US 6,320,701 B1Granted

Rear-focus-type zoom lens

AssigneeFuji Photo Optical Co., Ltd.

InventorAkiko Takatsuki

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Abstract

A rear-focus-type zoom lens having, in order from the object side, four lens groups of positive, negative, positive, and positive power, wherein the first lens group G1 and the third lens group G3 are fixed and the second lens group G2 and the fourth lens group G4 are moved during zooming. Focusing is accomplished by moving the fourth lens group G4. The first lens group G1 is formed of a negative lens element L1 and positive lens element L2 that are joined together, and a positive lens element L3. The second lens group G2 is formed of, in order from the object side, a negative lens element L4 and a lens formed of a negative lens element L5 and a positive lens element L6 that are joined. The third lens group G3 is formed of a single lens element L7, and the fourth lens group G4 is formed, in order from the object side, of positive, negative, positive, and positive lens elements L8-L11, respectively. Further, specified conditions are satisfied.

Claims9

Dependent claims

A rear-focus-type zoom lens comprising four lens groups of positive, negative, positive and positive refractive power, respectively, the first lens group and the third lens group being fixed relative to an image surface of the zoom lens, zooming is accomplished by moving the second lens group and the fourth lens group along the optical axis, and focusing is accomplished by moving the fourth lens group along the optical axis, wherein:

the first lens group is formed of, in sequential order from the most object side, a first lens formed of a negative lens element and a positive lens element that are joined, and a second lens which consists of a single lens element of positive refractive power;
the second lens group is formed of, in sequential order from the object side, a third lens which consists of a single lens element of negative refractive power, and a fourth lens formed of, in order from the object side, a negative lens element joined with a positive lens element;
and
the third lens group consists of a single lens element;
and
the fourth lens group is formed of, in sequential order from the object side, a lens element of positive refractive power, a lens element of negative refractive power, a lens element of positive refractive power, and a lens element of positive refractive power.

3 more elements

A rear-focus-type zoom lens comprising, in order from the object side:

four lens groups of positive, negative, positive and positive refractive power, respectively, the first lens group and the third lens group being fixed relative to an image surface of the zoom lens, zooming is accomplished by moving the second lens group and the fourth lens group along the optical axis, and focusing is accomplished by moving the fourth lens group along the optical axis, wherein:
the first lens group is formed of, in sequential order from the most object side, a negative lens element, a positive lens element, and a positive lens element;
the second lens group is formed of, in sequential order from the object side, a lens element of negative refractive power, and a joined lens formed of a negative lens element that is joined to a positive lens element;
the third lens group consists of a single lens element of positive refractive power;
and
the fourth lens group is formed of, in sequential order from the object side, a lens element of positive refractive power, a lens element of negative refractive power, a lens element of positive refractive power, and a lens element of positive refractive power;
the zoom ratio, defined by the focal length of the zoom lens at the telephoto end divided by focal length of the zoom lens at the wide-angle end, is greater than 9.5, and the following condition is satisfied:
0.4<|f2/(fW×fT)0.5|<0.64
where
f2 is the focal distance of the second lens group,
fW is the focal distance of the zoom lens at the wide-angle end, and
fT is the focal distance of the zoom lens at the telephoto end.

9 more elements

Dependencies are inferred from the claim text.