Compact size zoom lens system

Claim 2

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens group during a zooming operation, where the zoom lens system is characterized in that the zoom lens system comprises at least three aspherical surfaces for correcting aberrations, and that the most object side lens element includes at least one of the aspherical surfaces and the rear lens group includes the remaining two aspherical surfaces.

Claim 3

The zoom lens system according to claim 1, where the front lens group comprises at least two aspherical surfaces.

Claim 4

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the zoom lens system comprises at least one aspherical surface in the first lens group and at least one aspherical surface in the rear lens group, and the zoom lens system satisfies the following condition: 0.08<|(φ.sub.w φ.sub.T).sup.1/2 /(β·φ.sub.2)|<0.026, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is give by β=φ w /φ T .

Claim 5

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the zoom lens system comprises at least one aspherical surface in the first lens group and at least one aspherical surface in the rear lens group, and the zoom lens system satisfies the following condition: 0.08<|(φ.sub.w φ.sub.T).sup.1/2 /(β·φ.sub.2)|<0.026, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is give by β=φ w /φ T .

Claim 6

The zoom lens system according to claim 3, where the front lens group is composed of, from the object side to the image side, a lens element having a positive refractive power, a lens element having a negative refractive power and a lens element having a positive refractive power, and the zoom lens system satisfies the following condition: 0.10<|(φ.sub.w ·φ.sub.T).sup.1/2 /(β·φ.sub.1)|<0.27, where φ 1 : refractive power of the front lens group (φ 1 >0).

Claim 7

The zoom lens system according to claim 3, where the rear lens group is composed of, from the object side to the image side, a lens element having a positive refractive power and a lens element having a negative refractive power.

Claim 8

The zoom lens system according to claim 3, where the rear lens group is composed of a lens element having a negative refractive power.

Claim 9

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element, with an aspherical surface, having a positive refractive power, a lens element, with an aspherical surface, having a negative refractive power, and a lens element having a positive refractive power, and the rear lens group is composed of two independent lens elements, and the zoom lens system satisfies the following conditions: 0.07<(φ.sub.w φ.sub.T).sup.1/2 /(β·φ.sub.1)<0.35, and 0.07<|(φ.sub.w ·φ.sub.T).sup.1/2/(β φ.sub.2)|<0.35, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 1 : refractive power of the front lens group (φ 1 >0), φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is given by β=φ w /φ.sub.τ.

Claim 10

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element, with an aspherical surface, having a positive refractive power, a lens element, with an aspherical surface, having a negative refractive power, and a lens element having a positive refractive power, and the rear lens group is composed of two independent lens elements, and the zoom lens system satisfies the following conditions: 0.07<(φ.sub.w φ.sub.T).sup.1/2 /(β·φ.sub.1)<0.35, and 0.07<|(φ.sub.w ·φ.sub.T).sup.1/2/(β φ.sub.2)|<0.35, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 1 : refractive power of the front lens group (φ 1 >0), φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is given by β=φ w /φ.sub.τ.

Claim 11

The zoom lens system according to claim 7, where the rear lens group is composed of, from the object side to the image side, a lens element having a positive refractive power and a lens element having a negative refractive power.

Claim 12

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element having a positive refractive power, a lens element having a negative refractive power and a lens element having a positive refractive power, and the rear lens group is composed of a lens element having a negative refractive power, and the zoom lens system satisfies the following conditions: 0.07<(φ.sub.w ·φ.sub.T).sup.1/2 /(β φ.sub.1)<0.40and 0.07<|(φ.sub.w ·φ.sub.T).sup.1/2 /(β·φ.sub.2)|<0.50, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 1 : refractive power of the front lens group (φ 1 >0); φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is give by β=φ w /φ T .

Claim 13

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element having a positive refractive power, a lens element having a negative refractive power and a lens element having a positive refractive power, and the rear lens group is composed of a lens element having a negative refractive power, and the zoom lens system satisfies the following conditions: 0.07<(φ.sub.w ·φ.sub.T).sup.1/2 /(β φ.sub.1)<0.40and 0.07<|(φ.sub.w ·φ.sub.T).sup.1/2 /(β·φ.sub.2)|<0.50, where φ w : refractive power of the zoom lens system at the shortest focal length condition, φ T : refractive power of the zoom lens system at the longest focal length condition, φ 1 : refractive power of the front lens group (φ 1 >0); φ 2 : refractive power of the rear lens group (φ 2 <0), and β: zoom ratio, which is give by β=φ w /φ T .

