@whit2452

I’m assuming you are talking about a Sequential solution since you are referring to Multi-Configuration (MC). In Sequential mode, surfaces can have apertures. To add an aperture to a surface, double-click on the surface of interest in the Lens Data Editor (LDE), or press the down arrow at the top-left of the LDE with the surface of interest selected. This opens the corresponding surface properties. Then, navigate to Aperture, and choose an Aperture Type. In the list of Aperture Types, you’ll find Rectangular Aperture/Obscuration that might be useful. There are probably many ways to achieve what you want, here’s my take:

• Add Fold Mirror from the LDE (default shortcut Ctrl+Shft+F) to create a slanted reflective surface
• Add a Rectangular Obscuration with the size of your slit to the reflective surface

Rays that go through the slit will be obscured and rays that fall outside the slit aperture are reflected:

You can add a configuration to show rays that are going through the aperture using the MC Editor. To do that, you’d have to do the following in a new configuration of the MC Editor:

• Change the Aperture Type from Rectangular Obscuration to Rectangular Aperture (the size should be automatically conserved)
• Remove the MIRROR Material of the reflective surface
• Change the sign of the thicknesses after the aperture
• Change the sign of the return coordinate break of the Fold Mirror

The result should look like so:

I’m attaching my example to this answer.

I hope this helps.

Take care,

David