Endoscope illuminating optical system

An endoscope illuminating optical system to be disposed at a front end of an insertion portion of an endoscope, the endoscope illuminating optical system comprising:

• a lens formed by a transparent-resin molding having a function of a front-end frame, which is configured to be disposed at a front-end side of the insertion portion;
• and
• a light guide which is disposed adjacent to the lens, wherein:
• a surface of the lens facing toward the light guide is a composite concave surface in which two axisymmetric concave surfaces are overlapped, and has a gourd-shaped effective cross-section,
• an effective range of a distal end surface of the light guide has a shape of an ellipsoid, or an oval, or a gourd, and has a long axis in a longitudinal direction of the gourd-shaped effective cross-section of the surface of the lens facing toward light guide, and a short axis in a direction perpendicular to the long axis,
• the cross-section of the composite concave surface includes the distal end surface of the light guide, and
• the endoscope illuminating optical system satisfies the following conditional expressions (1), (2), and (3):
• 1.2<Llgl/Llgs<4 (1)
• 0.25<R′/√(Llgl/×Llgs)<0.6 (2)
• 0.4<Lofs/(Llgl-Llgs)<1.3 (3)
• where:
• Llgl denotes a maximum length in a long-axis direction of the distal end surface of the light guide,
• Llgs denotes a maximum length in a short-axis direction of the distal end surface of the light guide,
• R′ denotes a radius of curvature at a practical center of the axisymmetric concave surfaces, and
• Lofs denotes a distance between axes of the two axisymmetric concave surfaces.