PN G035.9-01.1 in Aquila

Sh2-71 (also cataloged as PN G035.9-01.1) is a bipolar planetary nebula located about 3300 light years away. The progenitor star was long assumed to be the bright blue star at center, which is a binary, but new research suggests a very faint star not visible in this image might be the parent. This is a bicolor narrowband image. Sh2-71 was mapped as Ha and OIII respectively for red and green, and an 85% OIII/15% Ha blend for blue. RGB was used for star colors.

Exposure: Total exposure time about 18.5 hours, 27:25 x 20 mins Ha:OIII, 16:16:16 x 2 mins R:G:B. All bin 1x1. Ha and OIII were captured in May and June 2018; RGB was added in October 2018.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: FWHM of best subs about 1.9 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: Full scale

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon 5nm Ha/SII, 3nm OIII, Type IIe LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.0.8
Guide SW: PHD2.6.3, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2
Processing Workflow by Workspace in PixInsight 1.85

1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
Subframe Selector to confirm selections and weight by FWHM and SNR
StarAlign to register frames
Local Normalization (scale 128 for Ha and OIII, 256 for RGB)

2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop

3. Narrowband Linear Processing
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask for deringing support (on Ha channel only, and only on nebula)

4. Narrowband Stretching
Histo Trans
Curves Trans
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred luminance frame as a mask to protect highlights

5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans
Curves Trans
Boost saturation on stars with Curves Trans
TGVDenoise

7. Color Combination
Merged narrowband channels in PixelMath, mapping Ha:OIII:(85% OIII + 15% Ha) to R:G:B
Very mild (radius 64, contrast 1.2) Local Histogram Equalization on nebula core to enhance contrast
Deconvolution (parametric) with mask to sharpen core
HDRMultiscale Transform (using Small Scale 24 and manual midtones balance) on nebula core to enhance contrast

8. Combine Core and Background Nebula Images in Photoshop
Layer HOO image on RGB stars
Set RGB as color for stars and background, using a mask to exclude the nebula
Use radial blur tool to reduce blue comatic halos on brighter stars
Save to Web as JPG