An optical system for receiving rays of light is provided in the present disclosure, including a first optical module. The first optical module includes a first optical element and a first optical path-adjusting element. The first optical element has a first optical axis. The rays of light pass through the first optical element in a first direction. The first optical path-adjusting element corresponds to the first optical element. The rays of light are redirected to a second direction by the first optical path-adjusting element. The first optical element and the first optical path-adjusting element are arranged along the first optical axis.