Zoom lens and zooming method

A zoom lens comprising:

• a front lens unit of negative refractive power, an intermediate lens unit of positive refractive power and a rear lens unit of negative refractive power, zooming being performed by varying a separation between said front lens unit and said intermediate lens unit and a separation between said intermediate lens unit and said rear lens unit, and said zoom lens satisfying the following conditions:
• 0.4<l.sub.1W /f.sub.W <0.8
• 0.21<l.sub.2W /f.sub.W <0.37
• 0.55<f.sub.12W /f.sub.W <0.92
• where f.sub.W is the overall focal length in a wide-angle end of the entire lens system, l.sub.1W is an axial air separation between said front lens unit and said intermediate lens unit in the wide-angle end, l.sub.2W is an axial air separation between said intermediate lens unit and said rear lens unit in the wide-angle end, and f.sub.12W is the overall focal length of said front lens unit and said intermediate lens unit in the wide-angle end.

A zooming method for a zoom lens, said zoom lens having, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit, comprising the steps of moving two lens units of said first, second and third lens units in unison to perform a first zooming operation from a wide-angle end to a medium focal length position, and, after that, taking said two lens units out of unison and moving at least one lens unit of said two lens units to perform a second zooming operation from the medium focal length position to a telephoto end,

• said method satisfying at least one of the following conditions:
• -0.5<(e1T-e1M)/(fT-fM)<0.1
• -0.5<(e2T-e2M)/(fT-fM)<0.1
• where, as said first zooming operation shifts to said second zooming operation, e1M is a principal point interval between said first lens unit and said second lens unit, e2M is a principal point interval between said second lens unit and said third lens unit, and fM is the focal length of the entire system;
• e1T is a principal point interval in the telephoto end between said first lens unit and said second lens unit, e2T is a principal point interval in the telephoto end between said second lens unit and said third lens unit and fT is the focal length of the entire system in the telephoto end.

A zooming method for a zoom lens, said zoom lens having, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit, in which, as zooming is performed by moving said first, second and third lens unit, two lens units of said first, second and third lens units are moved in unison to perform a first zooming operation from a wide-angle end to a medium focal length position and, after that, said two lens units are taken out of unison and moved in differential relation to perform a second zooming operation from the medium focal length position to a telephoto end,

• said method satisfying at least one of the following conditions:
• -0.5<(e1T-e1M)/(fT-fM)<0.1
• -0.5<(e2T-e2M)/(fT-fM)<0.1
• where, as said first zooming operation shifts to said second zooming operation, e1M is a principal point interval between said first lens unit and said second lens unit, e2M is a principal point interval between said second lens unit and said third lens unit, and fM is the focal length of the entire system;
• e1T is a principal point interval in the telephoto end between said first lens unit and said second lens unit, e2T is a principal point interval in the telephoto end between said second lens unit and said third lens unit and fT is the focal length of the entire system in the telephoto end.

A zooming method for a zoom lens, said zoom lens having, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit, comprising the steps of moving said first, second and third lens units to perform a first zooming operation and, after that, while keeping stationary at least one lens unit of said first lens unit and said third lens unit, moving said second lens unit to perform a second zooming operation,

• said method satisfying the following conditions:
• 0<fW(1/f1+2/f2+1/f3)<4
• 0<f23/fT<0.9
• where fi is the focal length of the i-th lens unit, f23 is the overall focal length of said second lens unit and said third lens unit in an arbitrary zooming position, and fW and fT are the focal lengths of the entire system in a wide-angle end and a telephoto end, respectively.

A zooming method for a zoom lens, said zoom lens having, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit, comprising the steps of moving said second lens unit, while keeping stationary at least one lens unit of said first lens unit and said third lens unit, to perform a first zooming operation, and after that, moving said first, second and third lens units to perform a second zooming operation,

• said method satisfying the following conditions:
• 0<fW(1/f1+2/f2+1/f3)<4
• said method satisfying the following conditions:
• 0<fW(1/f1+2/f2+1/f3)<4
• 0<f23/fT<0.9
• where fi is the focal length of the i-th lens unit, f23 is the overall focal length of said second lens unit and said third lens unit in an arbitrary zooming position, fW and fT are the focal lengths of the entire system in a wide-angle end and a telephoto end, respectively.

A zooming method for a zoom lens, said zoom lens having, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit, comprising the steps of, as zooming is performed by moving said first, second and third lens units, performing a first zooming operation from a wide-angle end to a medium focal length position by moving said first, second and third lens units in differential relation, and after that, performing a second zooming operation from the medium focal length position to a telephoto end by moving two lens units of said first, second and third lens units in unison,

• said method satisfying at least one of the following conditions:
• -0.5<(e1T-e1M)/(fT-fM)<0.1
• -0.5<(e2T-e2M)/(fT-fM)<0.1
• where, as said first zooming operation shifts to said second zooming operation, e1M is a principal point interval between said first lens unit and said second lens unit, e2M is a principal point interval between said second lens unit and said third lens unit, and fM is the focal length of the entire system;
• e1T is a principal point interval in the telephoto end between said first lens unit and said second lens unit, e2T is a principal point interval in the telephoto end between said second lens unit and said third lens unit, and fT is the focal length of the entire system in the telephoto end.

A zoom lens comprising:

• a front lens unit of negative refractive power;
• an intermediate lens unit of positive refractive power;
• and
• a rear lens unit of negative refractive power,
• zooming being performed by varying a separation between said front lens unit and said intermediate lens unit and a separation between said intermediate lens unit and said rear lens unit, and said zoom lens satisfying the following conditions:
• ##EQU10## where f.sub.W is the overall focal length of the entire lens system in a wide-angle end, f.sub.T is the overall focal length of the entire lens system in a telephoto end, f.sub.1 is the focal length of said front lens unit, f.sub.3 is the focal length of said rear lens unit, and l.sub.1W is an axial air separation between said front lens unit and said intermediate lens unit in the wide-angle end.

A zoom lens comprising:

• a front lens unit of negative refractive power;
• an intermediate lens unit of positive refractive power;
• and
• a rear lens unit of negative refractive power including a positive single lens and a negative single lens disposed just behind said positive single lens,
• zooming being performed by varying a separation between said front lens unit and said intermediate lens unit and a separation between said intermediated lens unit and said rear lens unit, and said zoom lens satisfying the following conditions:
• ##EQU11## where f.sub.W is the overall focal length of the entire lens system in a wide-angle end, f.sub.T is the overall focal length of the entire lens system in a telephoto end, f.sub.1 is the focal length of said front lens unit, and l.sub.1W is an axial air separation between said front lens unit and said intermediate lens unit in the wide-angle end.

A zoom lens comprising:

• a front lens unit of negative refractive power including a plurality of lenses separated from each other by respective air spaces;
• an intermediate lens unit of positive refractive power;
• and
• a rear lens unit of negative refractive power,
• zooming being performed by varying a separation between said front lens unit and said intermediate lens unit and a separation between said intermediate lens unit and said rear lens unit, and said zoom lens satisfying the following conditions:
• ##EQU12## where f.sub.W is the overall focal length of the entire lens system in a wide-angle end, f.sub.T is the overall focal length of the entire lens system in a telephoto end, f.sub.1 is the focal length of said front lens unit, and l.sub.1W is an axial air separation between said front lens unit and said intermediated lens unit in the wide-angle end.