Capturing the Veil Nebula: A Beginner's Guide to Guiding and Processing

Embarking on a journey into deep-sky astrophotography can be both exhilarating and challenging. My latest adventure led me to the magnificent Veil Nebula, and for the first time, I put guiding to the test. The results were nothing short of fantastic, allowing me to achieve crystal-clear 5-minute exposures with perfectly round stars!

The Setup and the Shoot

While I had the capacity for longer exposures, time constraints limited my integration to a total of 34 minutes, broken down into 8 exposures of 180 seconds and 2 exposures of 300 seconds. Here's a look at the gear that made it happen:

• Camera: Minicam8
• Filter: HPF (High Pass Filter)
• Mount: Eqm-35
• Guider: Meade LPI-GM on a ZWO OAG

Due to the limited time, I couldn't acquire calibration frames (darks, flats, bias). This is usually a crucial step for optimal image processing, but I decided to push forward and see what I could achieve.

The Processing Pipeline

For stacking and processing, I turned to Siril, a powerful and free open-source astrophotography software. I performed some basic stretches and color calibration to bring out the details of the nebula.

The Mystery of the Halo

As you can see in the image below, there's a distinct halo around a particularly bright star. This sparked a discussion among fellow astrophotographers:

Is the halo caused by the filter? Or something else?

One of the comments suggested that a good UV-IR blocking filter might help mitigate the halo. The lopsided nature of the halo could also indicate a collimation issue if using a reflector, or a tilt in the camera plane. Interestingly, another bright star in the frame exhibited a similar pattern.

My initial thought was that it might be related to the light pollution filter I was using. Further advice pointed towards potential culprits like the camera's AR window or the bandpass of the light pollution filter extending beyond 700nm. For 1.25" filters, a Celticbird UV-IR blocking filter, costing around $15 on Amazon, was recommended. It was also suggested that stacking the LP filter on top of the UV-IR blocking filter could be beneficial.

What's Next?

This first attempt at guiding and processing has been a valuable learning experience. I'm excited to explore ways to address the halo issue, perhaps by experimenting with different filters or ensuring proper collimation and camera tilt. The quest for the perfect deep-sky image continues!