I took photos of tarot cards and a crystal ball from the Stanford Light Field Archive and averaged them following a shift to produce the effect of changing the camera focus from far away to close up. Since the light field photos were taken in a 17x17 grid, I took each photo and found it's shift with it's grid value (u, v). I then multiplied this shift by a constant value: C * (u, v). Then, each photo was was actually adjusted by this weighted shift and averaged together. I set my C value from -3 to 2 incrementing by 1, and this created the effect of focusing the camera from close to far.
Below is a gif showing the transition from a far away focus (C = 2) to a closeup focus (C = -3).
I took took light field photos of the bunny and chose the [8, 8] image as the center image. I then took the average of photos around the [8, 8] image at a radius of 0, 3, 5, and 8. Below are the results of the adjustments from setting the radius at [0, 3, 5, 8] in that order. The lower radius mimics a smaller aperture while the larger radius mimics a wider aperture.
I learned that shifting the focus of images is surprisingly easy to implement, but requires a lot of carefully captured images to achieve such a simple looking effect.