Claim 14

A two group zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens groups is composed of two lens elements, and the most object side lens element of the front lens group comprises at least one aspherical surface.

Claim 15

A two group zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens groups is composed of two lens elements, and the most object side lens element of the front lens group comprises at least one aspherical surface.

Claim 16

The zoom lens system according to claim 10, where one of the aspherical surfaces of the front lens group is placed at the most object side.

Claim 17

The zoom lens system according to claim 10, where the front lens group comprises a lens element whose surfaces are both aspherical.

Claim 18

The zoom lens system according to claim 10, where the front lens group satisfies the following conditions: ν.sub.d(G1) <40, and ν.sub.d(G2) >50, where ν d (Ga) : Abbe number of the object side lens of the front lens group, and ν d (G2) : Abbe number of the image side lens of the front lens group.

Claim 19

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens groups is composed of only two lens elements, and the rear lens group comprises a lens element whose surfaces are both aspherical.

Claim 20

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens groups is composed of only two lens elements, and the rear lens group comprises a lens element whose surfaces are both aspherical.

Claim 21

The zoom lens system according to claim 14, where each of the front and rear lens groups comprises at least one aspherical surface.

Claim 22

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of a lens element with an aspherical surface on its object side having a positive refractive power and a lens element having a negative refractive power, and the rear lens group is composed of a lens element having a negative refractive power.

Claim 23

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of a lens element with an aspherical surface on its object side having a positive refractive power and a lens element having a negative refractive power, and the rear lens group is composed of a lens element having a negative refractive power.

Claim 24

A zoom lens system comprising, from the object side tot he image side, a front lens unit having a positive refractive power and a rear lens unit having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens units during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens units is composed of one lens element, and at least one surface of each of the lens elements is aspherical.

Claim 25

A zoom lens system comprising, from the object side tot he image side, a front lens unit having a positive refractive power and a rear lens unit having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens units during a zooming operation, where the zoom lens system is characterized in that each of the front and rear lens units is composed of one lens element, and at least one surface of each of the lens elements is aspherical.

Claim 26

The zoom lens system according to claim 17, where the lens elements are, from the object side to the image side, a positive meniscus lens convex to the image side and a bi-concave lens.

Claim 27

The zoom lens system according to claim 17, where the lens elements are, from the object side to the image side, a positive meniscus lens convex to the image side and a negative meniscus lens concave to the object side.

Claim 28

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object side to the image side, a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power, and the front and rear lens groups shift toward the object side with the air distance between the front lens group and the rear lens group decreasing and with the air distance between the first sub lens group and the second sub lens group of the front lens group increasing during a zooming operation from a shorter focal length to a longer focal length.

Claim 29

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object side to the image side, a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power, and the front and rear lens groups shift toward the object side with the air distance between the front lens group and the rear lens group decreasing and with the air distance between the first sub lens group and the second sub lens group of the front lens group increasing during a zooming operation from a shorter focal length to a longer focal length.

Claim 30

The zoom lens system according to claim 20, where the zoom lens system satisfies the following conditions: 0.01<|(A.sub.w -A.sub.T)/(B.sub.w -B.sub.T)|<0.8, where A w : the air distance between the first sub lens group and the second sub lens group of the front lens group at the shortest focal length condition, A T : the air distance between the first sub lens group and the second sub lens group of the front lens group at the longest focal length condition, B w : air distance between the front lens group and the rear lens group at the shortest focal length condition, and B T : air distance between the front lens group and the rear lens group at the longest focal length condition.

Claim 31

The zoom lens system according to claim 21, where the zoom lens system further satisfies the following condition: A.sub.w <A.sub.T, and 1.0<φ.sub.1T /φ.sub.1w <2.0, where φ 1w : refractive power of the front lens group at the shortest focal length condition, and φ 1T : refractive power of the front lens group at the longest focal length condition.

