If you look at almost any portrait or wildlife photograph, you’ll notice that the background is out of focus. The same is true of sports or action photos.
This shallow-focus quality, known to photographers as “depth of field” is a powerful way to control the viewer’s attention. For painters, controlling focal depth adds tremendous realism to close-ups, but surprisingly few artists use it.
This may be because our eyes naturally shift focus from near to far when we look at the real world. As a result, our minds construct the misleading impression that everything around us is in equally sharp focus.
The reason cameras produce a shallow depth of field is that when you photograph a subject with a telephoto lens or with the aperture wide open, the camera can only focus on one plane of distance at a time. Everything else is blurry, and the blur increases as objects get farther from the plane of focus. Very bright highlights burn out the film or digital sensors, and may appear as sharp-focused circles of various size.
These details are taken from oil paintings for Dinotopia: Journey to Chandara to show how I used this photographic effect for fantasy paintings. If you’re painting in oil, you can use larger brushes and a wet-into-wet handling to achieve this impression.
But don’t overdo it. Effects like this are like a spice or a perfume, better if they are sensed unconsciously by the viewer, rather than jumping out as an obvious trick.