Paraxial optics tells where bundles of light focus
–Can be traced even for rays that don’t get through system
Aperture stop limits rays from a given point on object
–A cone of rays gets through
–If there is more than one limit, than one will give the smallestcone
–Since rays carry light energy, the larger the cone, the brighterthe image
Field stop limits which points on object can produce an image
–In camera example, no image is recorded on the film if it falls outside of the film holder