What is the focus distance of a 3D screen?
There are a number of aspects to the perception of a 3D world. While looking into how cinema and TV 3D systems work recently, I found the following Wikipedia articles useful on how the illusion of a 3D world is generated:


Stereoscopy
Depth perception


The articles on 3D Television, 3D film and Head-mounted displays have some coverage of the issues with 3D display systems, since they do not work the same for all individuals.

Generally 3D display systems ignore convergence and accommodation as a mechanism for generating depth and instead depend on parallax and the brain being able to assemble an approximation of the 3D scene without the information from those cues.

In head-mounted display systems such as the Oculus Rift the image focus is usually at infinity.