I got to thinking today about my 35mm lens that I wrecked by use of a generic lens hood (which in and of itself was over-kill). I used the hood one day when it was still winter, and the snow was flying so I wouldn't have to take a glove off to change apertures.
A few days later when I went to take the hood off, it brought the aperture control ring with it, so I put the lens in the "To Repair" bin for a later date.
As I was dismantling the lens today, I had the rear cap still on the lens, so I wasn't paying attention to that end. The lens has a fairly basic construction. There is a barrel into which the aperture ring and lens optical block reside, and the internal lens mount is incorporated into the rear. The optical block (which includes the aperture blades) has a spacer ring that must not be lost. It does not always come out with the block, and if you don't watch out, could exit the barrel while you are not looking.
So my first thought was to take the aperture control ring off, since it was loose anyway. But that brought the optical block with it. So I'm trying to figure out how it all goes back in so it doesn't seize up like the last time I tried this. It turns out there is a retainer ring on the rear that is threaded onto the end of the optical block, and that it should have been removed first. This I found out when I heard it rattle against the rear lens cap, and it fell out when I took the cap off.
After that, it was just a matter of first putting the aperture control ring back on first (making sure it started on the same thread landing), setting it at f2.5. The spacer ring is next, it just drops into the lens barrel. Then opening the aperture on the optical block, and dropping it into the lens barrel so that the actuator knob for the aperture slipped into the slot in the aperture control ring. Lastly, turn the lens around and screw the optical block retainer back on. Voila!
But I was not quite finished yet. I wondered why the retainer ring came loose in the first place, and that's when I noticed there was a set screw on it. I went to tighten it, but someone before me had stripped the threads, so all I could do was get it back in place.
I'm planning on putting some nail polish on the retainer ring to 1: hold the set screw in place, and 2: keep the retainer ring from backing off. Then I should be able to use it again without fear of it falling apart again. It's either that, or invest in a very small tap and die set, and drill a new set screw hole. Nah, nail polish is less expensive. And comes in such wonderful colors.