JPH03154014A - Zoom lens - Google Patents

Abstract

PURPOSE:To attain to make the zoom lens small in size and light in weight, while securing a variable power ratio by constituting a lens system consisting of five groups of lenses, and also, allowing it to satisfy specific conditions. CONSTITUTION:A lens system is constituted of five lens groups having refracting power of positive, negative, positive, positive and positive successively from an object side, a first, a third and a fifth lens groups 1, 3 and 5 are fixed, a second lens group 2 is moved for varying power, and a fourth lens group 4 is moved in order to correct a focal position. In such a state, when a focal distance of an i-th lens group, a focal distance of a wide angle end of the whole system, a curvature of an n-th boundary surface, and an n-th boundary surface interval are denoted as (fi), (fw), Rn and Tn, respectively, the lens system is allowed to satisfy expressions I - V. In such a way, a first lens group 1 can be converted to a small aperture, and also, even at the time of power focus, the motor torque can be reduced, and it can be attained to make the zoom lens small in size even in the case of a high variable power ratio.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a so-called inner focus type zoom lens, and more particularly to a high variable power inner focus type zoom lens that can achieve a reduction in size and weight while ensuring a high variable power. [Conventional technology]

Traditionally, it has been a typical zoom lens. The 1st lens group, 2nd lens group, and 3rd lens group are placed in front of the relay lens, and the movement of the 1st lens group adjusts the focus, and the movement of the 2nd lens group performs magnification change. A so-called mechanically corrected zoom lens is known in which the accompanying image plane fluctuation is corrected by moving a third lens group.

[Problems to be solved by the invention]

However, in this type of zoom lens, the 1st) 71st group is extended significantly during close-up photography, so it is necessary to increase the aperture of the 1st) 71st group in order to prevent vignetting at the periphery of the lens. Along with this, when using so-called power focusing, a large-diameter first lens
) A problem also arises in that a high output motor is required to drive the 71st group. In addition to the movement space for the 1st) 71st lens group, space for the movement of the second lens group for changing magnification and space for the movement of the third lens group for correcting image plane fluctuations accompanying changing magnification is secured. Therefore, if you try to increase the variable power ratio and keep the aberrations within an appropriate range, this movement space will become longer and the overall length of the lens will become longer.

[Means to solve the problem]

The present invention was made in view of these problems, and
A zoom lens that allows for the miniaturization of the first (71) group and reduction of morph torque during power focusing without sacrificing close-up shooting ability, as well as shortening the overall length of the lens while increasing the variable power ratio. The purpose is to offer. The zoom lens of the present invention is: 5 having positive, negative, positive, positive, and positive refractive powers in order from the object side
Equipped with two lens groups. the first lens group, the third lens group, and the fifth lens group;
The lens group is fixed. The second lens group is not moved in the optical axis direction for zooming. The fourth lens group is not moved in the optical axis direction for correcting movement of the focal point position due to zooming and for focusing. The third lens group includes at least one lens having a negative curvature in which the object side curvature is stronger than the image side curvature. Let fl be the focal length of the first lens group. The focal length of the entire system at the wide-angle end is f. When binding, the curvature of the n-th boundary surface is R7, and the interval between the n-th boundary surfaces is T. 4.32<r+/fw<4.72 (
z) 108<l ft /f, 41
+210.26<f, /fs<0.36
+3) 0 <T'sT'+q< 0,
035 +41). 34< lR1
It is characterized by satisfying the following condition: w/fw |<1.39 (5).

