I had an interesting problem to solve before I could capturing the Bubble and Lobster.
Problem Statement
How do I setup a nights session to replicate a previous session, including the framing and orientation?
My scenario was that I had run a nights worth of imaging on the Bubble Nebula a few weeks earlier. I had saved my sequence but unfortunately, this sequence had used the Centre on Target without the rotation element being defined. Also, I quite often manually move the framing around:-
to try and position the target in more interesting positions (rule of thirds for example) or,
there maybe other interesting objects available in my fairly wide field of view that by adjusting the position of the primary target I can squeeze into shot
I have images from this previous night without all of the necessary information to subsequently reconstruct the session.
Simple Answer
Assuming you are using N.I.N.A. then re-load the 'Advanced Sequencer' Saved profile for the Target. Done!
Oh you did save that Sequence didn't you? and,
that sequence was with a specific Centre and Rotation not just a Centre wasn't it?
If the answer to the first question is No, then perhaps if you did not manually adjust the framing and just took the centre of the object co-ordinates from the Sky Atlas then you may simply be able to replicate this by doing the same again... of course this time you will save the sequencer for future won't you?
If the answer to the second question is No then you have a slightly sticky framing problem for your subsequent session. In this case, one option would be to simply not worry about it! If it is centred fairly accurately and you crop to remove the artefacts after registration and stacking around edges that did not overlap because of a different rotation and your entering inaccuracies you might get lucky, you may even have a square imaging sensor and therefore if you are centred on the target your rotation will be dealt with nicely during the registration. Still this all seems a little hit and miss.
My Solution
TL;DR
Use a plate solver to solve the location and rotation of one of the Lights from the previous session. Then feed these in as the target parameters and rotation in the Advanced Sequence in N.I.N.A. You can verify that this looks ok in the N.I.N.A. Framing assistance for verification of the result.
Specifics given the software and images I had at hand are provided below.
I have the ASTAP software installed on my imaging and planning laptop as it is used as the behind the scenes Plate Solver for N.I.N.A. Other options such as Astrometry.Net will also provide this information albeit much slower, you should have ASTAP installed if you are using N.I.N.A. souse that if at all possible.
Run ASTAP go to file and select one of the images from the previous session. Hit "Solve", you should get the location (Red box) RA top Dec below. Also the rotation from North.
We can then Open N.I.N.A. and verify that the look of the image in the Framing Assistant matches up with the image we have here. Enter the co-ordinates in the top red rectangle, hit Load Image and Set Rotation to roughly the one provided by ASTAP.
We can now plug the figures into the Target for the Advanced Sequencer.
Set the co-ordinates (top red box) and rotation, you will need to make sure that the Slew, Centre and Rotate is the instruction (second red box).
Subsequent image sessions should match pretty closely the original, making registration and stacking more accurate and therefore reducing any artefacts.
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