Hi Saif,

Thanks for posting here in the forum.

I understand you're encountering difficulties with exporting a STEP file that includes a flat dummy surface in Zemax. The issue might be related to how Surface 1 is defined in the Lens Data Editor. Surface 1 has zero thickness but also has a model material assigned.  Could you clarify the reason behind this setup?  In some cases, assigning a material to a zero-thickness surface can introduce unintended effects during export. (See Figure attached)

I noticed that you're using the first Coordinate Break to decenter the mirror, but you're also using the Aperture section within the Mirror Surface properties itself. In some cases, using both methods for decentering might introduce unintended effects.

There might be a simple solution worth trying. If you navigate to OpticStudio Preferences -> General -> Untick "Use Parasolid Library" and then try to export the CAD Geometry again. The outer walls of your mirror components are flat and normal towards the optical axis: (See Figure attached)

I have used Ansys SpaceClaim as the CAD Software to open the STEP File, but it should also show the same geometry in SolidWorks. Feel free to let me know if that is not the answer you`ve been looking for and I can try to help further,

Have a good day,

Akhil