7-panel mosaic in 110 minutes

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oopfan
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7-panel mosaic in 110 minutes

#1

Post by oopfan »

From Melotte 111, a bright Open Cluster in Coma Berenices, to NGC 4565, the Needle Galaxy.

It is an odd shape, but my plan is to use it in a video presentation. I'll be using some video processing techniques to make it more accessible.

The image size is 7515 x 854 pixels. The image height is approximately the height of my sensor: 1040 pixels. I had to crop it down to 854 pixels since the mosaic is curved.

The total time to capture was 3.5 hours from 9pm to 12:30am, all east of the meridian. I don't have a go-to mount or auto-focus, so I had to devise a plan. I knew that I needed to minimize the number of filter changes, so I decided on this:

1. Plate solve to the westward end of the mosaic.
2. Select luminance filter (actually a Wratten #12).
3. Focus.
4. Capture 12x 25-second frames for Panel #1.
5. Turn off the RA drive for exactly 3 minutes.
6. Capture 12x 25-second frames for Panel #2.
7. Turn off the RA drive for exactly 3 minutes.
8. Capture 12x 25-second frames for Panel #3.
9. Turn off the RA drive for exactly 3 minutes.
10. Capture 12x 25-second frames for Panel #4.
11. Turn off the RA drive for exactly 3 minutes.
12. Capture 12x 25-second frames for Panel #5.
13. Turn off the RA drive for exactly 3 minutes.
14. Capture 12x 25-second frames for Panel #6.
15. Turn off the RA drive for exactly 3 minutes.
16. Capture 12x 25-second frames for Panel #7.
17. Turn off the RA drive for exactly 3 minutes.
18. Luminance completed.
19. Repeat steps 1-18 for the Red filter but use a 34-second exposure.
20. Repeat steps 1-18 for the Green filter but use a 20-second exposure.

Next came processing in APP:
21. Create 7 RGB composite images for each panel using my technique for transforming W12, R, G data into LRGB.
22. Use HSL Selective Color to push Cyan to Blue and Orange to Red.
23. Do a minor stretch and saturation.
24. Export the panels.

Next came Affinity Photo:
25. APP refused to create a mosaic using noisy panels, so I had to denoise the panels first.

Back into APP:
26. Create the mosaic using the denoised panels.
27. Export the mosaic.

Back into Affinity Photo:
28. Crop.
29. Adjust curves.
30. Export.

William Optics 71mm f/5.9
Atik 314E CCD
GSO Wratten #12
Optolong Red and Green
U235-Pro Web App

Brian
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timh
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Joined: Mon Aug 26, 2019 5:50 pm

Re: 7-panel mosaic in 110 minutes

#2

Post by timh »

Hi Brian,

That is ingenious and worked very well. The colours are good - is this still the achromat?

It is also nice to see some 'real' astronomical thinking being applied. Some historical resonance to capturing sky strips like that too - I seem to recall that William and Caroline Herschel took a similar approach to systematically map the nebulae and star clusters as the heavens rolled by above their observatory in Slough in the eighteenth century. I sometimes think of their efforts - cold and perilously suspended high in the air above their speculum mirror - as I sit in the warm watching an image of Caroline's rose (and many other objects that they discovered) slowly build on the screen.

Something (maybe more) that I don't understand though. Once the luminance was done and you cycled back to the start of the strip with the other filters how did you find exactly the same RA start point for each filter? I am thinking that you would have had to plate solve on each occasion and then pick something specific (the needle galaxy?) and time or adjust the RA position manually to put it exactly centre-field or something?

Anyway interesting.
thanks
TimH
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oopfan
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Re: 7-panel mosaic in 110 minutes

#3

Post by oopfan »

Hi Tim,

I am glad you liked it. I just created a video and uploaded it to one of my channels at Rumble:
https://rumble.com/vegntl-serene-pursui ... uster.html

I was inspired by my love of simply shutting down tracking and watching stars go by. There is something very relaxing about it. It got me thinking that it might be cool to make a high(er) quality experience. With my kit, a stack of 16 minutes is still fairly noisy, but it is better than a 2-second exposure without the trails!

To answer your question, I formulated the plan using C2A planetarium software. I knew that I wanted to include the Needle Galaxy. It just happened that the 7th panel, west of The Needle, centered on a bright star that I could easily recognize and center without the aid of plate solving. So, the process of "rewinding" to the first panel was fairly painless. I did not plate solve after drifting to the next panel. But I did check the alignment against C2A. My first attempt at this mosaic was three days earlier when I learned how critical it is to drift EXACTLY 3 minutes. Being off by 1 second accumulates when you get to the last frame. Fortunately, I was having tracking problems that night, so I just chalked it up to a learning experience. Last night I put the failures behind me and got this result. APP fought me, but I got around it. Of course, it could use more integration time, but I am happy with it.

Thanks for your interest. I appreciate it.
Brian
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turfpit
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Re: 7-panel mosaic in 110 minutes

#4

Post by turfpit »

Brian

The video is very good - serene! I acknowledge your planning, persistence and stamina in collecting the data.

Dave
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