Objective optical system for endoscope and endoscope

An objective optical system for an endoscope consisting of:

• a front group having negative refractive power as a whole, an aperture stop, and a rear group having positive refractive power as a whole, in order from an object side,
• wherein the front group consists of a first lens, having negative refractive power, in which an absolute value of a curvature radius of a lens surface on an image side is smaller than an absolute value of a curvature radius of a lens surface on an object side, and at least one parallel planar member of which an incidence surface and an emission surface are perpendicular to an optical axis, in order from the object side,
• wherein the rear group consists of a second lens having positive refractive power, a third lens having negative refractive power, and a fourth lens having positive refractive power, in order from the object side,
• wherein the third lens and the fourth lens are joined together to constitute a cemented lens, and a cemented surface of the cemented lens has a concave surface directed to the image side, and
• wherein the following Conditional Expression (1) is satisfied.
• 0.02<f/fc<0.10 (1)
• where
• f:
• Focal distance of entire system
• fc:
• Focal distance of the cemented lens