With our default merit function setup, we can now optimize our Schmidt camera using the standard (local DLS) optimizer. Click on the “Opt” button in the button bar and select “Automatic” optimization. ZEMAX adjusts the radius of curvature and r⁴ coefficient of the front of our lens to improve image quality. Looking at the boundary constraint operands in the Merit Function Editor, it is clear that all of our boundary constraints are being met. The values of all three thickness boundary constraint operands have no contribution to the total merit function value:

Looking at the 3D Layout, though, there appears to be a problem with our lens’ thickness. While the thickness of the lens appears reasonable (i.e. neither too thick nor too thin) at the center and edges, the lens appears to be very thin at intermediate aperture locations:

By using the active cursor on the layout, you can establish that the thickness of the lens is less than 0.5 mm at these intermediate locations! Clearly this lens is so thin that it would likely be difficult to manufacture and/or mount.

The problem is that we did not establish any boundary constraints which restrain the thickness of the lens at these intermediate aperture locations. The default boundary constraints are designed for use with spherical and conically aspheric surfaces. Thus, they only constrain surface thicknesses at the center and edge. To address this limitation when using polynomial aspheric surfaces, we need to use a different type of boundary constraint operand, one that is more appropriate for polynomial aspheres.