
98 OPTICS FOR ENGINEERS
• In object space, we call these the entrance pupil and entrance window. In image space,
we call these the exit pupil and exit window.
• The pupil is the aperture that subtends the smallest angle from a point at the base of the
object or image.
• The window is the aperture that subtends the smallest angle from a point in the center
of the pupil.
• All other apertures have no effect on rays traveling through the system.
• The functions of the apertures might change if the object is moved. Such a change is
usually undesirable.
• In object space or image space, the pupil and window may be before or after the object
or image, but