JPS59228220A - Large diameter macro lens - Google Patents

Abstract

PURPOSE:To obtain a compact lens system while correcting spherical aberration, etc., by moving the 1st - the 3rd lens groups to an object side for focusing so that the air gap between the 1st and the 2nd lens groups and the air gap between the 2nd and the 3rd lens groups both increase. CONSTITUTION:The lens system consists of three groups, i.e. the 1st lens group I having positive refracting power, the 2nd group II having positive refracting power, and the 3rd lens group III having negative refracting power successively from the object side. When focusing from an infinite-distance object to a short-distance object is performed, the lens groups are all moved so that the air gap between the 1st lens group I and the 2nd lens group II and the air gap between the 2nd lens group II and the 3rd lens group III both increase. Further, the lens system is composed so that inequalities I and II may hold.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a large-mouth macro lens that is capable of continuously photographing objects from infinity to near the same magnification.

In conventional macro lenses, aberrations are best corrected near infinity for general photography lenses, but in consideration of aberration degradation due to changes in shooting distance, aberrations are corrected at a shooting magnification of around 1/10x. There is. However, even if the best aberration correction is set at short distances as described above, as the imaging magnification is further increased, the deterioration of spherical aberration, coma aberration, and astigmatism becomes noticeable, making it difficult to realize large-diameter macro lenses. It made it difficult. On the other hand, it is known that a large-diameter macro lens is realized by providing a so-called floating mechanism and correcting the aberration degradation caused by the short-distance focusing. By providing such a floating mechanism, it is advantageous to correct spherical aberration and coma aberration, but it tends to allow some variation in distortion and astigmatism, which are important for a macro lens. On the other hand, in order to be able to continuously photograph objects from infinity to close to the same magnification, focusing usually requires a focusing extension equivalent to the focal length of the lens, and the lens system alone is not compact enough. too,
The large focusing extension made the lens barrel structure complicated, making it impossible to create a compact lens as a whole.

The present invention has a wide photographic area from infinity to around the same magnification, has small fluctuations in distortion, and is well corrected for spherical aberration, coma aberration, and astigmatism (7 < lance 75; ° Repetition 1"" amount is small and con-
The objective is to provide a highly efficient large-diameter macro lens system.

The large V:, 1 diameter macrolens degree of the present invention is the 1st section 1 degree.
As shown in Figure 53, in order from the object side, the 1721st lens group (1) has a positive refractive power, and the second lens unit B has a positive refractive power.
￥(n), and the third lens group (
When focusing from an object at infinity to a nearby object, the 1721st lens group to the 3rd lens group are all moved toward the object side, and at this time, the distance between the 1721st lens group and the second lens group is air spacing and said second
It has a configuration that increases the air distance between both the lens group and the third lens group.

As described above, the present invention corrects the deterioration of R-plane aberration, especially coma aberration, by increasing the air distance between the 1721st lens group and the second lens group while extending them. The increase in distortion in the negative direction due to the extension of the 1721st lens group and the second lens group and the balance of astigmatism are corrected by increasing the air gap between the second and third lens groups. That is, the floating between the 1721st lens group and the second lens group mainly corrects spherical aberration and coma, and the floating between the 1721st lens group and the 3rd lens group
By mainly correcting distortion and astigmatism using 0-ting, various aberrations can be corrected separately, making it possible to perform better correction.

In addition, in the present invention, the negative third lens group having a predetermined refractive power is disposed closest to the image plane, and the air distance between the positive first V lens group and the positive second lens group is increased, so that it is possible to focus on nearby objects. By focusing, the amount of focusing movement of the 1721st lens group and the second lens group is made smaller.

The present invention is characterized by having the above basic configuration and satisfying the following conditions.

(1) -14< f3/f <-3 (2)
0.1 < m3/mz <O18 However, f is the focal length of the entire system, f3 is the focal length of the third lens group, and m2 is the focal length of the second lens group.
The amount of movement of the lens group, 1η3, is the amount of movement of the third lens group.

Conditional expression (1) defines the refractive power of the third lens group, and together with conditional expression (2), it is related to the amount of movement of the first and second lens groups from infinity to close-up. There is.

In other words, if the lower limit of conditional expression (1) is exceeded, the refractive power of the third lens group becomes too weak, and the amount of movement of the first and second lens groups from infinity to close-up (near the same magnification) becomes small. This would deviate from the purpose of the present invention, which is to realize the entire product in a compact mold. On the other hand, if the upper limit is exceeded, it becomes difficult to correct spherical aberration and astigmatism.

Conditional expression (2) defines the ratio of the amount of movement of the third lens group to the first and second lens groups, and together with conditional expression (1), the ratio of the amount of movement of the third lens group to the first and second lens groups is It is related to the amount of movement of the group, and at the same time, it is related to the correction of distortion aberration and astigmatism when approaching.

In other words, if the upper limit of conditional expression (2) is exceeded, the movement claws of the first and second lens groups from infinity to close-up cannot be made smaller, as in the case of conditional expression (1) above. If the lower limit of condition (2) is exceeded, condition (1)
It becomes difficult to correct astigmatism under such conditions, and the effective diameter required for the third lens group becomes too large if focusing is attempted to near the same magnification.

Furthermore, under the above conditional expression (IO2), the ratio of the amount of movement of the first lens group and the second lens group from infinity to close-up must have a reasonable value for good correction of spherical aberration and coma aberration. Decision 1
However, specifically, it is desirable to follow the following conditional expressions.

(3) 1.14 < ms/mz <1.22 However, lη1 is the amount of movement of the first V lens group.

Conditional expression (3) is related to correction of spherical aberration and coma aberration from infinity to close range. That is, if the - upper limit is exceeded, the spherical aberration at close range will be 1 square positive, while if the lower limit is exceeded (it becomes difficult to correct coma aberration while taking image surface properties into consideration).

In carrying out the present invention, it is desirable to follow Sarachi's conditional expression.

(4) 0.1(ΔdA//ΔdB (0,5 However,
ΔdA is the amount of change in the air distance between the first V lens group and the second lens group, and ΔdB is the amount of change in the air distance between the second lens group and the third lens group.

(5) 0.05 <'m3/ml< 0.7 The above conditional expression (4) defines the increase ratio of the air distance between the 1st and 2nd V lens groups and between the 273rd lens group, which both increase during focusing. If the upper limit is exceeded, it becomes difficult to correct variations in spherical aberration and coma aberration during close focusing, while if the lower limit is exceeded, it is difficult to correct variations in spherical aberration and astigmatism in a well-balanced manner. becomes.

Furthermore, conditional expression (5) is also related to conditional expressions (1) and (2), and if the lower limit is exceeded, the effective diameter of the third group must be increased, and correction of field curvature fluctuations becomes impossible. It will be enough. On the other hand, if the upper limit of conditional expression (5) is exceeded, the effect of reducing the amount of focusing movement of the first and second lens groups will be diminished, and it will become difficult to correct fluctuations in distortion.

A specific lens configuration of the present invention includes the following positive meniscus lens and negative lens, and the second lens group includes a negative lens with a surface with a strong curvature facing the object side, and a negative lens with a surface with a strong curvature facing the @ side. A cemented lens made by bonding a positive lens that faces toward the image side, and a cemented lens that has a strong curvature than a positive lens that faces the image side.
In addition, the third V lens group in ifJ is composed of a negative meniscus lens with a convex surface facing the object side.

In addition, as is clear from conditional expression (2), the negative meniscus lens constituting the third lens group in the above has weak refractive power and is less affected by fluctuations in the lens bank due to temperature changes, so it can be constructed from a plastic lens. It is possible. (See Example 3) Furthermore, if the specific shape of the third V lens group, which is a meniscus lens with a weak refractive power, is made of plastic, it will be easier to manufacture.

Next, the specifications of the infinity focus state of the embodiment of the present invention will be shown. In the example, ri is the radius of curvature of the first lens from the object side, di is the first axial distance from the object side, and Nl and νi are the refractive index of the first lens from the object side, respectively. It's a thicket.

