This is the first, "zebra" version, optically the same design as Pancolar 2.0/50. The aperture control switch ("tumbler") should have 2 positions, "A" is counter-clockwise when looking at the front element, "M" is clockwise when looking at the front element - not 3 positions. The rear part of the lens should have an actuator pin that, when pressed, makes the aperture to stop down. Take the lens out of the adapter, remove the lens cap, play with the switch, the pin, and the aperture ring, and you will see how it works. In "A" position the aperture is not closed until the pin is pressed, and should immediately return to open when the pin is released. In "M" position the pin does nothing, the aperture is opened/closed following the aperture ring position. Your adapter may be fixing the pin in a pressed position (not enabling auto-aperture feature), and in this case the position of the tumbler does not matter.