(Warning, speculation!
)
Most interesting! I almost wanted to say P.D.F. but something stopped me... the bayonet is a male, the P.D.F. usually is female... but who knows they made so many variations of P.D.F. for the army and every one is different... the advance knob also confuses me in regards to this being P.D.F. - if this one has automatic rewind then all the later ones that use Zorki-4 would probably have it... which makes me think it may be some kind of possibly medical application where quick advances are needed - like a predecessor of Zenit MT with same purpose?
But then again, the MT's do not have the automatic advance either. Which bring me to an idea of this camera being a part of a system like Yolochka to do rapid document copying.. just thinking out loud
...
