JPS62206516A - Rear focus zoom lens - Google Patents

Abstract

PURPOSE:To obtain the constitution where a variable power ratio is not greatly varied and an excess space is not required in a lens system, by providing four lens groups and satisfying specific conditions among focal lengths, lateral magnifications in the wide angle end and the telephoto end of the second lens group for an object in the infinity, and those in the wide angle end and the telephoto end of the third and fourth lens groups. CONSTITUTION:A zoom lens system consists of four lens groups having positive, negative, positive, and positive refracting powers in order from the object side; and in case of variable power from the wide angle end to the telephoto end, the second lens group is moved toward the image surface, and the fourth lens group is moved nonlinearly for the purpose of compensating the variation of the image surface accompanied with variable power. The fourth lens group is moved furthermore for the purpose of focusing to make an excess space unnecessary in the lens system, and the whole of the lens system is simplified and is made small-sized. Lens groups are so specified that conditions of inequalities (1) and (2) are satisfied, and the variation of the variable power ratio accompanied with the change of the subject distance is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a zoom lens suitable for still cameras, video cameras, etc. The present invention relates to a rear focus type zoom lens having a simple configuration.

(Prior Art) A 04n zoom lens is a zoom lens that has been widely used in still cameras, video cameras, TV cameras, and the like. This 4# zoom lens has a G19S second group for focusing in order from the object side, a third group for correcting body surface fluctuations due to zooming, and a focal length of the entire system @+ A 4th nth element is provided to balance the aberration correction.

The 4# zoom lens has a complete structure in which a total of three lens groups are moved: two lens groups for zooming and one lens group for focusing. For this reason, the lens barrel tends to be relatively complicated.When focusing on a close-range object, the first solution is extended to the object side, so if you want to secure enough off-axis light flux, the front lens diameter rarely tended to increase.

For this reason, various zoom lenses have been proposed that utilize the Kushoura rear focus method, in which all lens groups other than the first group are moved to perform focusing.

For example, in US Pat. No. 4,364,642, focusing is performed by moving 'M3m' in a 4# zoom lens. Also, in US Pat. No. 4,460.251, focusing is performed by moving the second #t1 and third groups integrally in a four-group zoom lens. Also, JP-A No. 58-136012 public mteti change+f! We have proposed a zoom lens that is composed of 5t-3 or more lens groups and focuses by moving some of the lens groups.

However, all of these rear focus type zoom lenses require a space for moving a movable lens group for focusing in addition to variable magnification, and furthermore, the variable magnification ratio changes as the object distance changes. For example, the zoom ratio tends to decrease as the distance object becomes shorter.

(Problems to be Solved by the Present Invention) Although the present invention employs a rear focus system, the variable magnification ratio does not change much with respect to changes in object distance, and additional space is required in the lens system. The purpose of the present invention is to provide a rear focus type zoom lens with a simple configuration that does not require a single lens.

(Means for solving the problem) From the object side, the first group has positive refractive power, and the second group has negative refractive power.
It has four lens groups: n, a third group, and a fourth group with positive refractive power. (For magnification change, the first and third groups are fixed) The second group is moved in one direction, and the second group is moved in one direction. 4 # The entire lens is moved, and focusing is performed by moving the 4th lens group 1.
The ratio of the focal length of the entire system at the telephoto end and the wide-angle end when the group is focused on an object at infinity, and 1 the ratio of the focal length of the entire system at the telephoto end and the wide-angle end when the fourth group is focused on a close object. The ratio of lateral magnification is approximately equal to 1, and the focal length of the entire system at the wide-angle end and the telephoto end is f.
w, fT-%The lateral magnification of the wide-angle end and the telephoto end of the second group when the object is at infinity. β3W 'β3T' The lateral darkness ratio at the wide-angle end and the telephoto end of the fourth lens group for a close-range object is approximately β4.

When β4T is set, 0.72<+(β3T/β3W)・(β4T/β4w month(1,30...-(2)) Add t'ii'i.

Other features of the invention are described in the Examples.

(Example) Figures 1 and 2 show an example 1 of the numerical failure of the present invention that is followed by a trough.
FIG. 2 is a side view of the lens No. 2. ■ In the figure.

II, 111, IV are respectively 1st\21st 31st 4th
It is a group.

