JPS6324213A - Compact wide angle lens - Google Patents

Abstract

PURPOSE:To make working simple by forming an aspherical surface on the image side of the 4th lens made of resin and satisfying the shapes, refractive indexes and Abbe numbers of respective lenses with specific conditions. CONSTITUTION:In a compact wide angle lens constituted of four lenses in four groups and having an aspherical surface on the image side of the 4th lens made of resin, conditions shown in inequalities 1-8 are satisfied. Provided that (f) is the composite focal distance of the whole system, d4 is the interval between the 2nd and 3rd lenses, d5 is the center thickness of the 3rd lens, d6 is the axial distance between the 3rd and 4th lenses, r7 is the radius of curvature on the object side of the 4th lens, n1, n3 are the refractive indexes of the 1st and 3rd lens media about a (d) line, and v2-v4 are Abbe number of the 2nd-4th lens media. Thus, the wide angle lens having the simple constitution consisting of four lenses in four groups has only one aspherical surface extremely restricted because of its difficult working and an excellent image reduced at its change due to focusing can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a compact photographic lens having a telephoto type refractive power arrangement, and more particularly to a wide-angle photographic lens characterized by the use of an aspherical surface.

Five plates of rice In recent years, as cameras have become more compact, compact photographic lenses have become desirable.

Here, in order to make the lens system compact.

It is known that a so-called telephoto type refractive power arrangement is advantageous.

However, telephoto lens systems are originally suitable for telephoto lenses with a small angle of view7, and when trying to obtain optical performance with a wide angle of view of 60" or more and a telephoto ratio of about 1.0, it is difficult to achieve high image quality. It is extremely difficult to satisfactorily correct lateral aberrations at corners.

Furthermore, as such a telephoto type wide-angle lens, one is well known that has a four-element structure in four groups, consisting of a positive lens, a biconcave negative lens, a positive lens, and a negative meniscus lens with the concave surface facing the object side from the object side. In many of this type, the fourth lens is made of resin, especially acrylic resin, and has an aspherical surface in order to satisfactorily correct various aberrations at a high angle of view.

However, with the fourth lens that uses acrylic resin, correction of off-axis chromatic aberration (lateral chromatic aberration and chromatic coma aberration) is insufficient; It had become.

The present invention was made in order to solve all the drawbacks of the prior art described above, and has an FNO of 3°5 and an angle of view of 6.
33. It satisfies the optical performance with a telephoto ratio of about 1.0.

Good aberration correction using only aspherical surfaces, especially coma aberration.

The purpose of the present invention is to provide a compact wide-angle photographic lens that corrects axial and off-axial chromatic aberrations in a well-balanced manner.

■]! As shown in FIG. 1, the lens configuration of the present invention includes, in order from the object side, the second lens of a positive meniscus lens with its convex surface facing the object side, the second lens of a biconcave negative lens, and the second lens of a biconvex positive lens. It is a compact wide-angle lens consisting of 4 elements in 4 groups, where the 3rd lens is a negative meniscus lens with the concave surface facing the object side, and the 4th lens is made of resin and has an aspherical surface on the image side. It is characterized by satisfying the following conditions.

(1) 0.17f<d number (0,2f (2) 0.8<d4/ l rr l <1.0(4N
, 65<n, <1.75 (5) 55<ν+<62 (6) 26<ν<30 (7) 39<ν, <49 (8) n, <n However, f: Whole system Synthetic focal length d: On-axis distance d between the second lens and third lens: Third lens
Lens center thickness d4: axial distance r between the third lens and the fourth lens, = 4th lens
Radius of curvature n+ +nl of the object side surface of the lens: refractive index s for the d-line of the medium of the first lens and the third lens, s1. Shisen: 2nd. Abbe number of the medium of the third and fourth lenses In addition to this condition, this compact wide-angle lens is characterized by satisfying the following conditions.

(9) rr” l r t 1 However, r5; Radius of curvature of the object side surface of the third lens r&: Third
Radius of curvature of image side surface of lens Each condition of the wide-angle lens according to the present invention will be explained below.

Condition (1) is a telephoto ratio of 1. This is to keep aberrations good while keeping the angle at about θ. If the upper limit is exceeded, the diameter of the first lunion increases and the lens system becomes larger. If the lower limit is exceeded, spherical aberration will be overcorrected, making it difficult to correct comatic aberration.

Condition (2) is the first condition. Second. This is to suppress changes in the image plane during focusing by extending the front group consisting of the third lens. If the upper limit is exceeded, at close range,
The image plane becomes over-corrected, and when the lower limit is centered, it becomes under-corrected.

