This lens is one of Pentax's three FA Limited offerings - the others being the FA 31m and FA 43.
It is a lens that really needs to be used to be appreciated. Build like a well-engineered watch, it delivers the much-maligned "3-D effect" even to folks who don't believe in the "3-D effect".
This lens will make you a believer. Sharpness, contrast, bokeh... pixie dust. It's probably my favorite overall telephoto in two mounts.
Some CA wide-open. Not a super-fast focuser. Really the biggest shame with this lens is that Pentax does not offer a FF camera to shoot it on.