ZEMAX can also model off-axis optical systems such as systems with fold mirrors, tilted components and off-axis conical reflectors.

Open the file "Samples > Sequential > Tilted systems & prisms > Tilted mirror.zmx". This file demonstrates the modeling of a fold mirror in ZEMAX. As you can see from the 3D Layout that opens with this file, the mirror surface (surface 3) is tilted creating a folded beam path.

Layout showing fold mirror

The mirror in this system is tilted using the "Coordinate Break" surface type. Click anywhere on the row corresponding to surface 2 in the Lens Data Editor. Now, scroll to the right using the right arrow key on your keyboard. Scroll past the Conic constant column. You will see columns for decentering and tilting. Notice that the Tilt About X parameter for the Coordinate Break has been set to 10. This indicates that the mirror is rotated by 10 degrees about the x-axis.

Tilt/decenter columns for the Coordinate Break on surface 2

Now, open the file "Samples > Sequential > Telescopes > Unobscured Gregorian". This is a telescope consisting of two conical mirrors. Observed from the Shaded Model layout that opens with this file that the primary and secondary mirror are tilted using a Coordinate Break. This moves the secondary mirror (surface 5) out of the initial beam path which eliminates the possibility of obscuration.

Shaded Model layout for Gregorian telescope

TIP:  Selecting a surface in the Lens Data Editor (by clicking on it) will highlight that surface in all layout windows. In the Shaded Model layout above, the primary mirror (surface 4) is highlighted.

The primary mirror in this telescope is an off-axis conical section. The decentered aperture on this surface aligns the mirror with the incoming beam. To see the aperture settings for the surface, double-click where it says "Standard" for surface 4 in the Lens Data Editor. This opens the Surface Properties dialog for surface 4. Now, click on the "Aperture" tab. Observe the settings for the decentered Circular Aperture on this surface.

Aperture tab of Surface Properties dialog

TIP:  Users of the full, licensed version of ZEMAX can explore off-axis optical systems further using the Knowledge Base article, "How to Tilt and Decenter a Sequential Optical Component"