The person who opened the door is a gentlemen. I won't pretend I didn't swear at him inside when I realized I was on the floor. But, he was very apologetic, and genuinely concern about my fall. We exchanged information, and he would pay for the the cost of the repair of the bike. Many people would just try to avoid any and all responsibility. In any case, the handle bar hit my upper left arm and my right rib. There is a huge bruise on my arm and my rib hurts like hell when I cough, laugh or sneeze. Again, my helmet probably saved me again. If you bike, please wear a good helmet. If you drive, please do look before opening the door, especially when parked on the street.
Back to gears. Soulnibbler wanted to see the picture of the focusing helicoids. You can see it below, along with the 17-31mm mounted on the 75mm f2 lens plus a bonus sample picture :-)
M42-mount helicoids: 12-17mm on left, 17-31mm on right.
17-31mm helicoid on the Taylor-Hobson 75mm f2 with the c-mount adapter. Click to see larger