Factors of optical realism

Depth of field or focal blur

Depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. It is controlled by the aperture size, focal length, and distance to the subject. A shallow depth of field creates a blurred background, while a deep depth of field keeps everything in focus.

The effect of depth is further amplified by the fact that we have two eyes. The difference in the images captured by each eye is used by the brain to determine the depth of objects in a scene. This also creates an effective blur corresponding to the distance of objects from the focal point.

Diffraction spikes in cameras

When light passes through a small aperture, it diffracts and creates a pattern of light and dark bands. This phenomenon is known as diffraction. In cameras, this creates the characteristic "starburst" effect around bright light sources.