In this example, zoom lens 1 - positive, negative,
From 4 lens groups with positive and positive refractive power! Ij! When changing magnification from the wide-angle end to telephoto 4, the 1st and 4th groups are moved non-linearly to the z#t-f quadrant side in order to correct the image plane fluctuations that occur when changing magnification. . Further, by moving the fourth group for focusing, no extra space is required in the lens system, thereby simplifying and downsizing the entire lens system. Then, the 4th group is focused on an object at infinity and the ratio of the focal length of the entire system at the telephoto end and the wide-angle end in the next state is C/, and the 4th lens group is focused on the total close object distance and the telephoto lens is 44 in a good state. By setting each lens group and focusing condition t so that the ratio Cβ of the lateral magnification of the entire system at the wide-angle end is approximately equal, the change in magnification ratio, IdJ, when the object distance changes is reduced. . .

In other words, the optical system of each lens group is adjusted so that an object of a certain length photographed at both telephoto and wide-angle zoom positions for both a distant object and a close-up object will have 9 dimensions on the imaging plane according to the zoom ratio. All conditions have been set.

Note that the above-mentioned focal length ratio Cf and lateral magnification ratio Cβ being substantially equal means that they are equal to the extent that fluctuations in the zoom ratio due to fluctuations in the object distance are allowed, specifically 0. .8 (Cf/Cf<1.2...-
...Means that the condition (3) is satisfied.

Furthermore, in this embodiment, each lens group is specified so as to satisfy the above-mentioned conditional expressions (11, +21) in order to reduce the variation in the magnification ratio due to variation in the object distance.〇Conditional expression (1) is Regarding the ratio of imaging magnification at the telephoto end and wide-angle end of the second group and the ratio of the focal length at the telephoto end and wide-angle end of the entire system when focusing on a swallow-limiting object, if the lower limit ll11t- is exceeded, the nominal magnification changes. If the effective zoom ratio is small compared to the ratio, or if the upper limit IIIL is exceeded, the effective zoom ratio becomes larger than the nominal zoom ratio. As the amount increases, the entire lens system becomes larger.

Conditional expression (2) is the 3rd # and 4th # when focusing on a nearby object.
When the lateral magnification at the telephoto end and wide-angle end of the group exceeds the lower limit, the effective zoom ratio for close objects becomes significantly lower than the effective zoom ratio for distant objects. Moreover, if the upper limit t is exceeded, the effective zoom ratio for distant objects will be significantly lower than the effective zoom ratio for close objects, and the lens will move further toward the telephoto side. This is not preferable because the amount increases in the object side direction, and in order to secure the space at this time, the distance between the third group and @ltF must be increased in advance, which increases the size of the entire lens system.

Next, numerical examples of the present invention will be shown. In the e example, a
t is the radius of curvature in the direction of the i1) eye lens in order from the object side,
DiFi 1st lens thickness and air spacing from the object side
, Ni and νi are respectively calculated from the refractive index and Abbe number of the glass of the fifth lens from the object side.

Also, the focal length #1f/ and the angle of view ω are 1
The lateral magnification β and object height are values when focusing on a short-distance object (17FL).

For reference, the telephoto end (T) and wide-angle end (
The ratio T/Wt of W) is shown.

At these values, the angle of view ratio is perfect! The effective magnification ratio - and the object height ratio for 121 lenses respectively correspond to the effective magnification ratio for a close object.

