Wednesday, November 4, 2015

Pacman Nebula, NGC 281

Pacman Nebula. 12.3 hour exposure captured on Sep. 7th, 13th, 15th and 17th, 2015.
Full resolution image with acquisition and processing details here.

After eight months of persistent cloud cover, coastal Virginia finally had a week of clear nights in September and I was imaging for most of them. The Pacman Nebula was my main target and I became determined to push 10 hours of total exposure on this target. Since most of these nights were during the workweek,I was a tired mess by the time clouds returned so I had no idea how much I actually collected until weeks later. I met my target and accumulated over 14 hours of subframes, though I ultimately tossed about 2 hours due to passing clouds and contrast degradation as the nebula slipped below 30 degrees altitude into the light dome to the west.

My choice of sub exposure duration (500 s) was an experiment to see what happens when the histogram background peak lies around 40% rather than 33% as is commonly recommended (i.e, sort of an “expose to the right” methodology). Plus, this was the first time I used an IDAS-D1 light pollution filter which necessitated longer exposures. That filter, by the way, worked exceptionally well at increasing contrast with the subject given my light pollution environment. It is a keeper. Anyhow, even though these longer sub exposures ensured the nebula signal was adequately sampled, the consequence was that several brighter stars were saturated so I worked in post processing to shove color back into the cores. I had intended to revisit this target with shorter exposures to better capture the stars, but the moon, clouds and enticement of other targets has led my attention elsewhere until next year. My conclusion from this experiment? I will probably lower my sub exposure time at my suburban imaging location.

The integrated image had quite nice SNR, comparable to what I have seen from 2 hours of integration time at a dark site. Let’s put that into perspective: 12 hours in suburbia versus 2 hours in the boonies. Argh, where is my free lunch?

In linear post processing, I followed David Ault’s excellent M42 tutorial for deconvolution and noise reduction (link below). His tips on mask generation for those processes contribute immensely to their success. This was also the first time I achieved good results with deconvolution which always made a mess of things in the past. For this image, it sharpen everything subtly which trickled to downstream processes without ill effect. Also, David’s linear noise reduction techniques worked marvelously. Usually, I struggled with noise reduction in the linear stage and pushed it off to ACDNR after non-linear steps. Here, it reduced noise effectively and I did not bother with any further noise reduction down the line.

I really didn’t push the processing too hard with this one. Even though the integrated image had good SNR at the onset, once I subtracted the light polluted background, the object SNR was on shaky ground. So, I just stuck to a basic histogram stretch and then micro-contrast curves to accentuate details in the nebula. I tried to not push the color saturation of the nebula too hard either, otherwise it would become monochrome red when in reality there is a bit of blue-green hues towards the middle due to OIII emission. I’ll need to add some OIII data to pull that out of this data. Another struggle was the mess of stars in this field of view which I shrunk slightly. I didn’t want to shrink them too far since most of the color was in the star halos and the cores are saturated. I think I struck a good balance.

Altogether, I am satisfied with the final image. It was worth the late nights and grumpy trips to Starbucks the following mornings.

Close-up of Bok globules and interesting morphology.

Sunday, October 25, 2015

Open cluster M103 in Cassiopeia

M103, open cluster in Cassiopeia. Total exposure 90 minutes (18 x 300 sec) at ISO800. IDAS-D1 filter.
Here is my image of the open cluster M103 in Cassiopeia that I captured on September 14th, 2015 as a break from the week long streak of clear nights where I banged relentlessly away on the Pacman Nebula. This was the first time I tried out the IDAS LPS-D1 light pollution filter on a star cluster and I am very pleased with the quality colors that are retained while noticeably suppressing background brightness.

I always prefer diffraction spikes on star cluster images, so I used braided fishing line taped to my dew shield to produce those seen here. I have experimented in the past with different thickness mono filament fishing line and I have yet to find one that I really like. In all cases, and including here, the diffraction spikes broaden with distance from the star and produce rainbow colors. It's kind of a neat effect, but I'm not sold on it. In the future I will try metal guitar string instead.

It took time to figure out the best framing for this cluster because a wide view makes it difficult to figure out what you are supposed to be looking at (i.e., the subject) and too close of a view makes it hard to recognize that this is a cluster rather than just a picture of a bunch of stars. I think I found a good balance here. Just for kicks I tried off-setting the cluster to the lower left or upper right following the rule of thirds, but no orientation had other bright stars that would lead the eye to the cluster and again the subject was lost. In the end, it just made sense to position M103 dead center. Sure, that's a lot of thought for a simple star cluster, but it is good practice for any image.

Full resolution image here:

Monday, October 12, 2015

Dark night out with the Bubble Nebula and my new QHY5L-II

Finally had a chance to image in some dark skies last night! A sudden break in the rain prompted a last-minute observing session at the NASA Skywatchers dark site, on a holiday weekend no less. It was nice to see the dust lanes of the Milky Way again and man the stars were bright! I've been imaging out of my driveway all this year while settling in with a new youngster so it was a treat to see the real night sky.

