Patent ID: 8854729

Claim:
A microscope adapter unit disposed on an optical path of illumination light leading from a light source unit having a light source to a sample surface via a microscope main body, wherein the microscope adapter unit is disposed on the optical path between the light source unit and the microscope main body, and the light source unit has an optical system that converges or makes parallel the illumination light emitted from the light source, the microscope adapter unit comprising: an afocal optical system which comprises a first lens group and a second lens group, wherein: the first lens group converts the illumination light into roughly parallel luminous fluxes, and makes the illumination light enter the second lens group; the afocal optical system comprises, in order along the optical path starting from the light source unit: a third lens that is included in the first lens group, and that has a positive power; a first lens that is included in the first lens group, and that has a negative power; a second lens that is included in the second lens group, and that has a negative power; and a fourth lens that is included in the second lens group, and that has a positive power; and the afocal optical system is configured such that (i) a distance between the first lens and the third lens in the first lens group is not variable, (ii) a distance between the second lens and the fourth lens in the second lens group is not variable, (iii) a distance between the first lens and the second lens is variable, and (iv) the illumination light that has been converted into the roughly parallel luminous fluxes by the first lens group has a smaller luminous flux diameter than that of the illumination light entering the microscope adapter unit and that of illumination light emitted from the microscope adapter unit.