Zoom lens system

A zoom lens system composed of, in order from an object side:

• a first lens group having negative refractive power;
• and
• a second lens group having positive refractive power, and
• upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group varying,
• the first lens group being composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing an image, and a positive lens,
• the second lens group including, in order from the object, a positive lens, an aperture stop for defining an f-number, and a negative lens component composed of a single negative lens and disposed to the image side of the aperture stop,
• at least one aspherical surface being included in both of the first lens group and the second lens group,
• focusing being carried out by the first lens group, and
• the following conditional expression being satisfied:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

A method for forming an image of an object and varying a focal length of a zoom lens system that consists of, in order from an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, comprising steps of:

• varying the focal length from a wide-angle end state to a telephoto end state by moving a distance between the first lens group and the second lens group,
• providing the first lens group composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing the image, and a positive lens,
• providing the second lens group which consists of three lens elements or less and includes, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens component including a negative lens and disposed to the image side of the aperture stop,
• focusing by moving the first lens group, and
• satisfying the following conditional expression:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

A method for forming an image of an object and varying a focal length of a zoomlens system that consists of, in order from an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, comprising steps of:

• varying the focal length from a wide-angle end state to a telephoto end state by moving a distance between the first lens group and the second lens group,
• providing the first lens group composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing the image, and a positive lens,
• providing the second lens group which includes, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens component composed of a single negative lens and disposed to the image side of the aperture stop,
• focusing by moving the first lens group, and
• satisfying the following conditional expression:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

A zoom lens system composed of, in order from an object side:

• a first lens group having negative refractive power;
• and
• a second lens group having positive refractive power, and
• upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group varying,
• the first lens group being composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing an image, and a positive lens,
• the second lens group consisting of three lens elements or less and including, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens group,
• the negative lens group including a negative lens disposed to the image side of the aperture stop, and
• the following conditional expressions being satisfied:
• −0.05<Da/fw<0.5
• 1.808090≦nd
• νd<40
• −0.6<fF/fR<0.3
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, fw denotes a focal length of the zoom lens system in the wide-angle end state, nd denotes refractive index of the negative lens in the negative lens group at d-line (wavelength λ=587.6 nm), and νd denotes Abbe number of the negative lens in the negative lens group at d-line (wavelength λ=587.6 nm), fF denotes a focal length of the most object side positive lens in the second lens group, and fR denotes a focal length of the lenses disposed from the negative lens to the image plane.

A zoom lens system composed of, in order from an object side:

• a first lens group having negative refractive power;
• and
• a second lens group having positive refractive power, and
• upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group varying,
• the first lens group being composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing an image, and a positive lens,
• the second lens group consisting of, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens component,
• the negative lens component being a single lens or a cemented lens,
• at least one aspherical surface being included in both of the first lens group and the second lens group, and
• the following conditional expression being satisfied:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

A zoom lens system composed of, in order from an object side:

• a first lens group having negative refractive power;
• and
• a second lens group having positive refractive power, and
• upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group varying,
• the first lens group being composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing an image, and a positive lens,
• the second lens group consisting of three lens elements or less and including, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens group,
• the negative lens group including a negative lens is disposed to the image side of the aperture stop,
• an f-number of the zoom lens system in the wide-angle end state being smaller than an f-number of the zoom lens system in the telephoto end state,
• at least one aspherical surface being included in both of the first lens group and the second lens group, and
• the following conditional expression being satisfied:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, fw denotes a focal length of the zoom lens system in the wide-angle end state.

A method for forming an image of an object and varying a focal length of a zoom lens system that consists of, in order from an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, comprising steps of:

• varying the focal length from a wide-angle end state to a telephoto end state by moving a distance between the first lens group and the second lens group;
• providing the first lens group composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing the image, and a positive lens;
• providing the second lens group which consists of three lens elements or less and includes three aspherical surfaces or less;
• providing the second lens group which includes, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens group;
• providing the negative lens group which includes a negative lens;
• and
• satisfying the following conditional expression:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

A method for forming an image of an object and varying a focal length of a zoom lens system that includes, in order from an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, comprising steps of:

• varying the focal length from a wide-angle end state to a telephoto end state by moving a distance between the first lens group and the second lens group,
• providing the first lens group composed of two lens elements which are, in order from the object side, a negative lens having a concave surface facing the image, and a positive lens,
• providing the negative lens of the first lens group which has an aspherical surface on an image side,
• providing the second lens group which includes, in order from the object side, a positive lens, an aperture stop for defining an f-number, and a negative lens component composed of a single negative lens, and
• satisfying the following conditional expression:
• −0.05<Da/fw<0.5
• where Da denotes a distance along the optical axis between the image side surface of the most object side positive lens in the second lens group and the aperture stop, and fw denotes a focal length of the zoom lens system in the wide-angle end state.