Hello, 

I am trying to simulate a laser triangulation setup and would like to use the “Marginal Ray Height” solve type for the thickness between the last lens surface and the image plane.  
To improve the simulation accuracy, I am adding two surfaces for the detector cover glass between the last lens surface and the image plane. Is there a way to set the “target” of the thickness calculation to the image plane instead of the cover glass?

Or is it only possible by defining the surface thickness as variable and optimizing it? 

Thank you for your help!