Re: G9 will not hold MF focus in Av mode with screen off, help?
Arrow501: that is a great suggestion, I had not thought of those "features."
Interesting: those features are not adjustable in the menu, if the screen is off (for shooting). But if I turn the screen on for shooting, then the menu shows those features as adjustable. Indeed they were turned on! I turned them off. That's the good news.
The bad news is, that when I set my manual focus, then turn the screen off for shooting, the camera reverts right back to auto-focus, plain and simple. Actually, I now discovered that even in manual exposure mode (M), it does the same thing. Canon must believe that manual focus cannot be useful unless the screen is on (in a way that's true - you can't very well adjust focus with the screen off. But I can think of many photo situations where you would shoot fixed focus, with the screen off, to obtain better responsiveness from the camera).
Apparently, I must now suspect that all of my time-lapse series have been shot with auto-focus on. I've just never noticed before, because if I'm shooting midday, with plenty of light, AF runs very quickly and consistently. Now that I'm shooting dusk scenes, with the light dimming down to darkness, the AF is taking variable amounts of time (ever longer as dusk progresses). Worse: as it gets darker, AF does not always settle on the same focus/distance setting, resulting in random, minute shifts in the image size of the exposures in the series.
I appreciate your great input, but alas my problem is not solved. Perhaps it is not solvable.