New Images from Calstar 2022

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Calstar 2022 was again held at Lake San Antonio, from Sept. 21-25, and we were there for 4 nights. This trip, we got a hitch and a cargo carrier tray installed on our car. It was helpful to have, and less nerve-wracking than the roof bag.

On 9/21 we unpacked and set up the camp, mount and telescope. I used a small refractor (Vixen) and Sky Safari to get an approximate polar alignment, since the mount doesn't have a polar alignment scope. According to a drift alignment test, the error was about 0.21 degrees, mainly along the elevation axis. On the first night, we observed the Dumbbell Nebula, the Veil nebula, Saturn, Jupiter (see below), Mars (see below), the Orion Nebula, and the Flame Nebula in Orion. The seeing was so-so, with only some glimpes of Cassini's division in Saturn, but it may have improved with time. We also had raccoons invade the car when we left the doors open! Fortunately I heard them before they got into the food, but one of them (the mom?) left muddy footprints all over the seats before I could chase them away. There were also some prints left on the rear window as shown below. We saw many other animals while we were there including deer, ground squirrels, turkeys, quail, a bunny, a gopher, and a large toad, along with wild boars and a couple of tarantulas when driving in.

On 9/22, the seeing was pretty bad initially, but we started long-exposure imaging with the SBIG camera. I had to work out some remaining bugs involving the shutter control, so we got started late again on acquiring data. On 9/23, the seeing seemed better, or at least comparable to the first night. 9/24 was a shorter night, since we had to break camp and drive out the following morning. At one point, I had a strange problem with the Gemini controller saying it was pulse guiding when it should not have been, and I ended up having to reboot it and then realign.

Telescope setup: Same as last year, we brought the C14 telescope and Losmandy G11T mount shown below. For dew control we had both a homemade dew cap made from rubber sheets, and a dew heater ring installed on the C14. This time, the dew cap was sufficient to avoid seeing any dew on the front corrector plate. I also have ventilation fans installed on the scope, and I ran them all 4 nights in hope of minimizing internal seeing degradation. The setup including laptop and cameras were powered with two marine batteries.

Photography setup: For high-speed imaging of planets, I used an Allied Vision Alvium 1800 U-319m camera (2064 x 1544 pixels, 3.45um pixels, global shutter). At f=3850 mm, this gives 0.184 arcsec / pixel and 6.36 x 4.76 arcmin maximum field of view. For deep-space photography, I continued using an SBIG ST-4K camera (2048 x 2048 pixels, 7.4um) along with a Celestron f/6.3 reducer/corrector, which gives approximately f/7 or f=2450 mm with the C14, resulting in 0.623 arcsec / pixel and 21.3 x 21.3 arcmin field of view. This was also the first Calstar where I tried using custom Python scripts for most of the data acquisition.

Image processing: For the long-exposure photography, I still used my old C code for aligning and stacking the images. However, I experimented with linear deconvolution techniques using some additional Python scripts. For this I estimated a point-spread function using stars in the image, and then computed a filter function that includes an offset in the denominator, as in Wiener deconvolution. The filter also included a high-frequency blurring term, so that a cross-section of the 2D filter function in the spatial frequency domain looked like the graph shown below. For the planet images, I experimented with using Registax to align, warp and stack the images before sharping, as described more below.

This year, I wanted to focus on image resolution, so all but one of the targets were planets or planetary nebulae.


10ms, green 10ms 20ms 50ms, green 50ms, green, gain 10 animated

Allied Vision camera, 9/21/22 Lake San Antonio, CA

When we started observing Jupiter, we saw that a moon was just starting to transit along with its shadow. At first, the moon was easy to see against the darker limb of Jupiter, but as it moved towards the center of Jupiter, it became difficult to see. From online data, I think the moon was Io. I took some frames with the Allied Vision camera, with and without a green color filter and with different exposure settings. The images with the green filter may show a bit more contrast. Each set had 2000 frames. The top row shows the best frame selected from each set, using an automatic sharpness metric based on Gaussian filters. The bottom row shows the results of stacking the best frames using Registax, and then applying a sharpening filter. The first image on the left used the best 200 frames (I needed more frames because of the low signal-noise ratio) while the other images used the best 50 frames.


10ms 50ms, green animated

Allied Vision camera, 9/21/22 Lake San Antonio, CA

Mars will reach opposition in December, but it is already getting bright, high in the sky, and showing visible detail. I took two sequences of 2000 frames with the Allied Vision camera, one without a filter and one with a green filter. The images without a filter have better contrast. The top row shows the best raw frame from each set (using an automated sharpness metric) and the bottom row shows the results of combining the best 50 frames with Registax and applying a sharpening filter.

