Celestial hemisphere:  Southern  ·  Constellation: Serpens (Ser)  ·  Contains:  Eagle nebula  ·  IC 4703  ·  M 16  ·  NGC 6611  ·  Sh2-49  ·  Star Queen nebula
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M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018, David Dearden
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M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018

Getting plate-solving status, please wait...
M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018, David Dearden
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M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018

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Description

It's interesting to compare the LRGB and narrowband versions of this image. I’ve tried a lot of different variations for processing this year’s narrowband data for M16. The final colors are very sensitive to what I do in early steps of the processing. Obviously the amount of stretching applied to the various channels matters a lot. I have a version I like a lot that is mostly in golds, but ultimately I think the best rendition is this one where I try to make the dark end of the histogram similar for all three color channels and the OIII still shows up as blue. This is a really nice target for SHO because there is significant emission at each of the three wavelengths. RGB stars were extracted from my RGB image, shrunk a bit with Carboni’s “make stars smaller”, then added using screen mode in Photoshop. Several rounds of “less crunchy more fuzzy” were applied, with the effects masked out for the Pillars and other places where there is detail I didn’t want to lose.

Date: 15-26 Jun 2018

Subject: M16, Eagle or Star Queen Nebula

Scope: AT8IN+High Point Scientific Coma Corrector

Filters: ZWO 31 mm diameter unmounted L, R, G, B, Hα, SII, OIII

Mount: EQ-6 (EQMOD 2.000j)+PEC

Guiding: Orion Thin Off-axis Guider + DSI IIc +PHD 2.6.5 (Win 10 ASCOM)

Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21

Acquisition: Sequence Generator Pro 3.0.2.91

Exposure: 51x180 L, 20x180 R, 20x180 G, 20x180 B, 36x300 SII, 48x300 Hα, 48x300 OIII

Stacking: Deep Sky Stacker 4.1.1 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5.

Processing: StarTools 1.4.332: Combined R, G, and B in StarTools. Binned 2x2, cropped, wiped, developed, HDR, color, deconvolution. Stopped tracking to smooth. Binned L 2x2, cropped, no wipe, and developed followed by HDR. Deconvolution followed by untrack smoothing. Combined L with RGB in Photoshop. Used some layer-masked saturation adjustments, both in the master and in the red channel, to try and retain the red color. A little of Carboni’s Astronomy Tools’ increase star color followed by less crunchy more fuzzy. Used StarTools’ Heal module to extract the stars. Separately processed Hα, SII, and OIII. Each was binned 2x2, cropped the same as the LRGB, developed rather aggressively, HDR optimized, and deconvoluted about 3 pixels. Untrack smoothed. Combined using Annie’s Astro Actions Hubble Palette Creation with dark points set similarly for each channel. Used a bit of curves and some adjustments to vibrance and saturation to brighten the nebula, and layered on the LRGB stars using screen combine. Several rounds of “less crunchy more fuzzy”, with a “reveal all” layer mask used to mask out the effects where there was detail I wanted to preserve. Slight darkening at the end using Levels. AstroFrame.

Comments

Revisions

  • M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018, David Dearden
    Original
  • Final
    M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018, David Dearden
    B

B

Description: This is an attempt to get a “truer” color version of M16 but including the contrast and depth you get with narrowband filters. I used a combination of Hα and L for the L layer, Hα and R for the R layer, G only for the G layer, and B+OIII for the B layer. Each of the 4 layers was processed separately and each was stretched roughly the same amount. Combination was done using StarTools’ LRGB module. I did some slight tweaking in Photoshop using Levels, Hue and Saturation, and Vibrance but otherwise didn’t process much after combining the layers. This is not stretched nearly as hard as the SHO image was, and I think this version turned out better than my straight-up SHO. The gentler approach wins.

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M16, Eagle/Star Queen Nebula, SHO Hubble Palette with RGB stars, 15-26 June 2018, David Dearden