M27 Under Backyard Skies: Testing the L-Enhance Dual Band Filter
As an astrophotographer, we often dream of clear, dark skies far from city lights. I'm usually spoiled with Bortle 1 conditions, but I decided to put my new L-Enhance dual band filter to the test right here in my backyard, under Bortle 5 skies.
While the L-Enhance doesn't boast the tightest bandpasses, I was curious to see its capabilities, especially when not battling severe light pollution. Here's what I captured:
The Gear and the Process
- Telescope: 150P Quattro at F/3.6
- Camera: Unmodified Canon 60D (still a limiting factor for Ha sensitivity, but allows for cleaner red stretching)
- Filter: L-Enhance Dual Band
Acquisition Details:
- Dual Band: Approximately 40 minutes of 3-minute exposures.
- No Filter: Approximately 40 minutes of 30-second exposures.
Processing Steps:
My workflow involved ASTAP for stacking, followed by SIRIL for an initial ASINH stretch, background extraction, and star reduction. For final touches like noise reduction, further stretching, and compositing, I used RawTherapee and GIMP.
Interestingly, I also used Starnet to remove stars from the filterless stack, then shrunk those stars and reintegrated them into the final nebula composite. To combat blocky stars upon zooming, I upscaled the image by 2x using Lanczos and sharpened it in RawTherapee.
Observations and Thoughts:
Even with an unmodified camera, the L-Enhance filter allowed me to stretch the red channel with noticeably less noise. It's a good reminder that while camera modifications can boost Ha sensitivity, filters can still provide valuable improvements, especially in moderate light pollution scenarios.
This experiment has definitely fueled my desire for more time under true Bortle 1 skies, especially when exploring the unfiltered potential of my setup. For now, I'm pleased with how M27 turned out!
What are your experiences with dual-band filters and unmodified cameras? Let me know in the comments below!
