Optical device

A display apparatus includes a housing and at least one mirror. The housing can be detachably mounted on a display and includes an entrance that allows light emitted from the display to enter the interior of the housing with the housing mounted on the display and an exit that allows the light having entered the interior of the housing through the entrance to exit to the exterior of the housing. The at least one mirror reflects the light having entered the interior of the housing through the entrance to the exit.