Patent ID: 8711461

Claim:
An aperture stop, comprising a plurality of stop blade members each having a filter portion formed on a part of or an entire surface of the stop blade member, thereby defining a filter area formed by the filter portions of the plurality of stop blade members, and an aperture area positioned inside the filter area, wherein: the filter area transmits light in a wavelength range corresponding to fluorescent light from an observed area of a subject, and reduces or blocks transmission of light in a wavelength range corresponding to illumination light to the subject; the aperture area transmits the light in the wavelength range corresponding to the fluorescent light from the observed area of the subject, and the light in the wavelength range corresponding to the illumination light to the subject; the light in the wavelength range corresponding to the fluorescent light from the observed area of the subject is not reduced, and an area of the aperture area is variable; and wherein a total thickness of the stop blade member in an optical axis direction in the filter area is the same as a total thickness of the stop blade member in an optical axis direction in the aperture area.