Today I managed to gather the best data so far in support of having visible filaments in oxygen, over the solar disk. Nota bene, they have to be dark and dense filaments, as seen in hydrogen alpha, but they are there. A nice addition to the smudges.
I used the a customized SolEx spectroheliograph, with an 1800 ln/mm holographic grating, an EO in-cone prefilter centered to 775nm, ML Astro’s slit, and Altair Astro’s IMX 678M camera implementation. The assembly was mounted to a 72/430 doublet.
Because oxygen darkens over plages, filament observation is extra hard. But blink comparing against AIA 1600 and the iron from below the oxygen triplet reveals no candidate plages.