M57 - Ring Nebula

Imax=30 Imax=15 Imax=2

SBIG ST-4K, 540s total exposure 9/22/22 Lake San Antonio, CA

First 60s exposure sequence of the Ring Nebula. The seeing was not great, and also I lost a frame to a remaining bug that was causing the tracking to keep going after the shutter closed.

M57 - Ring Nebula

Imax=30 Imax=15 Imax=2

SBIG ST-4K, 600s total exposure 9/22/22 Lake San Antonio, CA

Another sequence of 60s exposures after fixing the tracking bug.

M27 - Dumbbell Nebula

Imax=40 Imax=10 Imax=4 Imax=1 Deconvolved

SBIG ST-4K, 1200s total exposure 9/22/22 Lake San Antonio, CA

This was an attempt to improve on previous images of the Dumbbell nubula, but the results were dissapointing, maybe because I waited for it to be too low in the sky. I could get some sharpness increase using a deconvolution filter (right), but the brighter stars acquired unwanted structures.

IC 289

Imax=12 Imax=3 Imax=1 Deconvolved

SBIG ST-4K, 1200s total exposure 9/22/22 Lake San Antonio, CA

This planetary nebula in Cassiopeia has a ring structure, a purple color, and some ierregular dark features. Some faint outer structure can also be seen in the brightest-scaled version.


Imax=1.50 Imax=0.75

SBIG ST-4K, 1200s total exposure 9/22/22 Lake San Antonio, CA

A planetary nebula in Taurus with a blue color and many dark bubbles.

M57 - Ring Nebula

Imax=30 Imax=15 Imax=2 Deconvolved

SBIG ST-4K, 540s total exposure 9/23/22 Lake San Antonio, CA

One more sequence of 60s exposures I took because the seeing looked better than the previous night. Since the signal-noise ratio was pretty good for this image, I was able to get some useful sharpness increase using a deconvolution filter (right).

NGC 6881

Imax=30 Imax=1 Nonlinear

SBIG ST-4K, 600s total exposure 9/23/22 Lake San Antonio, CA

This tiny planetary nebula in Cygnus resembles a pink football in this photo. With nonlinear scaling, the color appears uniform from the center to the edge.


Imax=300 Imax=100 Imax=10 Nonlinear Deconvolved Deconvolved, nonlinear

SBIG ST-4K, 100s total exposure 9/23/22 Lake San Antonio, CA

We had difficulty finding this small proto-planetary nebula in Cygnus—we nicknamed it "Tiny," and you can see why. We first had to use a sky atlas to correct the pointing, and then found that the object is quite bright. In this photo, the two lobes appear as a pair of barely separated star-like objects with unequal color and brightness.

NGC 7293 - Helix Nebula

Imax=40 Imax=1 Imax=0.50

SBIG ST-4K, 1800s total exposure 9/23/22 Lake San Antonio, CA

The Helix Nebula is a very large but diffuse planetary nebula in Aquarius. Here I was trying to improve on my previous attempt that suffered from both a low altitude and wind problems. For this attempt, the altitude was again very low, but at least there was no wind. There appears to be a slowly moving object at about the 10 o'clock position.

IC 2149

Imax=200 Imax=20 Imax=1 Nonlinear Deconvolved, nonlinear

SBIG ST-4K, 900s total exposure 9/23/22 Lake San Antonio, CA

Another small planetary nebula in Auriga. There appears to be a central ray or jet that is visible in the nonlinearly scaled image.

NGC 7023 - Iris Nebula

Imax=200 Imax=20 Imax=2 Imax=0.50 Nonlinear

SBIG ST-4K, 1800s total exposure 9/24/22 Lake San Antonio, CA

This is a reflection nebula in Cepheus with a lot of interesting structure including dark regions and an opening. Initially I did not realize how large and diffuse it would be, or perhaps I would have planned for a longer exposure. I also did not take any useful flat-field data, so I resorted to using the sky glow from some test images taken in Palo Alto, where the camera alignment was probably different.

NGC 7139

Imax=1 Imax=0.50

SBIG ST-4K, 1500s total exposure 9/24/22 Lake San Antonio, CA

This dim planetary nebula in Cepheus combines an outer, reddish broken ring with a bluish interior.