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NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017, David Dearden
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NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017

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NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017, David Dearden
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NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017

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Description

I don’t think I’ve ever worked as hard on an image as I have on this one. I’m struggling to get good flats with the Tamron lens I’m using for this object, and eventually decided to just use darks and do the vignetting corrections in software. That worked fairly well, except it did not account for dust on the sensor very well so I had to fix that “by hand” after the fact. I got both narrowband and RGB data for this target, then played with both Hubble palette (to maximize contrast) and HSO (to try and make the image look closer to “true” color) combinations. Both of these narrowband approaches left me with star colors I didn’t like. So I took another look at the RGB and decided to attempt to put RGB stars in the narrowband DSO image. The approach I took this time worked better than things I’ve tried in the past. I had to doctor the RGB image to remove rather nasty blue halos from the stars, because apparently my blue data was not as well focused as the rest. I used Annie’s Astro Actions to produce separate star and DSO layers for the RGB and both the narrowband combinations. I then screen combined the RGB stars on top of the DSO layer, and used levels to brighten the stars enough to completely fill the holes left from removal of the narrowband stars. The resulting stars don’t look terrible to me except perhaps for some of the brightest where the 6-pointed diffraction pattern from the lens’ iris doesn’t look as good as I’d like. I’m not sure whether I like the Hubble palette or the HSO combination better (though probably the HSO), so I’m posting both and of course would welcome comments and/or suggestions.

Date: 30 Nov; 8, 10, 11 Dec 2017

Subject: NGC 1499, California Nebula

Scope: Tamron 135 mm f/2.8 lens stopped to f/4

Filters: ZWO 31 mm diameter unmounted Hα, OIII, SII (7 nm bandpass); R, G, and B

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

Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.4.5 (Win 10 ASCOM) using predictive PEC algorithm

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

Acquisition: Sequence Generator Pro 3.0.0.3

Exposure: 47x300 Hα, 24x300 SII, 29x300 OIII, 20x180 R, 28x180 G, 29x180 B

Stacking: Neb 4.1.6, darks only, trans+rot align, Nebulosity 1.5σ stack and align.

Processing: StarTools 1.4.328: Aggressively stretched and deconvoluted Hα & SII channels in StarTools; was less aggressive about OIII because I didn’t see much detail in it. Aligned the processed layers in Nebulosity then combined in Photoshop using Annie’s Astro Actions’ Hubble Palette module or the RGB module with Hα mapped to R, SII mapped to G, and OIII mapped to B. Likewise combined R, G, and B to produce an RGB image. Separated stars from DSO using Annie’s Astro Actions. Screen combined RGB stars on top of narrowband DSO-only image, and used Levels to brighten stars to the point that dark gaps no longer were apparent. Lots of other cosmetic cleanup.

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Revisions

  • NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017, David Dearden
    Original
  • Final
    NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017, David Dearden
    B

B

Description: Hα in R, SII in G, and OIII in B

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NGC 1499, California Nebula, HSO and SHO, 30 Nov+8,10,11 Dec 2017, David Dearden