In the first case, the system only uses partial caliber, so it can be designed according to the full caliber first, and then divided into blocks. In the second case, the off-axis system is equivalent, decomposed into subsystems, independently designed and optimized, and then combined and fine-tuned according to the actual situation. Zemax only provides one tool, what zemax can do for you. For example, you can learn about geometric optics and aberration analysis, zemax can help you design lenses, lens emitting mirrors that can be used for lighting, and so on. To sum up, the most important thing to learn zemax is to have a clear optical concept.