An optical system is provided. The optical system includes a first movable portion, a fixed portion, a first driving assembly, and a first sensing assembly. The first movable portion is used for connecting to an optical assembly having a main axis. The first movable portion is movable relative to the fixed portion. The first driving assembly is used for driving the first movable portion to move relative to the fixed portion. The first sensing assembly is used for sensing the movement of the first movable portion relative to the fixed portion.