JP2000292688A - Image pickup device having photographing lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device having a photographing lens having the short lens total length and maintaining optical performance of the whole image screen in a well-balanced state by adopting a triplet type, arranging a diaphragm in the rear of the lens diameter, and properly setting a lens shape of respective lenses and a refractive index of a construction material. SOLUTION: A first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a third lens G3 having positive refractive power and a diaphragm SP are provided in order from the object side. In a photographing image screen, the lengthwise direction is curved to the object side, and when a radius of curvature of an (i)th lens surface by counting from the object side is denoted by ri, a focal distance of an (i)th lens is denoted by fi and a focal distance of the whole system is denoted by (f), conditions of (0.84<f1/f<1.3, 0.5<r1/r2<0.9 and 1.8<-r3/r2<3.5) are satisfied. When a refractive index of a construction material of the (i)th lens is denoted by Ni and the length up to the final lens surface from a first lens surface is denoted by Σd, (0.18<Σd/f<0.23, n1>1.65, n2>1.7 and n3>1.7) are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus having a photographic lens, and more particularly, to an image pickup apparatus including three lenses as a whole, and having a diaphragm disposed behind the lens system to obtain a relatively wide angle of view and excellently over the entire screen. The present invention relates to an imaging apparatus provided with a photographing lens suitable for a lens shutter camera such as a photographic camera or a video camera, a digital camera or the like, having a short overall lens length that has been subjected to aberration correction.

[0002]

2. Description of the Related Art Conventionally, a triplet type photographing lens composed of a positive lens, a negative lens, and a positive lens in order from the object side has a relatively good optical constant with a small number of lenses. Etc. are often used for small cameras.

[0003] Of these triplet-type photographing lenses, the diaphragm-type photographing lens in which a diaphragm is disposed behind the lens system is relatively easy to downsize the entire lens system and has a simple lens barrel structure. Used in cameras.

[0004] Such a triplet type rear stop type photographing lens is disclosed in, for example, JP-A-1-133016, JP-A-4-97111, JP-A-7-13071, and JP-A-8-68935. Proposed.

[0005]

In order to reduce the size of a camera provided with a triplet type photographing lens for photographing, it is necessary to shorten the entire length of the lens including the back focus with respect to a screen size defined in the photographing lens. is necessary.

[0006] For this purpose, there is a method of reducing the telephoto ratio or shortening the focal length to increase the angle of view. In any case, even if an attempt is made to obtain a flat image surface, the characteristic of the triplet type lens is required. Field curvature is deteriorated. That is, the sagittal image plane is largely under at the intermediate angle of view, and largely over at the maximum angle of view, making it extremely difficult to correct. In particular, when the telephoto ratio is reduced, the coma aberration is greatly deteriorated. When the focal length is shortened and the angle of view is widened, the Petzval sum increases, and it becomes difficult to correct the aberration.

When the angle of view is widened, not only the aberration is deteriorated but also the peripheral light amount ratio is reduced. Therefore, in the case of a triplet lens having a rear stop, it is not practical to set the angle of view to 80 degrees or more.

Japanese Patent Application Laid-Open No. Hei 8-68935 discloses a camera having a triplet-type photographing lens with a rear aperture, in which the longitudinal direction of the photographing screen is curved toward the subject and the constraint condition of making the image plane flat is avoided. By doing so, it is proposed to reduce the cost, reduce the size, and improve the optical performance.

However, when an attempt is made to reduce the cost by using a plastic lens for the photographing system, the Petzval sum increases because the refractive index of the material is low. For this reason, the image surface is greatly curved. The conventional method of bending the shooting screen to match the curvature of the image plane of the shooting lens is that the shooting screen is curved not in a spherical shape but in a longitudinal direction in order to be bent in a cylindrical shape, but in a short direction. Since the side direction is linear, a focus position shift occurs between the long side direction and the short side direction.

As a result, there is a problem that a photographing lens having a bright F number and a small depth of focus is not suitable as a high-performance lens system.

Further, in the fourth to seventh embodiments of the above-mentioned publication, a spacer made of glass is necessary because a lens made of all materials requires a spacer between the lenses, and the final surface of the lens is close to the stop position. In the case of the focus adjustment and the automatic focusing mechanism, there has been a problem that the structure is complicated and the cost is considerably increased.

