That article is why I bought it, but, I confess that I didn't see the bit about the filter. The Pentax camera instruction book has a little about filters. Looking again at the small end of the lens, the flat glass there is held in by a roughened ring. It was a little loose and unscrewed all the way.
Surprise, it was a filter retaining ring.
I never saw the like but it works great.
Now I have 2 filters as one was already in there.
