Hi Greg, hi Peter, hi Schorsch, hi Radiance-Fans, many thanks for your responses. Like you mentioned in your Emails, i will now use a photon mapping to simulate the behavior of my specific HOE's. I have written Roland Schregle to get support (I hope he will answer). Meanwhile, for a first try, i will use prism1/2 or dielectric materials. I am curious about the results. Best regards -Frank