Condition (3) is intended to satisfactorily correct positive distortion. If the upper limit is exceeded, the distortion becomes good, but the amount of peripheral light decreases, and in order to prevent this, the first. It becomes necessary to increase the diameter of the second lens, and if the lower limit is exceeded, it becomes difficult to correct positive distortion.

Condition (4) is intended to reduce the bulge of spherical aberration, to satisfactorily correct coma aberration up to a high angle of view, and to maintain the Petzval sum at an appropriate value. When the lower limit is exceeded, the spherical aberration increases, and when the upper limit is exceeded, the Petzval sum becomes too small.

Condition (5) defines the Atsube number of the resin material of the fifth and fourth lens, and is a restriction due to the resin material that can be used for photographic lenses in terms of optical properties and moldability.

Conditions (6) and (7) are to maintain good on-axis chromatic aberration and off-axis chromatic aberration (color aberration and chromatic coma aberration) under conditions ('1) and (5). When removing 1.

It becomes difficult to achieve a good balance between the above-mentioned bichromatic aberrations.

Condition (8) is a condition for satisfactorily suppressing coma aberration up to a high angle of view.

In addition to the above conditions, the present invention preferably satisfies the following conditions. It is (9)r, =
l r&l.

This condition (9) is mainly desired from the assembly and processing aspects.6 In other words, in a biconvex lens such as the third lens, the radius of curvature on both sides is close. If they are made the same, the trouble of determining one during assembly will be reduced.

Next, examples of the present invention will be shown.

However, ri: radius of curvature of the lens surface at the first aperture in order from the object side di: interval ni, ν1 between the first aperture and (i+I) i-th aperture surfaces in order from the object side; The refractive index and Atsube number f of the medium of the first lens for the d-line: the focal length of the entire system ω: the half angle of view TR: the retraction ratio. When the direction is vqa, the intersection of the vertex of the lens surface and the X-axis is taken as the origin, and the paraxial radius of curvature is r.

It is given by the following formula.

However, C= 1/r K, A4. A≦, AtIA+6 is aspheric coefficient Example 1 f=LOOFNO=3.5 2ω=63' TR
=0.999r, =30.208d, =
9.398 nl :1.6968 vl =55.
46r, = l'19.073 d, = 2.61
9r, ==-134,10945=2.735
n, = 1.7552 V, = 27.53r4
= 59.994 d+= 7.245r, =
75.962 dr= 7.74 n@ =1.7
2 V5 =42.02rt =-91,383d
4=19.03ty=-19,791d7=4.
394 n4 = 1.4915 94 = 57.8r
t ” -33,368 Aspheric coefficient (8th surface) K=O A4=-1,481901ExlOA4=2.2029
45X10-'A! =-1.150DO7X10A
+o = 1.403118xlO-”Example 2 f=loo FNO=3.5 2=63” TR
=L, 1111r, : 30.832 d+ =
9.531 nl =1.69G8 v, =55
．． □16r, = 92.509 d, = 2.513r
=-126,314d, =2.718n,
=1.71736 v, =29.5r4 =
55.4354 = 7.823rp = 71.2
83 dy = 6.666nx” 1.7003
v5 =47.8jrz =-89,182dc
= 19.623r1 =-21,Q29 d7 =
4.85614 = 1.491 v4 = 61.4
r, =-35,563 Aspherical coefficient (8th surface) K=O Anow=7.590430XLOA+=2. LO718
8xlG-Ryu A, =-9,343424x 10 A+. = 2
．． 606837 X 10 Example 3 f=100 FNO=3.5 2ω=63' TR
=0.999r, =30.203d, =9.
629 rll = 1.6935 νH = 53.34r
, = 88.729 tlh = 2.735r, Ko1
31.939 ds = 3.084 nz = 1.
76182 V) “2G, 55r4 = 60.22
ds = 7.244r, = 72.284d,
= 7.12703 =1.70154v, =41
．． 15r&=-38,43d&= 18.764r4
=-19,785d, = 4.393 H4:L71
915 v4 =57.8r=-33,348 Aspheric coefficient (8 surfaces) K=O A+ ”” 1.839948 X 10 r~=
3, 034060 x 10As”-6,571G7
7X10 A+o =1.0310GOX10-''Example 4 f=IQo FNO=3.5 2ω=63' TR
=0. 93r1=30-434 ds=9,65
2 nl = 1.6968 Vl = 55.46 rJ =
103.778 d, = 2.667r, :(37,
679ds = 2,696 n, =L, 7552 □ = 27.531', = 58.405 ds =
7.884r, = 85.871 dt = 6.26
In! =1.70154v) =41.15r, =
-85,871dh = 19.101r7=-19,
713dy = 4.37714 = 1.4915V
4 =57.8rw ”-32,307 Aspheric coefficient (8th surface) =-0,325666 A4=-9,664720XLOAa=-2,9154
94X10'A, =-11,363011xlOAu
=-2,741080X10 Example 5 f=100 FNO=3.5 2ω=63' TR
=0.997r=30.218d+=
9.6-I nl =1. G935 Vl
=53. '34r, ” 'jO,069d, = 2
．． 724r, =-Lll, 811d, = 3.09
4 nL=1.76182v, =26.55r4=
60.148 d4 = 7.1Hr, =: 72.
632 dt=7.2G5 n, =1.702
v5 =40.2ri --88,474ds =18
．． 11r, =-19,792dl = 4.395
H4=1.4'319%'4 =56.1r, =-
33,571 Aspheric coefficient (8th surface) K=G A÷” 1.544712 X 10 A4 =-3
, 13475L X LQ-'.

