Abstract: An optical system affixed to an electronic apparatus is provided, including a first optical module, a second optical module, and a third optical module. The first optical module is configured to adjust the moving direction of a first light from a first moving direction to a second moving direction, wherein the first moving direction is not parallel to the second moving direction. The second optical module is configured to receive the first light moving in the second moving direction. The first light reaches the third optical module via the first optical module and the second optical module in sequence. The third optical module includes a first photoelectric converter configured to transform the first light into a first image signal.

Abstract: A printing head structure of calculator, including a belt type printing head the outer periphery of which is disposed with at least one group of fine characters and at least one group of coarse characters. The fine characters have the same symbols and numerals as the coarse ones, while having different thicknesses and letterforms. By means of a printing control program of the calculator, the printing head is able to print out a positive or negative result respectively by fine characters or coarse characters so as to apparently visually distinguish the positive result from the negative one and thus achieve a reliably reminding effect.