Vari-focal lens system

A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and an aperture stop arranged after said third lens unit, said system being adapted so as to perform variation of focal length by varying the airspaces reserved between the lens units, and wherein the lens system includes at least one graded refractive index lens having a refractive index distribution in the direction along the optical axis.

A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and an aperture stop arranged after said third lens unit, said system being adapted so as to perform variation of focal length by varying the airspaces reserved between said lens units, and wherein the lens system includes at least one aspherical surface.

A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and an aperture stop arranged on the image side of said third lens unit, and wherein said system is adapted so as to perform variation of focal length by varying the airspaces reserved between the lens units, said first lens unit, said fourth lens unit and said aperture stop being kept fixed for the variation of focal length.

A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power and an aperture stop, and wherein said system is adapted so as to perform variation of focal length thereof by varying the airspaces reserved between the lens units, said first lens unit and said aperture stop being kept fixed for the variation of focal length.

A vari-focal lens system comprising, in the order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and an aperture stop arranged on the image side of said third lens unit, and wherein said system is adapted so as to perform variation of focal length thereof by varying the airspaces reserved between the lens units.