This is a great technique to separate your subject from the background. I have used this before for portraits and wildlife shots. However have not tried to compose the out of focus areas as much as with these shots.
The spring flowers are coming into bloom in our local woods whilst some winter and autumn colours are still around. I thought it would be good to try to capture the spring colours with the autumn colours out of focus to give a varied position to the new life.
The blossom was over and in front of a body of water. This was distracting at f8 but I could see it added context to the potential of a shot. I experimented and was most happy with f5.6 as at f2.8 the back of the blossom was out of focus and the effect had gone too far.
The dandelion was surrounded by Petals from the blossom that the breeze was bringing off the trees. I wanted to show the colour and more detail so the viewer knows what the colour is. The shallow depth of field both in front and behind give just the right amount of detail. At f5.6 the foreground detail became too sharp and so distracting.
I wanted to separate one flower in this shot but have it surrounded by other patches of colour so the viewer can see it is part of larger collection of flowers in a sea of green. In actuality four flowers are on the plane of focus so better planning could have achieved the shot I aimed for.
After the previous shot not quite working on my way home I had been thinking about the level focal plain and it started to hail. I thought if I could apply this plane to the hail. So I set up the camera and auto focused on a patch of grass then turned off the auto focus. Allowing me to capture the hail against the trees and farming machinery in the background. Even though the whole scene isn’t in focus you get the composition.