To remove protuding two pins in the upper half, dismount lens back by loosening the 3 bright screws.
Then, better lift off the back with the back downwards, cause here's what's underneath: Two tiny metal pins sitting on springplates. I was lucky that they did not fall into the lens. Take the pins away.
That's what the pins transmit: 6 different contacts are seen. The aperture ring has 14 click-positions. Wonder how accurate this thing is :-)
I've finally put tape over the two holes from the pins. Not the best way in the world, but does the job for the time being as a dust seal.
Full open bokeh, near distance. Tree is some 5m+ away.
Full open, little further focus.
Stopped down ca. f/11. Here's the effect of the square aperture - the square stands on the tip, so you're getting 45° angles to the frame.
