Working on the AL Bright Nebula List

The last week has been amazing for this part of the world in that it's been clear six nights in a row. This has given me the opportunity to get my AL BN list work underway. Here are some of the results:

The Crescent Nebula

The Crescent is a bi-color shot (Ha and OIII) with synthetic green.

The Propeller

The Propeller is a fairly bright and decidedly strange looking nebula.

The Elephant's Trunk

The Elephant's Trunk is a much-imaged object, and this is one of my poorer efforts. Polar alignment was far off and the drift has caused artifacts in the image.

The Cocoon Nebula

The Cocoon is another popular target because the emission nebula at its heart is so bright. This image was composed to emphasize the dark lane (Barnard 168) extending westward from it.

Details for these images can be found on my AstroBin pages.

Most of my AL BN imaging will be in H alpha only. This is because my sky is very bright (urban/suburban) and some of the nebulae are very dim. So far I've been shooting mostly large objects with my AT65EDQ and will soon move on to smaller targets using my C925.

I've started using PHD guiding to do my polar alignment. All in all it seems to work very well, but I've found that the instructions for doing the alignment are generally incomplete. I'll see if after some experimenting I can write up something better.

The AstroBin Voting System

Like many web sites that allow people to vote on contributions, AstroBin has run afoul of troll voters.

Currently AstroBin voters use a 5-point scale. The text descriptions of each vote are:

1. "It's a start, but it needs better data"
2. "It looks good, but it needs better processing"
3. "Good data, good processing"
4. "Great Result!"
5. "Top Quality!"

Each vote is weighted by a scheme that reduces the effects of outliers, and people aren't allowed to vote for their own images. Salvatore Siovene gives of his own time to comb the votes for those cast by dummy accounts. I have only the highest praise for Salvatore and his efforts regarding AstroBin, which is a labor of love on his part. If some parts of it become commercially successful, more power to him!

In a perfect world, everyone votes on an image based on the image's technical and artistic merit. But we all know how difficult that can be from watching judged sporting events such as skating and gymnastics. In a hobby where egos can run rampant there's little hope of ever doing away with votes cast with dishonest intent. Troll voters adapt quickly to remedies; after it was announced that 1-votes would likely bring scrutiny, the trolls began voting 2s, often for images that were clearly excellent.

Another web site I visit has been plagued by troll voting, and many people have suggested alternative systems for legitimizing voting:

• Change to a 1 to N scale, usually with N being a number like 10 (This is much like electronic zoom, it accomplishes nothing)
• Clip the distribution of votes more strongly (Like median stacking, this works well only when there are many votes--usually there aren't)
• Allow only selected members to vote (Aside from not being very democratic, this leads to other problems, such as favoritism)

I gave the problem quite a bit of thought a few years ago and came to the conclusion that the voting system that would work best was a binary one: a 1 vote indicates that you think the image is above average, and not casting a vote suggests you think it's below average. Note that there is no 0-vote. If you don't think an image is very good, you simply cast no vote.

A binary system is imperfect. Ghost accounts can still pollute the voting. While their effect can reduced by tracking IP numbers, they can never be entirely eliminated .

Another failing of binary voting is that the number of votes depends in part on the interest in the target object. For example, photogenic nebulae may get more attention and more votes. If one image gets 100 1-votes out of 500 "looks," does that mean it's a better image than one that gets 5 votes out of 25 looks? Not really. But 100 votes looks a lot better than 5.

At the moment AstroBin is polling its members to see if it should switch to a simple "like" system. This is basically the binary system that I've been talking about, so I voted for the change. Personally, I wish that the poll had included the option to do away with voting entirely.

All of the above, I suppose, explains why I just opted out of the voting system entirely.

Dealing with the Heat

I went to three star parties this summer. While planning for them, I realized they all held the potential to be dangerously hot. Several years ago the Jeffers party had reached a heat index of 117F! What saved us was that the visitor center was open and air conditioned. I would go outside and sit in shade every now and then, but after 20 minutes would have to retreat indoors.

How does one deal with that kind of heat and humidity? The most important thing to do is to avoid direct sunlight. That 117 heat index leaps over 130 and into very dangerous territory if you're not in shade. What I've seen people use at star parties is usually the four-pole canopy. These are nice, but sometimes aren't that sturdy. A strong wind can take them down, perhaps bending a pole and making them useless. For myself I looked for something smaller (and less expensive--it's me, Mr. Cheap). What I found was something from Coleman called the Road Trip Beach Shade.

Coleman Road Trip Beach Shade

It's hard to judge the scale here, but I could easily sit in my chair within the quarter-sphere it provides. The back panel becomes a screen opening to allow air flow, a nice touch. I don't find this shelter the easiest thing to set up, and folding it for storage in its little carrying case is an adventure. Metal stakes are included, which is nice because it needs to be staked down. The biggest con reviewers noted was the fiberglass poles seemed prone to breaking. I've had no problems in two setups and tear downs--but I'm keeping my fingers crossed.