According to the present invention, a triplet type is adopted, an aperture is arranged behind the lens system, the lens shape of each lens, the refractive index of the material and the like are appropriately set, the overall length of the lens is short, and the entire screen is reduced. It is an object of the present invention to provide an imaging device including a photographing lens that maintains optical performance in a well-balanced manner.

[0013]

According to the first aspect of the present invention, there is provided an image pickup apparatus provided with a photographic lens, comprising a first lens having a positive refractive power, a second lens having a negative refractive power, It has a third lens having a refractive power and a stop, and the photographing screen has a longitudinal direction curved toward the object side, the radius of curvature of the i-th lens surface counted from the object side is ri, and the focus of the i-th lens is Assuming that the distance is fi and the focal length of the entire system is f, 0.84 <f1 / f <1.3 (1) 0.5 <r1 / r2 <0.9 (2) 8 <−r3 / r2 <3.5 ‥‥‥ (3)

According to a second aspect of the present invention, when the refractive index of the material of the i-th lens is Ni and the length from the first lens surface to the final lens surface is Δd, the ratio is 0.18 <0.18 < {D / f <0.23} (4) n1> 1.65 (5) n2> 1.7 (6) n3> 1.7 (7) It is characterized by doing.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the respective lenses contact each other or set a lens interval via a spacer, and an air gap between the second lens and the third lens. The distance is d4, the distance between the third lens and the diaphragm is d6, and the radius of curvature of the i-th lens surface is ri.
0.003 <d4 / f <0.02 {(8) 0.035 <d6 / f <0.05} (9) 1.1 <r5 / r4 <1.6} The condition (10) is satisfied.

[0016]

FIG. 1 is a lens sectional view of a numerical example 1 of the present invention described later. In FIG. 1, LE denotes a photographing lens, SP denotes an aperture, and IP denotes an image plane. The substrate of the image plane (imaging screen) IP is held by holding means (not shown) so that the longitudinal direction of the image plane is curved toward the object side. Then, a photosensitive material such as a film is positioned on the substrate.

The taking lens LE includes a first meniscus positive lens G1 having a convex surface facing the object side in order from the object side, a negative second lens G2 having both concave lens surfaces, and a positive second lens G2 having both convex lens surfaces. It has three lenses G3 and a stop SP.

In this embodiment, as shown in FIG. 1, by appropriately setting the lens shape, the refractive power, and the like of each lens, it is possible to reduce the size of the entire lens system and widen the angle of view of the photographing. An angle of view 7 in which various aberrations generated at the time, particularly coma aberration and astigmatism from the middle to the periphery of the screen are corrected well.
A rear stop type photographing lens having a high optical performance of about 5 degrees is obtained.

Next, the technical meaning of each of the above conditional expressions will be described. Conditional expression (1) is a condition for satisfactorily aligning the image plane with the film surface when the film surface is curved. Exceeding the upper limit causes the image plane to fall too much,
If the f-number cannot be made brighter, and if the f-number exceeds the lower limit, the power of each lens becomes too strong, causing a problem that coma flare becomes large.

Conditional expression (2) indicates the balance of the power between the first lens surface and the second lens surface of the first lens.
If the upper limit of the conditional expression is exceeded, the balance between astigmatism and distortion will be poor, making it difficult to achieve both. If the lower limit is exceeded, the power of the first lens surface will be too strong, so that spherical aberration cannot be corrected.

Conditional expression (3) indicates the shape of the air lens between the first lens and the second lens. When the value exceeds the upper limit of the conditional expression, it becomes difficult to correct astigmatism. When the value exceeds the lower limit, the coma flare component of the off-axis light flux increases rapidly, which is not good.

The image pickup apparatus provided with the taking lens, which is the object of the present invention, is achieved by the above configuration, but it is more preferable to satisfy at least one of the following conditions.

