The illumination optics (1) has a liquid lens (4) with variable radio frequency for changing focus of illuminating light bundle. A turning wheel (3) is provided for changing focus of illuminating light bundle. The liquid lens is moved along optical axis (7) and a main unit is provided for changing an opening angle of illuminating light bundle. Independent claims are included for the following: (1) an observation device； and (2) a method for producing illumination light bundle with variable light distribution.
