NGC 3372, Ha/OIII 4-panel mosaic, Argentina/UK collaboration

[turfpit]

Many thanks to Leandro for capturing the data and producing the Ha and OIII stacks.

The images are a 4-panel Ha/OIII mosaic of NGC 3372 (part of the Carina Nebula). Leandro (@leandro from Argentina) captured the data during March/April 2024, over 16 nights to avoid the moon and bad weather. Leandro performed calibration and integration to produce the Ha and OIII stacks. I (@turfpit from the UK) worked with Leandro to produce the mosaic using Astro Pixel Processor. The resultant mosaic was a 600Mb FITS file with dimensions of 9500x6000.


Produced using HOO-2 palette in Tools > combine RGB:

NGC3372_HOO-2.JPG (141.52 KiB) Viewed 5972 times

Produced using HOO-1 palette in Tools > combine RGB:

NGC3372_HOO-1.JPG (121.61 KiB) Viewed 5972 times

Produced using HOO-1 palette in combine RGB plus Tools > HSL Selective Color to reduce green pixels in the HOO-1 image:

NGC3372_HOO-1_HSL.JPG (117.1 KiB) Viewed 5972 times

• Equipment: Montura NQH 3 Orion GoTo System; Telescope Sky Watcher 200 x 1000 Reflector Newton; Filter Optolong L-eNhance 1,25"; Camera Altair Astro 183C Pro; Guiding SkyWatcher Evo 50 x 240 mm + camera Altair 130 M + PHD2; Focus by Bahtinov Mask and SharpCap Tools

• Software: SharpCap Pro 4.1 64 bit, Astro Pixel Processor v2.0.0-beta29

• Data: Lights 90x10s, 60x30s, 45x60s, 30x120s @ gain=400; 10 darks for each exposure; 50 flats; 50 bias frames

• Location: Argentine, Latitude 24°S, altitude 1287m, Bortle 6

An example camera settings file (10s exposures):

Capture_00001.CameraSettings-10seg.txt

(2.17 KiB) Downloaded 202 times

The following document was written based on the information given at:
https://www.astropixelprocessor.com/mos ... by-mabula/
and describes the steps to calibrate/integrate the panels and create the mosaic:

APP-mosaics-v2small.pdf

(97.15 KiB) Downloaded 188 times

Some points to note:

• Use of Astro Pixel Processor at least v2.0.0-beta29 is recommended as this version includes fixes and improvements to LNC and MBB functions resulting in more accurate and faster mosaic construction.

• The data for each panel was calibrated, registered, normalised and integrated before attempting construction of the mosaic.

• LNC (local normalisation and correction) and MBB (multi-band blending) were used during integration to provide cleaner panels.

• LNC (local normalisation and correction) and MBB (multi-band blending) were used during construction of the mosaic.

• Once the Ha and OIII mosaics had been produced, they required registration, normalisation and 'save normalised frames' otherwise combine RGB would not function due to size mismatch.

Again, many thanks to Leandro for the 16 nights to capture the data and testing out the document after we had developed it.

Dave & Leandro

[oopfan]

Congratulations Dave and Leandro! Outstanding collaborative work.

Brian

[turfpit]

Thanks Brian.

Dave & Leandro

[turfpit]

Results of some experimentation to obtain stronger colours.

Using GIMP's Hue-Saturation with Saturation = 20 and applied twice:

NGC3372_HOO-2-saturated2.JPG (148.43 KiB) Viewed 5748 times

GIMP-Saturation.JPG (106.64 KiB) Viewed 5748 times

Using PixInsight Processes StarMask and CurvesTransformation:

NGC3372_HOO-2-starmask.jpg (364.8 KiB) Viewed 5748 times

The original image:

NGC3372_HOO-2.JPG (141.52 KiB) Viewed 5748 times

Dave & Leandro

[timh]

That is an outstanding image Leandro and Dave - really good detail and colour contrast across the entire mosaic! Tim

[turfpit]

Thanks Tim.

Dave & Leandro

[Menno555]

Great colab with outstanding result!
Is there a higher res version somewhere? Would love to see that!

Menno

[turfpit]

Thanks Menno.

This is scaled down to 33% of original size and saved as a JPG with quality 78% to get under the forum 1Mb limit.

HOO2_combine-crop-lpc-cbg-St-scaled .jpg (969.05 KiB) Viewed 5663 times

The 4-panel mosaic is 9341x5770.
The FITS out of Astro Pixel Processor is 616Mb.
Saved as a PNG is 88Mb.
Saved as a JPG with 90% quality is 15Mb

Dave & Leandro

[turfpit]

Some evaluation was carried out, to see if any settings could be improved. An adjustment to the black level (from 30 to 85) resulted in the following for a single panel. Some improvements to nebulosity were obtained.

NGC3372_HOO-2_60x120s.JPG (84.97 KiB) Viewed 5323 times

It was noticed that the histogram for a single 120s exposure was black clipped. The histogram at the left hand side had a value of zero, no gap, meaning some faint data was lost.

120_exposure_bl-30.JPG (51.6 KiB) Viewed 5323 times

This is the bias frame for black level = 30. Note the histogram hitting the left hand side.

black_level-30.JPG (53.77 KiB) Viewed 5323 times

The black level was adjusted upwards and test bias frames captured. Once we had reached black level = 85, the histogram for the bias frame was clear of the left hand side (and the right hand side).

black_level-85.JPG (56.42 KiB) Viewed 5323 times

This resulted in a 120s light frame having a gap of 1072. The gap ensures no faint data is lost.

120_exposure_bl-85.JPG (49.84 KiB) Viewed 5323 times

To ensure consistency and trouble free calibration, the black level of 85 was used for bias, flat, dark and light frames.

This black level of 85 is good for a gain of 400 on this camera. If a different gain was to be used then the black level would need to be re-evaluated using the bias frame technique.

NGC3372 is not in a good position now but at least the settings are established for next year. The Carina Nebula is huge and warrants a 3x3 mosaic (or even 4x4).

The star reduction facility in Astro Pixel Processor was used on this image. Here is the comparison with reduced stars on the left.

sr_v_no-sr.JPG (30.84 KiB) Viewed 5286 times

[Note: On the Altair camera this setting is called black level, on a QHY camera this is called offset, on a ZWO camera this is called brightness]

Dave & Leandro