Despite some guiding challenges, I captures just over 2.5 hours of eight minute subs of the Bubble Nebula and neighboring M52. Here is a first look without darks, bias or flats and just a quick 20 minute processing. Not bad for a night’s work! I plan to capture another 2 hours at least on this object at the Staunton River Star Party next week to really drive it home.

I am happy to report that my new QHY5L-II autoguider worked exceptionally well. The sensitivity is noticeably higher the SSAG so I had plenty of guide stars to choose from. Plus, no horizontal banding noise like my SSAG. Did it improve my guiding? Well not entirely. Most if my concern is high frequency movements at every guide cycle. I was able to tame the declination oscillation by reducing the dec aggressiveness and increasing the min motion. Similar adjustments in RA only helped so much; there was still a lot of wiggling going on even with an east heavy bias and guide exposures of 2 seconds. I am now wondering how the quality of my guide scope impacts the guide star centroid calculation. I’ve always noticed a halo around stars in that scope so I wonder if that is a factor. Some more troubleshooting I suppose. Autoguiding is a finicky thing.

In the meantime, gear is packed for the Staunton River Star Party this weekend...clear skies are in the forecast.

Saturday, October 10, 2015

Upgrading guide camera. Goodbye, SSAG...Hello, QHY5L-II.

For a while now I have been troubled by the strong horizontal banding in my StarShoot Auto Guider (SSAG). These bands appear when the gain is set to 95% (default value) in PHD2 and turn into a checkerboard pattern at gains near 10%. Here is a PHD2 screen capture of a SSAG dark frame showing the horizontal bands.

SSAG dark frame. 0.05s exposure @ 95% gain.

To compound the problem, the bands shift up and down slightly, so dark frames do not help because the pattern is not consistent. Not all SSAG users report on this issue, but those who do have narrowed it down to either excessive USB cable length or sensitivity of the camera to high frequency noise in the computer USB port. I did my own detective work and found the same issue on all USB ports on two computers and with three different USB cables, so I never found a way to resolve the issue with my current hardware.

If the problem were benign, I would not worry. However I have noticed consistently that the movement of these lines affect the centroid calculation of my guide star when autoguiding. Since my image to guide scale is nearly 3:1, this causes unnecessary corrections at every guide cycle as evidenced between the correlation between horizontal band movement and the guide star profile. In short, I am convinced the centroid follows the bands.

After much thought I have decided to move on to a new autoguider. Today, a brand spanking new QHY5L-II monochrome planetary/guide camera just showed up my home, courtesy of OPT Corp and the money I raised by selling an old telescope. This autoguider comes highly recommended due to its small pixel size and sensitivity. After following the advice of folks on Cloudy Nights to install the high compatibility driver from QHY, the camera worked perfectly with PHD2 (Ver. 2.5). I am relieved to see that horizontal lines are not present in the dark frame:

QHY5L-II dark frame. 0.05s exposure @ 95% gain.

I have not tried the autoguider functionality of QHY5L-II just yet since the purchase of new gear always brings clouds - especially near new moon. Until then, this looks to be a promising upgrade to an essential piece of gear. As for my SSAG, it will serve as a nice camera for outreach events.

Tuesday, October 6, 2015

Lunar Eclipse Montage - Sep. 27-28, 2015

Here is a montage of the best images I captured during the last half of the lunar eclipse on September 27-28, 2015. It’s amazing I was able to observe this much given the persistent cloud cover that night. It was tricky to determine the correct exposure while it changed dramatically during brief windows through the clouds. Somehow I managed to pull off enough images to make this sequence. For that, I am thankful.

Ok, moon. You've had your get lost so I can go back to dark sky imaging!

High resolution version (Astrobin)

Exposure details (all times EDT):
Total eclipse:
11:03 pm: 2s, ISO800
Partial phases (clockwise from lower-left):
11:45 pm: 1/20s, ISO100
11:59 pm: 1/50s, ISO200
12:08 am: 1/50s, ISO200
12:10 am: 1/50s, ISO200
12:25 am: 1/50s, ISO200
12:42 am: 1/250s, ISO800

Monday, September 28, 2015

Lunar eclipse from York County, VA - despite the clouds!

What an incredible view of the lunar eclipse last night! Despite persistent cloud cover, there were enough gaps to catch the best moments here in York County, Virginia. Since the southerly view at my house is blocked by trees, I ended up wheeling my telescope to a cul-de-sac nearby and found the perfect vantage point. Neighbors were out enjoying the view as well, enhancing the feeling that something big was happening. I intermittently took about 5GB of photos from the beginning of totality until the end of the eclipse...and oh my, it was dark during totality! I was surprised by the exposure length required. The picture above is a first cut at processing one of the better images of the night, taken about 10:45 p.m. EDT during mid-totality. I will post more refined images in the coming days, possibly a mosaic of the latter half of the eclipse.

Technical details:
Explore Scientific ED127mm Apochromatic Refractor, Canon 550D DSLR, Exposure: 2 sec @ ISO800, time: 11:03 p.m. EDT.