a value Example I F-10, 18-29.82 FNO=l:L
8 2ω-429°~15.3°Rl-80,83D
l-1,30N l-L 80518 C1-25.
4R2= 27.06 02-5.20 N 2-1
．． 62299 &l 2”5&2R3--81810
3-0,15 R4=2Z21 D4-3.80 N3-1.62
374y347. lR5-9L39 D5-
0.38-11.63R6-57, 24D 6-0.7
0 N 4-L 78590 ν 4-4
4.2R7-9,41D 7-150 118--IL 75 D 8-0.60 N
5-1.70154 5-4L2R9-110
1D9-140 N6”L84666 u6-2i
9RID--4 & Go DIO-1 & 46~
7.20R11--7,52Dll-0,6587-1
, 71300 sear 5 fu 8 RIZ ko →, 84 01
2-0. t5R13--36,05Di3-2-10
N 8-L 59270 v 8=3
& 3R14--1λ37 D1←LOG R15-String L)15-1.50 R16-1λ13 016- :lL 4G
N 9-L 62230 ν 9-5L 2R
17-54mu07 D17-α15R1111=
lfL 02 01&-2,, TON10-L 5
1742 ylo=5Z 4R19-62197D
19-0.50 R20--7SL 50 02G-(L 7G
Ni1-L 84666 Shi1l-249R
21-1α47 11! l-3,27~189R2
2-5431022-140N12-L 51633
C12-641R23--Y54 023-0.
15R2← 1a82 D2←L 10 Nt
a-t, 48749 v13-70.2R25-
-15 & 69 1) 25-2.50~L 88R2
1y= -D26= 5.50 N14-L 5
1633 u14-641R27-- Numerical implementation [3112? -&68~27.23 FNO-1:λ0 2ω
-49,5″~16.9°R1-50,52D I-1
30N 1-1.80518 Si1-2a4R2
-27,31D 2-5.50 N 2-1.6
2299 ν 2-58.2R3--153α0
9 D 3-0.15R4-22, 56D 4-41
0 N > 1.69680 y 3-5 & 585
-83. O D 5-0.50~1L75R6
-19,6606-0,70N 4-1.78590
ν 4-442R7-7, 5307-170 R8--13, 7108-0, 60N5-L70154
shi5-41.2RO-9,36D 9-190
N 6-1.84666 &16=2&9RIO-
-234251) 10 San 14; 68~&42R11-
-5,66Dll-0,65N 7-L 59270
y 7-3 & 3R12--9, 22D12-0
．． 15 tζ13- -29.65 013 meals L, 80
N8 matte L 60311 ν 8 Shizuku 60
．． 7R14--1135D14- LOG R15-Aperture 5 [115-1,50R16-
11140Li2S-ZOON9=L62230
y9-5L2R17--19,161) 17-0.1
5R18= 17.28 018- Z 10
Nl0-L 51742 ulO-51
4R19--10468019-0, 10R20-17
,43020-0,70Ni1-L 84666
yll=2:L 9R21-7,84D21-485~
a 18R22= 12L 44 022-2
．． 70 N12-L 48749 y12
-70.2R23--111L82 D23-45
0R24--D24- Fh, 50 N15=L
51633 y13-641R Shisuke (Effect of the invention) According to the present invention, the number li! As shown in the embodiments, by specifying each lens group t so as to satisfy the above-mentioned conditions, it is possible to achieve a rear focus type zoom lens having a simple structure in which the magnification ratio does not change much with respect to changes in object distance. I can do it.

[Brief explanation of drawings]

Figures 1 and 2 are numerical implementations according to the present invention - Example 1.2, respectively.
3 and 4 are aberration diagrams of Example 1.2 of the present invention. In the aberration diagram, the aberration at the wide-angle end 5 (B) is the aberration at the telephoto end. Circular 1. n, 1. M is the first, second, third, and fourth group, S is the sagittal image plane, M is the meridional image plane, and d
#'id embroidery, g is g-a.

Claims (1)

[Claims] In order from the object side, the first group has a positive refractive power, and the second group has a negative refractive power.
It has four lens groups: a lens group, a third group, and a fourth group with positive refractive power, and when changing magnification, the first group and the third group are fixed, the second group is moved in one direction, and the second group is moved in one direction. Focusing is performed by moving the fourth group, and focusing is performed by moving the fourth group, and focusing is performed by moving the fourth group.
The ratio of the focal length of the entire system at the telephoto end and the wide-angle end when the group is focused on an object at infinity, and the ratio of the focal length of the entire system at the telephoto end and the wide-angle end when the fourth group is focused on a close object. The ratio of lateral magnification is approximately equal, and the focal length of the entire system at the wide-angle end and the telephoto end is f.
_W, f_T, the lateral magnification of the wide-angle end and telephoto end of the second group for an object at infinity are β_2_∞_W, β_2_∞_
T, the lateral magnifications of the wide-angle end and telephoto end of the third group for close-range objects are β_3_W and β_3_T, respectively, and the lateral magnifications of the wide-angle end and telephoto end of the fourth group for close-range objects are β, respectively.
When _4_W and β_4_T, 0.9<|(β_2_∞_T/β_2_∞_W)/(f
_T/f_W) |<1.580.72<|(β_3_T
/β_3_W)・(β_4_T/β_4_W)|<1.
A rear focus zoom lens that satisfies the following conditions: