Optimization is the process by which a design is improved by changing the values of a set of parameters (called variables) such that the value of a merit function is reduced, or ideally, driven to zero.

Damped Least Squares (DLS) uses numerically computed derivatives to determine a direction in solution space which produces a design with a lower merit function. This gradient method has been developed specifically for optical system design and is recommended for all imaging and classical optical optimization problems.

In the optimization on pure non-sequential systems however, DLS is less successful. Because detection is performed on pixelated detectors, the merit function is inherently discontinuous and this can cause the gradient method to fail.

ZEMAX has an optimizer specifically for cases where gradient methods are ineffective. It is very useful in optimization problems like illumination maximization, brightness enhancement, and uniformity optimization.