Also, collapse this shelter if you anticipate a storm; If its standing when the winds come, it will be a great wind scoop for a few seconds before it rips or sails off.

$45 from Target.com.

Number two on the must-have list is water. Keeping yourself hydrated is essential, particularly if the air is dry and there's a wind. Get yourself a large water carrier, a drinking bottle, and chug more than you think you need to.

A nice convenience I found was a small 12V fan:

Coleman Ozark Trail Camping Fan

This normally runs off 8 D-cell batteries, but I had an old 12V 7Ah power supply that was perfect for it. Fortunately the fan has a jack built into its side, and I was able to build a little patch cord to connect it to the battery. The battery is a good ten years old, and it kept the fan running on low for 12 hours. It made a nice breeze, even outside. A steal from Walmart for $16.

And no, I don't work for Coleman. I just like their stuff. Stay cool!

Iowa Star Party 2013

Another star party, and continuing poor weather. This was probably the hottest ISP ever. Thursday: high temperature of 94F, dew point temperature of around 70F (heat index = 100F) Friday: high temperature of 97F, dew point of 72F (heat index = 106F) Saturday (the nice day): 91F and 61F, (heat index = 91F) Speaker's talk in the Barn: 86F and 66F (heat index = 88F) That was a very sticky 88! Some relief was found at midday on Friday in the Oakridge house, but unfortunately the A/C unit was unable to keep pace with the heat: it actually froze up. I bailed out around 3 P.M., preferring to face the heat outside where the air occasionally moved.

Friday was also public night, and the attendance was significantly smaller than I recall from my last visit. Between the heat and the fact that it was the opening night of high school football, it's understandable if people decided to be elsewhere.

And how about the sky? Thursday night was grand, although around 1 A.M. the south wind began shoving clouds northward and the southern sky started to deteriorate. Friday night was great for the public, but about the time they left the clouds moved in. The sky went partly cloudy during the early morning, but at 4 when I woke up it was about 50% cloud cover. Visual observers could deal with that, but imagers not so much.

Saturday night usable sky was all of  90 minutes pinched between the end of twilight and clouds rushing southward ahead of thunderstorms. It never cleared for any substantial time after that, and in fact around 3 A.M. a thunderstorm with heavy rain and gusts to about 44 mph (at Carroll) hit us. From what I saw the next morning no one sustained serious damage from the winds, although a couple of screened sun shades looked like they needed some repair.

Yes, imaging time was scarce, but I managed to get three objects in. Thursday night started with M8 and surroundings:

Messier 8, the "Lagoon"

Click this for a larger version. There are a number of objects here, not just the big old Lagoon. At lower left is globular NGC 6544. At about 10 O'clock from the lagoon and next to a bright double star is the pretty reflection nebula IC 5070. On the left edge of the picture about 1/5 of the way down from the upper left corner is emission/reflection nebula IC 4685. The lagoon itself is a confusing construct of NGC objects.

At this point it was a bit before midnight, and my sense was I didn't have much "awake" left in my tank. Some years ago at Jeffers I'd imaged M33 with my DSLR and TV102, so I  thought I'd try it here with the AT72ED and CCD. Here's the result:

Messier 33, the "Pinwheel"

The AT72 is really too short a scope for this object, but it was the scope at hand. I'm not happy with the color balance of this; judging by the star colors I'd almost say that the green channel is too strong. I'll doubtless reprocess this.

Friday night was clear for a while, and I was able to learn my target's star field while entertaining/educating the public. I  think I collected one frame before having to shut down.

Saturday I raced from the meeting barn to the observing field and was able to get everything running and my target composed in under 30 minutes (a not-so-minor miracle). In fact, I even had to toss my first light frame because it was still twilight. about 90 something minutes later it was over. The NA and Pelican are bright!

Nebulae NGC 7000 "North America" (left) and  IC 5070 "Pelican" (right)

Don't know why the stars bloated so badly in this one. Poor focus, most likely.  Clouds rolled in while there was still plenty of time for another image, so I count this as half a night.

Details for these images, along with their full-size versions can be found on AstroBin.

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The last year's star party log sheet runs like this:

HOASP (Autumn 2012): three nights of rain.
WOW: Registered but did not attend; I would have had one good night at best out of three.
Jeffers: 2 good nights out of 3.
South Dakota: 1 out of 3.
Iowa Star Party. 1.5 out of 3

Add those up and it was 5.5 good nights out of 15. Disappointing. Perhaps this autumn will be better? If it is, I'll probably be making more runs to the club's dark-sky sites. Stay tuned.

