Endoscope objective optical system
Provided is a small endoscope objective optical system that allows stereoscopic viewing even though a wide angle is used, that reduces the F-number, and that also reduces vignetting. Provided is an endoscope objective optical system that consists of, sequentially from the object side, a negative first lens group, a positive second lens group, and a pair of third lens groups that are disposed side-by-side in the direction of parallax and that form two optical images with parallax, wherein aperture stops are individually provided in the third lens groups, and conditional expression M below is satisfied: Fob _ n/Fob _ p>−0.5 ( 1 ), where Fob_n is a focal length of the first lens group, and Fob_p is a focal length of the second lens group.
1. An endoscope objective optical system that consists of, sequentially from the object side, a negative first lens group having a single central axis, a positive second lens group having a single central axis, and a pair of third lens groups that are disposed side-by-side in a direction of parallax and that form two optical images with parallax,
wherein the negative first lens group consists of, sequentially from the object side, a negative lens, a positive lens, and a negative lens;
wherein the positive second lens group consists of, sequentially from the object side, a cemented lens and a positive lens; and
wherein aperture stops are individually provided in the third lens groups, and
conditional expression (1) below is satisfied:
Fob _ n/Fob _ p>− 0.5 (1),
where Fob_n is a focal length of the first lens group, and Fob_p is a focal length of the second lens group.
2. An endoscope objective optical system according to claim 1 that satisfies conditional expression (2) below:
fs/fb< 2.5 (2),
where fs is a distance from a position of the aperture stop to an imaging surface, and fb is a distance from a final lens to the imaging surface.
3. An endoscope objective optical system according to claim 1 , wherein reflection optical systems having two reflection surfaces are individually disposed between the third lens groups and the imaging surface.
4. An endoscope objective optical system according to claim 3 that satisfies conditional expression (3):
fb/ihy> 4 (3),
where fb is a distance from a final lens to an imaging surface, and ihy is a maximum image height in the direction of parallax.