Interested to compare notes with anyone else who is adjusting lens focus. Before turning the lens I put two white dots, one on lens and one on lens housing, so I could see the rotation angle. Hold lens cell with one set of thin pliers, turn lens with another set. What I find is:
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angle that lens is unscrewed : focal distance
0 degrees: focus at infinity (initial, stock position)
45 degrees: focus at 32 cm
90 degrees: focus at 15 cm
170 degrees: focus at 7 cm
this is true: to achieve a focal length of "FL", turn the lens CCW by this amount:
For example, if you want FL = 10 cm, unscrew 3.5/10 = 0.35 turns = 126 degrees.
after about one full turn, the lens will be completely unscrewed and fall out, and dust will start accumulating inside the lens housing on the IR filter surface, etc.