JPH01307712A - Photographic lens - Google Patents

Abstract

PURPOSE:To realize compact constitution and to obtain excellent performance over a wide view angle range by composing the photographic lens of two lens elements, i.e. a 1st positive meniscus lens which has a convex surface on its object side and a 2nd negative meniscus lens which has a concave surface on its object side in order from the object side. CONSTITUTION:The whole lens system has two-group, two-element constitution of one positive meniscus lens and one negative meniscus lens, i.e. two lens elements in total; and the 1st positive meniscus lens has the convex surface on its object side and the 2nd negative meniscus lens has the concave surface on its object side. Then there is some interval between the two lenses and a diaphragm is placed between the 1st and 2nd lenses. Consequently, the longitudinal aberration and lateral aberration are compensated with good balance and the excellent performance of the photographic lens is obtained over a wide view angle range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) This invention relates to camera lenses, particularly those with a half angle of view of 20° to 30°.
This relates to 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, there is a hyperbon type lens that corrects aberrations using a combination of convex surfaces, as disclosed in U.S. Pat. No. 2,586,418. 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. In addition, in the latter type, axial chromatic aberration cannot be corrected due to its power arrangement, spherical aberration etc. are large, the F number cannot be reduced, and the lens is only practical to the extent of Fil. The size of the camera has also 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 overcomes the drawbacks of the prior art and is compact and has a wide angle of view.

The objective is to obtain a camera lens with an extremely simple structure and good performance.

More specifically, the F number is about 8 and the half angle of view is 20'~
The objective is to obtain a two-element camera lens with a diameter of approximately 30''.

(Means for solving the problem) The photographing lens of the present invention includes: 1) First of all, from the object side to the condyle, the first lens is a positive meniscus with a convex surface facing the object side, and a concave surface facing the object side. It is characterized by being composed of two negative meniscus second lenses.

2) Next, when the focal length of the first lens is f and the focal length of the second lens is f2, 0.05≦lft/f2
It is desirable to satisfy the condition 1≦0.50.

3) Furthermore, it is desirable that at least one surface of this lens system is aspheric.

4) Also, regarding the Atbe number of the material forming the lens, let γ1 be the Atbe number of the material of the first lens, and ν2 be the Atbe number of the material of the second lens, then ν1>50, ν2<5
It is desirable to satisfy the condition 0.

5) Also, the focal length of the entire lens system is f, the first lens and the second lens.
When the axial air distance of the lens is d.

0.02f < d < 0.2f It is desirable to satisfy the following conditions.

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

(Function) In this invention, the entire lens system has a configuration of two lenses in two groups each consisting of a total of two lenses, one positive meniscus lens and one negative meniscus lens, and the first positive meniscus lens is on the object side. The first feature is that the convex surface faces the object side, and the negative meniscus second lens has the concave surface facing the object side. This is because if a telescope objective lens type is used as in the prior art described above, it will not be possible to obtain a wide angle of view, so by creating a configuration such as the above condition (1), field curvature and distortion aberration can be suppressed. That is what it is.

In addition, the condition (2
). If the upper limit of this condition (2) is exceeded, the power of the concave lens becomes strong, and the symmetry of the lens system is greatly disrupted.
Distortion aberration and coma aberration increase. Conversely, if the lower limit is exceeded,
The power of the concave lens becomes weaker and the lens becomes larger.
Compactness cannot be achieved.

If an attempt is made to make the lens brighter after satisfying the above conditions (1) and (2), spherical aberration will increase. Furthermore, correction of astigmatism, distortion, and coma aberration is not sufficient. In order to solve these problems, condition (3) is to use an aspheric surface for at least one surface of the lens system. For example, if an aspherical surface is used for the object-side surface of a lens system, i.e., the object-side surface of a convex lens, if the aspherical surface is set so that the curvature of the surface becomes steeper as it moves away from the optical axis, the astigmatism This is advantageous for correcting aberrations and comatic aberrations.

On the other hand, if the final surface of the lens, that is, the image-side surface of the concave lens, is made aspheric, it is advantageous to correct distortion if the aspheric surface is set so that the curvature of the surface becomes gentler as it moves away from the optical axis. It is. Of course, it goes without saying that a plurality of surfaces may be made aspherical at the same time.

Condition (4) indicates a desirable condition for the material of the lens from the viewpoint of monochromatic aberration correction. This condition (
4) and condition (2), longitudinal chromatic aberration and lateral chromatic aberration can be corrected in a well-balanced manner. Condition (4
), but if the value falls below the lower limit of condition (2), the axial chromatic aberration will be under-corrected.

Also, for photographic lenses, in order to obtain a wide angle of view, it is desirable to have a certain distance between the two lenses. This condition is the lower limit of (5), and if it falls below this, it will be difficult to provide a half angle of view of about 20 to 30'' as a general photographic lens.On the other hand, if it exceeds the upper limit, the overall length will increase. Therefore, it becomes impossible to achieve compactness.

In addition, 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 second lenses. Placing the aperture in front of the lens system increases underflare due to coma aberration.

