The chief ray is that ray that passes through the aperture stop. In the object is an on-axis point source, its chief ray will go though the AS.
What if the object is a planar object, located where the on-axis point source is? Will the chief rays from the off-axis points making up the planar, extended object all pass through the center of the AS too?
Will these off-axis points see the same aperture as the aperture stop for the system?
If an object is 3-dimensional, can we still select one aperture in the optical system to be the AS? A 3D object is composed of point sources located on different planes....