Oh Boy, it looks like I got something going here ! I knew this would work because I've used it in the past on other types of my research. All that is needed is a thin coating from a Day Glow yellow green marker on a clear filter that one screws into the eyepiece. I'll do a little research and see if I can find a dye that absorbs exactly at 395nm and re-emits in the visible. These types of dyes are used all the time as molecular probes in chemist. Also Wah is correct that many "plexiglasses" like the yellow and pink colors are absorbing UV and re-emitting in the visible.
Here is another thought,that I wonder if Coronada has looked into. They seem to be using a achromat as the objective. I know that is the case in the Ha PST version. The lens is cemented together with a UV curable adhesive. May times these materials also absorb strongly in the near UV even after curing. This one reason I use quartz optics in my research. Just wondering if the adhesive in the lens and also the coatings on "standard" eyepieces isn't absorbing at 395nm and the dimming the image farther ?

- Dave