Abstract: An illumination optical system includes a prism disposed on an incident optical axis and a lens that is disposed between the light source and an incident surface of the prism or between an emitting surface of the prism and an illuminated object, at least one of the reflection surfaces being a transmission/reflection surface. Additionally, an illumination optical system includes a prism having a surface that is disposed so as to obliquely intersect with an incident optical system, that transmits a part of the entering light to be emitted therefrom, and that deflects at least part of the rest of the light in a direction that intersects with the incident optical axis to be emitted therefrom. Furthermore, an illumination optical system has a rod lens that is disposed so that a longitudinal direction thereof is inclined with respect to an incident optical axis is provided.

Abstract: An objective lens for endoscopes has a front lens unit and a rear lens unit with an aperture stop between them. The front lens unit includes a first lens element with negative refracting power and a second lens element with positive refracting power, and the rear lens unit includes a third lens element with positive refracting power, a cemented lens component of a fourth lens element with positive refracting power and a fifth lens element with negative refracting power. The objective lens satisfies the following conditions: ?2<SF<?0.9 0.94<D/(f×sin ?)<1.7 0.86<(D1+D2?f1)/(2×f3)<1.

Abstract: An objective lens for endoscope comprises, in order from an object side, a front lens group having negative refractive power as a whole; a brightness aperture stop; and a rear lens group having positive refractive power as a whole, wherein said front lens group comprises in order from the object side, a first lens having negative refractive power; and a second lens group where a lens surface closest to the image side is convex form directed toward the image side, and it has positive refractive power as a whole; and the following condition (1) is satisfied: |f0/f1|?1.1 ??(4) where f0 is a composite focal length of said front lens group, and f1 is a focal length of said the first lens.

Abstract: An objective lens for endoscopes has a front lens unit and a rear lens unit with an aperture stop between them. The front lens unit includes a first lens element with negative refracting power of a meniscus shape, with a convex surface facing the object side and a second lens element with positive refracting power, and the rear lens unit includes a third lens element with positive refracting power, with a surface of the minor radius of curvature facing the image side and a cemented lens component of a fourth lens element with positive refracting power and a fifth lens element with negative refracting power. The objective lens satisfies the following conditions: ?2<SF<?0.9 0.94<D/(f×sin ?)<1.7 0.86<(D1+D2?f1)/(2×f3)<1.

Abstract: An endoscope system has a light source apparatus and an endoscope including an illumination optical system and an objective optical system. At least the objective optical system of the endoscope is provided with an adjustable diaphragm, and in a light path in one of the light source apparatus, the illumination optical system, and the objective optical system, an insertable/retractable filter for observation for special light is provided. The adjustable diaphragm performs a closing operation or an opening operation only when the filter for observation for special light is inserted into the light path.