Zoom lens and video camera comprising the same

A zoom lens, comprising:

• a first lens group having positive refracting power and being fixed with respect to the image plane;
• a second lens group having negative refracting power and varying power by moving along an optical axis;
• a third lens group having positive refracting power and being fixed with respect to the image plane;
• and
• a fourth lens group having positive refracting power and moving along the optical axis so that the image plane varied by a movement of the second lens group and a movement of an object is kept at a predetermined position from a reference plane,
• the first, second, third, and fourth lens groups being arranged in this order from an object side to an image plane side,
• wherein
• the first lens group comprises a negative lens, a positive lens, and a positive meniscus lens arranged from the object side in this order, the positive meniscus lens having a convex surface on the object side,
• the second lens group comprises a negative lens, a double-concave lens, and a positive lens arranged from the object side in this order, and includes at least one aspherical surface, the double-concave lens and the positive lens being cemented with each other,
• the third lens group comprises a positive lens and a negative plastic lens arranged from the object side in this order, and includes at least one aspherical surface, and
• the fourth lens group comprises a positive plastic lens and a negative plastic lens that are arranged from the object side in this order and cemented with each other, and includes at least one aspherical surface,
• wherein an expression (10) below is satisfied:
• 5<|(fp1+fp2+fp3)/fw1<12 (10)
• where
• fp1 represents a focal length of the negative plastic lens of the third lens group,
• fp2 represents a focal length of the positive plastic lens of the fourth lens group,
• fp3 represents a focal length of the negative plastic lens of the fourth lens group, and
• fw represents a combined focal length of the entire system at a wide position.

A zoom lens, comprising:

• a first lens group having positive refracting power and being fixed with respect to the image plane;
• a second lens group having negative refracting power and varying power by moving along an optical axis;
• a third lens group having positive refracting power and being fixed with respect to the image plane;
• and
• a fourth lens group having positive refracting power and moving along the optical axis so that the image plane varied by a movement of the second lens group and a movement of an object is kept at a predetermined position from a reference plane,
• the first, second, third, and fourth lens groups being arranged in this order from an object side to an image plane side,
• wherein
• the first lens group comprises a negative lens, a positive lens, and a positive meniscus lens arranged from the object side in this order, the positive meniscus lens having a convex surface on the object side,
• the second lens group comprises a negative lens, a double-concave lens, and a positive lens arranged from the object side in this order, and includes at least one aspherical surface, the double-concave lens and the positive lens being cemented with each other,
• the third lens group comprises a positive lens and a negative plastic lens arranged from the object side in this order, and includes at least one aspherical surface, and
• the fourth lens group comprises a negative plastic lens and a positive plastic lens that are arranged from the object side in this order, and includes at least one aspherical surface,
• wherein an expression (19) below is satisfied:
• 5<|(fp1+fp2+fp3)/fw|<12 (19)
• where
• fp1 represents a focal length of the negative plastic lens of the third lens group,
• fp2 represents a focal length of the negative plastic lens of the fourth lens group,
• fp3 represents a focal length of the positive plastic lens of the fourth lens group, and
• fw represents a combined focal length of the entire system at a wide position.

A zoom lens, comprising:

• a first lens group having positive refracting power and being fixed with respect to the image plane;
• a second lens group having negative refracting power and varying power by moving along an optical axis;
• a third lens group having positive refracting power and being fixed with respect to the image plane;
• and
• a fourth lens group having positive refracting power and moving along the optical axis so that the image plane varied by a movement of the second lens group and a movement of an object is kept at a predetermined position from a reference plane,
• the first, second, third, and fourth lens groups being arranged in this order from an object side to an image plane side,
• wherein
• the first lens group comprises a negative lens, a positive lens, and a positive meniscus lens arranged from the object side in this order, the positive meniscus lens having a convex surface on the object side,
• the second lens group comprises a negative lens, a double-concave lens, and a positive lens arranged from the object side in this order, and includes at least one aspherical surface, the double-concave lens and the positive lens being cemented with each other,
• the third lens group comprises a positive lens and a negative plastic lens arranged from the object side in this order and cemented with each other, and includes at least one aspherical surface, and
• the fourth lens group comprises a negative plastic lens and a positive plastic lens that are arranged from the object side in this order and cemented with each other, and includes at least one aspherical surface,
• wherein an expression (1) below is satisfied:
• 5<|(fp1+fp2+fp3)/fw|<12 (1)
• where
• fp1 represents a focal length of the negative plastic lens of the third lens group,
• fp2 represents a focal length of the negative plastic lens of the fourth lens group,
• fp3 represents a focal length of the positive plastic lens of the fourth lens group, and
• fw represents a combined focal length of the entire system at a wide position.