JPH0271219A - Photographic lens - Google Patents

Abstract

PURPOSE:To obtain a satisfactory performance throughout a wide field angle by constituting a lens system of two lenses of two groups, namely, a first negative meniscus lens having the convex directed to the object side and a second positive meniscus lens having the concave directed to the object side which are arranged in order from the object side. CONSTITUTION:One negative meniscus lens and one positive meniscus lens, namely, two lenses in total are combined to constitute the whole of the lens system, and the first negative meniscus lens has the convex directed to the object side and the second positive meniscus lens has the concave directed to the object side for the purpose of obtaining the bright and compact lens system of wide field angle. Shapes of the negative lens and the positive lens are constituted in such a manner to obtain the lens system of wide field angle where the curvature of the screen, the distortion aberration and the astigmatism are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to a camera lens, particularly a camera lens with a half angle of view of 20° to 30°.
This is about a low-priced camera lens.

(Prior art) Conventionally, lens systems that correct aberrations using one convex and one convex lens include a laminated lens like the objective lens of a telescope, or a type that consists of two lenses in one group with a very slight spacing between them. It has been known.

Apart from this, as a type in which aberrations are corrected by a combination of convex curves, there is a hyperbon type as disclosed in US Pat. No. 2,586,41.8. The former has good performance on and very close to the axis, but when the angle of view is widened, the curvature of field becomes large, and it cannot be used as a photographic lens. Furthermore, in the latter type, axial dichromatic aberration cannot be corrected due to its power arrangement, spherical aberration, etc. are large, and the F number cannot be reduced, so that it is practically only practical up to the level of Fil. In addition, the size of the lens has become quite large, making it extremely difficult to achieve the compact size required for current cameras.

(Problems to be Solved by the Invention) The present invention aims to overcome the drawbacks of the prior art and obtain a camera lens that is compact and has an extremely simple configuration that has good performance over a wide angle of view. That is.

More specifically, the objective is to obtain a two-element camera lens with an F number of about 5.6 to 8 and a half angle of view of about 20° to 30°.

(Means for Solving the Problem) The features of the photographic lens of the present invention are as follows: 1) First of all, starting from the object side, the first lens is a negative meniscus with a convex surface facing the object side, and a first lens with a concave surface facing the object side. The lens is constructed with two lenses in two groups, each consisting of a positive meniscus second lens.

2) Second, it is desirable that the following conditions be satisfied: 2.0 < l f, /f, l < 6.0, where f1 and f2 are the focal lengths of the first lens and the second lens, respectively.

2') In order to brighten the F number to about 5.6, it is necessary to use the range of 2.0<If□/f21<3.0 among the above conditions.

3) Also, when the focal length of the entire lens system is f, and the axial air distance between the first lens and the second lens is d, 0.02f
It is desirable to satisfy the condition <d<0.2f.

4) Furthermore, when the Arabesque numbers of the materials of the first lens and the second lens are Y1 and ν2, respectively, ν1<50 v
It is desirable to satisfy the condition 2>50.

5) Furthermore, it is desirable that at least one surface of the lens system is an aspherical surface.

6) Furthermore, it is desirable to provide an aperture that determines the F-number luminous flux between the first lens and the second lens.

(Function) In the lens system of the present invention, each lens system has 1
Total of 2 pieces of negative meniscus lens and positive meniscus lens
The first lens, which is a negative meniscus, has a convex surface facing the object side, and the second lens, which has a positive meniscus, has a concave surface facing the object side. This is required in order to solve the problems of the prior art described above and to obtain a bright, compact, and wide-angle lens system. By configuring the shapes of the negative lens and the positive lens in this manner, it is possible to obtain a lens with a wide angle of view in which field curvature, distortion, and astigmatism are suppressed.

Condition (2) is also required in order to make the lens compact and to obtain a good balance of various aberrations. When the lower limit of this equation is exceeded, the focal lengths of both the first lens and the second lens become shorter, that is, the power of each lens becomes stronger. As the power of the negative first lens becomes stronger, barrel distortion becomes larger, and the overall length of the lens system becomes longer, making it impossible to make it compact.

Conversely, when the upper limit is exceeded, the focal lengths of both the first and second lenses become longer, and the Petzval sum becomes larger.
It becomes difficult to achieve a wide angle of view.

