The problem described on the previous pages of this article will only occur when fold mirrors are added manually to an optical system. Why add such components manually to a system when there is a tool to do so automatically?

Re-open the original starting file:

            F FILE: “Fold_Mirror_Start.ZMX”

Delete surfaces 2 through 4. You will also need to honor the Thickness sign convention in ZEMAX by setting the Thickness of all of the surfaces to be positive (since there no longer is a mirror in this system). An easy way to reverse the sign of a parameter is to type in *-1 in each cell that you wish to reverse the sign of. Here is the resulting Lens Data Editor:

Update the 3D Layout. Notice the rays are still focusing at the image surface just as they were with the fold mirror in the system. We are now modeling our system as if there had never been a fold mirror in it:

Now, use the “Add Fold Mirror” tool via the menu option, “Tools > Coordinates > Add Fold Mirror”. Set the “Fold Surface” to “2” (our dummy surface) and click “OK”:

Notice that ZEMAX has done all of the work for you! The Coordinate Breaks have been setup and the fold surface has been assigned the Glass type “MIRROR”. Notice also that the Thickness of each surface is setup correctly such that the layout is drawn correctly: