When we design optical systems we like to write the merit function to include constraints that will make the lens more manufacturable. One of the most important things to constrain is the surface spherical contribution. This is just the amount of spherical aberration that each surface contributes to the total. If this is done properly, it will reduce the sensitivity of the lens elements to decenter. This is because the lateral shear of spherical wavefronts creates coma, which will significantly reduce MTF.
In Zemax, the spherical contribution of individual surfaces can easily be constrained with the SPHA (spherical) and the ABLT (absolute value less than) operands as seen below.
The amount of surface spherical to allow is somewhat subjective, but it is common to keep the maximum surface spherical (in waves) to < 215/ (f/#) for commercial optics and < 22/ (f/#) for diffraction limited optics. If the design is too constrained by these, be sure to make those components centerable so they can be adjusted during assembly.
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