Illumination lens and illumination optical system for an endoscope

An illumination lens that is used in an illumination optical system for an endoscope, the illumination lens consisting of two lenses consisting of a first lens and a second lens arranged in this order toward an object side from a light source side,

• wherein surfaces of all the lenses have a planar shape or a convexly spherical shape,
• an incident surface of the first lens on which light generated from a light source is to be incident is a convex surface,
• an emission surface of the second lens from which light toward an object is to be emitted is a flat surface,
• an intersection of a ray incident on the incident surface in parallel to an optical axis at a height of 0.25×H from the optical axis and a ray incident on the incident surface in parallel to the optical axis at a height of 0.5×H from the optical axis is positioned only inside the illumination lens in a case in which an outer diameter of the first lens in a direction perpendicular to the optical axis is denoted by 2H,
• in a case in which a thickness of the second lens along the optical axis is denoted by t, a position of the intersection in a direction of the optical axis is positioned closer to the light source than a position, which is apart from the emission surface of the second lens to the light source side by 0.4×t, and
• Conditional Expression (1) expressed by “0.61<f/f1<1.5 . . . (1)” is satisfied in a case in which a focal length of the illumination lens is denoted by f and a focal length of the first lens is denoted by f1.