I could have (and would have) used a a one-button switch to toggle AF on and off.
You can set E-510 to manual focusing mode and assign either Fn or AEL
button (don't remember at the moment) to auto focus. So basically you
have manual focusing with one-touch AF. That would have certainly
helped. A longer lens with its focusing range limiter would have
helped a bit, too.
On the second thought, you can also set E-510 to S-AF + MF. That is,
to auto focus with manual override on half-pressed shutter. Or that
was too much hustle in those conditions?
Thanks for posting this, because it allows me to go into more detail. I had started to give more explanation on my website, but decided it was getting too wordy.
I did try manual focus, and setting the function button to provide one-touch AF, and liked it OK...but for 95% of the shots AF was better, and I got tired of hitting the function button all the time. Plus, as discussed below, I decided I needed the function button for something else.
I also tried setting the function button so that the camera went into MF when the function button was held down. I liked it well enough that I used it that way for quite a while, and did get a few shots I would otherwise have missed.
But ultimately it was more useful for me to set the function button to turn on auto-bracketing, so that's the way I used it most of the time. For, say, a troupe of baboons moving between shade and sunlight, I just really couldn't tell what the best exposure would be, and I wanted to be able to bracket really quickly. But for most shots I wanted to pick the right exposure and leave it. So I eventually settled on using the Fn button to switch on bracketing.
The problem with half-press for AF, with manual override, is that you can't use the manual focus until the AF has focused on
something . As with the small-subject-among-moving-grasses photo that I mentioned on my site, the AF hunted the whole time the bird was sitting there. In principle I could have quickly focused on some distant object so that the AF would stop hunting, then recomposed and focused manually...but this wouldn't have worked in practice. For one thing, once I had moved the camera away from my subject, it would take a second just to get him back in the frame again.
All in all, just an AF/MF switch --- preferably one that I could control with my left hand --- seems like the best solution to me. (I'd prefer if it were on the left hand because the right hand already has so much to do).