Based on a quite resonable seeing prediction on the 6th of March 2025, I decided to test the lucky imaging capabilities of the Player One Poseidon-C combined with the C 14 at f7.7. FWHM estimations in Sharpcap revealed reasonable good seeing conditions with ~ 1.5" - 1.7" FWHM. Unfortunately, exposure times below 1 s did not significantly improve the FWHM values, so I opted for exposure times of 2 s resulting in a higher s/n ratio. In order to acquire a reasonable amount of data, the FWHM threshold in Sharpcap was set to 1.7". Creating 60 s stacks with the live stacking option in SharpCap worked flawlessly. However, the dithering interval was a little bit too large, so the fixed pattern noise in the final stack is still quite dominant.

If you want to process the data yourself, I uploaded the raw stack straight out of SharpCap, cropped and aligned to synthetic reference stars in PI here

Equipment

+ C14 & Celestron 0.7 reducer @ 2747 mm (f/7.7)
+ Player One Poseidon-C (cooler = off)
+ Celestron EF
+ Tempest Cooler
+ Omegon Dew Heater
+ Astrozap Dew Shield for C 14 Hyperstar
on CGE-Pro mount

Autoguiding:
Artesky 70 mm Guidscope (f=400 mm)
ZWO ASI 120 MM mini
PhD2 (Multistarguiding)
Dither every 60 s by 5 px

Data Acquistion

light frames:

2025-03-06
- OSC (gain=550, offset=1200) - 900 x 2 s

acquired with Sharpcap

calibration frames: 60 x 1 s bias frames

Average FWHM:
Final stack: 1.6"

N.I.N.A:
collimation, auto-focus, three-star polar alignment, plate-solve on NGC 2392

SharpCap:
To avoid the processing of 900 x 2 s subs, I used the live stacking option and saved the resulting subs every 1 min, so regular processing workflows can be applied to the resulting subs. While this approach simplifies the data processing significantly, it also introduces an additional overhead for aligning and stacking of the subs during the data acquisition. Another advantage of SharpCap is the FWHM filter, so you only record subs below a given FWHM threshold. As mentioned above, I also applied dithers every 60 s by 5 px to separate the signal from fixed pattern noise. Finally, make sure that you allocate enough RAM for Live-Stacking, define the output format as 16 bit Fits and write the stacks to separate directories.

Post-Processing (PixInsight)

Calibration & Stacking - image calibration (bias only)- image registration
- image integration with pixel rejection (windsorized-sigma clipping)
- drizzle integration (drop shrink = 0.7, scale = 2)

OSC (linear stage)

- 1st dynamic crop
- Script -> Image Analysis -> Image Solver
- create synthetic starfield image using the "Catalog Star Generator" under "Script->Render"
- align RGB channels of data to synthetic starfield
- RGB Color Combination to create new RGB image with improved channel alignement
- 2nd dynamic crop
- Script -> Image Analysis -> Image Solver
- DBE using GraXpert (Subtraction of background)
- BXT (AI version 4, sharpen stars= 0.33, Adjust star halos = 0.0, Automatic PSF, Sharpen Nonstellar = 0.53, LuminanceOnly = on)
- SPCC failed, so I used the AutoColor script by Hartmut Bornemann instead
- GHS

OSC (non-linear stage)

- reduce noise with NXT, AI version 3, Intensity/color separation, Denoise Intensity: 0.75, Denoise Color: 0.9, Iterations: 2
- extract stars with SXT

OSC (starless image)
- create luminance mask
- apply and invert lum mask and darken/desaturate sky background by curves transformations
- remove lum mask
- set new black point by GHS
- apply lum mask
- MMT - Bias = 0.1 on layer 4
- LocalHistogramEqualization (Kernel Radius: 126, Amount: 0.2, Histogram Resolution 12-bit)
- Color Saturation enhancement of the nebula
- remove lum mask

OSC (stars)
- Color Saturation enhancement

OSC (final image)
- blend stars with pixel math combine(RGB,stars,op_screen()) back into the image
- create, apply and invert lum mask
- set final black point of the image by Histogram Transformation
- final 1080p 16:9 dynamic crop

Location: Schwentinental (Germany)

- CS Daniel