First Pass at the Veil Mosaic

I finally had enough data to make a very flawed Veil mosaic. Here it is at 1/5 scale:

Click for 1/5 scale image

And here is the link to download the full-scale image. You can use the cloud site's .jpg to look at it, but I suggest you use your own image viewer. Minor advisory, this is a large image, about 10K by 10K pixels and the file size is 12.5Mb.

You should immediately see some interesting things in the full image, some of which I'll detail here. I'll start with the major flaws (all the images below are at full scale if you click on them).

1) What's the big circular thing?

Bad Flat!

This is in the upper left mosaic panel, and results from improper calibration (using an outdated flat, rookie mistake.)

2) What's all that noise?

So Noisy!

Again in the upper left mosaic panel and comes from not only the poor calibration but also insufficient data.

3) What's with all the black pixels?

Pepper Spray

This is found in the upper and middle left panel; it results from pushing the panel a little too aggressively in one post-processing stage.

4) That green thing can't possibly be right!

Streaks to Left of Center: Not Really Green!

So far as I know there aren't any green nebulae. For reasons I don't understand this feature shows up rather strongly in the green channel compared to the red and blue channels; it's quite strong in luminance. I've seen one other LRGB image of this area, and it didn't have these green bits, so I must conclude something in my processing is at fault here.

The Dastardly 52 Cygni

There was one other flaw I had to skate around. I used the script Star Reduction from Blanshan and Cranfield to perform star reduction. It requires a starless image; this can be made either using StarXTerminator (aka SXT) or StarNet2. I used SXT, and it had a lot of difficulty with Magnitude 4.2 52 Cygni (see above image). It essentially suppressed the northern end of NGC 6960! So I switched over to StarNet2 and it handled things fine. 

Notice that StarNet2 didn't handle it 100% cleanly either, giving it what look like (but aren't) diffraction spikes. Looks kind of cool, I think, but then I grew up as a Newt user.

Now for some positives:

1) No seams. I used Photometric Mosaic, and not only didn't it produce seams, but it avoided the pinched stars that GradientMergeMosaic plagues me with. 

2) Color calibration by SpectrophotometricColorCalibration (SPCC). I can't say enough positive about SPCC. My old workflow made color correction very fiddly, with the result depending on how I felt the day of processing more than any sort of objective measure.

3) Not narrowband. For good reason the Veil is usually imaged in narrowband, but that results in false colors. It's nice to see things more as they "really" are (aside from a Green nebula).

4) Not oversaturated. In my opinion oversaturation is very common now. I've said before that a guiding principle of processing should be that less is more; this idea applies to sharpening, stretching, and also color enhancement. I did bump this a half step using ColorSaturation, but pushing it further seemed like too much of a good thing.

5) Reasonably sharp. Here's a neat feature at the south end of of the East Veil. This looks good thanks mainly to BlurXTerminator (BXT). In fact, aside from the one issue seen in SXT, I think the triad of BXT, SXT, and NoiseXTerminator (NXT) is difficult to beat.

An Optical Spiral That's Probably Not a Real Spiral

   

I suspect this curly-thing at center is nothing more than an undulation in a plane seen edgeways, but it does look fun.

So, with those issues listed above this thing obviously isn't done yet. The other night I shot additional light frames for the two panels that suffered from noise (along with same-night flat frames), and I think I can make sure that pepper spray of black pixels can be avoided.

This means doing much the processing over again, but that's life.

Iowa Star Party Imaging

I'm back from the Iowa Star Party! This is held each year at Whiterock Conservency; the observing field is located about five miles southeast of Coon Rapids, and 60 miles from the center of Des Moines.

2024 ISP had some differences from my previous attendances:

• This year's October party was much more pleasant than the steam baths provided by the usual summer dates. Every night had nice cool sleeping weather for us tenters
• The usual evening banquet wasn't prepared on-site and served in the picnic area; instead it was catered and held indoors at the very comfortable Bur Oak Visitor center. It was moved to lunchtime so that it wouldn't interfere with public night. The earlier time also allowed us to be at the field well before dark
• The field was in great shape, and the addition of a modern bathroom / shower facility was very welcome. I had the distinction of setting up farthest from the bathroom, so it was easy for me to get my daily steps in!
• Saturday night was clear, but the high winds during the day put a lot of dust in the air and really enhanced the brightness of local light domes, which have grown much more prominent in recent years. The low, very dark southern horizon may be thing of the past

But let's get to the imaging.

Friday night I was all set up, polar aligned, and ready. First target was Panel2 of my Veil Nebula mosaic, and the scope was doing its slew, center, and rotate thing. But it never finished because something was causing it to throw errors related to the mount control. 

