Both of the examples below, from my own 2015 ‘Large Format 52’ project, show use of selective focus to isolate detail and focus attention.
In ‘Reed’ I had pre-visualised the idea of a reed head with a very out-of-focus background, and spent some time experimenting with aperture, eventually settling on f/8 with a 150mm lens on 5×4. I found the background tree first, set against the water of the lake, then found an isolated reed. I like the image because I believe it says something about the sort of wetland locations that reed grows in.
In ‘Into the unknown’ I made use of camera movements to deal with perspective and to place the plane of focus horizontally on the third step (with the left shoe) so that the staircase blurred progressively above and below our imaginary walker. With hindsight, I should have focused on the second step in order to maintain reasonable sharpness in the step below, and to blur the upper part of the staircase further.
The same effect could be imitated in software, such as Nik Analog Efex but I prefer to do it in-camera and ‘old school’.