Don't own a Lytro but still want to play around with the focus of your images after you've shot them? The Chaos Collective has a hack for your DSLR to create a similar effect as to that of a light field camera like Lytro. First thing you have to do is shoot just a few seconds of video.
They write, "The idea is simple; take lots of pictures back to back at various focal distances (collecting the same information, but over time). Then later, we can sweep through those images to pick out the exact focal distance we want to use. But wait... A sequence of images is just a video! And since most digital SLRs these days make it super easy to capture video and manually adjust focus, that's all you need. Just hold the camera very still (a tripod is nice, but not necessary), shoot some video, and adjust the focus from near to far. That's it."
Read their full set of instructions here.