I'm wondering if anyone has any advice, or experience on this: how to make self-portraits using a field camera with a little more precision than guess work and months of trial and error.

Over the past couple of years, I've made a lot of self portraits. It's not just an ego thing (honest) it's more that I'm the most likely person around when I want to make photographs, and experiment with new ideas. With pinhole it's pretty straightforward: I can set up, then wander into frame and even if the shutter's open a little that will just vanish in an exposure of several minutes, and, like magic everything is in focus. Many hundreds of sheets of film mean I know pretty much what my favourite pinhole camera sees, and how it eats light, so I'm happy composing a shot without any viewfinder or ground glass.

But now I'm playing with lenses, everything has become far more complicated. I could, of course, just stop down to f64 but I'd rather not.

The picture attached is sort of a semi-self: I had a lot of help from my beloved. i.e. I set things up and, with him sitting, got things composed and focused, and then switched seats with him. He then gave me directions until I was back in the right place so my eye was sharp (and, given that this was the first time he'd really looked at an image on gg, the whole left-a-bit-right-a-bit process was, um, long-winded) and, while trying not to move at all, I then talked him through the process until the exposure was made. I think we did pretty well, as a team, but I'd rather work alone and not stretch his patience much further.

What I'm trying to work out is how on earth I can do this on my own. The knotted string trick works for checking the point of sharp focus, but I can't figure out a way to get to that point without being in two places at once. Short of cloning, am I missing something really obvious? Any brainwaves?

(details on this one: toyo 45cf, with a wollensak raptar 101mm, wide open at f4.5, for about half a second in window light on FP4+.)