Blue specs in image - flats, darks, calibration, camera or user error?

[sixburg]

The attached is a crop from an unprocessed RGB image (just LRGB combination).  The underlying frames were batch processed with the script.  Note the blue spots in the image.  What are the likely causes of this?  For reference, these spots or voids appear even in uncalibrated images (I aligned the raw subs and stacked them without calibration and got the same results).  Also not that these appear only in the blue-filtered images.  Lastly, I examined another recent RGB image and didn't see the same spots, or at least not to the same degree in terms of size and population.  Thanks!

[bianry]

Are you sure this is not something real that is only picked up by the blue filter? If you look at the Veil Nebula or something from The Pleiades you will see faint blue light. Maybe you picked up something like that. Where is the image from? What object?

regards

Mats

[sixburg]

It's definitely not something like M45's blues. This s a crop of M63 and very clearly a defect in the image.

[lucchett]

Have you checked the blue channel? What do you see in the same locations?
Thanks, andrea

[Andi42]

Could it be reflections from a coma corrector? What's beyond the symmetry point (center of image) of these spots?

Cheers
Andreas

[sixburg]

Attached is an annotated version of the uncalibrated blue channel (~9x600, 850mm, f/8) ("Blue Spots").  This is a crop of the stack of uncalibrated images.  Many of the defects are marked.  I'd like to understand first if this is somehow mechanical or really a vestige of processing (using ImageIntegration, WSC).  If the latter what are the likely causes?  I did a number of tests to zero in on the latter hypothesis regarding processing problems.  Images will be in subsequent posts.

1)  I suspected defective darks frames and so used various dark frames at the same temperature (-25C) and duration (600 seconds).  I've tried with few (4-5) and many (18-20).  I performed the calibration with the script, and "by hand".  These defects appear in all cases.  The flats appear normal.

2) In another test I aligned and stacked the uncalibrated frames which also exhibit the same defects in the blue channel (see "uncal" in "Tests", lower right image).  I've had some success at minimizing the spots in the uncalibrated by changing the settings in Imageintegration (see "integration18" in "Tests").

3) With new knowledge gained in test #2, I redid Imageintegration on the calibrated frames and minimized the spots further (see "calibrated...STF", the upper right image in "Tests".  The upper left image is the same with AutoSTF)

So, after I put it all back together it seems that the issue is controllable via sigma hi and lo settings.  A preliminary LRGB is attached as well demonstrating the lack of the blue speck problem (as well as demonstrating the need to develop processing skills further).

Any further guidance would be appreciated.

Thanks. 

[sixburg]

Further image with blue spots marked...

[sixburg]

Finally...a preliminary processed image that needs work, but hasn't the blue spot problem.