Chapter 3

Paraxial Rays and First-Order Optics

Suppose we trace a number of meridional rays through a lens from a given object point, the incidence heights varying from the marginal ray height Ym down to a ray lying very close to the lens axis. We then plot a graph (Figure 3.1) connecting the incidence height Y with the image distance L′. This graph will have two branches, the half below the axis being identical with that above the axis but inverted. The precision of the various point locations is good at the margin but drops badly when the ray is very close to the lens axis, and actually at the axis there is no precision at all. Thus by ordinary ray tracing we can plot all of this graph with the exception of the portion lying near the axis, and ...

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