[Function] In the present invention, the magnification change effect is achieved by moving the second lens group with negative refractive power in the optical axis direction, and the image plane fluctuation accompanying the magnification change is caused by the movement of the fourth lens group in the optical axis direction. Corrected by Further, the first (71) lens group is fixed, and focusing is also performed by moving the fourth lens group in the optical axis direction. [Embodiment] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an optical axis sectional view of a zoom lens according to an embodiment of the present invention, where 1 is a lens group with positive refractive power, 2 is a second lens group with negative refractive power, and 3 is a positive lens group. 3rd with refractive power
Lens group 4 indicates a fourth lens group with positive refractive power, 5 indicates a fifth lens group with positive refractive power, and the lens group l, the third lens group 3, and the fifth lens group 5 are each fixed. has been done. Further, the second lens group 2 moves in the optical axis direction for changing magnification, and the fourth lens group 4 moves in the optical axis direction for correcting image plane fluctuations due to changing magnification and for focusing. . Further, 6 indicates an aperture. In the present invention, since the 1st) 71st lens group 1 is not moved out for focusing, the 1st lens group 1 only needs to have an aperture that can prevent vignetting in the wide end infinity state, and a special large aperture is not necessary. In addition, by moving the fourth lens group 4 in the optical axis direction, correction of image plane fluctuations associated with zooming and focusing are performed at the same time! The moving space length to be maintained is reduced, and the overall length can be shortened. Next, R7 to R0 each indicate the boundary surface from the object side, and T
0 to T0 each indicate the interval between adjacent boundary surfaces. Also, the third lens group 3 includes at least one lens L whose object side curvature is a stronger negative curvature than the image side curvature. Furthermore, the zoom lens of the present invention has the following features:
When we define the focal length of the th lens group as fl, the focal length of the entire system at the wide-angle end as fw, the curvature of the n-th boundary surface as R1)+"th interval between the boundary surfaces as T7, 4.32<fl/ r@ <4.72 (
1) 108<lft/fw l
[210,26<f,/fs<0.36
(3) 0 < Tll T17 < 0, 03
5 (4) 1.34<lR+,
/fw|<1.39 (5) It is configured to satisfy the following condition. Among these conditions, condition (1) defines the refractive power of the lens group 1, and is involved in the correction of 1-spherical aberration and coma. When the refractive power of the first lens group exceeds the lower limit of condition +1), the spherical aberration on the telephoto side becomes overcorrected, and conversely, when the refractive power of the first lens group exceeds the upper limit of the condition fll. If it becomes weak, the spherical aberration on the telephoto side will be insufficiently corrected, and off-axis outward coma will occur. Condition (2) defines the refractive power of the second lens group 2, and is involved in the amount of movement of the second lens group 2 and the curvature of field during zooming. When the refractive power of the second lens 2 becomes strong beyond the lower limit of condition (2), the amount of movement of the second lens group 2 during zooming decreases, but the negative curvature of field increases. Condition (3) defines the ratio of the refractive powers of the fourth lens group 4 and the fifth lens group 5, and is used to correct spherical aberrations and image plane fluctuations due to zooming. Involved in the amount of movement. If the ratio of the refractive power of the fourth lens group 4 to the refractive power of the fifth lens group 5 becomes smaller than the lower limit of condition (3), one spherical aberration will be overcorrected, and the refractive power of the fourth lens group 4 will become smaller. When the ratio of the refractive powers of the fifth lens group 5 increases beyond the upper limit of condition (3), the amount of movement of the fourth lens group 4 to correct image plane fluctuations due to zooming becomes large, and the total lens length increases. increases. Condition (4) is the lens Ll1 that constitutes the fourth lens group for correcting image plane fluctuations and focusing due to zooming.
It defines the difference between the thickness of lens L and the distance between lens L1° and is involved in correction of 2-spherical aberration and coma. If this difference exceeds the upper limit of condition (4) and increases, spherical aberration will be insufficiently corrected, and if this difference exceeds the lower limit of condition (4) and becomes small (becomes negative), off-axis inward coma will occur. do. Condition (5) defines the curvature of the boundary surface R1 between the lens L1° and the lens L1) that constitute the fourth lens group for correcting image plane fluctuations due to magnification and focusing. Involved in correcting curvature and coma. If the curvature exceeds the upper limit of condition (5), the curvature of field will be insufficiently corrected, and if one curvature exceeds the lower limit of condition (5), an off-axis outward coma will occur. As an example in which more specific numerical values are defined, the first example is shown in Tables (1-1) and (1-2). The second embodiment is shown in Tables (2-1) and (2-2), and the aberration curve diagrams of the first and second embodiments are shown in Figs. 2 to 4 and 5, respectively. This is shown in FIGS. 7 to 7. Note that Tn shown in Tables (1-2) and (2-2) below corresponds to the variable n-th boundary surface interval T7 in the corresponding Tables (1-1) and (2-1) at the wide end, These are shown for each standard and tele end. Also, the focal path 1r in Table 1 (1-2) and Table (2-2)
is expressed as a ratio when the wide end is set to 1. Also, all tables show the case of focusing at infinity. Furthermore, in the aberration curve diagram, d and g represent the d-line and g&i, respectively, sc represents the sine condition, and D
S indicates the sagittal direction, and DT indicates the meridional direction. Table (1-1) Table (2-1) Table (1-2) Table (2-2)

【effect】

As explained above, according to the present invention, the diameter of the first lens group can be reduced, and the torque of the motor can be reduced during power focusing. Furthermore, since zooming, correction of image plane fluctuations, and focusing can be performed by moving the second and fourth lens groups in the optical axis direction, the space in which the lens groups can move can be shortened even if the zoom ratio is increased. , it is possible to achieve miniaturization of the entire lens.

[Brief explanation of the drawing]

Fig. 1 is an optical axis sectional view of a zoom lens according to an embodiment of the present invention, Fig. 2 is an aberration curve diagram of the first embodiment at the wide end, and Fig. 3 is a diagram of the aberration curve of the first embodiment at the standard time. FIG. 4 is an aberration curve diagram at the telephoto end of the first embodiment, and FIG.
The figure is an aberration curve diagram of the second embodiment at the wide end, FIG. 6 is an aberration curve diagram of the second embodiment at the standard time, and FIG. 7 is an aberration curve diagram of the second embodiment at the telephoto end. . 3...Third lens group 5...Fifth lens group 4...Fourth lens group 6...Aperture

Claims (1)

[Claims] 5 having positive, negative, positive, positive, and positive refractive powers in order from the object side.
the first lens group, the third lens group and the fifth lens group;
The lens group is fixed, the second lens group is moved in the optical axis direction for zooming, and the fourth lens group is used for correcting the movement of the focal position due to zooming and for focusing. Therefore, the third lens group has at least one lens having a negative curvature where the object side curvature is stronger than the image side curvature, and the i-th lens group When the focal length of is f_i, the focal length at the wide-angle end of the entire system is f_w, the curvature of the n-th boundary surface is R_n, and the distance between the n-th boundary surfaces is T_n, then 4.32<f_1/f_w<4.72(1)108<|
f_2/f_w | (2) 0.26<f_4/f_5<0.36(3) 0<T_1
_8-T_1_7<0.035(4)1.34<|R_
A zoom lens characterized by satisfying the following condition: 1_9/f_w|<1.39(5).