Reprocessed IFN Using PixInsight's WBPP

The image in the last post was really not very well processed, with the culprit being me. I suspect I twice subtracted bias or something. It was so bad that I decided to reprocess immediately, adding in some color channel data I collected. The best way I could see to avoid messing up again was to plunge right into using PixInsight's popular Weighted Batch Preprocessing script (WBPP).

Was it easy to use? Yes! If you disagree, I suggest watching the series of WBPP tutorials by Adam Block.

Did it work well with all the default settings? Yes, it did for me. The only step I skipped was Cosmetic Correction. I'll have time to learn how to incorporate CC between now and when I need to process new data collected later this month. 

Was it fast? I fed it my 72 luminance frames, 36 color frames, 100 bias frames, 30 dark frames, and 100 channel flats. WBPP made master frames, calibrated my light frames, and registered and integrated the lights, and finished by doing a crop of all four channels. All that in 51 minutes. Wow!

I know there's some sort of WBPP Fast Integration thing that can reduce this even further, but I'm saving that for the future.

The WBPP result is so much better. Here is the master luminance after post-processing:

Polaris IFN as processed by PixInsight WBPP

The full scale image is on AstroBin. Because Astrometry.net as employed by AstroBin seems to have issues with this, I'll pass along ASTAP's solution:

ASTAP solve of above image.
North is up; the celestial pole is a little beyond the top edge

This is exactly the composition I want: Polaris sitting at top center and giving the illusion of shining its light down on the nebulosity. Which it probably isn't actually doing, but artistic license is allowed, right? 😏

Not only is that ugly vertical banding gone, the stars are better shaped. ASTAP puts the tilt at only 3% ("none") compared to the previous "moderate." I continue to be amazed that so much nebulosity can be captured with less that two hours of total exposure at a Bortle 4 site with a nasty high-in-the-sky first quarter moon.  

The color image was not adequate and you won't see it here. It looked as if the background flattening of the three channels had gone awry. I'll need to play with the color channels and see if I can do better.

The night I collected the color frames give me hope for my camping trip. PHD2 guiding was almost perfect. Of 36 frames, none were rejected. With dithering turned off there were no hiccups. I retrained PHD2 beforehand, this time with the correct focal length for the guide scope, and it seemed better behaved. 

Reacquiring the image area worked great. The evening was the third time I told NINA to go to the target. It seems to be doing this quite well: almost nothing has been lost due to mistargeting: 

Portion of full image removed by WBPP cropping (red)

Everything considered, it all worked as intended. That's a little scary; I have to wonder what mischief my hardware has planned for me when I take it to the dark-sky campground.

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While the tariff wars have devolved into confusion over what, when, and how much, the Rokinon 135 mm f/2 lens for Canon hangs in there at the same old $449. If you've been watching the astronomy gear dealerships, you've probably noticed that many items are no longer in stock. Buyers seem to be rushing their purchases to avoid the expected higher prices.

Integrated Flux Nebula Mini-Test Result

 Let's get right to the image:

Polaris IFN luminance trial

The total exposure was a scant 1.8 hours (72 x 90 s). NINA ran the acquisition and PixInsight handled the processing. Flat frames were used. The nonlinear stretch was the PI Screen Transfer function and no attempt was made to enhance contrast beyond what it provided.

This is so far beyond my expectations that I don't know what to write. It was a not-very-dark site, the moon was at first quarter high in the ecliptic between Cancer and Leo, and there was a thin layer of smoke aloft. I really didn't expect to get much if any nebulosity in the image. But there it is.

The night's goal was to fully test the imaging setup and perhaps answer a few questions:

• Would go-to compose the image reliably? I started it once, collected a dozen frames, shut it all down, parked the scope and did the entire startup again. Plate solving shows the center changed by 67.5 seconds in RA and 7 seconds in Dec. Translating the RA difference to arcseconds at the equator, it's actually more like 27 arc seconds. That's total shift of about 28 arcseconds. The difference in image axis rotation is also tiny, about 0.11 degrees. So the answer is Yes, go-to works very well!
• Would guiding work so close to the pole? I had made some changes in PHD2--activating multi-star guiding and predictive PEC, and using the calibration assistant to make sure that was done optimally. Through the evening it collected 72 light frames, and only one had to be rejected (when PHD2 timed out after a dither). Tracking was next to perfect. I'm nor sure the ASI 2600 benefits much from dithering, so I'll disable it.
• Some people have indicated issues with field rotation when guiding near a celestial pole. I saw no sign of that. Possibly the excellent polar alignment from PoleMaster should get credit for this.

I do like the composition of the image, with Polaris shifted off center northward and looking as if it's shining light down onto the nebulosity. It's nice to see that the offset doesn't produce any significant internal reflection.

There are issues with this image, though. Although ASTAP reports moderate tilt I don't see any evidence of it. (Maybe it's some sort of algorithmic issue?) There are a lot of vertical bands in this that snuck in during the processing. I'll have to find a way to make sure to avoid them. [EDIT 12 May: see the reprocessed image here.]

PHD2 was doing something that seemed odd. Every now and then it would make a too-large declination adjustment and then follow that with smaller corrections. This may also have been my fault as I had the wrong guide scope focal length entered. This has been corrected, so I'll see if that takes care of the issue. 

Tonight I'll be out again to test my RGB acquisition scheme. Basically, I'll try the good old 3:1:1:1 channel ratio, meaning 24 frames for each color channel. How will the colors turn out?