My objective last night was to experiment with various exposure durations, and to image the M46/M47 complex.
The NP101 remained on the mount from the last session. I used the ASI6200MM, 2” filter wheel, and the OAG as the main imaging package. The ASI290 Mini was used for guiding. While I am still in the early stages of re-learning DSO imaging, I decided to simplify by leaving autofocus out of the equation. My focus solution was to manually focus once with the Bahtinov mask, and leave it at that for the remaining 1.5 to 2h imaging session.
As usual I connected the imaging equipment to the telescope at about 1800, which is just after sunset, and came back out at 1850 when it was dark enough to polar align, focus the main and guiding cameras, and run a PHD calibration. It was about 36 degrees, the wind had died down and there was no threat of dew. I did not notice that seeing was an issue at any time during the session. Working at a short focal length helped in this regard.
A small correction in polar alignment was required, presumably due to the tripod settling. The PHD calibration looked perfect, and subsequent guiding was about 1” total RMS. I managed these activities with only one small fumble. I accidentally left the Bahtinov mask on the scope after focusing and had to make an extra trip outside to remove it.
Once inside at 1715, I first conducted an experiment to make sure that I was not overexposing my stars. Using the L filter, I executed a 150s exposure. I noted that NINA was showing me a max exposure value of 65,535 (expected for a 16-bit sensor), and about 16,000 in parenthesis. I surmised that 65,535 was the maximum capability of the sensor, and that 16,000 was the maximum exposure value recorded for any pixel on the sensor. I doubled the exposure to 300s, and found that 16,000 had also doubled to 32,000. I accepted this to mean that as long as I kept the parenthetical value to less than 65,535 I would not have any centers of bright stars blown out. This concluded my experiment.
For M46/M47 imaging, I set up a sequence in NINA that consisted of slewing to the target, plate solving and centering, starting PHD guiding before the actual imaging started. For the actual imaging, set up three lines (one each for R, G, and B) for 8 exposures of 360s each. I elected to not shoot L and instead I will pull luminance out of the RGB image in PS to see how that works with DSO. I imagine that this approach might work pretty good.
I checked the first image right away and it looked pretty decent with round, focused stars. I was not completely happy with the framing, but I was happy enough that I did not interrupt the sequence. I have already worked out how to set sensor rotation at the telescope, but I must remember to do that when setting up an imaging session. I also need to pay closer attention to framing when I am testing my exposure duration. In this case, I was surprised at how much of the full frame that the two Messiers filled, and I think there is an NGC cluster in there too.
My ideal approach to setting camera rotation is that I decide what sensor rotation that I want in Stellarium. Then on the scope, I know how to set my camera at pretty close 0 and 90 degrees by eyeballing the relationship between the saddle plate and the camera. This covers 180 and 270 degree rotations as well, because at worse the image will be upside down, in which case it can be easily inverted in PS. The in-between rotations can be estimated if needed.
I checked on the session again about 30 minutes later, and I was not able to reconnect to the remote desktop session, the same problem I had experienced a week or so ago. I went out side and could see that the minicomputer was still powered on. I tried connecting via Ethernet, which will usually connect when nothing else will, and that didn’t work either. I decided to leave the computer alone so that it could complete the capture sequence if the computer was still running.
I shut down at about 2200, and came inside. Postmortem today will consist of seeing if the entire capture sequence ran, and troubleshooting the inability to re-establish the remote connection. I have already done some reading and have some things to try that look like Greek to me.
At the very least, I should be able to post a single-frame test shot. Hopefully I will have something to process and present a full image.
On the up side of all of this, I have been better at taking the best advantage of the limited and very cold opportunities to begin working things out. I expect to be ready to work on some smaller details at the scope as soon as slightly warmer weather comes along. All of this I think, should position me for some quality DSO work this summer, and if I have everything working reliably, I should be able easily to image through next winter.
