Charting New Celestial Territory: My First Foray with Sloan Photometric Filters

As an amateur astrophotographer, the quest for new techniques and clearer skies is an endless journey. Recently, I decided to venture into the world of photometric filters, specifically the Sloan set, with my QHY Minicam 8. My goal? To see how these filters, designed for precise photometric measurements, could be creatively employed in capturing the beauty of deep-sky objects.

The Setup: Precision Meets Practicality

To achieve this, I assembled a capable setup:

• Camera: QHY Minicam 8
• Filters: QHY Sloan g’, r’, i’, and also the Ha and Oiii for the nebula.
• Mount: RST-135e
• Telescope: WO Pleiades 68
• Autoguiding: QHY OAG + 290mini

For capture, I relied on NINA, a powerful and flexible tool for astronomical imaging. Post-processing was handled by the industry-standard PixInsight.

Capturing IC59: A Dual Approach

My target for this initial test was the captivating nebula IC59. I employed a dual-filter strategy:

• Nebula Imaging: The classic Hydrogen-alpha (Ha) and Oxygen-III (Oiii) filters were used to capture the gaseous structures of the nebula in a striking HOO combination.
• Star Imaging: This is where the Sloan filters came into play. I used the g’, r’, and i’ filters to capture the stellar population. The real experiment lay in the mapping: I mapped Blue to g’, Green to r’, and Red to i’.

The Processing Pipeline

My PixInsight workflow was geared towards efficiency while aiming for quality. It followed these steps:

1. Weighted Batch Preprocessing (WBPP): To handle calibration, stacking, and registration.
2. Dynamic Background Extraction (DBE): To remove background gradients.
3. LinearFit: To align flux levels.
4. PixelMath Combine: To merge the different filter data.
5. Super-Pixel Calibration (SPCC): For color calibration.
6. NoiseX: To reduce noise.
7. StarX: To separate stars.
8. Dynamic Curves: For contrast adjustments.
9. PixelMath: For the final combination of nebula and stars.

First Results and Future Plans

This initial test provided some fascinating results, showcasing a unique rendition of IC59 with stars rendered in an unexpected color palette due to the Sloan filter mapping. The broader bandpasses of the selected Sloan filters (g’, r’, i’) were chosen for this initial experiment as I didn't have sufficient time to image with the full Sloan set.

While this is just the beginning, I'm eager to explore the capabilities of the Sloan u’ and z’ filters in future sessions. The potential for detailed photometric analysis and novel color rendering is immense, and I'm excited to see where this new avenue of astrophotography takes me.

Stay tuned for more celestial explorations!

Acquisition Details: Sloan filters: 30 frames @ 60s each. NB filters (Ha, Oiii): 30 frames @ 180s each.

Processing Software: NINA (Capture), PixInsight (Processing).