"Isozentrum und Fokus-Achsabstand" (https://youtu.be/wNMQKMRlVOA) by Prof. Hilke Vorwerk (https://www.youtube.com/channel/UCpBHT7vSwpHdOQdVJ2IYdGA) can be reused under the CC BY-SA license (https://creativecommons.org/licenses/by-sa/4.0/).