US2008297901A1PendingUtilityA1
Zoom lens system, optical apparatus, and method for forming an image

Assignee: NIKON CORPPriority: May 29, 2007Filed: Apr 30, 2008Published: Dec 4, 2008
Est. expiryMay 29, 2027(~0.8 yrs left)· nominal 20-yr term from priority
Inventors:Shinichi Mitsuki
G02B 15/144113G02B 27/646
PatentIndex Score
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References
Claims
Abstract

Providing a zoom lens system having a high zoom ratio being compact with high optical performance. The system includes, in order from an object along an optical axis, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, at least one lens group having positive refractive power, and an n-th lens group GN being disposed to the most image side. The n-th lens group GN with positive refractive power includes, in order from the object, a front group GNa and a rear group GNb having positive refractive power. Focusing on an object is carried out by moving the rear group GNb along the optical axis, and a given conditional expression is satisfied.
Claims

exact text as granted — not AI-modified
1 . A zoom lens system comprising, in order from an object along an optical axis:
 a first lens group having positive refractive power;   a second lens group having negative refractive power;   at least one lens group having positive refractive power; and   an n-th lens group being disposed to the most image side,   the n-th lens group with positive refractive power including, in order from the object, a front group and a rear group having positive refractive power,   focusing on the object being carried out by moving the rear group along the optical axis, and   the following conditional expression being satisfied:
   0.05 &lt;D/fNb&lt; 0.50 
   where D denotes a distance along the optical axis between the most image side surface of the front group and the most object side surface of the rear group, and fNb denotes a focal length of the rear group.   
   
   
       2 . The zoom lens system according to  claim 1 , wherein the n-th lens group is a fourth lens group in order from the object, and a third lens group having positive refractive power is included between the second lens group and the fourth lens group. 
   
   
       3 . The zoom lens system according to  claim 2 , wherein the focal length of the zoom lens system is varied by varying a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group, and a distance between the third lens group and the fourth lens group. 
   
   
       4 . The zoom lens system according to  claim 1 , wherein a lens group capable of moving in a direction perpendicular to the optical axis is included between the first lens group and the n-th lens group. 
   
   
       5 . The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   0.20 &lt;D/(   fw×ft ) 1/2 &lt;0.50   where fw denotes a focal length of the zoom lens system in a wide-angle end state, and ft denotes a focal length of the zoom lens system in a telephoto end state.   
   
   
       6 . The zoom lens system according to  claim 2 , wherein 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 increases, a distance between the second lens group and the third lens group decreases, and a distance between the third lens group and the fourth lens group decreases. 
   
   
       7 . The zoom lens system according to  claim 1 , wherein upon zooming from a wide-angle end state to a telephoto end state the first lens group is moved to the object. 
   
   
       8 . The zoom lens system according to  claim 2 , wherein upon zooming from a wide-angle end state to a telephoto end state the third lens group and the fourth lens group are moved to the object, and the second lens group is moved. 
   
   
       9 . The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   −0.16 &lt;f 2 /f 1&lt;−0.08   where f1 denotes a focal length of the first lens group, and f2 denotes a focal length of the second lens group.   
   
   
       10 . The zoom lens system according to  claim 2 , wherein the following conditional expression is satisfied:
   0.75 &lt;f 3 /f 4&lt;2.00   where f3 denotes a focal length of the third lens group, and f4 denotes a focal length of the fourth lens group.   
   
   
       11 . The zoom lens system according to  claim 1 , wherein the front group of the n-th lens group includes at least one aspherical surface. 
   
   
       12 . The zoom lens system according to  claim 2 , wherein the third lens group includes, in order from the object, a front group having positive refractive power and a rear group having negative refractive power, the rear group of the third lens group can be moved in a direction perpendicular to the optical axis, and the following conditional expression is satisfied:
   −1.00 &lt;f 3 a/f 3 b&lt;− 0.40   where f3a denotes a focal length of the front group of the third lens group, and f3b denotes a focal length of the rear group of the third lens group.   
   
   
       13 . The zoom lens system according to  claim 2 , wherein the following conditional expression is satisfied:
   2.00 &lt;f 3 /fw&lt; 4.00   where f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in a wide-angle end state.   
   
   
       14 . The zoom lens system according to  claim 12 , wherein the rear group of the third lens group includes at least one aspherical surface. 
   
   
       15 . The zoom lens system according to  claim 1 , wherein the rear group in the n-th lens group consists of a single lens or a cemented lens. 
   
   
       16 . A zoom lens system comprising, in order from an object along an optical axis:
 a first lens group having positive refractive power;   a second lens group having negative refractive power; and   an n-th lens group being disposed to the most image side,   a lens group capable of moving in a direction perpendicular to the optical axis being included between the first lens group and the n-th lens group,   the n-th lens group with positive refractive power including, in order from the object, a front group and a rear group having positive refractive power, and   focusing on the object being carried out by moving the rear group along the optical axis.   
   
   
       17 . The zoom lens system according to  claim 16 , wherein the following conditional expression is satisfied:
   0.05 &lt;D/fNb&lt; 0.50   where D denotes a distance along the optical axis between the most image side surface of the front group and the most object side surface of the rear group, and fNb denotes a focal length of the rear group.   
   
   
       18 . The zoom lens system according to  claim 16 , wherein at least one lens group having positive refractive power is included between the first lens group and the n-th lens group. 
   
   
       19 . The zoom lens system according to  claim 16 , wherein the n-th lens group is a fourth lens group counted from the object, and a third lens group having positive refractive power is included between the fourth lens group and the second lens group. 
   