Claim 32

The zoom lens system according to claim 22, where the front lens group comprises at least one aspherical surface.

Claim 33

The zoom lens system according to claim 23, where the rear lens group comprises at least one aspherical surface.

Claim 34

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object side to the image side, a lens element having a negative refractive power and a sub lens group, and the air distance between the lens element and the sub lens group of the front lens group slightly varies for correcting aberrations according to a shift of the front lens group or the rear lens group along the optical axis of the zoom lens system for a focusing operation.

Claim 35

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object side to the image side, a lens element having a negative refractive power and a sub lens group, and the air distance between the lens element and the sub lens group of the front lens group slightly varies for correcting aberrations according to a shift of the front lens group or the rear lens group along the optical axis of the zoom lens system for a focusing operation.

Claim 36

The zoom lens system according to claim 25, wherein the sub lens group has a positive refractive power comprising at least one lens element having a positive refractive power.

Claim 37

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and each of the front lens group and the rear lens group comprises at least one lens element that is made of lens material satisfying either the following condition a) or the following condition b): a) N.sub.d ≦1.60 and ν.sub.d ≦35.0, or b) N.sub.d 1.50, where N d : refractive index of the lens material for the d-line, and ν d : Abbe number of the lens material for the d-line.

Claim 38

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and each of the front lens group and the rear lens group comprises at least one lens element that is made of lens material satisfying either the following condition a) or the following condition b): a) N.sub.d ≦1.60 and ν.sub.d ≦35.0, or b) N.sub.d 1.50, where N d : refractive index of the lens material for the d-line, and ν d : Abbe number of the lens material for the d-line.

Claim 39

The zoom lens system according to claim 27, where the front lens group comprises at least one aspherical surface.

Claim 40

The zoom lens system according to claim 27, where the rear lens group comprises at least one aspherical surface.

Claim 41

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and the rear lens group comprises at least one lens element that has an aspherical surface at the object side and is made of lens material satisfying either the following condition a) or the following condition b): a) N.sub.d ≦1.60 and ν.sub.d ≦35.0, or b) N.sub.d ≦1.50, where N d : refractive index of the lens material for the d-line, and ν d : Abbe number of the lens material for the d-line.

Claim 42

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and the rear lens group comprises at least one lens element that has an aspherical surface at the object side and is made of lens material satisfying either the following condition a) or the following condition b): a) N.sub.d ≦1.60 and ν.sub.d ≦35.0, or b) N.sub.d ≦1.50, where N d : refractive index of the lens material for the d-line, and ν d : Abbe number of the lens material for the d-line.

Claim 43

The zoom lens system according to claim 30, where the front lens group comprises at least one lens element that is made of lens material satisfying either the following condition a) or the following condition b): a) N.sub.d ≦1.60 and ν.sub.d ≦35.0or b) N.sub.d ≦1.50, where N d : refractive index of the lens material for the d-line, and ν d : Abbe number of the lens material for the d-line.

Claim 44

The zoom lens system according to claim 30, where the front lens group comprises at least one aspherical surface.

Claim 45

A two group zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and the two lens elements of the front lens group are made of plastic.

Claim 46

A two group zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that each of the front lens group and the rear lens group is composed of two lens elements, and the two lens elements of the front lens group are made of plastic.

Claim 47

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the most object side lens element of the front lens group has two aspherical surfaces.

Claim 48

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the most object side lens element of the front lens group has two aspherical surfaces.

Claim 49

The zoom lens system according to claim 34, where the rear lens group comprises at least one aspherical surface.

Claim 50

The zoom lens system according to claim 34, where the front lens group comprises at least three aspherical surfaces.

