M42 screw-mount, fixed focus lens, 160° on the diagonal. 12mm outside camera! in production from 1963 to 1967.
It’s nice to see how much the scheme resembles Hill’s Sky Camera lens
To get an idea of how small the lens is I pictured it on an old Pentax ES II, (thanx to my friend and ultrawide lover Franco Zampetti)
The original rigid case for this lens is a microscopic pochette.