Well... I couldn't resist. I was going to wait until tomorrow.. but I just turned the right screw about 1/3 revolution (vaguely educated guess), went out into the backyard, and magically everything seems to be coming together!
It's not perfect.
But it's 100% better than it was before. I could happily live with my binoculars as they are right now.
After the improvement I've just seen from a dumb guess, I'm looking forward to tinkering with them in the daylight tomorrow. There's only so much you can do in PJs and slippers, using a wheelie bin as a tripod.
