Why is ZEMAX drawing the mirror substrate on the wrong side for a user-defined aperture?

I’m working on a model for galvanometer mirrors that have a polygonal shape. For the mirror surface, when I set the aperture to the user-defined file (X,Y points clockwise, without a redundant endpoint), and draw the surface as a flat substrate with some thickness, the rays appear to travel through the substrate and reflect on the other side. 


I would like the mirror to be on the side that the rays see first. Is there a way to change that?


Best answer by MichaelH 18 May 2023, 21:46

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4 replies

Userlevel 5
Badge +3

Check the signs of your thicknesses coming at and leaving the mirror.  The thickness sign always reverses at a mirror.  If you have two negative or two positive thicknesses either side of a mirror, Zemax will just do what it is told, which in this case would be incorrect.

Thanks for the reply. I did check to make sure that thicknesses are defined correctly. It appears that the rays are traced correctly when I have these galvanometer mirrors defined in a separate file, copied and pasted out of the master file I’m working on. Is there another potential solution given that there’s nothing wrong with the thicknesses?

Userlevel 6
Badge +2


I would have guessed the same as @Mike.Jones to be fair. Can you fletch your rays to be sure everything is defined correctly? Also feel free to share your file here or on the support.

Userlevel 6
Badge +2

Hi Ilya,

Can you run the System Check utility? 

If this shows 0 Warnings and 0 Errors, then I would simply make the substrate thickness a negative value.  

The Substrate Thickness is a non-optical value and only effects the display on a layout, but it has no effect on ray tracing (in fact, nothing in the Draw properties effects the ray trace, it only effects the layout plots).  So if there are no errors and you’re only concerned about the visual layout, just swap the signs of the substrate.