The usual power cycling didn't clear it. What followed was several hours of swapping cables in and out and trying every other remedy I could imagine. Eventually I started to get the sense that the problem was my Pegasus Powerbox, so I recabled everything to remove it from the USB data flow (it remained acting as a 12V power hub, though). This worked, but it left me with no way to power and control my dew straps. Thank goodness it was as dry as it was, dew prevention was not needed that night or the next. 

To confirm where the fault was, I ran a USB cable to the Powerbox but did not connect anything to its output USB ports. The same errors returned suggesting that simply having the Powerbox as an active USB device was enough to cause the problem. 

I've read that the Powerbox can be harmed by connecting a 12V input line to its Adjustable Voltage port, and I know I've done that at least once recently. The poor Powerbox may have run afoul of Stupid User Error and had finally given out at ISP. Bummer. 

Anyway, I was up and running again and was able to collect light frames for my Veil mosaic.  I got everything I needed for Panel 2 Friday night, along with luminance for Panel 3 and a full set of flat frames. Saturday night I collected RGB for panel 3, along with some frames for the odd object seen in Panel 6 data.

Here is the Panel 2 LRGB result (click to see 1/4 scale version):

Panel 2 (NGC 6974, 6979, Pickering's Triangle, and the northern tip of NGC 6960)

Here is Panel 3: 

Panel 3 (NGC 6995, IC1340, and the Southern Knot) 

I've started to work on the full mosaic and noticed that my Panel 1 luminance frames were badly flatted and need to be reshot. If I can manage that this week, next time I'll have a first attempt at the full Mosaic!

Mosaic Detours and a small surprise

 The mosaic is coming along, but there have been several detours along the way.

That difficulty I had with my guide camera resulted in too many bad frames in two of the panels' luminance and red frames. Why those two channels?  I think it's mainly because of how they fall in the filter sequence, but it could just be chance. These will need to be reimaged, meaning no finished mosaic until later this year.

Something was wrong with my luminance flat frame, too. It was leaving a large light circle in the calibrated images:

Lacking a time machine that could let me reshoot the flats as they were at the time the light frames were collected, I opted to create a synthetic flat of sorts by using PixInsight's ABE. This worked well enough, leaving only a few dust motes to be cleaned up by CloneStamp.

One last issue was a sort of swiss-cheese texture produced by the script StarReduction and by StarXTerminator. This was minimized using CurveTransformation twice: first to reduce the brightness difference between the "holes" and the "cheese," followed by a mild stretch to de-emphasize the background.  You could probably use a masked application of MLT to deal with it, too.

Here's a comparison between the starry original and the final reduced star version

Before

After

Vastly better, I think. Here is the portion of the workflow that is used to take luminance from star-filled linear integrated to nonlinear with fewer and smaller stars:

1. Open the original calibrated, aligned and integrated image (it's still linear at this point)
2. Delinearize the original using STF and HT, save as "NL"
3. Open StarReduction script, set target to NL and click the "Generate starless view" button. If you have both StarNet2 and StarXTerminator installed you'll be asked which to use and what options there are for it.  (I used StarNet2 with a 2x upsample.) When that's completed, close StarReduction and save the new starless image as NL_Starless
4. Enhance NL_Starless as you see fit. Certainly make cosmetic repairs. I sharpened it with MLT using layer biases (layer 1 = -0.2, layer 2 = -0.1, layer 3 = +0.15) Save the result as NL_Starless_Enhanced.
5. Reopen StarReduction, set target to NL, starless view to NL_Starless_Enhanced. Choose the reduction method and any associated parameters, and write them down so that they can be used for the other panels. (I used the Transfer method with a scale factor of 0.1) Check "Create new star reduced image" and if you want to use PixelMath or some other means of combining the stars and starless data check "Create 'reduced stars only' image".
6. Click the green checkmark to apply. Save the resulting image as NL_ReducedStars
7. If your image suffers from "Swiss cheese", deal with it now. Save the result as NL_Done. 
8. This isn't actually "done done." It will need cropping and normalizing before it becomes part of the luminance mosaic.

The settings you choose for MLT sharpening, StarReduction, and possible 'cheese' removal will depend on many factors, so play with them to see what what works best for you. It's probably a good idea to create and save process icons once you've found settings you like.

Lessons learned: Shoot flats ASAP after imaging. Inspect light frames ASAP after imaging to see what you collected.

