Pinwheel Galaxy (M101) and Equipment Tuning

With Astrospheric indicating that the transparency would be great, even though the seeing would be poor, I thought that it would be a good opportunity to work with the telescope and camera to tune skills and equipment tonight, and maybe even accomplish the dress rehearsal that I want to do before going to the farm.

Start Up:

The NP101 was already on the G11. At 1800 I added the ASI6200 and connected power to everything and was ready for darkness in just a few minutes. Even though the Sun was shining brightly, the wind made it feel uncomfortably chilly.

As I wanted to make this my full dress rehearsal, I used batteries were my only power source, and I had hoped to rely strictly upon the field router’s wifi, or Ethernet at worst.

I went out to power up, start software, and connect software to devices at 2052. The wind had calmed way down with only an occasional slight breeze discernable. Temperature was 68F and dew point was 44F. The wind and the temp-dew point spread suggest that there will be no dew. Astrospheric is projecting 0% cloud cover, above average transparency, and poor seeing.

At power up I encountered expected problems with RDT, which is already on my to-do list. I have been working on the list but I haven’t gotten to RDT yet. Last night it would connect to either the home wifi or the field nano router, but if Ethernet cable was connected. It would not connect to either wifi network without the Ethernet cable, nor would it connect via the Ethernet cable alone. As the farm is potentially just a week away, this item needs to float to the top of my priorities. All other powerup activities went smoothly.

Polar alignment took nearly 15 minutes, which was a little more time than usual. I did a second run and got a different result from the first run.. Not being happy with that outcome I did a third run, which yielded a different result from the second run. I tried a fourth and accepted that result as the 3rd and 4th were the same.

After polar alignment, I did my initial focus while still on the NCP region. Polaris is a nice bright star for initial focus with the Bahtinov mask. I was able to see nice bright spikes with just .5s exposures. Focus of the main and guide cameras went smoothly.

Before leaving the NCP region, I did test exposures. I settled on 60s for L, and using the G filter as a proxy for all three color filters I came up with 180s.

PHD2 Calibration and GA run went well. In calibration, orthogonality was off, but the curved plot for one leg of the graph seemed to suggest that it is off due to backlash. Guiding RMS after calibration was .78”, .32”, and .92” for Ra, Dec, and Tot, respectively. GA reported PAE of 4.2’ and that a backlash was 2830ms. I would like to see the backlash come down some more. After the GA run, RMS errors were worse at 1.46”, 1.32”, and 1.92” for Ra, Dec, and Tot, respectively. These errors are approximately the TV/6200 image scale, so the guiding result shouldn’t be too bad. The wind had picked up and could have contributed to the increased RMS error.

Lights Capture

I initiated the imaging sequence just before the end of astronomical twilight. From the equator-meridian position, NINA slewed to the target, plate solved and centered on the target, and initiated an auto focus run. All of this executed almost flawlessly. A slight problem was that I left the G filter in place after doing the exposure test, and this was the filter that was used for the first auto focus run. The first exposure line in the exposure sequence called for an L filter, and the filter change from G to L drove a second autofocus run immediately after the first one. Since everything was otherwise going smoothly, I let the second run continue, but I made a note to put a step in my work plan to cycle back to the L filter after doing exposure tests.

The imaging sequence was L: 15 x 60s, R, G and B: 15 x 180s. Gain 100. Dither on.

The back to back autofocus runs made me start thinking more deeply about filters and focus. I have read that many times filters in less expensive sets will require slightly different drawtube positions to be in focus. Now that I have an L and color filters by different makers, and now that I am getting highly reliable autofocus runs, I think that I can measure the offsets between filters and include that in the exposure sequence.

Guiding RMS improved after slewing to M101, which at this time was about 70 degrees elevated. I was getting .65”, .40”, and .75” for Ra, Dec, and Total RMS, respectively. I believe that the guiding improved because the angular tracking speed needed near the equator is higher than the angular tracking speed needed at higher declinations. After thinking about this for a moment, I etired to the house at 2240

2325 Checkup: It was 63F and pretty breezy when I went out to check on things at 2330. I was chilly with a light jacket on. Still on the first 33AH battery with 12.3V remaining. No danger of mount crash or cable snag. Images are coming in with round stars. Still getting about .72” total RMS guiding!!!!!!

