Geometrical Optics 
The parallel rows of corn yield  
projections to the eye that  
converge at the horizon. 
 
What a scene looks like in a  
camera obscura, on the retina,  
or through a camera is a  
function of geometrical optics,  
the propagation and projection  
of light on a surface. All that we  
need to know about geometrical  
optics to understand the  
formation of the image derives  
from two simple principles: (1)  
light travels in straight lines,  
and (2) the angle formed by the  
two rays of light from any two  
points in the scene as they  
enter the eye is proportional to  
the angle between the rays as  
they are projected on the  
retina. Thus, the size of the  
image cast on the retina is  
determined by the visual angle 
—–the angle formed by the  
incoming rays. How these  
principles determine the  
precise image formed on the  
retina depends on whether or  
not the object viewed is in the  
frontal plane—–that is to say, in  
a plane perpendicular to the  
line of sight—–and also on the  
object’s distance.