If the aperture is placed at the back of the lens system, the 1-magnification chromatic aberration 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 shown below. These Examples satisfy the following conditions in addition to the conditions (1) to (6) above.

In addition to the diaphragm that determines the F-number, it is also desirable to place a diaphragm in front or behind the lens system that determines the luminous flux at the peripheral angle of view. 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 depending on the 1-periphery light intensity ratio and the size of coma flare.

Furthermore, from the viewpoint of workability, cost, etc., it is desirable to use plastic as the material for the lens.

Furthermore, in order to obtain a wide angle of view, it is desirable to satisfy the following condition in addition to condition (5).

(r knee rz) / (r1+ r2) < 0, 2
Here, rl and r2 are the paraxial radii of curvature of the object side surface and the image side surface of the positive meniscus first lens, respectively. If this condition is not met, the object-side surface of the first lens will have a sharp curvature, and as a result, the spherical aberration generated in the first lens will be under-corrected, resulting in insufficient correction.

The aspherical shape is defined by the apex curvature as C1 and the conic coefficient as K in a rectangular coordinate system with the origin at the apex of the surface and the optical axis direction as the X axis.
, the aspheric coefficient is A1. When the width number of the aspherical surface is PI.

h=(Y”+Z” It is expressed as

Each symbol in the table indicates the following.

ri: Paraxial radius of curvature dl: Surface spacing n4: Refractive index of the lens material at the d-line ν, 1: Atsube number F: F number 2ω: Angle of view Example 1 Focal length 100 mm F8.5 2ω=616 Surface number ri d + n, 1
v 41 20.1g2 6,47 1.492
00 572 50.850 1.47 3 Aperture 2.65 4 -15.651 5.89 1.58600
305 -20.504 0.59 6 Aperture aspherical coefficient 1 surface K = 1.33206 A 1 = 1.61577 X 10-' P
L = 4.000A 2 = 1.39070
X 10-' P 2 = 6.000A3=
-2,18106X10-' P3= 8.00
0A4= 1.52317X10-” P4=10
．． 0005 plane K = 8.22319 X 10-”A 1 =
1.58778 x to-' P 1 =
4.000A 2 = 3.40370 x 1
0-' P2=6.000A3=-
2,47424X10-' P3=8.00
0A 4 = 5.17063 x 10-”
P 4 = 10.000 Example 2 Focal length 100 mm F8.5 2ω = 60.6° Surface number rl dB na v
al 24.665 6.67 1.4920
0 572 58.881 1.52 3 Aperture 4.55 4-20.118 6.0? 1.58600 30
5 -23.478 0.61 6 Aperture aspheric coefficient 1 surface K = 7.06122 X 1O-1A 1 =
1.47401 x 10-@P 1 = 4.0
00A 2 = 1.19334 x 10-'
P2 = 6.000A3 = -1,760
40X10-' P 3 = 8.0QOA 4
= 1.15639 X 1O-11P 4 =
10.0005 planes = 1.03612 A 1 = 1.44847 X 10-' P
L, = 4.000A 2 = 2.9206
7 x IP' P 2 = 6.000A 3
= -1,99703X10-'' P 3 =
8.000A 4 = 3.92554 x 10-
” P 4 = 10.000 (Effect of the Invention) As can be seen from the above embodiments and drawings, the lens system of the present invention has an extremely simple structure of two elements in two groups, and Both aberrations and lateral aberrations are corrected with good balance, and good performance as a photographic lens can be obtained 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 cross-sectional view of a first embodiment of the lens of the present invention, FIG. 2 is a longitudinal aberration diagram thereof, and FIG. 3 is a transverse aberration diagram thereof. Similarly, FIG. 4 is a sectional view of the lens of the second embodiment, FIG. 5 is a diagram of its longitudinal aberration, and FIG. 6 is a diagram of its transverse aberration. Patent applicant Konica Co., Ltd. Applicant's agent Patent attorney Fumio Sato (and 2 others) Figure 1 Figure 2 Spherical aberration Astigmatism Distortion -d@ ---G machine Figure 3

Claims (1)

[Claims] 1) It is characterized by being composed of two lenses, in order from the object side: a positive meniscus first lens with a convex surface facing the object side, and a negative meniscus second lens with a concave surface facing the object side. 2) A patent characterized in that the following condition is satisfied: 0.05≦|f_1/f_2|≦0.50, where the focal length of the first lens is f_1 and the focal length of the second lens is f_2. Claim 1
3) The photographic lens according to Claim 1, characterized in that at least one surface is an aspherical surface. 4) The Abbe number of the material of the first lens is ν_1, and the material of the second lens is Claim 1 is characterized in that it satisfies the following conditions: ν_1>50 ν_2<50, where the Atsube number of is ν_2.
Photographic lens described in Section 5) 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<d<
Claim 1 characterized in that it satisfies the condition: 0.2f
Photographic lens described in section 6) The aperture that determines the F number luminous flux is the first lens and the second lens.
Photographic lens according to claim 1, characterized in that it is provided between lenses.