M 31 from the South Dakota Star Party

New dew controller in hand (see last entry) I was ready for the South Dakota Star Party. I had a short list of targets--The Iris Nebula, the Lagoon Nebula, the Heart Nebula. The one chosen would depend on the sky conditions. So much for plans.

Thursday night was partly cloudy with heavy dew and fog. I stayed home. Friday night started with high clouds, but went mostly clear as twilight ended. The view to the Lagoon was full of light from Sioux Falls, which was only about 15 miles away. I decided on the northern sky. I did a bore-sight polar align and tried to start with M 103. I switched over to M31 because I wanted to image something prettier. I got everything set up and running, but the first few frames were bad because the autoguider was losing the guide star in the remaining cirrus. There was a bright star at the edge of the autoguider's FOV, so I used that instead.

I set up the camera control to shoot five lights through each of the LRGB filters and then loop. That was at about 11:30. Amazingly, the system continued to run unattended for almost five hours! Focus held steady all that time, and tracking remained solid on all but one frame.

In the end I had to toss 25 frames because of clouds, one for tracking, and a couple because satellites passed right across M 31. Here's the result

Messiers 31, 32, and 110

Click for a larger version. Visit Astrobin for image details and a full-scale version.

I know the cores are overexposed, and maybe I need to do something about the blue fringing on some of the stars, and maybe I left it all a little dark. But I think I like it. Thank goodness I didn't cut the imaging short to chase after another object.

Dew controller and image noise

Well over a year ago I began noticing bands of noise on my images. Here's an example:

Stretched Light Frame showing noise band

And here's a patch of it at full scale (look just below the nebulosity). The appearance of the band will vary from frame to frame, but it's always a horizontal strip of hash. Longer exposures have more bands. Here's what it looks like at full scale:

Noise band at full scale

When that band covers your target, it overlays a great deal of noise that is difficult to remove. ImagesPlus noise removal reduces it, but you can be left with a light band.

I could not figure out what the source was. At first I thought it might be AC line noise (I was running using AC power). Moving to battery power didn't get rid of it. Bad cables to the CCD were suggested by others, but lots of cable swapping didn't fix it. Maybe it was the CCD camera itself? Online searches didn't suggest the camera had any problems like that. I did see some implications of interference from other devices being powered by shared batteries, so I isolated the CCD. The noise remained.

This was an intermittent problem, however. I didn't tumble to the cause until last week at Jeffers, while I was imaging M20/21. Almost every frame was noisy. For some reason I turned off the dew controller, and like magic the noise was gone. I imaged M17 the next night with no dew control (it wasn't needed) and every frame was free of the noise.

A more directed online search led me to a comment about the controller I use, the Model VI:

The Culprit: Kendrick Model VI

I immediately launched into more research and was happy to learn that Kendrick made an RFI-free controller that was in my budget range, the Standard Dual-Channel Controller (SDCC). $114 and shipped free from Astronomics.

The Solution: Kendrick Standard Dual-Channel Controller

A night of imaging with the SDCC keeping everything dry produced images that were all RFI noise-free.

If you're imaging and seeing a lot of horizontal noise bands, it may be your dew controller.

Two images from last weekend: M17, M20/21; Processing workflow.

I'm REALLY pleased with how this image of M17 came out:

Messier 17 (Omega or Swan Nebula), click for full size

The previous night's image was not quite as successful--M20 and 21. More about why in the next blog entry.

M20 (Triffid) and M21

Both images are full-frame. For all the gory details of acquisition, look at my gallery on AstroBin. By way of a quick summary, both are LRGB images made with an SBIG ST8300M CCD, TeleVue 102 apo and autoguided CGEM mount under mag 6+ skies. Dark and bias frames only, no flats.

Imaging is SO much faster doing LRGB in the dark than it is to use narrowband filters under light-polluted skies. 

I realize that the colors in the M17 image may look a little muted to you, but I kind of like them this way. What's particularly pleasing about the image from my standpoint is three-fold: The stars are nice and round right out to the edge of the field, meaning that my field flattener is doing its job perfectly; The merging of the LRGB channels seems to be spot-on. And finally, guiding with the Orion mini-guider works great at the 700mm focal length of the TV102 to correct mount errors. I'll eventually try out the mini on my C925.

My processing workflow continues to evolve. These two images were made by ping-ponging back and forth between Images Plus and Photoshop:

• Calibrate, align and stack using IP
• Stretch using PS
• Noise cleanup and star size reduction in IP
• LRGB combine in PS using Annie's Actions
• Color balance in IP
• Masked sharpening in PS

Yes, I know that's a mess, and some will say that all can be done in IP or PS or Maxim or whatever. Good for you if you can function with only one software package, but at this point I can't. I'm using IP 4.5, so probably some of the changes that have gone into later versions would make it a better processing tool.