Focus

Focus was an aid item unused

Gameplay
Focus only exists as a Pip-Boy 3000 icon image, found in the game files, depicted as an eyedropper bottle with "FOCUS" written on it.

Behind the scenes
According to Joshua Sawyer, Focus' effect would've been to decrease the field of view slightly, and even more so when aiming down sights, allowing for larger visual profiles of distant enemies. The effect, however, did not work when using scoped weapons.