(A-1) When the refractive index of the material of the i-th lens is Ni and the length from the first lens surface to the final lens surface is d, 0.18 <{d / f <0.23} ‥‥ (4) n1> 1.65 ‥‥‥ (5) n2> 1.7 ‥‥‥ (6) n3> 1.7 ７ (7)

Conditional expression (4) relates to the range of the thickness (total lens length) from the first lens surface to the final lens surface. Exceeding this upper limit makes it difficult to secure the amount of peripheral light, while exceeding the lower limit makes the F-number extremely dark and makes it difficult to correct spherical aberration.

The triplet type photographing lens of this embodiment can reduce the higher order components of various aberrations by making the curvature of each lens slower than the power of the lens, and the glass having a relatively high refractive index can be obtained. It is better to use materials.

In particular, as shown in conditional expressions (5), (6) and (7), the material of the first lens has a refractive index of 1.65 or more, and
By using a glass material having a refractive index of 1.7 or more for the material of the lens and a refractive index of 1.7 or more for the material of the third lens, the image surface can be favorably formed on a curved film surface in a state where the entire length of the lens is short. Are matched.

(A-2) The distance between the second lens and the third lens is set to d4, the distance between the third lens and the stop is set to a distance between the second lens and the third lens. Where d6 is d6 and the radius of curvature of the i-th lens surface is ri 0.003 <d4 / f <0.02 {(8) 0.035 <d6 / f <0.05} (9) The condition of 1.1 <r5 / r4 <1.6 (10) is satisfied.

In the present invention, in order to achieve both simplification and compactness of the entire lens system, it is desirable that all three lenses of the triplet type photographing lens be in contact with each other (or through a thin spacer).

In order to obtain good performance under such conditions, it is preferable to satisfy conditional expressions (8) and (9), and it is more preferable to satisfy conditional expression (10).

Conditional expression (8) relates to the air gap between the second lens and the third lens. If the value exceeds the upper limit, it is difficult to secure the amount of peripheral light, and if the value exceeds the lower limit, astigmatism and field curvature occur. Balance is deteriorated. Conditional expression (9) indicates the ratio between the final lens surface of the third lens and the stop. Exceeding the upper limit of the conditional expression increases the outer diameter of each lens, and reduces the off-axis halo component and coma component. It gets bigger.

If the lower limit is exceeded, the stop and the lens are too close to each other, making it difficult to incorporate a mechanical mechanism for adjusting the variation in focal length. This is not good because it causes a complicated mechanical configuration due to interference between the mechanism and the mechanical part.

Conditional expression (10) indicates the shape of the air lens between the second lens and the third lens. When the value exceeds the upper limit, the amount of astigmatism increases, and when the value exceeds the lower limit, the spherical aberration increases. It is not good because the bend becomes large.

