February 2019 – AstroTuna

NGC 6791

By B. Morgan | February 23, 2019

Acquisition Date: June 18, 2018

This was my first attempt at color with a monochrome camera. It was a real learning experience.

The image you see uses synthetic luminance which I created from the RGB stacks with the help of StarTools. A couple weeks earlier, I imaged in actual luminance but made the mistake of not taking the full suite of calibration frames. This failure affected its appearance so I rejected it in favor of synthetic luminance.

Factoid: NGC 6791 is an enigma. The stars are twice as old as our Sun but have an Iron-to-Hydrogen abundance ratio (metallicity) that is more than twice that of the Sun. This flies in the face of the rule of thumb that “older means metal-poor”. NGC 6791 is one of the most studied star clusters

Technical Details:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong LRGB filters
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding

Gain 100 (FWD: 15ke-, 3.66 e-/ADU)
Offset: 20 ADU

Captured over 2 nights:
R: 80x 50s
G: 80x 50s
B: 80x 60s

Total integration time: 138 minutes

PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289

NGC 896 – Fish Head Nebula

By B. Morgan | February 23, 2019

Acquisition Date: September 7, 2018

I am not sure if Fish Head Nebula is official but people do refer to it as such. It is part of the Heart Nebula but it has a different NGC designation.

Technical Details:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong luminance filter
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding

Gain 100 (FWD: 15ke-, 3.66 e-/ADU)
Offset: 20 ADU
Exposure: 50s
Camera rotation: 3.8 deg E of N

Luminance:
69.0 degF: 8 frames
69.5 degF: 54 frames
70.0 degF: 26 frames
70.5 degF: 12 frames
Darks:
69.0 degF: 269 frames
69.5 degF: 141 frames
70.0 degF: 86 frames
70.5 degF: 113 frames
Flats: 100
Bias: 100
Total integration time: 66 minutes (it really needs more time)

SharpCap 3.1.5219
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289

Update:

In these past couple weeks I’ve transitioned away from using Deep Sky Stacker and StarTools to using Astro Pixel Processor (APP). Here is a comparison of the two.

Deep Sky Stacker and StarTools:

Astro Pixel Processor (APP):

I like the APP image better. I am hoping that APP’s developer (Mabula) is working on noise reduction controls.

This summer I plan on re-imaging this object using Gain 200 instead of Gain 100. I have reason to believe that the bright stars will be less ‘fat’ since this bothers me. Recently I’ve experimented with Gain 200 and found that it greatly improves stars and reduces noise. The trade-off is that it lowers my full well depth from 15,000 electrons to 7,500 electrons. It will be an interesting experiment!

NGC 7635 – Bubble Nebula

By B. Morgan | February 22, 2019

Acquisition Date: September 7, 2018

I really do like my uncooled Altair 290M camera but one thing is missing: a sensor temperature readout. This has stood in my way of creating a Darks Library. Having a Darks Library would free up my time to concentrate on capturing Light frames.

There is nothing worse than having to waste an hour collecting darks under the stars. Furthermore, I committed the sin of collecting darks after my lights when the temperature was usually much cooler (if anything, you should collect them before.) So I was getting sub-optimal noisy images with the hint of raining noise when the temperature of my darks were very different than my lights.

I decided to do something about it. I built a Temperature Logger with an Arduino, a high-precision temperature sensor having an accuracy of 0.25C, an SD card reader/writer, and a LIPO battery. I position the unit near my telescope. It records ambient temperature once per minute and writes it with a timestamp to the SD card. I’ve had it running for 11 hours straight on a single charge. It could probably go longer.

On those cloudy nights I collect darks. Then the following morning I download the image files and the temperature log, and segregate the image files by temperature. These past couple nights the weather cleared to try it all out. I like the results. Smoother, less noisy prints with no hint of raining noise.

Technical Details:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong luminance filter
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding

Gain 100 (FWD: 15ke-, 3.66 e-/ADU)
Offset: 20 ADU
Exposure: 50s
Camera rotation: 3.8 deg E of N

Captured over 2 nights:
Luminance:
70.5 degF: 1 frame
71.0 degF: 22 frames
71.5 degF: 48 frames
72.0 degF: 4 frames
72.5 degF: 69 frames
Darks:
70.5 degF: 113 frames
71.0 degF: 69 frames
71.5 degF: 94 frames
72.0 degF: 96 frames
72.5 degF: 96 frames
Flats: 100
Bias: 100
Total integration time: 83 minutes

SharpCap 3.1.5219
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289

Soul Nebula in Ha

By B. Morgan | February 22, 2019

Acquisition Date: September 30, 2018

The inspiration for this image came from Sara Wager — an incredible, creamy smooth color image using three narrowband filters and over 37 hours total integration time. My equipment doesn’t come close to hers but I wanted to give it a try.

Due to a spate of bad weather I could only manage one clear night to image in Hydrogen-Alpha (Ha). That explains why my image is black & white and Sara’s is color.

