Some white light solar imaging

Solar imaging is not exactly my specialty. However, I find it very interesting, especially now, in a period when our star is very active, so that a wealth of details (mainly sunspots) can be observed on its surface even in white light. Having recently purchased a second-hand Lunt Herschel prism and a Baader Continuum filter, I did an imaging session.

The Baader Continuum filter is a 10-nm bandpass filter, centered at a 540-nm wavelength.Visually, it appears bright green: its purpose is to increase the contrast of the features on the solar surface in white light (solar filter or Herschel prism). As much as it improves the view in telescopes with refractive elements (refractors, particularly achromats, but also catadioptric reflectors), it becomes totally useless for H-apha imaging, which takes place at a markedly different wavelength.

Therefore, I decided to try my hand at solar imaging for the first time in years, also enticed by the huge number of sunspots. For imaging I used my Pentax 75 refractor, my Lunt Herschel prism, my Baader Solar Continuum filter, a 2x Orion barlow lens (producing a 1000-mm equivalent focal length), a QHYIII290 B/W camera, and a Losmandy G11 mount.

All footage was acquired at 1024x768 pixel resolution, 8-bit color depth, 70 fps, with individual SER videos lasting between 60 and 90 s. The images were obtained by aligning and stacking 30% of the frames from each video in Autostakkert! 4. Final sharpening was done in Registax 6 and colorization in Photoshop.

What really astonished me is the crispness of the final images produced with this optical configuration compared to a “traditional” full-aperture filter (e.g. made from Astrosolar): probably the small scope aperture played a role in terms of susceptibility to seeing. However, I can say without a doubt that these below are my sharpest white-light solar images ever. Enjoy!

PS many thanks to my good friend Alessandro Gambaro for his useful tips!