, November 14, 2010

Learning from the Sisters

As you can tell from my previous posts I've been spending a lot of time learning the basic fundamentals of PixInsight.  Using the Pleiades data that I gathered in the October new moon cycle, I've come to the conclusion that the Seven Sisters are an ideal training ground for astroimage processing.  Nice color, detailed nebulosity without being overly tricky (ala M42), some star color, and brightness variations to throw a little challenge into the mix.  A zillion amateur and professional images available on the net are also a help.  In other words a little bit of everything and nothing too difficult.

The fact that there is a detailed processing example on the PixInsight website helped a bit too.  Here is my current, um, version.  As always, click to flickr.

Encouraged by my early progress (see a couple posts back) I subsequently languished in a discouraging cycle of dead ends and restarts.  Trying more sophisticated tools against my image lead to worse results.  I finally discovered the NoiseEvaluation script and found that I was inexorably raising the noise floor as I processed deeper.  Even though I was keeping the data linear for as long as possible things just plain got noisier.  My tendency was to overstretch and otherwise use too aggressive settings and got to a place where even the sophisticated noise reduction tools in PI couldn't compensate.

Eventually I tackled learning how to do all the calibration processing in PI as well.  This is an area where PI does need some workflow streamlining - not for the faint of heart.  Nebulosity is much much easier.  But the tools in PI are powerful.  After I plowed through it I was able to get my subs to about 5-8x lower sigma SNR.  Pretty cool.  So now I was able to start post-processing with more headroom.

And well, I did only have an hour worth of exposure time.  I really shouldn't expect so much.  Two minute subs too.  But I think it is a very worthwhile learning experience to work with the same data set over and over to see just how much you can squeeze out of the noise.  Experiment often. Reprocess much. You will learn a lot which you can bring to bear on your subsequent images.

I have about 4 or 5 other image sets waiting to be processed but I've patiently spent hours and hours of time with the Seven Sisters while I learn PixInsight fundamentals.  Oh so pretty and alluring they are.  Not entirely painful company!


Taken at Lake San Antonio, CA  October 8, 2010
Canon T2i (stock), Astrotech AT80LE, 480mm  f5
Astrophysics AP900 mount

Guiding: SSAG/50mm Orion finder, PhD
30 120sec exposures @ ISO1600
94 darks
14 flats (1sec ISO 100

128 bias frames
calibration, registration and post-processed in PixInsight

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