@Tomasz.Pozniak:
I think the best approach depends on what exactly you would like to model. If you just want to segment an otherwise continuous mirror surface, then you can use sequential mode with a user-defined aperture (UDA) for each segment. The UDA’s can be moved around on the surface to see how changes in their relative locations alter the imaging performance. If, however, you want to tip/tilt the individual segments or move them along the z-axis (piston motion), then a mixed-mode model is the way to go. In this case the mirror and its segments are all defined in a non-sequential group that is embedded inside a sequential model.
Erin Elliot (at Zemax) gave a very nice webinar on how to use both of these techniques to simulate the James Webb telescope. Here’s the link: Modeling the James Webb Telescope segments in OpticStudio
Regards,
Jeff