Wheatstone’s contemporary,
Sir David Brewster, invented another method of achieving 
stereoscopic vision of separate 
pictures, this time using 
lenses. Brewster’s stereoscope 
is still in use today because it is 
so compact and simple a device. 
Half-lenses in front of the eyes 
serve to collimate the incoming 
light (i.e., to render the rays 
parallel as if they were coming 
from a great distance). Thus, 
accommodation relaxes, and 
the directions of gaze of the two 
eyes can be parallel as if they 
are viewing a very distant 
object. Each eye can then view 
its own picture by looking 
straight ahead.