Originally Posted by Steve Mack
Sorry, I was unclear about the camera the lens is stuck on: it's a Honeywell Pentax H1a. No batteries that I know of.
Thanks to all who have replied so far.
With best regards.
Wow, an H1a. What a classic. I agree it is the stop=down pin hitting the trip bar at the bottom of the mirror chamber. Make sure the switch on the lens is set at A instead of M.
John, Mount Vernon, Virginia USA