New scenes with depth of field

[vromaniello]

For an educational work I have the goal of creating different scenes to show the use of depth of field on different objects.
I already got a simple scene thanks to your following example on using a big aperture of camera.

Here are my results

Now i need to simulate the same functionality on other different simple scenes. I can also use external images, external libraries or objects as shown in the books. What do you suggest about it?

Thanks a lot.