Don't forget the funny DIY focus adjustment on some Zenithar lenses.
These come unfocused from the factory so you have to uncouple the
focusing ring and reposition it in a way that allows the lens to
focus at infinity. Not difficult but strange.
See: http://etischer.com/zenitar/zenitar16mm.html
Although I have already grown to hate the M42 screw adapter, the
Peleng is much more fun than the Zenithar. It is also surprisingly
sharp!
http://web.telia.com/~u40938461/PinkyPentax/KonsthallFE.jpg
Bertil