JPH02101417A - Photographic lens - Google Patents

Abstract

PURPOSE:To obtain a bright wide-angle photographic lens which is reduced in cost and improved in performance by constituting the lens of specific four pieces of Topogon type plastic lenses constituted in four groups so that the lens can satisfy specific conditions. CONSTITUTION:This lens is constituted of four lenses of four groups of, from the object side, a 1st group of convex meniscus lenses 10 with a convex surface on the object side, a 2nd group of concave meniscus lenses 12 with a convex surface on the object side, a 3rd group of concave meniscus lenses 14 with a convex surface on the image side, and a 4th group of convex meniscus lenses 16 with a convex surface on the image side and a diaphragm 13 is provided between the 2nd and 3rd groups. The all lenses are made of plastic materials and the image-side surface of the 2nd group and object-side surface of the 3rd group lenses are formed to nonspherical surfaces. Moreover, this lens is caused to satisfy Inequalities I-III, where the fi, nui, and (f) respectively represent the focal distance and Abbe's number of the i-th group lens and resultant focal distance of the whole system. Therefore, the angle of view of the lens can be widened and the FNO can be reduced. Moreover, since the lenses are plastic lenses, the lens can be reduced in weight and cost and can be worked easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photographic lens, that is, a lens for camera photography.

[Prior Art] A tobogon type camera lens has been proposed as a photographic lens that can be realized at relatively low cost (for example, Japanese Patent Laid-Open No. 8932/1983).

[Problem to be solved by the invention] However, the conventionally known tobogon type lens is FN
O is large and the angle of view is narrow.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to realize the invention at a lower cost;
Our goal is to provide photographic lenses that are bright, have a wide angle of view, and have good performance.

[Means to solve the problem] The present invention will be explained below.

As shown in FIG. 1, the photographic lens of the present invention has an object side (
The first to fourth groups are sequentially arranged from the left side in FIG. 1 to the image side (right side in the figure).

The first group is a convex meniscus lens 10 with the convex surface facing the object side.
, the second group is a concave meniscus lens 1 with the convex surface facing the object side.
2. The third group is a concave meniscus lens 1 with the convex surface facing the image side.
4. The fourth group is a convex meniscus lens 1 with the convex surface facing the image side.
6, therefore, the lens structure of the photographic lens of the present invention is four elements in four groups, and has an aperture 13 between the second and third groups.

Each lens 10.12.14.16 of the first group to the fourth group is formed of plastic.

Furthermore, aspherical surfaces are employed for the image-side lens surface of the second group and the object-side lens surface of the third group.

Furthermore, the focal length and Atsube number of the first group are respectively f
+, ν1, and when the composite focal length of the entire system is f, these are (I) 0.75f < f, < 0.85f (I
I) 0.65f < I f21 < 0.80f.

0.65f < f3 < 0.80f (III)
(ν1+ν4)/2)−(ν2+ν3)/2}>20 is satisfied.

[Operation] Since each surface of the Kotobogon type is almost concentric with respect to the aperture, astigmatism is small and a wide angle of view is possible. However, since spherical aberration and chromatic aberration are relatively large, FNO
is difficult to make small.

Therefore, in the present invention, aspherical surfaces are used for the image-side lens surface of the second group and the object-side lens surface of the third group to correct spherical aberration and comatic aberration that could not be completely corrected with spherical surfaces alone. , it was possible to achieve a wide angle of view and to reduce the FNO to 4.

The image-side lens surface of the second group is an aspherical surface with a radius of curvature increasing from the optical axis toward the outer diameter direction, and corrects spherical aberration and coma aberration on the upper ray side.

The object-side lens surface of the third group is an aspherical surface whose radius of curvature decreases as it goes from the optical axis toward the outer diameter direction, and corrects spherical aberration and coma aberration on the lower ray side.

Further, even though all the lenses in the first to fourth groups are made of plastic, good performance can be ensured by satisfying the above three conditions.

Condition (I) relates to the focal length of the first group and the focal length of the entire system, and by satisfying this condition, good image plane properties can be maintained. If this condition is exceeded, the balance between spherical aberration and astigmatism is lost, resulting in poor image quality.

Condition (II) concerns the focal length of each of the second and third groups and the focal length of the entire system, and a good image plane is maintained only when this condition (II) is satisfied along with condition (■). be able to.

Condition (III) concerns the distribution of the Atsube number of the four lenses, with the first and fourth groups having low dispersion, and the second and third groups having low dispersion.
This is a condition for maintaining the symmetry of the group with high dispersion, suppressing the occurrence of lateral chromatic aberration, and maintaining good paraxial and image plane chromatic aberrations.

If the difference in Abbe's number becomes smaller than the lower limit of condition (III), chromatic aberration cannot be corrected unless the power of each lens is increased beyond the range specified by conditions (I) and (II), and coma aberration increases. It occurs excessively and high performance cannot be obtained.

In addition, as is well known, plastic lenses are superior to glass lenses in that they are lightweight, inexpensive, and easy to process, but on the other hand, there are a limited number of plastic materials that can be used as lenses, and temperature There is also a problem that the position of the image forming plane changes due to this.

In the present invention, although the lens material is plastic as described above, by optimizing the power distribution and surface spacing of each lens, image plane properties and longitudinal chromatic aberration are corrected, and good performance is ensured. . In addition, in response to temperature changes, both the positive and negative lenses are made of plastic, which cancels out the movement of the image plane position due to each positive and negative lens, and suppresses the overall fluctuation of the image plane position. did it.

[Example code] Below, three specific examples will be given.

In each example, FNO means brightness, f means the combined focal length of the entire system, and ω means the half angle of view (degrees). Also, the radius of curvature r of each surface, (i = 1 to 9), the distance between the surfaces d + (i □ 1 to 8)
, refractive index nj (j・1~4), Atsbe number ν, (j・1
-4) are taken as shown in FIG. 1 from the object side to the image side.