-----------------------

Here's the surprise in panel 6 containing the southern portion of NGC 6960:

Panel 6, luminance, starless version

Look in the lower right corner, that thing that looks alike a ball on a stalk. At first I thought it was an artifact, so I looked at other images on AstroBin. I couldn't find it in any of the images there. Astrometry.net didn't ID it in a plate solve, either, so I went to NINA's Framing Assistant where I could quickly see the area in several surveys. This is what it looks like in the downloadable image files:

Panel area from NINA

And there it was. It shows up in the Nasa Sky Survey and HIPS 2, so it's real and not an artifact. But what exactly is it?  I processed my color frames and got this:

Panel 6 RGB composite

It's got a bluish tinge to it, so my guess is that it's a very faint reflection nebula. So far as I can find it doesn't have a designation. Is there anyone out there who can ID it?

Mosaic Workflow

I've been working on my Veil Mosaic project and here is the first tentative result, the luminance mosaic:

Original Luminance Mosaic

The full scale version of this is 10257x9687 pixels in size! This has a number of issues, but it really was just an exercise in stitching together six panels. That part worked flawlessly. The main issue I have with this is the stars. There are just so many of them that they obscure the nebulosity. The other issue is how to extend my workflow to incorporate the chrominance channels and deliver a full LRGB mosaic.

Most people suggest building an LRGB mosaic from channel mosaics, so that's what I will do. As for the mosaic-building tools, advice is mixed with most people indicating a preference for GradientMergeMosaic. My experience with GMM has been disappointing; many of my images include dense star fields, and GMM has had problematic issues with stars at the edge of panels. Instead, I'll use PhotometricMosaic.

The workflow might go something like this for each panel/channel combination, although the last two steps operate on channel or panel groups. It's assumed you've already created master frames for dark, bias, and flat frames.

1. Cull bad images from light frames (Blink)
2. Calibrate light frames (ImageCalibration)
3. Clean up residual hot pixels (CosmeticCorrection) 
4. Assess calibrated frames for quality and select reference frame (SubframeSelector)
5. Align light frames (StarAlignment)
6. Integrate light frames (ImageIntegration)
7. Sort all the resulting frames by panel; for each panel group use DynamicCrop to insure all the channel images for a given panel cover the same sky and have no edge artifacts from dithering. This insures the channel mosaics have identical dimensions and won't require aligning.
8. Background correction (ABE, DBE, or both)
9. Reduce noise (NoiseXTerminator)
10. When all this has been done, sort the panels by channel. If you're archiving images, this is a good time to send all the intermediate products off to storage, they're no longer needed. Only the images from step 9 will be needed.

Because the luminance images will become pseudo-masks for chrominance they need extra attention. Do these steps for each luminance panel:

1. Create a starless version (StarXTerminator or StarNet2, both have strengths and weaknesses)
2. Enhance the starless image (MultiscaleLinearTransform, UnsharpMask, NoiseXTerminator, etc.)
3. Reduce star bloat (StarReduction), apply the same reduction to all luminance panels.

Care should be taken to insure all the enhancements and applications of StarReduction are identical. This is an opportunity to learn how to use PI Containers.

Within each channel, normalize the images using LocalNormalization. The hope is that LocalNormalization will deal with background disparities and that the splining of PhotometricMosaic will make any remaining issues imperceptible. 

Next, create the channel mosaics by repeating these steps for each channel. 

1. Plate solve each panel (ImageSolver)
2. Register each solved panel (MosaicByCoordinates)
3. Merge the panels (PhotometricMosaic)
4. Reduce noise again (NoiseXterminator)

After you've done all four channels you're ready to combine them all as you would any single LRGB image. 

Taking the channel mosaics nonlinear requires you to try to stretch them in roughly the same manner, perhaps starting with the luminance mosaic and applying that same stretch to each of the chrominance channels. PI lets you do this using the STF process. Having done that you're ready to combine the channels and get on with color balancing, etc.

Notice I'm not using the usual PixInsight noise reduction and deconvolution processes. I think NoiseXTerminator provides superior noise reduction and the PixInsight Deconvolution process? I have never had any real luck with that thing. If your stars are round you're better off using StarReduction, which works exceedingly well and is free, too. Here is a too-quick application of StarReduction:

One pass of StarReduction

This image shows the effect of a single pass of StarReduction. There are a lot of blockish artifacts in this resulting from StarXTerminator being applied to the mosaic rather than individual panels.

With this workflow now defined I can get on with the processing!

Panels and Pieces

September update with shouting headlines:

GUIDING WOES SOLVED!

After an August imaging session that featured repeated guide camera disconnects I decided that it was time to move on from my QHY5L-II. I'd read somewhere (CloudyNights?) this was one of its traits. Disconnects have been a repeating problem during its service to me. There have been nights I've retreated to my good old StarShoot Autoguider.

