My targets for this session were M31 and M81/82, both in LRGB to complement the Ha data that I captured at home earlier in the week. I captured some good data on both targets, but due to focuser issues I probably didn’t get as much data as I would have liked.
We arrived for Farm IX at 1420 and began setting up camp before setting up telescopes. Set up went nominally and there was plenty of time to grab dinner after setting up camp, and before the sky was dark enough to start working at the scopes.
Sunset was at 1644 and astronomical dark arrived at 1621. Expected conditions were below average seeing that was to improve to average at around midnight. Transparency was to be average throughout the night. Low temp of 19F, and frost was expected.
Start up was nominal as well. Dusk activities, to include initial main camera focus, polar alignment, guide camera initial focus, PHD calibration and PHD GA run all went well. I took some test exposures in L and RGB to determine how short of an exposure in the Farm’s Bortle 4 sky would still have a comfortable 300-800 ADU separation from the left histogram edge. I selected 60s for L and 90s for RG and B.
I initiated the NINA sequence at 1755. Flats in LRGB were captured by 1805, and the sequence was waiting for astronomical dark to arrive at 1821.
I noticed that my first M31 images looked a little soft, and I was getting average HFR well above 3. Really bad looking autofocus charts led me to suspect that cause was the 3s autofocus exposure setting that I adopted while transitioning to filter offset focusing, I paused the sequence, and increased it to 6s. I resumed the session, and then I was getting tighter stars and the average HFR was at the 1.7-ish level that I usually get.
The session appeared to run nominally until just after midnight, at which time the main camera images went wildly out of focus. I physically examined the focuser and saw that the drawtube was fully extended. I then disconnected the focuser in NINA, physically ran the drawtube all the way in, reconnected the focuser with a “Set to 0” instruction, and then instructed the focuser to move to the 3210 position, which is the near perfect focus position. I invoked an autofocus run which executed successfully. I restarted the sequence and it appeared to operate nominally.
I left the session on its own at 0200, and checked it again after waking up at around 0900. I found the telescope parked at CWD and the flats panel was closed. Examining the capture folder I found that capture ended at 0617, which was consistent with the arrival of astronomical dawn.
Analysis:
On closer examination of the M81 capture, I found that no B was captured, and that the images went slowly out of focus over the span of about 8 sub exposures starting at 0437. I inspected the focuser and found that the drawtube had once again fully extended.
Efficiency:
M31
L: 73 x 60s = 01:13:00
RGB: 16 x 90s each filter = 01:12:00
Total integration: 02:25:00
M82:
L: 114 x 60s = 01:54:00
R: 32 x 90s = 00:48:00
G: 64 x 90s = 01:36:00
Total Integration: 02:18:00
Total integration time: 04:43:00
Total Session time: 1821 to 0612 = 11.9h
Efficiency = 4.0/11.9 = 40%
I found 32 interruptions in guiding, many of which were probably autofocus runs. The system seemed to struggle with focus throughout the night. I suspect that the cold may have been the issue, but I do want to check some NINA autofocus settings.
Thinking about autofocus issue, it occurred to me that the awful looking autofocus curves could be the result of the autofocus exposure value being too low. I checked NINA and found that was 5s, and that value has worked well at home. I increased it to 8s, and will check it during the next session.
Conclusions:
The reason for the not having any B images is that an out of date sequence was loaded when I restarted NINA just after midnight to recover the session. Just prior to starting the session, I noticed that the sequence line that I had intended for B was set to G. I changed to B as originally intended, but I did not save the sequence.
The high number of guiding interruptions surely contributed to the very low efficiency for this session. Further investigation is need to determine what was really going on.
Update: The autofocus runs in the 12/15 session looked perfect after changing the exposure from 5s to 8s.
Lessons learned.
Save the NINA sequence after making changes, append the file name to indicate the version number of the sequence. This will provide for better troubleshooting after NINA has been closed. And it will ensure that the updated sequence can be loaded if the session needs to be restarted.
To Do list
Capture M81 with 32 R and 64 B to match the 64 G that were captured.
Check NINA autofocus settings.