What is the difference between an extensible digital camera lens (such as Sony T9) and an inextensible lens (such as Ricoh R3)?

A lens that can be extended like R3 is called external zoom, and a lens that cannot be extended like T9 is called internal zoom. The external zoom mechanism is relatively simple, and the optical path is not affected, but the zoom mechanism requires a certain thickness of the fuselage. Internal zoom and periscope zoom lens are usually used on the card machine, mainly to reduce the thickness of the machine body. Because the refractive mirror is added and the link is increased, it has little influence on the optical path. There is also a fixed-focus lens without optical zoom, which only appears on low-end machines.