I had tried to work with the camera. It seemed as though the issue was insufficient power, so I used shorter and shorter USB cables, then a powered USB 3 port and a very short cable. The disconnects became less frequent but imaging time was still being lost. 

Something had to be done; I can tell you that it is not fun fussing around at 2 or 3 AM trying to get things going again after a disconnect. So I went all-ASI and purchased an ASI 120MM Mini (mono). My only qualms about the Mini were possible software collisions with my imaging camera, an ASI 2600M, and if it would be compatible with the QHY mini guide scope.

The only camera confusion was mine when I gave PHD2 the wrong camera to use. The ASI120 seems to work well with the QHY mini guide scope, although it may need a little more backfocus. And during an evening of imaging not a single disconnect, so for the moment I'm declaring problem solved. I may swap out the QHY guide scope for my old Orion 50mm guide scope, just for the added aperture.

MOSAIC DATA COMPLETED!

My ~57 megapixel mosaic of the Veil nebula has taken long enough, hasn't it? Panel 1 (of 6) was imaged June 19. Panels 2, 3, and 4 were imaged August 25 and September 11. The final panels, 5 and 6, were imaged September 17. The long summer delay was thanks to smoke, air quality, heat, clouds, and my availability. It's been a summer. 

I don't yet know how good the light frames are of these but they will have to do. Each panel is made of approximately 48 minutes of luminance, and 24 minutes of each color channel. This means it's not particularly deep, but this is the Veil Nebula and hardly the dimmest object in the sky. I could collect more data, but I'd like to move on to other targets.

DISASTER AVERTED, TWICE!

This is how my night imaging the last two panels started....

Disaster #1: The dew strap for my FSQ's objective had a short that I first noticed as a wild variation in the Pegasus Ultimate PowerBox current. It was hopping between a low, reasonable value and 4+ amps as it tried to control the situation. Its control probably prevented the Powerbox's demise, a meltdown of the strap's cable (it did become too hot to touch) and perhaps even damage to my AC to DC power supply. 

Disaster #2: Without the dew strap imaging could last only until I saw dew beginning on the imaging scope's objective. I hoped I'd be able to get at least one of the two remaining Veil panels done but it seemed doubtful. There was no breeze to keep the ambient temperature from cooling rapidly and because I was imaging almost straight up the objective would probably dew quickly.

Maybe it was convection from the power supply and the cooled imaging camera or just plain good luck but it somehow stayed dew-free for the time required to get both panels imaged.

NEBRASKA STAR PARTY 2023: SMOKE AND CLOUDS!

Okay, I didn't attend. I'll sit in judgement of it anyway, partly to justify my staying home but mainly to question the wisdom of traveling to distant places for imaging. Which is not to say I won't go next year, if someone could do something about all that smoke. As for the heat--it's not NSP without a day or two of 100-degree temperatures or hotter, is it?

Here are the day-by-day NSP 2023 imaging conditions as gleaned from the weather service and air pollution monitors.

Saturday Night: red category air quality and terrible transparency. I'm of an age that puts me in the group the air quality people always caution about being active when the air is this bad. We had a couple of days this summer where I live that were as bad as this and the surface smoke was so thick that it looked like a thin fog. Setting up camp was not something I'd have wanted to do in red air. And of course, with the smoke the greatly reduced transparency for imaging negates the point of going someplace dark like NSP.

Sunday Night: Saturday night all over again.

Monday Night (First "official" night of NSP): Clouds and a thunderstorm.

Tuesday Night: Probably clear from Midnight to 2 AM, then rain around 3 AM. Very humid (dew point temperature near 70 degrees) so super uncomfortable sleeping in a tent on the observing field.

Wednesday Night: Partly cloudy all night. 

Thursday Night (my last night at NSP had I attended): Partial clearing around 12:30 AM, then partly cloudy until 3.

So maybe a couple of hours of imaging Tuesday night and again Thursday night; for maybe a total of four hours of smoky sky imaging across six nights. Add to that unhealthy air quality on two nights.

Some years NSP can be a fun vacation in the wilds of Nebraska with very dark sky. Some years not so much. If the wildfire smoke becomes an annual problem NSP will difficult to justify as a travel destination.

On the other hand, with summer smoke affecting most of the region, where else would you go?

That's all for this dramatic update!

The Start of a Mosaic

It's been kind of wild since the last post. We've had many days of air quality alerts, most of which have been for excessive surface ozone, a byproduct of smoke and sunlight and "normal" air pollution. Smoke at times thickened to concentrations similar to what was seen earlier on the East Coast. It wasn't healthy at all; hospitals reported a surge of people with breathing difficulty.

