To reassemble the aperture retention ring, place the ball bearing on the farthest left detent spot. Put the spring in the retention ring with a dab of silicon grease on it to keep it in place. Star to screw on the ring until it starts to catch on the bearing--Get the bearing to align with the bored hole it rest in. Use the same process as disassembly to continue screwing the ring in. Use a credit card or tweezers to hold the ball up until it is retained inside the hole. Continue screwing the ring down until the blades are fully open. The detent ball bearing will be in the "f2.5" click spot (the one pictured with the bearing in it is the f2.5 detent)
Dab of silicon grease on the spring to keep in in place.
Here's your last chance to make sure all those elements are clean. I use naphtha on a micro fiber cloth to clean all the elements. Don't soak your cloth in it, just a few drops. Rocket blow everything--Once its back together, it would really suck if your OCD kicks in and you see a dog hair inside the element and you disassemble it again to remove it.
