It is well known that the first-order properties of an optical system are sufficiently specified by the tracing of two meridional paraxial rays through the system, namely the marginal ray, which originates at the center of the object plane and passes through the edge of the stop, and the chief ray, which originates at the edge of the object and passes through the center of the stop. Wherever the marginal ray crosses the axis an image plane is located and wherever the chief ray crosses the axis a pupil plane is located. Moreover, the height of the chief ray at an image plane gives the size of the image and the height of the marginal ray at a pupil plane gives the size of the pupil.
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