The Ray Tracer Challenge

Focal Blur

Focal blur helps bring the viewer’s attention to the subject of the image by making it appear sharply in focus. Objects that are too far from—or too near to—the camera will appear out of focus. Here’s an example:

The focus here is on the three balls in the foreground; the smaller balls in the background and the reflections on the walls are blurred to emphasize their distance and lack of importance.

To make this work, you need to simulate a camera with a larger aperture—the hole through which light enters the camera. By default, your ray tracer mimics a pinhole camera, with a hole exactly large enough for a single ray of light. This ...