Optical device

Patent Granted PROBLEM TO BE SOLVED: To provide an optical device capable of changing a focal position for observation without moving an objective or data sample, and an image forming method using the optical device; and to provide an optical device achieving the facilitation of the correction of a focal distance because of the difference of wavelength, an optical device capable of obtaining two different focal positions as one image or an optical device capable of obtaining two images whose magnifications are different as one image, and an image forming method using the optical device.