"smc Pentax 15mm F3.5"
The ultimate wide angle lens Pentax 15mm F3.5 is rumoured to have some association with Zeiss design.....
And some of the very early version are said to have an aspherical element, the first of its kind.
But was abandoned due to high production cost.
smc Pentax 15mm F3.5 Ultra Wide Angle with Pentax LX and Action Finder