The Focus Adjustment is in the Service Manual.
It adjusts "focus." I am not trying to be smart, I just don't know another word.
It's like the focus on a pair of binoculars. Moving the focus lever up or down makes the picture go blurry.
When you hit the Menu button, the Focus Lever makes the text characters razor sharp or go blurry. Also, if you get close enough to be able to see the pixels on the screen, moving the Focus Lever will make them very sharp or blurry.