Ikeda-san, you are a great teacher. So kind of you to share your experience. If ok, I have some suggestions to add some valuable links as well: In 10. Find YouTube videos on lens design: https://www.youtube.com/c/DesignOpticsFast/videos In 11. Join an online or offline course in lens design, the address/link for "International Summer School Advanced Lens Design" might be checked; I suggest also a valuable link (archived lectures from the Institute of Applied Physics from Jena): https://www.iap.uni-jena.de/Institute/Teaching/Archive.html. With full respect for your kind educative topics and sharing effort, Mico