Cata-dioptric system and image capturing device

An image capturing device comprising:

• a reflective optical system configured to reflect incident light through a plurality of reflective surfaces;
• a refractive optical system configured to refract the incident light that is reflected by the reflective optical system;
• an image sensor configured to sense the refracted incident light and to output an electrical signal;
• an image processor configured to process the output electrical signal;
• and
• a controller configured to perform focusing through movement of at least one of the reflective optical system and the refractive optical system,
• wherein internal diameters of the plurality of reflective surfaces are disposed on the same perpendicular line as that of external diameters of other reflective surfaces adjacent to the respective internal diameters of the plurality of reflective surfaces, or at a closer distance from a perpendicular line including a top surface of the refractive optical system.