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Creating DSO mosaic - in this case Lagoon Nebula - Advice please


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I have created a 4 panel mosaic of the Lagoon Nebula, but as can be seen the Oiii channel is out of sync on 1 or 2 panels. My process was to capture Ha for each panel, then Oiii and then Sii over 3 nights, then stack, align and mosaic each channel, then align each mosaic. Is that the best way or would it be better to do all the channels for each panel over say 4 nights? The images are 5x each NB for 300 seconds each, then aligned ,stacked and mosaicked in ASTAP and processed in GIMP. Equipment- HEQ5 Pro rowan mod, SW 200pds, ZWO ASI1600MM-cool, Astrodon 5nm HA, Optolong 7.5nm Oiii and Sii, controlled by NINA. Any hints most welcome. Ignore the excessive green hue.

PS I have learned that I need aa beefier computer and a camera rotator. All donations kindly accepted 😉

Adrian

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Have you tried manually aligning each stack by their corresponding stars in gimp?

I basically do a nights imaging with one filter, stack, pre process then import into PS. Use one stack (usually ha) as the reference on the bottom layer, then set the S2 or o3 at a lower opacity so it's see though over the top of the ha layer, then move, rotate and scale it until the stars line up. Once one of them is done, do the other.

Siril can do this automatically if you go through the process of registering your images and working through the process but I find it just as quick to do it manually. You can also do this in Deep Sky Stacker by keeping one of your light frames in the stacking list as the reference frame but unchecked as you don't want to stack it with your next set of narrowband images. I don't tend to automate this as I like to see how the target has changed orientation during a session or between different nights.

Edited by Elp
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21 hours ago, Elp said:

Have you tried manually aligning each stack by their corresponding stars in gimp?

 

Hi

Yes I did try. The problem seems to be in two plates only in Oiii, so when I move those stars to coincide with the other channels, the stars from the other 2 plates move out of alignment. I tried aligning and stacking each plate, then mosaicking each channel, then aligning the mosaicked channels before importing into GIMP, and I got the same misalignment in 2 of the plates. Looks as if there is a problem with the astronometric alignment in ASTAP. As its only the Oiii channel, I think I will need to run another imaging session for all 4 plates and see what happens, if the clouds part before it gets too low and the Moon comes again.

21 hours ago, Elp said:

I basically do a nights imaging with one filter, stack, pre process then import into PS. Use one stack (usually ha) as the reference on the bottom layer

Exactly how I did it.

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If you upload the images here prior to stitching them together I'm sure someone will come up with something.

I have sometimes found when imaging in o3 that the stars especially towards the edges tend to be further out compared to other bandpasses, a bit like how blue channel moves further out compared to red channel if they're not precisely focussed.

Edited by Elp
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  • Cornelius Varley changed the title to Creating DSO mosaic - in this case Lagoon Nebula - Advice please

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