In this lens system, if you try to make the F number as bright as about 5.6, the depth of focus becomes shallow, so it is necessary to make the field curvature flatter. To this end, by further narrowing condition (2) and using the range of condition (2'), it is possible to reduce the Petzval sum and the curvature of field.

Also, as a means of reducing the Petzval sum to widen the angle of view, the distance between the lenses may be increased, but the condition (3)
) shows the range in which this means and compactness can be achieved simultaneously. If the value is below the lower limit, the Petzval sum becomes large and a wide angle of view cannot be achieved, and if the value exceeds the upper limit, the lens system becomes large and compactness cannot be achieved.

Furthermore, condition (4) is required for chromatic aberration correction, in which chromatic aberration opposite to the chromatic aberration occurring in the positive second lens is generated in advance in the negative first lens, and the chromatic aberration as a whole is reduced. The idea is to keep it small. Condition (4
) can satisfactorily correct longitudinal chromatic aberration on condition (2).

If an attempt is made to make the lens brighter, spherical aberration increases in the case of a lens composed only of spherical surfaces, causing a decrease in resolution. Furthermore, correction of astigmatism, distortion, and coma aberration is also insufficient. In order to solve this problem, condition (5) is that at least one surface of the lens system should be an aspherical surface. For example, when the power of the negative first lens increases,
Strong barrel-shaped distortion occurs, but if an aspheric surface is used on the surface closest to the object side of the lens system, the curvature of which becomes gentler as it moves away from the optical axis, this barrel-shaped distortion can be corrected. can do. In addition, in such a lens configuration, excessive coma flare occurs in the light flux passing around the second lens, but in such a case,
Comatic aberration can be effectively corrected by employing an aspheric surface whose curvature becomes steeper as it moves away from the optical axis on the surface closest to the image side of the lens.

Additionally, there are three possible positions for the aperture that determines the F-number luminous flux: in front of the entire lens system, between the first and second lenses, and at the back of the entire lens system. It is desirable to place this aperture between the two lenses. If the diaphragm is placed in front of the lens system, underflare due to comatic aberration will increase, and if the diaphragm is placed after the lens system, the chromatic aberration of magnification will be excessive, making it difficult to correct in either case. By placing the aperture between the first lens and the second lens, both comatic aberration and lateral chromatic aberration can be corrected well.

(Example) Examples of the lens system of the present invention will be described below.

In addition to satisfying each of the above conditions, these examples also satisfy the following conditions.

That is, in these lens systems, in addition to the diaphragm that determines the F number, it is effective to place a diaphragm that determines the luminous flux at the peripheral angle of view in front or behind the lens system. The aperture that determines the F number may not be enough to remove coma flare that occurs with light beams with a large angle of view. Placing the aperture after the lens system can effectively remove undercoma flare, and placing the aperture in front of the lens system By setting the aperture, overcoma flare can be removed. The diameter of this diaphragm should be determined based on the peripheral light intensity ratio and the size of coma flare.

Furthermore, in terms of workability, cost, etc., the material was selected from Example 4.
Plastic is used except for.

The aspherical shape has a vertex curvature of C in a rectangular coordinate system with the apex of the surface as the origin and the optical axis direction as the X axis.

K is the conical coefficient, AI is the aspherical coefficient, and Pl is the aspherical insole.
When , it is expressed as h = vy2 + z2.

Each symbol in the table indicates the following.

r□: Paraxial radius of curvature dl: Surface spacing nd: Refractive index of the lens material at the d-line νd: Atsube number F: F number 2ω: Angle of view Example 1 Focal length 100 mm F8.5 2ω = 60.8.

Surface number r+ d+ na v
al 23, 506 5.56 1.5
8600 302 19, 490 1.
393 Aperture 2.50 4 -80.413 6.11 1.49
200 575 -25.902 0.5
66 Aperture aspherical coefficient on 1 side = 5.21518 = I A2= A3= A4= Example 2 Focal length 100 mm Surface number rl 1 22.172 2 16.806 3 Aperture 4 -81.522 1.72788 4.71087X 10-6 -6.61648X 10-8 - 6.25678X 10-” 2.69004 X 10-”” F8.5 5.69 3.41 2.28 6.26 I P2= P3= P 4 = P L = P2= P3= P 4. = 4.0000 6.0000 8.0000 10.0000 4.0000 6.0000 8.0000 io, ooo.

