4 replies to this topic

[james7ca]

This image of the Saturn Nebula (NGC 7009) was taken at the prime focus of a Takahashi FC-100DZ fluorite doublet refractor using an uncooled ZWO ASI678MC "planetary" type camera. I combined 448 subs that were each exposed for 4 seconds so the total integration time was 29 minutes and 52 seconds. The capture scale with this setup is 0.52 arc seconds per pixel but I did a 2X drizzle during the processing and then reduced that to 67% and thus the reproduction below has an image scale of 0.39 arc seconds per pixel (probably near to critical sampling for this 4" refractor). The limiting magnitude on this shot is approximately 18 (ASTAP says 18.8) and north is oriented up.

 

I posted an earlier version of this image with fewer subs and without a drizzle over in "Beginning Deep Sky Imaging" but with the drizzle processing and some PixelMath to neutralize a little background color mottle this version probably needs to go in the "experienced" topic. However, if you want to see what the Saturn Nebula looks like with just over two minutes of total integration time (from a Bortle 7+ site) then you can link to that thread as given above.

 

I had some problems getting the drizzle integration to work because apparently PixInsight's file cache for ImageIntegration had been corrupted and even though the file list in the process was correct and complete PixInsight wan't using all of the subs during the standard, 1X integration. It did not log any errors during the normal integration but when I went to do the drizzle it reported that some information was missing from the source files (those ended up being the XDRZ files although that was NOT mentioned in the error messages). It took me an hour or more to figure out what was wrong and then I remembered that I'd had similar problems in the past that were fixed by clearing the file caches that are maintained by the integration process (accessible under the "wrench" icon at the bottom of the ImageIntegration process window). So, I reset the file caches (all of them) and redid the image integration and then the XDRZ files were properly undated allowing the drizzle integration to run.,

Image capture with N.I.N.A. using direct "guide" with dither, image processing with PixInsight and Photoshop 2024. There are additional capture details in the image captions. Click on the preview to see the full-sized image.

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Edited by james7ca, 10 August 2024 - 12:18 PM.

[TelescopeBah]

Very nice! I did a EAA session on this last night, but didn't catch near the detail here.

[vidrazor]

Nice.

[MHamburg]

Sweet image!

Michael

[james7ca]

TelescopeBah, vidrzor, and Michael, thanks for the comments.

 

I think the detail in this shot is pretty good and it compares favorably with some of the better images taken with much larger instruments (like a C11 or even larger). The details in my image look very much like what is shown in the Saturn Nebula image that is used in SkySafari and that is attributed to Brad Ehrhorn/Adam Block and NOAO/AURA/NSF, perhaps taken in the early 2000s at Kitt Peak with a fairly large, observatory-class telescope.

 

I guess I had pretty good seeing on that night and I was somewhat hesitant to try this object since it doesn't reach a very high elevation in the sky. But in that respect, I'm definitely better off than someone who lives farther north although I did image when the nebula was passing through my local meridian. This object is also bright enough that I don't think it was bothered too much by the light pollution that is notably worse toward my southern horizon. Most nights I'm in a Bortle 7+ state when measured directly at the zenith but to my south I have an obvious light dome that's probably equivalent to a Bortle 8 location.

 

I also processed this image using PixelMath although a direct 1:1 visual comparison showed no difference in the detail or structure of the nebula itself between the image without any PixelMath to the one that was processed in PixelMath to remove some very faint color mottle from the background sky.

 

But, it's kind of interesting to look at a difference image (subtracting one image from another and plotting the absolute difference) that shows what was removed by my PixelMath processing. Below is a HIGHLY stretched version of the image difference. Without the extra histogram stretch the non-linear difference looked like a nearly, solid black frame, very similar to what you'd see in a master dark frame except without any bright pixel artifacts or amp glow. In any case, I could have strengthened or weakened the removal by changing some PixelMath parameters but this was from my first attempt and I didn't see any reason to make any more adjustments. This image is at the same scale and size as my original post (i.e. 0.39 arc seconds per pixel and 1560 x 1120 pixels). Black areas in this difference image indicate areas of no change. You can see that most of the color mottle was in the red channel (that seems typical) although there were areas that were green or blue.

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Edited by james7ca, 11 August 2024 - 12:05 AM.