Friday, December 27, 2013

Christmas Astrophotography from Prude Ranch

This Christmas holiday, after visiting family in Las Cruces, we stopped at the Prude Ranch in the Davis Mountains for a week of hiking, birding, and astrophotography. This is the location of the Texas Star Party but, over the week of Christmas, very few guests are around.

In the picture below I am on a ridge of the Skyline trail in the Davis Mountains State Park during an afternoon hike.  From this overlook, you can see the main telescope domes at the McDonald Observatory as well as our setup at the Prude Ranch. The inset photo is taken from the same spot at full zoom on the Canon SX-50.  From a photo taken from 2.5 miles away, I can make out the handles on the Pelican boxes next to the telescopes!


Here is the setup at the southern end of the upper field. We had three imaging setups.  Danielle used a combination of a 400mm Canon lens and 100mm refractor on an Orion Atlas mount. I setup the TMB-130SS on the CGE from the home observatory. It has been a few years since I took this combination into the field. I also borrowed Danielle's little Vixen Polarie to do some wide-field DSLR imaging.

We are able to run AC power from our trailer site up onto the field. Unlike during a star party, several street lights were left in addition to the lights in occupied cabins. This would not be pleasant if we were observing visually, but not too much of an issue for photography.  Much less of a light dome here than at Canyon of Eagles. Though, while attending the public star party at the McDonald Observatory on our last evening, we were made aware of a pretty strong light dome north near Pecos, TX originating from all of the oil drilling rigs.



On this trip, we were also able to make use of our extended WiFi antenna project. You can just make out the antenna on the pole at the back of the trailer.  We used this to connect to the hot-spot provided by the ranch and make it available on our private WiFi network that links the telescopes on the field to an iPad in the trailer. Using RealVNC software, we are able to remotely control and monitor the telescopes. Very nice as the temperature dipped down into the teens.


Frost was a continual problem. The temperature was regularly dropping to around 20F with high humidity. By early morning, our setup was covered with furry frost. Dew heaters took care of the optics, fortunately. However, we had to let the equipment warm up and dry out in the sun each morning before covering again for the day. Though the transparency was reasonable, the seeing was mediocre. Ah well, I am thankful we had any clear nights given the weather of the previous week.

Bolloid Gets the Week Started

On my first evening of setting up, Dec 22, I was facing south looking into the eyepiece to perform a star alignment. I saw a bright light reflected in my glasses and looked back thinking for one absurd moment that the full moon was out.  Instead, I was surprised to see a large bolloid metor breaking up to the north. I could very clearly see the greenish core of the meteor and orange flickering particle trail behind it. Boy, I wish I had had one of those Russian dash-cameras running at the time as this is the brightest event I have seen.

Camera on Vixen Polarie

I took one set of images using a Vixen Polarie star tracker. This was a fun little device to use though the stiction of the pan-head camera tripod I was using to orient it made polar-alignment more challenging than expected.

With my somewhat heavy Canon 60Da camera, I was limited to a small zoom lens due to weight issues. In this first shot, I set the lens to 18mm and took a series of images of Orion and Canis Major over the hills south of the field. I stacked the images to show some of the nebulosity around Orion. I then took one un-tracked image of the foreground to combined in Photoshop. I was also able to see the bright star Canopus between two hills to the right of this frame during the same period of time, something I never see at home.

Milky Way Over Prude Ranch - Canon 60Da / 18-55 IS - 18mm, ISO-1600, f/3.5, 30x120s

I took a couple of other images at 18mm using the Polarie. The first shows the regions around Auriga and Taurus including the Pleiades. The California and Flaming Star nebulae show up as well.

Auriga and Taurus - Canon 60Da / 18-55 IS - 18mm, ISO-1600, f/4, 17x120s
The second image includes Taurus, Gemini, and Orion. The bright object in Gemini is Jupiter; the moons are not evident at this resolution. In addition to the nebulosity in and around Orion, the Rosette Nebula can be seen at the bottom center.

Taurus, Gemini and Orion - Canon 60Da / 18-55 IS - 18mm, ISO-1600, f/4, 17x120s
In each of these images, I applied the Minimum filter at radius 1.0 in Photoshop followed by a Fade Minimum operation of 10% .  Doing this a few times improved the appearance of nebulae within a star field, especially at wide angle. Without it, the stars swamped the nebulae completely. When pixel peeping, some deterioration of star shape can be seen. I understand that a similar star-minimizing effect can be obtained by using a UHC filter. Before uploading, I reduced all of the images to 1600px wide as that is all that this blog site supports.

In the next three images, I increased the focal length of the lens to 35mm. The Polarie still tracks well for 120 seconds. The first images provides more detail of Auriga in addition to the part of Perseus containing the California nebulae.  The three open clusters in Auriga, M36, M37, and M38 are visible as is the Flaming Star Nebula.

Auriga - Canon 60Da / 18-55 IS - 34mm, ISO-1600, f/4.5, 21x300s
The second image is centered near the Double Cluster and contains Cassiopeia to the left and part of Perseus to the right. The Heart and Soul nebulae are visible at the bottom. The small open cluster at center-right is M34.

Cassiopeia - Canon 60Da / 18-55 IS - 34mm, ISO-1600, f/4.5, 13x300s
The third image is centered on the most recognizable part of Orion. The red star is Betelgeuse and the brightest blue star is Rigel. The belt and sword are in the middle of the frame.  The red curve of nebulosity is Barnard's Loop and the Rosette Nebula is at the far left.