Another obvious difference is that my image is ‘noisier’. The primary reason is that Sara’s camera is cooled and mine is not. Images from cooled cameras suffer less from thermal noise. Finally, she’s got 37 hours of integration time and I’ve got 2 hours. Noise tends to cancel with increased time due to its random nature

Technical Details:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Orion 6nm Hydrogen Alpha filter
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding

Gain 389 (1.0 e-/ADU, FWD: 4ke-, Read Noise: 1.38e-)
Offset: 30 ADU
Exposure: 200s
Camera rotation: 355 deg E of N

Ha:
48.0 degF: 8 frames
48.5 degF: 21 frames
49.0 degF: 11 frames
49.5 degF: 1 frames
Darks:
48.0 degF: 20 frames
48.5 degF: 21 frames
49.0 degF: 32 frames
49.5 degF: 29 frames
Flats: 50
Bias: 100
Temperature-matching disabled until I have more darks per temperature bucket.
Total integration time: 136 minutes

75% waning gibbous Moon high in the sky

SharpCap 3.1.5219
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289

Do your filters fit your filter wheel?

By B. Morgan | February 22, 2019

After purchasing my first monochrome camera 10 months ago I went on a shopping spree buying filters. In total I have four Optolong LRGB filters, two Astrodon Photometric filters, three Orion narrowband filters, and one Orion dark filter. My first filter wheel was an Orion 5-position manual model. A while later I purchased a ZWO 5-position Electronic Filter Wheel (ZWO MiniEFW).

I really liked the finish of the ZWO MiniEFW and that it was light-tight, the Orion FW not so much. I loaded the MiniEFW with my Optolong LRGB filters and the Orion dark filter. It worked great for many months until yesterday when I decided to swap out the LRGB filters with my Orion narrowband filters. I discovered quite unexpectedly at the telescope that the wheel would not turn. I scrambled to move the narrowband filters back into the manual wheel so I could continue imaging.

So here is the problem. The ZWO MiniEFW requires that the thickness of the filter cell, minus the threads, be less than 7mm. Unfortunately all of my Orion filters and Astrodon filters are 7.5mm. Only the Optolong filters meet the requirement at 5.5mm. For the astute reader you might have caught that I reported a fully functional wheel having four 5.5mm filters and one 7.5mm filter. The best I can figure is that the stepper motor could overcome the drag from that one 7.5mm filter but not four of them.

I thought this might be helpful for those of you who like me “mix and match” — beware!

It’s quite frustrating that there isn’t greater effort to agree on labeling standards among astronomy equipment manufacturers. I dabble in electronics and have always been impressed with the attention to detail in manufacturers’ datasheets. It’s as if they really want you to buy their products! Granted the electronics industry is much larger than the astronomy industry so maybe they have money to burn on good documentation.

Sadly, astronomy retailers don’t pick up the slack. They simply copy the specs that the manufacturers publish. Would you believe I had to dig down into the Q&A section of the ZWO site in order to find the 7mm clearance limit for the MiniEFW? And with regards to filter cell height, I can’t find a thing from the filter manufacturers.

M101 – Pinwheel Galaxy – Ha

By B. Morgan | February 22, 2019

Acquisition Date: February 17, 2019

This is a work in progress with the goal being a color image. As more data becomes available I will post updates.

Spiral galaxies like M101 contain ionized hydrogen regions. This is where star formation occurs and it is mainly found in the arms of the galaxy. There is a type of narrowband filter which is designed to pass the Hydrogen Alpha (Ha) emission line. This photo was taken with an Ha filter.

One of the advantages of imaging in narrowband is that it can be performed during all phases of the Moon. In fact, the Moon was 91% illuminated when I acquired this image. The downside is that the required exposure is quite long: 3 minutes 20 seconds for each of the 32 frames in this case. Wideband imaging, by comparison, typically uses exposures in the range of 30 to 60 seconds but images will be washed out by the light of the Moon. Wideband filters are typically named Luminance, Red, Green, and Blue (i.e. LRGB).

As this project matures to color I will provide more detailed technical information. The image shown above is a screenshot of Astro Pixel Processor (APP).

NGC 4565 – Needle Galaxy

By B. Morgan | February 21, 2019

Acquisition Date: February 10, 2019

I wanted to do more color with my monochrome camera but the number of steps involved with capturing calibration frames and light frames using four different filters was overwhelming to accomplish manually in a single evening. For a while I thought I would simply spread imaging over four nights: one night for luminance, the second for red, etc. But then I realized that clear nights are hard to come by. Sometimes it takes well over a month to accumulate four nights. So that’s when I decided that I needed to come up with an automated solution to get an entire LRGB sequence in one night.

I took a three month rest from imaging while I developed a “Flip-Flat” work-alike since I couldn’t get myself to part with the $500 cost for the original. I ended up spending more on development but the experience was worth it. I call mine The Flatinator. I will write more about it later.

Ordinarily I use SharpCap software for image acquisition but in this instance I chose INDI/Ekos due to its advanced automation. The next version of SharpCap promises better features.

Technical Details:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong LRGB Filters
Unitron Model 142 GEM
The Flatinator
Passive tracking with PEC
No active guiding

Gain 200 (1.74 e-/ADU, FWD: 7100e-, Read Noise: 1.55e-)
Offset: 25 ADU
Exposure: Multiple
Camera rotation: 5 deg E of N

Luminance: 72x 25s
Red: 30x 30s
Green: 30x 30s
Blue: 25x 36s

Flats: 100x per channel
Darks: 20x per channel
Bias: 100x all channels

Total integration time: 74 minutes
Total time at telescope: 122 minutes

SharpCap 3.1.5219 for Polar Alignment and Periodic Error Correction
INDI/Ekos for Image Acquisition
APP 1.071 for Stacking and Image Processing