0015 Checkup: 61F. Still on first battery, which is at 12.1V. Wind has died down. Total RMS is up to .85”, which seems reasonable now the target has descended to 54 degrees elevation.

0150 Checkup: Still on first battery which is at 11.9V. Wind died down. It was 57F. The last frame was being exposed. I noticed that the PHD FWHM was nearly 7. I was able to refocus id down to 4.5. Guiding was Ra: .81”, Dec: .70”, and Tot: 1.04”. The target was 44 degrees elevation

Flats Capture

This was my first attempt at a full Flats capture – 30 Light frames and 30 matched Dark frames for each filter. Set up (20 min) and capture were about 1.5 hours. Much longer than I expected. The filter times were L: 5.25s, R:10.99s, G: 28.11s, and B 5.75s. This was with the bare panel on low, and I had to insert 2 sheets of card stock for the colored filters. This doesn’t seem to make sense. There may be ways to reset the way the Flat Wizard finds exposure times to reduce the 10s and 28s exposures. I have some work to do here.

The NINA Flat Wizard is convenient in that once it is set up properly it will cycle through whichever filters that I designate on its own. I am prompted to cover the scope after the last set of Flats is captured, and then it starts capturing Dark Flats.

Looking at the Flats during capture, the L, R, and G images looked weird. The B images looked as I expected

I swapped batteries while the Dark Flats were being captured. The “old” battery was 11.8v

The scope, which sits forward in its rings, slipped downward in the rings when I pointed the scope to the vertical and put the Flats panel on top/front of the scope.

Wrap up

That guiding is better nearer the NCP than the equator is not surprising as the angular movement is faster near the equator and slower near the NCP. I need to keep this in mind until I can improve the mounts performance, and as I begin to work with the Meade.

I have to think about the guide camera being so far out of focus at the end of the session. It seems that as the main camera was periodically refocused the guide camera would also remain in focus. It also seems possible that if different filters come to focus on the main camera sensor at different draw tube extension distances then it might impossible for the guide camera to remain in focus across all filters.

Not that I was trying, but coincidentally the first image was snapped right at the end of astronomical twilight. Any earlier the sky would have been too bright, and later would have meant lost time that I could have been capturing. Getting past polar alignment, initial focus, and test exposures by the end of twilight will be a goal going forward.

The dew heater was off all night, and there was no dew on metal surfaces by the end of the session. In retrospect, I wish that I had turned it on to assess the impact on the batteries.

The Samsung laptop battery was at 40% at the end of the session. I had it open and running more way than absolutely needed as I am still in the learning phase and watching everything very closely.

Even though the wifi router kept this session from being exactly as I hope to operate in the field, I was still able to have a very good imaging session. I would not have been disappointed if this had happened at the farm.

This is a big report, but I have two big take aways:  First, poor seeing nights are certainly just fine for tuning equipment and skills. It remains to be seen how the data look, so I don’t know if a poor seeing night is good for short focal length DSO work. I know that this condition does not work for long focal length planetary work. Also, as a result of being more disciplined about writing things down, I think that I am still paying closer attention to more details that might not have been noticed, or that would have been soon forgotten.  I still am not anywhere near where I want to be with respect to DSO imaging, but I feel like I am getting there.

To-do List:

  • Make RDT a higher priority
  • Check for Windows updates on the mini computer
  • Adjust Dec backlash after New Moon period
  • Measure filter offsets
  • Add longer range items (Like Gemini Lvl 6 upgrade this winter) to to-do list as the come to mind for tracking
  • Research how others are taking Flats with an eye toward reducing the amount of time it takes to set up and capture. Read about Dynamic Exposure in the Flat Wizard
  • Put one wrap of friction tape around the OTA where the rings are clamped on
  • Capture Bias frames
  • Seeing how the Flat exposure times varied by filter, I need to do test exposures for each filter.
  • Update NINA on the mini computer
  • Process images
M101 - 2022-06-18
The Pinwheel Galaxy (M101)

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