Claim 51

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the most object side lens element of the front lens group has two aspherical surfaces, and the rear lens group comprises at least one aspherical surface, at least one of the aspherical surfaces of the rear lens group satisfying the following condition: for a height y from the optical axis of the zoom lens system satisfying 0.8y MAX <y<1.0y MAX where y MAX is the maximum effective radius of the aspherical surface, -0.10<φ.sub.2 ·(N'-N)·d{x(y)-x.sub.o (y)}/dy<0, where φ 2 : refractive power of the rear lens group, N: refractive index of the medium at the object side of the aspherical surface, N': refractive index of the medium at the image side of the aspherical surface, x(y): axial deviation of the aspherical surface from its vertex at the height y, which is given by x(y)=(r/ε)[1-{1-ε(y.sup.2 /r.sup.2)}.sup.1/2 ]+ΣA.sub.i y.sup.i (summation Σ made for i≧2) x o (y): axial deviation of the reference spherical surface of the aspherical surface from its vertex at the height y, which is given by x.sub.o (y)=r[1-{1-(y.sup.2 /r.sup.2)}.sup.1/2 ] r: radius of curvature of the aspherical surface at the vertex, ε: quadric surface parameter, A i : aspherical coefficient of the i-th order, and r: radius of curvature at the vertex, which is given by (1/r)=(1/r)+2A 2 .

Claim 52

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the most object side lens element of the front lens group has two aspherical surfaces, and the rear lens group comprises at least one aspherical surface, at least one of the aspherical surfaces of the rear lens group satisfying the following condition: for a height y from the optical axis of the zoom lens system satisfying 0.8y MAX <y<1.0y MAX where y MAX is the maximum effective radius of the aspherical surface, -0.10<φ.sub.2 ·(N'-N)·d{x(y)-x.sub.o (y)}/dy<0, where φ 2 : refractive power of the rear lens group, N: refractive index of the medium at the object side of the aspherical surface, N': refractive index of the medium at the image side of the aspherical surface, x(y): axial deviation of the aspherical surface from its vertex at the height y, which is given by x(y)=(r/ε)[1-{1-ε(y.sup.2 /r.sup.2)}.sup.1/2 ]+ΣA.sub.i y.sup.i (summation Σ made for i≧2) x o (y): axial deviation of the reference spherical surface of the aspherical surface from its vertex at the height y, which is given by x.sub.o (y)=r[1-{1-(y.sup.2 /r.sup.2)}.sup.1/2 ] r: radius of curvature of the aspherical surface at the vertex, ε: quadric surface parameter, A i : aspherical coefficient of the i-th order, and r: radius of curvature at the vertex, which is given by (1/r)=(1/r)+2A 2 .

Claim 53

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element having a negative refractive power and a lens element having a positive refractive power, and the rear lens group is composed of, from the object side to the image side, a lens element having a negative or non-refractive power and a lens element having a negative refractive power.

Claim 54

A zoom lens system comprising, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group is composed of, from the object side to the image side, a lens element having a negative refractive power and a lens element having a positive refractive power, and the rear lens group is composed of, from the object side to the image side, a lens element having a negative or non-refractive power and a lens element having a negative refractive power.

Claim 55

The zoom lens system according to claim 38, where the front lens group comprises at least one aspherical surface.

Claim 56

The zoom lens system according to claim 38, where the rear lens group comprises at least one aspherical surfaces.

Claim 57

The zoom lens system according to claim 38, where the zoom lens system comprises at least one lens element whose surfaces are both aspherical.

Claim 58

A zoom lens system consisting of, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object said to the image side, a first sub lens group and a second sub lens group, and the air distance between the first sub lens group and the second sub lens group of the front lens group slightly varies for correcting aberrations according to a shift of the front lens group or the rear lens group upon the optical axis of the zoom lens system for a focusing operation, wherein the first sub lens group has a positive refractive power comprising at least one lens element and the second sub lens group has a positive refractive power comprising at least one lens element.

Claim 59

A zoom lens system consisting of, from the object side to the image side, a front lens group having a positive refractive power and a rear lens group having a negative refractive power, the zoom lens system being operated by changing the air distance between the front and rear lens groups during a zooming operation, where the zoom lens system is characterized in that the front lens group comprises, from the object said to the image side, a first sub lens group and a second sub lens group, and the air distance between the first sub lens group and the second sub lens group of the front lens group slightly varies for correcting aberrations according to a shift of the front lens group or the rear lens group upon the optical axis of the zoom lens system for a focusing operation, wherein the first sub lens group has a positive refractive power comprising at least one lens element and the second sub lens group has a positive refractive power comprising at least one lens element.