Patent ID: 7235799

Claim:
An objective lens comprising: an upper part comprising an upper thin plate portion made of ferromagnetic material and having its longitudinal axis in an X-axis direction and a first thick plate portion in a rib structure surrounding circumferentially said upper thin plate portion, said upper thin plate portion including a plurality of tubular protrusions at locations corresponding to optical axes of electron beams; a lower part comprising a lower thin plate portion made of ferromagnetic material and having its longitudinal axis in the X-axis direction and a second thick plate portion in a rib structure surrounding circumferentially said lower thin plate portion, said second thin plate portion including a plurality of apertures at locations corresponding to the optical axes of said electron beams; and a coil disposed in a space formed between respective thick plate portions of said upper and lower parts when said upper and lower parts are combined together with their portions corresponding to respective optical axes configured in common and with a predetermined gap formed therebetween, said coil wound in the direction orthogonal to said respective optical axes.