You're confusing a few ideas here. Focus has to do with the fact that the real world can only be projected on to our retina sharply at one distance. The letters

You're confusing a few ideas here. Focus has to do with the fact that the real world can only be projected on to our retina sharply at one distance. The letters in your peripheral vision are hard to make out not because they are out of focus but because they are falling on a part of the retina that has low resolution (also see "visual crowding"). The wikipedia page on optical focus has a good explanation of focus blur. Suffice it to say real scenes have dynamic focus blur and computer screens don't and we can subliminally tell the difference. This tech will make rendered scenes look more like real ones.