2ω=60.4° d 1.58600 30 1.49200 5 -23.204 Aspheric coefficient Page 1 To- I 5th page 1.15534 2.493] 3X 10-' 1.23] 01 X 10-7 7.65187X]0-” 4.79286X 10-” I A2= A3= A4= Example 3 focal length 100mm Surface number 1 Aperture 2 19.422 3 13.659 5.76923X 10-' 1.20724 X 10-5 3.18936 X 10-' 2.46554 X 10-” 7.40835X 1O-12 F5.8 0.00 6.928 3, /124 I 4.0000 6.0000 8.0000 ], 0.0000 4.0000 6.0000 a, ooo.

10.0000 2ω=66.36 ],,583 aperture -104,862 -21,990 aperture Aspheric coefficient 2 sides 2.8056 3.1092X 10-' -7,5594X 10-' 5.1775X10-” -6,9257X10-13 A1= A2= A3= A4. ＝ 6 sides ni= A1= A2= A3= A4= Example 4 Focal length 11 [100mm Surface number　　　rl 5.3554X 10-” -3,6866X 10-5 -5.7391 X 10-” -1,0913X 10-9 9.4347X 10-12 0.856 6.885 4.280 vinegar F5.8 1.492 P3= P4. ＝ P 3≠ P4= 4.0000 6.0000 8.0000 ], 0.0000 4.0000 6.0000 8.0000 10.0000 2ω=66.4' 1 22.000 2 15.600 3 Aperture 4 -84.493 5 -24.1.31 6 Aperture Aspheric coefficient Page 1 To- I A4. ＝ 5th page ni= A1= A3= A4= 3.3939 2.5838X 10-5 7.8791X10-' 3.8424X 1.0-”’ -1,0966X10-” -1,1391 -3,3544X 10-5 -2.7608X 10-I' -4,9247X 10-” 6.8684X10-12 6.949 3.434 0.859 6.906 4.293 1.68893 1.58913 31.1 61.2 I F2= P3= P1= P3= P4= 4.0000 6.0000 8.0000 10.0000 4.0000 6.0000 a, ooo.

10.0000 (Effects of the Invention) As can be seen from the second embodiment and the drawings, the lens system of the present invention has an extremely simple configuration of two lenses in two groups, but has both longitudinal and lateral aberrations. It is corrected with good balance, and can provide good performance as a photographic lens over a wide angle of view, making it possible to provide a low-cost photographic lens with excellent performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the lens of the first embodiment of the lens of the present invention, FIG. 2 is its longitudinal aberration diagram, FIG. 3 is its transverse aberration diagram, and FIG. 4 is a lens sectional diagram of the second embodiment. Fig. 5 is a longitudinal aberration diagram, Fig. 6 is a transverse aberration diagram, and Fig. 7 is a cross-sectional view of the lens of the third embodiment.
FIG. 8 is a diagram of its longitudinal aberration, FIG. 9 is a diagram of its lateral aberration, FIG. 10 is a cross-sectional view of the lens of the fourth embodiment, and FIG. 11 is a diagram of its longitudinal aberration.
FIG. 12 is a lateral aberration diagram.

Claims (1)

[Scope of Claims] 1) Two lenses in two groups consisting of, in order from the object side, a negative meniscus first lens with a convex surface facing the object side and a second positive meniscus lens with a concave surface facing the object side. 2) A photographic lens characterized by satisfying the following condition: 2.0<|f_1/f_2|<6.0, where the focal lengths of the first lens and the second lens are f_1 and f_2, respectively. 3) Photographic lens according to claim 1, satisfying the following condition: 2.0<|f_1/f_2|<3.0, where the focal lengths of the first lens and the second lens are f_1 and f_2, respectively. 4) The photographic lens according to claim 1, which satisfies the following condition: 0.02f<d<0.2f, where f is the focal length of the entire lens system, and d is the axial air distance between the first lens and the second lens. 5) Photographic lens according to claim 1, characterized in that, when the Abbe numbers of the materials of the first lens and the second lens are ν_1 and ν_2, respectively, ν_1<50 ν
6) The photographic lens according to claim 1, characterized in that the photographic lens satisfies the following condition: _2>50 6) The photographic lens according to claim 1, characterized in that at least one surface is an aspherical surface.