   
       20 . The zoom lens system according to  claim 16 , wherein the following conditional expression is satisfied:
   0.20 &lt;D /( fw×ft ) 1/2 &lt;0.50   where D denotes a distance along the optical axis between the most image side surface of the front group and the most object side surface of the rear group, fw denotes a focal length of the zoom lens system in a wide-angle end state, and ft denotes a focal length of the zoom lens system in a telephoto end state.   
   
   
       21 . The zoom lens system according to  claim 16 , wherein the following conditional expression is satisfied:
   −0.16 &lt;f 2/ f 1&lt;−0.08   where f1 denotes a focal length of the first lens group, and f2 denotes a focal length of the second lens group.   
   
   
       22 . The zoom lens system according to  claim 19 , wherein the following conditional expression is satisfied:
   0.75 &lt;f 3 /f 4&lt;2.00   where f3 denotes a focal length of the third lens group, and f4 denotes a focal length of the fourth lens group.   
   
   
       23 . The zoom lens system according to  claim 19 , wherein the third lens group includes, in order from the object, a front group having positive refractive power and a rear group having negative refractive power, the rear group of the third lens group can be moved in a direction perpendicular to the optical axis. 
   
   
       24 . The zoom lens system according to  claim 23 , wherein the following conditional expression is satisfied:
   −1.00 &lt;f 3 a/f 3 b&lt;− 0.40   where f3a denotes a focal length of the front group of the third lens group, and f3b denotes a focal length of the rear group of the third lens group.   
   
   
       25 . The zoom lens system according to  claim 19 , wherein the following conditional expression is satisfied:
   2.00 &lt;f 3 /fw&lt; 4.00   where f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in a wide-angle end state.   
   
   
       26 . The zoom lens system according to  claim 16 , wherein the rear group in the n-th lens group consists of a single lens or a cemented lens. 
   
   
       27 . An optical apparatus having the zoom lens system according to  claim 1 . 
   
   
       28 . A method for forming an image of an object by a zoom lens system comprising steps of:
 providing the zoom lens system comprising, in order from the object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, at least one lens group having positive refractive power, and an n-th lens group being disposed to the most image side, the n-th lens group with positive refractive power including, in order from the object, a front group and a rear group having positive refractive power;   moving the rear group along the optical axis upon focusing on the object; and   satisfying the following conditional expression:
   0.05 &lt;D/fNb&lt; 0.50 
   where D denotes a distance along the optical axis between the most image side surface of the front group and the most object side surface of the rear group, and fNb denotes a focal length of the rear group.   
   
   
       29 . The method for forming an image of an object according to  claim 28 , wherein the n-th lens group is a fourth lens group counted from the object, and a third lens group having positive refractive power is included between the fourth lens group and the second lens group. 
   
   
       30 . The method for forming an image of an object according to  claim 28 , wherein the rear group in the n-th lens group consists of a single lens or a cemented lens. 
   
   
       31 . A method for correcting an image blur of an zoom lens system comprising steps of:
 providing the zoom lens system comprising, in order from an object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and an n-th lens group being disposed to the most image side, the n-th lens group with positive refractive power including, in order from the object, a front group and a rear group having positive refractive power;   moving the rear group along the optical axis upon focusing; and   shifting a lens group disposed between the first lens group and the n-th lens group in a direction perpendicular to the optical axis for correcting the image blur.   
   
   
       32 . The method for correcting an image blur according to  claim 31 , further comprising a step of:
 providing a fourth lens group counted from the object as the n-th lens group, and a third lens group having positive refractive power between the fourth lens group and the second lens group.   
   
   
       33 . The method for correcting an image blur according to  claim 32 , further comprising steps of:
 providing the third lens group including, in order from the object, a front group having positive refractive power, and a rear group having negative refractive power;   shifting the rear group of the third lens group in a direction perpendicular to the optical axis; and   satisfying the following conditional expression:
   −1.00 &lt;f 3 a/f 3 b&lt;− 0.40 
   where f3a denotes a focal length of the front group of the third lens group, and f3b denotes a focal length of the rear group of the third lens group.   
   
   
       34 . The method for correcting an image blur according to  claim 32 , further comprising a step of:
 satisfying the following conditional expression:
   2.00 &lt;f 3 /fw&lt; 4.00 
   where f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in a wide-angle end state.   
   
   
       35 . The method for correcting an image blur according to  claim 32 , wherein the rear group of the third lens group includes at least one aspherical surface. 
   
   
       36 . A method for zooming a zoom lens system comprising steps of:
 providing the zoom lens system comprising, in order from an object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, at least one lens group having positive refractive power, and an n-th lens group being disposed to the most image side, the n-th lens group with positive refractive power including, in order from the object, a front group and a rear group having positive refractive power, moving the rear group along the optical axis upon focusing on the object;   varying a distance between the first lens group and the second lens group, a distance between the second lens group and the positive lens group, and a distance between the positive lens group and the n-th lens group upon zooming; and   satisfying the following conditional expression:
   0.05 &lt;D/fNb&lt; 0.50 
   where D denotes a distance along the optical axis between the most image side surface of the front group and the most object side surface of the rear group, and fNb denotes a focal length of the rear group.   
   
   
       37 . The method for zooming according to  claim 36 , further comprising a step of:
 moving the first lens group to the object upon zooming from a wide-angle end state to a telephoto end state.   
   
   
       38 . The method for zooming according to  claim 36 , further comprising a step of:
 providing a fourth lens group counted from the object as the n-th lens group, and a third lens group having positive refractive power between the fourth lens group and the second lens group.   
   
   
       39 . The method for zooming according to  claim 38 , further comprising a step of:
 moving the third lens group and the fourth lens group to the object, and the second lens group upon zooming from a wide-angle end state to a telephoto end state.   
   
   
       40 . An optical apparatus having the zoom lens system according to  claim 16 .
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