Surface 5, the problematic surface, is a “dummy” surface—it has no optical properties. Thus, the surface is simply a placeholder surface. As such, moving the thickness value of surface 5 to surface 4 has no effect, from an optical perspective, on our system. Try this now.

 

Copy the Thickness value of surface 5 to surface 4 and then set the Thickness of surface 5 to zero:

Lens Data Editor showing adjusted thicknesses

Update and unzoom the 3D Layout window. Notice that the system is optically equivalent but the dummy surface has been moved beyond the fold mirror surface location and the virtual ray propagation is no longer present:

3D Layout showing original system with rays propagating behind mirror  3D Layout showing fixed system

Since surface 5 is a dummy surface, this problem is purely a visual one. The optical performance of this system is not affected by the original location of surface 5. As a result, there is another way to fix this problem.

 

Re-open the original starting file:

 

            F FILE: “Fold_Mirror_Start.ZMX”

 

Open the Surface Properties dialog for surface 5 and check the “Skip Rays To This Surface” and “Do Not Draw This Surface” check boxes:


Settings for "Draw" tab of Surface Properties dialog

Update the 3D Layout. Once again, the problem has been addressed. Rays are no longer propagating behind the fold mirror and the dummy surface co-located with the fold mirror is hidden from view:

Zoomed up 3D Layout showing problem is fixed