Hi Rick,

One easy thing you could try, assuming you use a Spot image quality criterion in your Merit function is to try and reduce the weight of your centre field. For example, you could have a Weight of 0.5 instead of 1.0 on the On-axis Field:

But this isn’t guaranteed to make all the spots with the same size.

My solution would be to use an operand such as RSCE (RMS spot size with respect to centroid position):

I made a dummy example with a singlet:

And this is the Merit function:

Operand 1 to 3 use RSCE to measure the spot size at different field position (controlled by Hy). 0.5 is halfway, and 1.0 is the edge of your field. Only the second operand has a weight (it contributes to the Merit function calculation) and a target of 150 um.

Operand 4 and 5 take the difference of the centre and edge with the halfway field. Operands 6 and 7 take the absolute value of this difference and target it to 0.0 (they also have a weight of 1.0 so these contribute to the Merit function calculation as well).

As you can see, the system found a nice solution:

I’m also attaching my file to this answer.

Hope this helps and take care,

David