Example 1 f=100. OFNO,=28 LB,=78.674
, Radius of curvature Distance between upper surfaces of shaft Refractive index (Nd)
Dispersion (νd) rx 360.308 d 1 4.660 Nr 1.72000
rl 50.31r2 -167084 d2 0.291 ra 41310 d34B54 N2 1.77250 ν2
49.77r4 109yu32 d4 2.136 ra -806933 ds 6.602 N3 1fi0342
ν3 3801r7 -34380 d7 5D68 N4 1.67339 ν4
2925r8 -131;? 67 ds 6.718 NS 1.71300
ν5 5393r9 -40.011 d9 C)291 rlo 464.140 dto 6.446 N6 1.77250
White 49.77r12 105.011 Σd=53960 Next β-0,995 d6'=27.266 d
+t'-54,214L, B',=112.721 f3/f=-6,67, ms/mz=0.39.
m1/m2=1.17, m3/m1=0.3
3d6'-d6 ΔdMΔdB=d□,'-71. = 0.28 Example 2 f=xoo,o FNO,=2.8 L, B:=8
0.876 Radius of curvature Axis top surface interval Refractive index (Nd)
Dispersion (νd) rl 354.106 Σd= 51803 When rice β--0,997 d6'=23.944 a
lt'=32.27'4L, B',=129.226 f3/f--333, ms/m2=0.61. ml
/m2=1.15, m37m1=053 Example 3 f=too, o FNO=2.8 L, B7=78
．． 058 Radius of curvature Axis top surface interval Refractive index (Nd)
Dispersion (νd) rl 374.036 d2 0. II! 91 r3 41.480 d4 2D30 rs-1144216 r7 -34.653 rl2 102945 Σd=54200 When rice β= -0,997 d6' =28.012
dxt' =83.903L, B', =s 9.3
63 f3/f--1333, ms/m2=012. mz/m
2=1.18. ms/m1=o, 10ds'-d6 ΔdMΔdB-dtt'-dt□=0.20

[Brief explanation of drawings]

1 to 3 show respective lens configuration diagrams of Examples 1 to 3 of the present invention, and FIGS. 4 to 6 show various aberration diagrams of Examples 1 to 3, respectively. ■...Luns group ■...Second lens group II...Third lens group Applicant: Minolta Camera Co., Ltd. Fig. 1 Fig. 2 ■ Fig. 3 Leni 0 low Y' = β・- 1-me Y'・1' \ \ \ \ \ Tsu, 5 ・42Y'-42 5 =42 DsY'=42 9-cho-11-] 015 -7 2 lA
Figure 6 β・-10 o'clock D5Y'=42 42 D3 Y'=4Z

Claims (1)

[Claims] 1. A lens group (I) having positive refractive power in order from the object side.
), a second lens group (It) having a positive refractive power, and a third lens group (1u) having a negative refractive power. The lens group from the lens group to the third lens group are all moved toward the object side so that the air distance between the lens group and the second lens group and the air distance between the second V lens group and the third lens group are both increased. A large-diameter macro lens knee that performs focusing and satisfies the following conditional expressions: 14 < fs/f <-a 0.1 < m3/mz (0,8 where f: focal length of the entire system , f3: Focal length of the third lens group, m2: Amount of movement of the second lens group, m3: Amount of movement of the third lens group.2. Large diameter macro lens described in item 1: 0.1 (ΔdA/JdB < 0.5, however, ΔdA:
Amount of change in the air distance between the second lens group and the second lens group, JdB: Amount of change in the air distance between the second lens group and the third lens group. 3. A large-diameter macro lens according to claim 1, which further satisfies the following conditions: 0.05 (m3/ml (0.7) where ml is the amount of movement of the lens group. 4. In order from the object side, the lens group consists of a positive lens, a positive meniscus lens with a convex surface facing the object side, and a negative lens, and the second lens group is a negative lens with a surface with strong curvature facing the object side. It consists of a cemented lens made by bonding together a positive lens with a surface with strong curvature facing the image side, and a positive lens with a surface with strong curvature facing the image side, and the third lens group has a negative lens with a convex surface facing the object side. 5. The large-diameter macro lens according to claim 1, characterized in that the lens comprises a meniscus lens. 5. The large-diameter macro lens according to claim 4, characterized in that the third lens group is a plastic lens. Large-diameter macro lens. 6. The large-diameter macro lens according to claim 1, further satisfying the following conditions: 1.14 (m+An2 (1,22 m1: movement of the 1721st group, l:.