Thanks for the comments, Pierovera.
For the deep DOF landscape you're referring to, I used 9mm at f/7.1 on a m4/3 body. This is equivalent to around 18mm f/14 on a 35mm camera. I was crouched behind the edge of the rice field and focused a couple of metres into it. According to http://dofmaster.com/dofjs.html
this creates a DOF from around half a metre to infinity, so everything is in sharp focus. In fact, I could have probably used f/5 and still had sufficient DOF.
One of the benefits of cropped sensors and UWA lenses!