An unbalanced Seidel sum will alert the designer that he or she must change the system in order to achieve third-order aberration correction before significant progress can be made. Possible changes are: Change the stop position. Add elements with opposing values of the offending aberrations. In general, this means negative elements if the offending aberrations are primarily from positive elements, and vice-versa. Total system power can be maintained by use of the power vs. marginal ray height theorem the power an element contributes to the – system is proportional to its own power times the height of the marginal ray at that element. The system must be re-optimized and re-evaluated after any changes. Often, adding operands that limit third-order aberrations to the Merit Function is a valuable way to constrain computerized optimizations to desired forms. There is a place for global computer searches (if you have plenty of time and are out “no-holds-barred” of ideas, say), but often all that is needed is to refine a system without making radical changes. Constraining the Seidel aberrations (combined with the default ray-based merit function) is a good way to do that. Seidel Diagram from Zemax for a camera lens: Lens: Seidel Diagram:
An unbalanced Seidel sum will alert the designer that he or she must change the system in order to achieve third-order aberration correction before significant progress can be made. Possible changes are: Change the stop position. Add elements with opposing values of the offending aberrations. In general, this means negative elements if the offending aberrations are primarily from positive elements, and vice-versa. Total system power can be maintained by use of the power vs. marginal ray height theorem – the power an element contributes to the system is proportional to its own power times the height of the marginal ray at that element. The system must be re-optimized and re-evaluated after any changes. Often, adding operands that limit third-order aberrations to the Merit Function is a valuable way to constrain computerized optimizations to desired forms. There is a place for “no-holds-barred” global computer searches (if you have plenty of time and are out of ideas, say), but often all that is needed is to refine a system without making radical changes. Constraining the Seidel aberrations (combined with the default ray-based merit function) is a good way to do that. Seidel Diagram from Zemax for a camera lens: Lens: Seidel Diagram:
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