Approach to investigating the spherical aberration variation with the object position in an aplanatic system

In a general optical system, spherical aberration will arise when the on-axis position of an object is changed from its optimum position to another point. Induced spherical aberration can be used to compensate the aberration caused by inserting or removing a medium plate with any thickness that has a refractive index that differs from that of the original. To generate a degree of adequate aberration to balance the aberration from a thin layer, it is necessary to estimate the amount of arising aberration correctly when a point object deviates from its aberration-free position. We analytically induce the exact form of an arising spherical aberration with an on-axis object position for general optical systems that satisfy the Abbe sine condition and express a fourth-order approximation of that form using simple parameters that are conventionally used for the aberration of a thin lens. To verify the correctness of the proposed formula, a comparison between this analysis and simulation results is applied to several sample optical systems using commercial lens-design software.