| 摘要 |
PROBLEM TO BE SOLVED: To provide an imaging optical system having a wide angle of view and a large aperture ratio, and capable of performing quick focusing easily and obtaining a long back focus easily.SOLUTION: The imaging optical system includes, in order from the object side to the image side: a first lens group having a positive refractive power; a second lens group having a negative refractive power; an aperture stop; and a third lens group having a positive refractive power. When focusing from a long distance object to a short distance object, the second lens group moves toward the image side. The third lens group includes, in order from the object side to the image side, two lenses whose concave surfaces face each other with the largest air interval in the third lens group therebetween, and a positive lens. The focal distance f of the entire system, and the focal distance f2 of the second lens group are appropriately set. |
