M35 and Equipment Tuning

Seeing unexpected clear sky shaping up in the late afternoon, I made a last-minute decision to uncover the telescope. My objectives were to determine at what time I could safely capture light panel flats without light leakage in the imaging train, and to determine where flats capture best fits into my workflow. Time permitting, and since the waxing gibbous moon was high in the sky, I would capture a stars-only target like M35.

The daytime temperature had been near 60 degrees and I did not spend much time at the scope, so I was comfortable outside without doing more than throwing on a coat as I went out the door. The temperature was in the 40s, and there was no dew on any surface during the session. I could not detect any breeze at all. Seeing was forecast to be below average, but that was not a factor at my image scale.

In order to test for light leakage, I took the first test flat at 1630 while the sun was still shining directly onto the telescope. I had wrapped the imaging train with a small tarp, but as expected I could clearly see evidence of light leakage. The next test flat was taken at 1700, and by then the telescope was in the shadow of the cottage. I could not see any evidence of light leakage. To be sure, I waited until just after sunset and took another test flat at 1730. It looked exactly like the first one, so I concluded that sunset or later is a safe time to capture light panel flats.

I proceeded to capture 30 x LRGB flats right after inspecting the 1730 test flat. My light panel setup (full brightness with two layers of t-shirt material) and NINA Flats Wizard settings were perfect. I captured the full complement of 120 frames in about five minutes.

Polar alignment was off by a slight amount. Running through the process and adjusting went off smoothly. It occurred to me to check the bubble levels, and they were off significantly due to settling. I don’t recall how long it had been since the tripod was last set up and leveled.

There was a small issue with calibration. After slewing to 0,0 I stepped right into calibration, which threw a backlash error. I had forgotten to nudge north before initiating calibration. When I gave the telescope a nudge north prior to repeating the process, it slewed 24 degrees east. I slewed back to 0,0 and retried twice with the hand controller and got the same result. I next tried with the Gemini.net ascom software controller, and got the same result. I restarted the mount, and that cleared the problem. I cannot think of anything that would cause this to occur.

Capture of M35 went well. I had setup a sequence to slew to and center the target, initiate an autofocus run, and capture 21 L, and 7 each RGB with an autofocus run after each focus run. This went off start to finish without a hitch, but intermittent clouds rolled through and ruined several frames. I will probably only process them enough to check how well a prominent dust mote gets flatted out.

Guiding was about as good as I have been able to get lately. Ra/Dec/Tot RMS for the longest session (42m) were .67”/.28”/.72”. Even with Ra being nearly 3x that of Dec, stars appeared round in the images. I would like to get Ra under better control, but that might night happen until Level 6 upgrade, which might help by itself, and GEM-Pro is available.

Even with the clouds, the session was productive. With practice, flats capture has become easy and fast, and I have a better sense of how Flats fit into my session start up. With respect to efficiency and how smoothly I am able to get a session started, I am at least back to the point that I had reached last summer, perhaps even better.

I somewhat later realized that while being close to focus from the last session, I would have preferred to have waited until after focusing before capturing flats. I took a few minutes to think about where to fit flats into workflow. Dusk sky flats doesn’t work because the telescope hasn’t been focused. Dawn sky flats doesn’t work because I do not want to create a requirement to stay awake until the sky gets bright enough. That leaves me with light panel flats capture needing to be incorporated into my start up, which I strive to have complete by the end of astronomical twilight (about 90 minutes after sunset).

My pre-flats routine was to polar align (about 35 minutes after sunset), initial focus, and calibration. There are two primary considerations in sequencing with flats capture inserted into session start up: 1) focus needs to be done before capturing flats, and 2) I don’t want to do flats after polar alignment because of jostling the telescope when removing the flats panel could perturb the polar alignment.

The sequence that I want to test next time is to monitor the main camera to determine how soon after sunset that I can see stars well enough to focus. I am guessing that it will be about 35 – 40 minutes after sunset. If that’s the case, then I can focus and capture flats without delaying polar alignment more than about 20 minutes compared to the previous workflow. With end of astronomical twilight being the goal for completing start up, I still have 30 minutes or more to complete calibration. I think that this is workable.

There are three things for me to work on before my next session. I had to use the home wifi for remote connectivity, because I could not connect through either of the Mango nano routers. I suspect that resetting them is all that is required, but I’d like to know why they stopped working after performing so well for several weeks. I would feel better about the tripod being level, so I want to straighten that out. And finally, and this is a hold over from measuring per filter focus positions, I want to take apart the focuser clutch to see if I can figure out why the focuser position for the same filter is always smaller on subsequent measurements. Since rain is likely to prevent me from working on it today, I will probably reach out to Ron at Moonlite to see what he advises.

M35 - 2023-01-30 - Annotated
An Annotated Image
Flats Exammple
Flat Frame Calibration

Leave a Reply