Orion - Canon 60Da / 18-55 IS - 36mm, ISO-1600, f/5, 10x300s
As an experiment, I tried a larger 100mm fixed macro lens on the camera.  This combination really pushes the capabilities of the Polarie and the little ball-head mount I was using. The image below, centered on the sword of Orion, had pretty decent tracking. The Witches Head Nebula is now faintly visible as a blue-gray smudge in the upper right corner of the image. The dark Horse-Head nebula is also recognizable in the red glow around Alnitak, the lower most star of the belt. The Orion Nebula, of course, is at the lower center of the frame.

Orion's Belt and Sword - Canon 60Da / 100 US Macro - 100mm, ISO-1600, f/2.8, 21x120s
A later image, with the same equipment but different orientation of the camera in order to get better framing of the Witches Head Nebula, tracked terribly so this lens combination was not very successful on the Polarie.  Perhaps performance would be improved with one of the home-brew counterweight systems I have seen on-line.

Piggy-Back Camera

On my last night of imaging, I put the Polarie away and used my Canon 70-200mm f/4L lens riding piggyback on the TMB-130SS to get some more detailed nebula images.

This first star field, at the border of  Gemini and Orion, is centered on the triple star Propus (Eta Geminorum) which, with Mu Geminorum below forms the foot of one of the Gemini twins. Between these two red stars is the Jellyfish Nebula.  In the upper right is the Monkey Head Nebula and to the left is the open star cluster M35.

Jellyfish and Monkey Head Nebulae - Canon 60Da / 70-200 f4L - 200mm, ISO-1600, f/4, 20x360s
This next image shows the rich scene at the center of Auria, glimpses of which can be seen in earlier images. The large open cluster near the top center is M38, the smaller one towards the lower left is M36.  At the right of the image, the comma-shaped nebula is IC-405, the Flaming Star Nebula.  If you enlarge the image, you can see that the nebulosity above the central star really looks like flickering flames.

Flaming Star and Tadpole Nebulae - Canon 60Da / 70-200 f4L - 200mm, ISO-1600, f/4, 35x360s
At the bottom of the image is the nebula IC-410 which contains two bright shapes called the Tadpoles. These are too small to make out at this resolution but the Hydrogen-Alpha image below, which I took in 2009, clearly shows the tadpoles in the upper left of the central nebula.

Tadpoles in IC-410 (2009) - TMB-130SS. Canon 450Da, Halpha filter, ISO-800, 8x2400s

CCD Imaging with Telescope

While I was using the DSLR and Polarie to obtain wide-field images, I also took several evenings of narrow-band data with the QSI-540 camera and the TMB-130SS refractor.  The main target I was interested in was NGC 2359, Thor's Helmet Nebula in Canis Major.  Similar in nature to the Bubble Nebula, this nebula is formed by the action of a Wolf-Rayet star on a surrounding molecular cloud.

Unfortunately, I did not account for the position of the waning moon very carefully and was only able to get some exposures at the end of the week. I took frames with both Hydrogen-Alpha and Oxygen-III filters. This is an interesting target in that the OIII signal is more dominant than H-alpha. In composing a final color image, I mapped the H-alpha data to red and the OIII data to green and blue.

Thor's Helmet - TMB-130SS / QSI-540 - Ha (4x1800s), OIII (7x1800s) 
Since I had to defer the imaging my primary target, I spent the earlier part of the week gathering data on the NGC-281, the Pacman Nebula, which was well situated high in the sky in Cassiopeia. I gathered several hours of H-alpha, OIII, and SII data in 30 min exposures.

Based on an idea posted by Keith E. (microstar) on cloudynights.com, I tried a different approach to generating a color image.  In that post, the author stated:
It's in a natural color narrowband palette with R=75%Ha+25%SII; G=OIII; B=80%OIII+20%Ha but with the SII blended back in at about 25% as Yellow. 
In attempting to translate this recipe into Photoshop actions, I came up with the following approach. I processed each monochrome layer separately with the usual gamma stretch, noise reduction, and selective sharpening. I then applied a Hue/Saturation adjustment layer to each of these with the following Colorize settings, tweaking the curves for each layer to neutralize the background in the combined image:

Natural-Color Palette Hue Saturation Intensity
Hydrogen-alpha 344 (purple-red) 100% -50
Oxygen-III 168 (blue-geen) 100% -50
Sulphur-II 44 (yellow-orange) 100% -50

Note that for a Hubble Palette, each narrow-band filter is assigned to a single RGB color as shown below whereas here, the filters are assigned to intermediate hues.

False-Color Hubble PaletteHueSaturationIntensity
Hydrogen-alpha124 (green)100%-50
Oxygen-III248 (blue)100%-50
Sulphur-II0 (red)100%-50

Keith's approach is first to synthesize blue from both the blue-green of OIII and from the H-alpha signal serving as a proxy for H-beta. The second trick is to include SII as a orange hue rather than as pure red. No physical motivation for this but helps get the colors of the brightest stars correct.. These ideas are realized by the choices above. This approach worked surprisingly well on the Pacman Nebula.  I will try it on other targets as well.

Pacman Nebula - TMB-130SS / QSI-540 - RGB (6x300s), Ha (8x1800s), OIII (10x1800s), SII (5x1800s)
I separately processed data taken with RGB filters for comparison purposes. The narrow-band hue values I came up with in the table above visually reproduce the RGB data pretty closely.  In the end, I created the final image by directly combining the RGB data and the hue-mapped narrow-band data.

Trip to McDonald

On our last day, Dec 28, the conditions were not favorable for imaging so we opted to go to the public star party at the observatory. The facility has improved since our last visit.  the walking areas are now borded with ribbons of red-lights.  A brand new dome has been installed with an impressive 24" truss Ritchey–Chr├ętien telescope. We listened to an excellent tour of the night's constellations including a great rendition of the myth of Andromeda.  By 9 pm or so, the sky was very hazy and we packed it in for the night.


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