Compact size zoom lens system

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<.vertline.(.phi..sub.w .phi..sub.T).sup.1/2 /(.beta..multidot..phi..sub.2).vertline.<0.026,
• where .phi..sub.w :
• refractive power of the zoom lens system at the shortest focal length condition,
• .phi..sub.T :
• refractive power of the zoom lens system at the longest focal length condition,
• .phi..sub.2 :
• refractive power of the rear lens group (.phi..sub.2 <0), and
• .beta.:
• zoom ratio, which is give by .beta.=.phi..sub.w /.phi..sub.T.

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<(.phi..sub.w .phi..sub.T).sup.1/2 /(.beta..multidot..phi..sub.1)<0.35, and
• 0.07<.vertline.(.phi..sub.w .multidot..phi..sub.T).sup.1/2/(.beta. .phi..sub.2).vertline.<0.35,
• where
• .phi..sub.w :
• refractive power of the zoom lens system at the shortest focal length condition,
• .phi..sub.T :
• refractive power of the zoom lens system at the longest focal length condition,
• .phi..sub.1 :
• refractive power of the front lens group (.phi..sub.1 >0),
• .phi..sub.2 :
• refractive power of the rear lens group (.phi..sub.2 <0), and
• .beta.:
• zoom ratio, which is given by .beta.=.phi..sub.w /.phi..sub..tau..

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<(.phi..sub.w .multidot..phi..sub.T).sup.1/2 /(.beta. .phi..sub.1)<0.40and
• 0.07<.vertline.(.phi..sub.w .multidot..phi..sub.T).sup.1/2 /(.beta..multidot..phi..sub.2).vertline.<0.50,
• where .phi..sub.w :
• refractive power of the zoom lens system at the shortest focal length condition,
• .phi..sub.T :
• refractive power of the zoom lens system at the longest focal length condition,
• .phi..sub.1 :
• refractive power of the front lens group (.phi..sub.1 >0);
• .phi..sub.2 :
• refractive power of the rear lens group (.phi..sub.2 <0), and
• .beta.:
• zoom ratio, which is give by .beta.=.phi..sub.w /.phi..sub.T.

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 .ltoreq.1.60 and .nu..sub.d .ltoreq.35.0, or
• b) N.sub.d 1.50,
• where N.sub.d :
• refractive index of the lens material for the d-line, and
• .nu..sub.d :
• Abbe number of the lens material for the d-line.

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 .ltoreq.1.60 and .nu..sub.d .ltoreq.35.0, or
• b) N.sub.d .ltoreq.1.50,
• where N.sub.d :
• refractive index of the lens material for the d-line, and
• .nu..sub.d :
• Abbe number of the lens material for the d-line.

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.sub.MAX <y<1.0y.sub.MAX where y.sub.MAX is the maximum effective radius of the aspherical surface,
• -0.10<.phi..sub.2 .multidot.(N'-N).multidot.d{x(y)-x.sub.o (y)}/dy<0,
• where .phi..sub.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/.epsilon.)[1-{1-.epsilon.(y.sup.2 /r.sup.2)}.sup.1/2 ]+.SIGMA.A.sub.i y.sup.i
• (summation .SIGMA. made for i.gtoreq.2)
• x.sub.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,
• .epsilon.:
• quadric surface parameter,
• A.sub.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.sub.2.