I really like the app so far. My one piece of feedback would be that I'd like the focus button where the aperture number is, so I could have quick, one handed access to it.
I'd go even farther, although it hadn't occurred to me until you wrote this: what I'd really like is an easy-to-reach focus toggle, automatic or macro. I typically only need manual focus when I'm trying to get as close as possible to something.