The air quality did improve for a bit and I was able to get out and do a little imaging. In fact, I managed to start one of my learning projects!

One item on my to-image list is a mosaic of the Veil Nebula that spans both the east and west sides. The Veil isn't immense like Barnard's Loop, but it's large enough to require something like a 250mm lens to fit it all in a single frame. My FSQ-106 has a focal length of 530mm and it really needs something like a 2x3 mosaic to encompass the Veil. That's 6 frames, and at about 2 hours exposure time for each it will make a good summertime project that could last into September.

Despite the ever-present smoke I was able to collect the data for subframe 1 which includes most of the East Veil (NGC 6992) and the Network Nebula (NGC 6995): left click the image below, then right click the enlarged image and choose "Open Image in New Tab" to see the image at 1/2 scale:

 

 

For fun, here's a try at a starless version using StarNet2 in PixInsight:

 

This is LRGB with all exposures 120s, L = 20 lights, R = 11, G = 12, and B = 12.

I think I dark-clipped this a little in my processing haste, but it will get another processing eventually.  Here it is tucked into its place in the eventual mosaic:

 

6995 is in the overlap area between subframes 1 and 3. The next target will be subframe 3 to complete the Eastern Veil and give me some practice using PixInsight to create a mosaic.

Some other tidbits from this too-rare night of imaging:

• The QHY-5II guide scope was flawless with over two hours of guiding without a single disconnect. It really does need USB3, it seems. 
• Not only that, but tracking errors were limited to 2 frames in 58. A rate of 1 bad frame in 29 is a lot better than the 1 in 6 that I had experienced earlier this year.
  
• NINA's Advanced Sequencer finished subframe 1 and started subframe 3 imaging without any attention on my part. This was the first time I had tried this. I wasn't willing to do another two to 3 hours of imaging so I reluctantly shut it down at that point.
• More NINA: Its mosaic feature is nicely integrated into the Framing Assistant and sets up the Advanced Sequencer for all the subframes with simplicity.
• Even More NINA: If you want to use the Framing Assistant with images while you're someplace without Internet, go to the NINA download page and grab the Offline Sky Map Cache file (2 GB) It replaces the existing cache folder AppData >  Local > NINA > Framing Assistant Cache. Don't forget to change the Framing Assistant Screen's Image Source setting to Offline Sky Map! Incidentally, installing this allows you to zoom out and use Framing Assistant like a (rather strange) planetarium.
• I seem to have gotten the hang of PI Deconvolution. I don't know why it was so temperamental before, but the key seems to be in the Deringing settings. A Global dark of 0.03 to 0.02 seems to work well, with Global bright typically between zero and 1/2 of Global dark.
  

 

Back from the 2017 Nebraska Star Party

Ah, to be back in the land of 10,000 lakes and high dew points!

NSP 2017 is over, and it was a memorable one. Sunday (7/23) was clear and about as good a night as I've ever enjoyed at NSP--or anywhere, for that matter. The day had been in the low 90s, but the temperature dropped quickly as the sun set. There was a strong and gusty breeze that kept the mosquitoes away. (I realize big scope owners didn't like the wind, but I was imaging with a 200mm lens wildly overmounted on a CGEM.) The transparency was exceptional overhead; the Milky Way was nothing short of spectacular.  I don't think you could read by its light as one person predicted, but it was definitely casting a subtle, diffuse shadow.

I was able to collect some light frames of my current target, the Rho Ophiuchi Cloud Complex, then switch over to the Sadr area for the Butterfly:

The Rho frames have yet to be processed. The next night I decided to spend the entire night imaging the Veil:

What I like about this 200mm lens is how flat it is at f5.6, and free of vignetting.  There are two new things about these images:

1. Instead of stopping down the lens with its internal iris I used a step down ring. This gets rid of the diffraction spikes caused by  the blades of the iris.
2. I used PHD and BackyardEOS to dither the images.  It seemed to work very well!

The last night was cut short by clouds, so I only got five frames of the Rho area at 135mm:

As you can see, this lens has substantial vignetting.

By the way, 2017 NSP was on the hot side.  The Monday and Tuesday highs were 106 and 107 degrees, respectively. But it was the usual "dry heat" and both days had those great strong breezes.  I spent the afternoons sitting and reading semi-comfortably in the shade of the supper area canopy. Thank goodness NSP didn't happen the previous week when it had been both hot and humid.

Now it's on to eclipse planning and back to meteor counting!