An optical device (1) including a fixed focus camera having a predetermined depth of field with an optical axis (55), wherein the optical device (1) comprises a diaphragm (5) positioned in the optical axis (55) of the camera and comprising a light passing aperture (53) for increasing the predetermined depth of field of said camera to provide an increased depth of field, wherein the diaphragm is attached to the camera, wherein the light passing aperture (53) of the diaphragm (5) is circular shaped within an opaque screen and positioned to have its centre point coincide with the optical axis (55) of the camera and wherein the optical device (1) further comprises illumination means evenly positioned around the optical axis (55) for evenly illuminating an object positioned within the increased depth of field of the camera.