First image, decent, using the Altair Astro NUV 7nm 395nm filter.
It should be similar to the Baader CaK filter, and I only got it because it costs less ...
So far I have tried it with the 90mm refractor, but the results were poor.
I was beginning to think that the filter was also poor.
Then I remembered that there is a possibility that some refractors may be opaque to UV rays, so they may work poorly in that region of the spectrum.
I then mounted my old Astrosolar filter (I haven't used it for 10 years) on the 90mm Mak and put the filter on the nose of the ZWO ASI178mm.
I have finally achieved a decent result.
Of course not at the level of the Cak Lunt or Daystar modules, but still at a lower cost.
Baader Astrosolar ND5
mak 90mm Skywatcher
Altair Astro NUV 7nm 395nm
Autostakkert3 and AstroSurface processing