Next, numerical examples of the present invention will be described. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air space from the object side, and ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. In the numerical examples, r8 indicates the radius of curvature of the photographing angle of view in the longitudinal direction. -Numerical Example 1-f = 27.53998 fno = 1: 6.2 2ω = 76.3 ° r1 = 7.516 d1 = 2.40 n1 = 1.77250 ν1 = 49.6 r2 = 10.131 d2 = 0.97 r3 = -18.888 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 8.563 d4 = 0.18 r5 = 12.051 d5 = 1.70 n3 = 1.83400 ν3 = 37.2 r6 = -16.232 d6 = 1.12 r7 = Aperture r8 = -350 -Numerical Example 2- f = 27.75351 fno = 1: 6.2 2ω = 75.9 ° r1 = 7.276 d1 = 2.15 n1 = 1.77250 ν1 = 49.6 r2 = 9.929 d2 = 0.91 r3 = -18.227 d3 = 0.70 n2 = 1.72825 ν2 = 28.5 r4 = 8.794 d4 = 0.19 r5 = 13.044 d5 = 1.50 n3 = 1.83400 ν3 = 37.2 r6 = -15.485 d6 = 1.12 r7 = Aperture r8 = -350-Numerical example 3- f = 27.49299 fno = 1: 6.2 2ω = 76.4 ° r1 = 7.522 d1 = 2.40 n1 = 1.77250 ν1 = 49.6 r2 = 10.258 d2 = 0.97 r3 = -18.838 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 8.674 d4 = 0.20 r5 = 12.523 d5 = 1.70 n3 = 1.83400 ν3 = 37.2 r6 = -16.022 d6 = 1.12 r7 = Aperture r8 = -450 -Numerical example 4-f = 27.57753 fno = 1: 6.2 2ω = 76.2 ° r1 = 7.104 d1 = 2.40 n1 = 1.72000 ν1 = 50.3 r2 = 9.211 d2 = 1.03 r3 = -18.431 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 7.629 d4 = 0.14 r5 = 9.829 d5 = 1.70 n3 = 1.83400 ν3 = 37.2 r6 = -16.501 d6 = 1.12 r7 = Aperture r8 = -350 -Numerical Example 5- f = 28.30555 fno = 1: 6.2 2ω = 74.8 ° r1 = 7.174 d1 = 2.40 n1 = 1.77250 ν1 = 49.6 r2 = 9.899 d2 = 0.92 r3 = -27.007 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 7.883 d4 = 0.21 r5 = 11.469 d5 = 1.70 n3 = 1.80440 ν3 = 39.6 r6 = -19.672 d6 = 1.12 r7 = Aperture r8 =- 350-Numerical Example 6-f = 27.63960 fno = 1: 6.2 2ω = 76.1 ° r1 = 7.506 d1 = 2.40 n1 = 1.77250 ν1 = 49.6 r2 = 9.794 d2 = 0.97 r3 = -19.111 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 8.226 d4 = 0.13 r5 = 10.813 d5 = 1.70 n3 = 1.83400 ν3 = 37.2 r6 = -16.934 d6 = 1.12 r7 = Aperture r8 = -200 -Numerical Example 7- f = 27.27447 fno = 1: 6.2 2ω = 76.8 ° r1 = 6.944 d1 = 2.40 n1 = 1.72000 ν1 = 50.3 r2 = 8.412 d2 = 1.15 r3 = -15.647 d3 = 0.75 n2 = 1.72825 ν2 = 28.5 r4 = 6.335 d4 = 0.11 r5 = 7.314 d5 = 1.70 n3 = 1.80100 ν3 = 35.0 r6 = -14.202 d6 = 1.12 r7 = Aperture r8 = -350

[0034]

[Table 1]

[0035]

According to the present invention, as described above, the triplet type is adopted, and the aperture is arranged in the publication of the lens system.
By appropriately setting the lens shape of each lens, the refractive index of the material, and the like, it is possible to achieve an image pickup apparatus including a photographic lens having a short overall lens length and a well-balanced optical performance of the entire screen.

In particular, in a camera having a curved film surface, a compact and high-performance optical system can be constructed. Also, since the distance between the lens and the aperture can be set relatively long, the mechanical structure can be simplified, and a high-performance camera can be easily configured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram of Numerical Embodiment 1 of the present invention.

[Explanation of symbols]

 LE photographing lens SP aperture IP image plane G1 first lens G2 second lens G3 third lens d d-line g g-line S sagittal image plane M meridional image plane

Claims (3)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
It has a lens, a second lens having a negative refractive power, a third lens having a positive refractive power, and an aperture, and the photographing screen is curved in the longitudinal direction toward the object side, and the i-th screen is counted from the object side.
When the radius of curvature of the second lens surface is ri, the focal length of the i-th lens is fi, and the focal length of the entire system is f, 0.84 <f1 / f <1.3 0.5 <r1 / r2 <0. 9 1.8. An imaging apparatus provided with a photographing lens, characterized by satisfying the following condition: 1.8 <−r3 / r2 <3.5. 2. The material of the i-th lens has a refractive index of Ni,
When the length from the first lens surface to the final lens surface is Δd, the condition 0.18 <Δd / f <0.23 n1> 1.65 n2> 1.7 n3> 1.7 is satisfied. An imaging apparatus comprising the photographing lens according to claim 1. 3. A lens spacing between the lenses is set by contacting the lenses with each other or via a spacer, the air spacing between the second lens and the third lens is d4, and the spacing between the third lens and the diaphragm is d. d6, where ri is the radius of curvature of the i-th lens surface: 0.003 <d4 / f <0.02 0.035 <d6 / f <0.05 1.1 <r5 / r4 <1.6 An image pickup apparatus comprising the photographing lens according to claim 1, wherein a condition is satisfied.