Imaging optical system, and imaging apparatus incorporating the same

1. An imaging optical system comprising, in order from an object side to an image side:

a first lens group having positive refracting power,

an aperture stop, and

a second lens group having positive refracting power,

wherein there is no lens group other than said first lens group and said second lens group,

said first lens group consists of three lens subgroups, including in order from the object side to the image side, a first lens subgroup having positive refracting power, a second lens subgroup having negative refracting power, and a third lens subgroup having positive refracting power,

said second lens group consists of two lens subgroups: in order from the object side to the image side, a fourth lens subgroup and a fifth lens subgroup,

said first lens subgroup consists of one positive lens component convex on its image-side surface,

said second lens subgroup consists of one negative lens component concave on its image-side surface,

said third lens subgroup consists of one positive cemented lens component,

said positive cemented lens component in said third lens subgroup includes a positive lens convex on its object-side surface and a negative lens concave on its object-side surface,

said fourth lens subgroup consists of one cemented lens component,

said cemented lens component in said fourth lens subgroup includes a double-convex positive lens and a double-concave negative lens,

said fifth lens subgroup comprises a negative meniscus lens concave on its image-side surface and a double-convex lens,

wherein each of the lens components is a lens block having only two refractive surfaces in on-axis contact with air, including an object side-surface and an image side-surface,

the total number of negative lenses included in said imaging optical system is four, and

upon focusing from an object at infinity to a near distance object, said first lens group remains stationary, and said second lens group moves to the object side.

2. The imaging optical system as recited in claim 1 , wherein:

said fourth lens subgroup has positive refracting power.

3. The imaging optical system as recited in claim 2 , wherein:

said fourth lens subgroup includes the negative lens that is a lens positioned on the most object side in said fourth lens subgroup.

4. The imaging optical system as recited in claim 2 , wherein:

said fifth lens subgroup includes a plurality of positive lenses.

5. The imaging optical system as recited in claim 2 , wherein:

said fourth lens subgroup and said fifth lens subgroup each include an aspheric lens surface.

6. The imaging optical system as recited in claim 1 , wherein:

said first lens subgroup includes an aspheric lens surface.

7. The imaging optical system as recited in claim 1 , wherein:

said third lens subgroup consists of one cemented lens including a positive lens and a negative lens.

8. The imaging optical system as recited in claim 1 , which further satisfies the following Condition (2):

0.3 <D 12/IH<4  (2)

where D12 is an on-axis length from an image side-surface in said first lens group to an object side-surface in said second lens group upon focusing on an object at infinity, and

IH is a maximum image height.

9. An imaging apparatus, comprising:

the imaging optical system as recited claim 1 , and

an imaging device located on the image side of said imaging optical system.

10. The imaging optical system as recited in claim 1 , wherein:

said positive lens component in said first lens subgroup is a double-convex positive lens.

11. The imaging optical system as recited in claim 1 , wherein:

said positive lens component in said first lens subgroup is a meniscus lens.

12. The imaging optical system as recited in claim 1 , wherein:

said positive lens in said third lens subgroup is a double-convex lens, and

said negative lens in said third lens subgroup is a double-concave lens.

13. The imaging optical system as recited in claim 1 , wherein:

upon focusing from the object at infinity to the near distance object, said aperture stop remains stationary.

14. The imaging optical system as recited in claim 1 , wherein:

the negative meniscus lens and the double-convex lens in the fifth lens subgroup are located on the optical axis and spaced away from each other.

15. An imaging optical system comprising, in order from an object side to an image side:

a first lens group having positive refracting power,

an aperture stop, and

a second lens group having positive refracting power,

wherein there is no lens group other than said first lens group and said second lens group,

said first lens group consists of three lens subgroups, including in order from the object side to the image side, a first lens subgroup having positive refracting power, a second lens subgroup having negative refracting power, and a third lens subgroup having positive refracting power, and

upon focusing from an object at infinity to a near distance object, said first lens group remains stationary, and said second lens group moves to the object side, which further satisfies the following Condition (1):

4<( LTL+fB )/ fB< 15  (1)

where fB is an on-axis distance, as calculated on an air basis, from an image side-surface in said second lens group to an image plane upon focusing on an object at infinity, and

LTL is an on-axis distance from an object side-surface in said first lens group to the image side-surface in said second lens group.

16. An imaging optical system comprising, in order from an object side to an image side:

a first lens group having positive refracting power,

an aperture stop, and

a second lens group having positive refracting power,

wherein there is no lens group other than said first lens group and said second lens group,

said first lens group consists of three lens subgroups, including in order from the object side to the image side, a first lens subgroup having positive refracting power, a second lens subgroup having negative refracting power, and a third lens subgroup having positive refracting power, and

upon focusing from an object at infinity to a near distance object, said first lens group remains stationary, and said second lens group moves to the object side,

said second lens group consists of, in order from the object side to the image side, a fourth lens subgroup and a fifth lens subgroup of positive refracting power, wherein:

said fifth lens subgroup consists of three lens components including, in order from the object side to the image side, a first positive lens component, a second positive lens component and a negative lens component, wherein each of the lens components is a lens block having only two refractive surfaces in on-axis contact with air, including an object side-surface and an image side-surface.

17. An imaging optical system comprising, in order from an object side to an image side:

a first lens group having positive refracting power,

an aperture stop, and

a second lens group having positive refracting power,

wherein there is no lens group other than said first lens group and said second lens group,

said first lens group consists of three lens subgroups, including in order from the object side to the image side, a first lens subgroup having positive refracting power, a second lens subgroup having negative refracting power, and a third lens subgroup having positive refracting power, and

upon focusing from an object at infinity to a near distance object, said first lens group remains stationary, and said second lens group moves to the object side, wherein:

said third lens subgroup includes a negative lens, and a positive lens located more on the image side than said negative lens.

18. An imaging optical system comprising, in order from an object side to an image side:

a first lens group having positive refracting power,

an aperture stop, and

a second lens group having positive refracting power,

wherein there is no lens group other than said first lens group and said second lens group,

said first lens group consists of three lens subgroups, including in order from the object side to the image side, a first lens subgroup having positive refracting power, a second lens subgroup having negative refracting power, and a third lens subgroup having positive refracting power, and

upon focusing from an object at infinity to a near distance object, said first lens group remains stationary, and said second lens group moves to the object side, which further satisfies the following Conditions (4) and (5):

0.80<φ/ f< 1.5  (4)

40°<2×ω<70°  (5)

where φ is a maximum diameter of an entrance pupil of said imaging optical system,

f is a focal length of said imaging optical system, and

ω is a maximum taking half angle of view of said imaging optical system.