A, =-2,690861X 10 A,. = 3
．． 8-H679X 10~I? Example 6 f=100 FNO=3.5 2rw =63a
TR=0.995rl=29.809ds=
10.154 rl+ =1.6583 v+ =5
7.26r, = 111.127 d, = 2.44r
B -140,924d3 = 3.09 1. =1
．． 72825y, =28.32r4=58.65
2 d+=8.259rr='11. L93
dy=5. BO2n, =1.72 v, =
42.02rb = -91,193d6 = 17.8
36r, =-19,855d, == 4.3811
4 = 1.4915 v4 = 57.8 rv = -3
2,617 Aspheric coefficient (8 surfaces) K = -0,40 = 1266 A4 = -5,917351X 10 At 5.2
1f; 908 x 10″At= 4.784520X
10 AIa =-8,755808XlO-"Example 7 f=100 FNO-3,52ω=63' TR=
0.99Fir, := 29.75 d+=lO,
175n, = 1.6383'! ', :57.26r
, = 90.299 d-= 2.578r, =-11
5,751dB = 2.927Ill
=1.72825 vx =28.32r+”
62.244 d4 = 8.008rw = 66
．． 5014r=5.931nl=1.6689
2νy = 44.91rt = -82,871d4 =
17.744r7 = -20,63L d2 =
'1.4 n4 = 1.491
v4: 61.4ry = -37,474 Aspheric coefficient X2 (8th surface) = O A+ = 1.159728
63XIQ-''.

A, = 9.653485X10 A+#=2.78
4667 It is compact at 1.01 or less, and even when using a simple distance adjustment method in which only the front group is extended, there is little change in the image plane due to focusing, which is good.In addition, even at high angles of view, there is no coma aberration, axial aberration, etc. This provides the effect of good external chromatic aberration.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of Example 1 of the wide-angle lens according to the present invention, FIG. 2 is an aberration diagram of the lens according to FIG. 1 for an object at infinity, and FIG. 3 is a lens configuration diagram of the lens according to FIG. 1. The aberration diagrams when the imaging magnification is −1740 times, and FIGS. 4 to 9 are aberration diagrams for objects at infinity in Examples 2 to 7, respectively. Patent applicant: Ricoh Co., Ltd. Ricoh Optical Co., Ltd. Sine Susaku FNo, = J W = tll, I'
1Af= JfJ” sine strip pattern frame F/vI17.=,j,f −W4f,,fo
-w4fJ'Komabomugi

Claims (1)

[Claims] 1. In order from the object side, the first lens is a positive meniscus lens with its convex surface facing the object side, the second lens is a biconcave negative lens, the third lens is a biconvex positive lens, and the concave surface is directed toward the object side. A compact lens with a four-element structure in four groups, which is composed of a negative meniscus lens with a negative meniscus lens oriented toward Wide angle lens. (1) 0.17f<d_6<0.2f (2) 0.8<d_4/|r_7|<1.0 (3) 0.4<d_4/(d_4+d_5)<0.6 (4) 1.65 <n_3<1.75 (5) 55<ν_4<62 (6) 26<ν_2<30 (7) 39<ν_3<49 (8) n_1<n_3 where f: Composite focal length of the entire system d_4: Second lens On-axis distance between and the third lens d_5: Center thickness of the third lens d_6: On-axis distance between the third lens and the fourth lens r_7: Radius of curvature of the object side of the fourth lens n_1, n_3: First lens and d of the medium of the third lens
Refractive index ν_2, ν_3, ν_4 with respect to the line: Abbe number of the medium of the second, third, and fourth lenses is 2, and in addition to the conditions of claim 1, the following conditions are further satisfied. Compact wide-angle lens (9) according to claim 1 r_5=|r_6| and r_5: radius of curvature of the object side surface of the third lens r_6: radius of curvature of the image side surface of the third lens