Solar CaK

(Edit)
I have a 2" Baader CCD Blue filter (#245847B) sitting about 60mm in front of the stack as an ERF.
Then a 1.25" Omega 40nm 394nm, an Omega 390nm UV cut, and then a Omega 2A 393.7nm. The final filter is a #1 filter (yellow) from a CaK PST.
Last time I measured the bandwidth it was around 1A centered just to the blue side of the CaK core.

This is a very interesting set of filters! I bought an Omega CaK filter on eBay about 12-15 years ago, but I didn't know how to use it properly and sold it because the result looked more like a photosphere. I'm currently using the Lunt CaK + Antlia CaK + Antlia ERF. Overall, I like it; it allows me to see prominences in calcium. I especially enjoy shooting timelapses in calcium and hydrogen.