Objective optical system for endoscope

An objective optical system for endoscope, comprising in order from an object side:

• a first lens group having a positive refractive power;
• a second lens group having a negative refractive power;
• and
• a third lens group having a positive refractive power, wherein
• at a time of focusing to an object point at a short distance, the first lens group and the third lens group are fixed, and, the second lens group moves, and
• the third lens group consists of a front group having a positive refractive power and a rear group having a positive refractive power, and
• the front group includes one cemented lens and the rear group includes one single lens, and
• the following conditional expressions (1-1), (1-2), (4-1), and (4-2) are satisfied:
• 1≤fG3f/fG3r≤5 (1-1)
• 0.1≤dG3fr/dG3r≤1 (1-2)
• −8≤fc/rc≤−2 (4-1)
• −7≤fG2/fG3≤−2 (4-2)
• where,
• fG3f denotes a focal length of the front group,
• fG3r denotes a focal length of the rear group,
• dG3fr denotes a distance along an optical axis from a surface nearest to an image of the front group up to a surface nearest to an object of the rear group,
• dG3r denotes a total thickness along the optical axis of the rear group,
• fc denotes a focal length of the cemented lens,
• rc denotes a radius of curvature of a cemented surface of the cemented lens,
• fG2 denotes a focal length of the second lens group, and
• fG3 denotes a focal length of the third lens group.