In recent years, the precision of the manufacturing process for optical surfaces has improved tremendously. As a result, freefrom surfaces have become more attractive options for imaging applications with increased accuracy requirements. However, with regards the integration into an optical system, performance is often limited due to surface imperfections, such as mid-spatial frequency errors and alignment errors. This demonstrates the need for a more holistic description of systems, including multiple freeform components, which enable performance predictions based on the system as a whole. In this work, a solution for such a simulation is presented and verified by a comparison with the experimental data. This procedure not only predicts system performance but also supports tolerancing and easier alignment.