With my usual setup, the EQ3-mod, mountpusher, Baader Astrosolar ND3.8 Film, TS-Optics 76/342 TS76EDPH, ?filters?, ASI 178MM (cooled), I though what if I got creative. I put in the IRpass 850 filter from ZWO, and added an additional ND1.3 filter, because the ND5 front filter was a bit out of reach. Afterthought: I don’t know the transmittance curve of the ND filter, so maybe what I photographed is actually undefined-ish.
With the above in mind, the transmittance curve of the ZWO IR pass filter, along with the response curve of the camera, gives us a gentle hill around the magic 850 nanometer region, which is where the Calcium II triplet resides, and should draw the active regions in a similar way the CaK does. No matter what filters I used, these active regions show up in all of them, from UV, through CaK, deep blue, even in oxygen III, solar continuum, and 7nm Hα.
Digging out the details did take a good while, since the granulation (I guess it is that) on the surface of the Sun causes a sort of pixel noise to appear that doesn’t fare well with my emphasizing solutions. This „pixelnoise” is also present in my CaK images, and looks exactly the same on the DSO resources I checked at 160 and 170 nanometers.
ND1.3 and telescope glass aside, this is the wavelength-intensity area that should be in the photo. Telluric absorption is not that interesting in this region, and is uniform across the solar disk anyway.