Also, the mark * represents an aspherical surface. For an aspheric surface, r is the radius of curvature on the optical axis, k is the conic constant, A, B, C, and D are higher-order aspheric coefficients, the direction of the optical axis is the Z axis, and the direction perpendicular to the optical axis is the Y axis. As is well known, when the intersection of the spherical surface and the optical axis is the origin of the X and Z axes, Z・[(1/r)Y2/(1+vff'z1)−Fll
) This is the shape obtained by rotating the curved shape represented by 7゛] + AY' + BY'CY' + DY' around the optical axis, and is determined by A, B, C, and D in the above r. Ru.

Example 1: f"100. FNo"l: 4.2
ω”58 degrees.

f+=0.8of, l fz l =0.71f,
l f31: 0.76f.

((ν1+ν,)/2)-(ν2+ν3)/2)・28
．． 5i rid, j n
, νJ1 26.11 13.42 1
1.492 57.82 64.33 2.
75 3 26.54 3.26 2 1.5
854” 75.43 9.425 (
1) (Aperture') 6.226"-75,273,
1431,5857-24,980,25 8-52,3210,3441,4929-17,31 Aspheric surface r4: k=-0,0024°A=-2,1244・10-', B=3.9481・
1O-80=-6,5342・10-'', D=1
．． 5291・10−+2r6: k:o, 2794°A=−1,5483・10−′, B=−7,5520
・1O-8C=-5,7440・10-", D=
-1,6797・IQ-11 Example 2: fzloo
, FNO=1:4.2 ω=58 degrees.

f, =0.8of, I f21 =0.72f, l
fl + =0.75f.

((ν1+ν,)/2)-(ν2+ν3)/2)・28
．． 51 r, d, J nj l 2B, 11 13.35 1 1.492
2 65.38 2.16 29.3 29.3 57.8 ν.

57.8 3 26.31 3.91 2 1.
5854" 75.32 9.485
(X) (Aperture) 6.288'-75,75
3,2131,5857-24,990,26 8-51,6510,2441,4929-17,24 Aspheric surface r4:k”-0,0022°A=-2,1492・10-', B=4. 1180・
10-'C=-6,6713・10-'', D=1.60
02・1o-12ra: k: 0.2757°A=-1,5621・10-5. B=-7,8881
・1O-8C=-6,0438・10-", D=
-1,7500・1o-11 Example 3: f=100.
FNo: 1:4.2ω”58 degrees.

fl;0.81f, l fz l =0.72f,
l f31: 0.76f.

((ν1+ν,)/2)−(ν2+ν3)/2)=28
．． 51 r s d + J
nJl 26.21 13.13 1 1.4
922 63.96 1.99 29.3 29.3 57.8 ν.

57.8 3 26.51 3,74 2 1.5
85 29.34” 75.38
9.385 ■(Aperture) 6.22 6”-75, 233, 1431, 58529, 37-2
4,920,26 8-52,1310,3241,49257,89-1
7,26 Aspherical surface r4: k=-0,0023°A=-2,1395・10-', B=4.0014・
1O-8C=-6,6422・10-'', D=1
．． 5581・10th 2r6: k=0.2746°A=-1,5548・10-', B=-1,6419
・1O-8C=-5,8431・10-", D・-1,
7160/IQ-11 FIG. 2 shows an aberration curve diagram for Example 1, FIG. 3 shows an aberration curve diagram for Example 2, and FIG. 4 shows an aberration curve diagram for Example 3.

In each aberration diagram, DSA is d-line spherical aberration, GSA is g-line spherical aberration, S and C are sine conditions, DS is d-line sagittal ray, GS is g-line sagittal ray, and open is d-line. Meridional ray of GMT and g-line,
DST indicates distortion aberration.

As is clear from these aberration curve diagrams, aberrations are well corrected in each example.

[Effects of the Invention] As described above, according to the present invention, a novel tobogon type photographic lens can be provided as a lens for camera photography.

This photographic lens has a small number of lenses, consisting of four elements in four groups, and all lenses are made of plastic, so it can be realized at low cost.

Plastic lenses do not require a coating to prevent burns because they do not cause burns on the surface.

Furthermore, by using an aspherical surface, various aberrations can be corrected well.

Furthermore, since the positive and negative lenses form a pair, it is possible to effectively suppress fluctuations in the imaging position due to temperature changes in the plastic lens.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the lens configuration of the present invention, and FIGS.
The figure is an aberration diagram corresponding to Examples 1 to 3. 10. First group convex meniscus lens, 12. , second group concave meniscus lens, 14. ,, third group concave meniscus lens, 16. ,, convex meniscus thread of the fourth group) ρ ward ■ square

Claims (1)

[Claims] The first to fourth groups are arranged sequentially from the object side toward the image side, and an aperture is provided between the second and third groups, and the first group has a convex surface facing the object side. The second group is a concave meniscus lens with the convex surface facing the object side, the third group is a concave meniscus lens with the convex surface facing the image side, and the fourth group is a convex meniscus lens with the convex surface facing the image side. It has a four-element configuration in four groups, each lens of the first group to the fourth group is made of plastic, and aspherical surfaces are adopted for the image side lens surface of the second group and the object side lens surface of the third group. The focal length and Abbe number of the i-th group are f_i and ν, respectively.
_i, and the combined focal length of the entire system is f, these are (I) 0.75f<f_1<0.85f (II) 0.65f<|f_2|<0.80f, 0.65
f<|f_3|<0.80f (III) {(ν_1+ν_4)/2}-{(ν_2+ν
A photographic lens, characterized in that it satisfies the condition:_3)/2}>20.