JPH052204B2 - - Google Patents

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.

Prior Art In recent years, as cameras have become more compact, compact photographic lenses have been desired.

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 view, 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, various problems occur at a high angle of view. It is extremely difficult to properly correct aberrations.

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, when using acrylic resin for the fourth lens, correction of off-axis chromatic aberration (lateral chromatic aberration and chromatic coma aberration) is often insufficient, which has been a problem for some time. Ta.

Purpose The present invention was made in order to solve all the drawbacks of the prior art described above, and FN0=
3.5, an angle of view of 63°, and a telephoto ratio of approximately 1.0, and provides a compact wide-angle photographic lens that satisfies the optical performance of a 63° angle of view and a telephoto ratio of approximately 1.0, and provides excellent aberration correction using only one aspherical surface, especially coma, axial, and off-axial chromatic aberrations in a well-balanced manner. The purpose is to

Configuration As shown in FIG. 1, the lens configuration of the present invention includes, in order from the object side, a first lens that is a positive meniscus lens with its convex surface facing the object side, a second lens that is a biconcave negative lens, and a biconvex lens. A compact wide-angle lens consisting of a third lens that is a positive lens and a fourth lens that is a negative meniscus lens with its concave surface facing the object side.The fourth lens is made of resin and has an aspherical surface on the image side.It is a compact wide-angle lens that is composed of 4 elements in 4 groups. It is characterized by satisfying the following conditions.

(1) 0.17f＜d ₆ ＜0.2f (2) 0.8＜d ₆ ／｜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: Combined focal length of the entire system d ₄ : Second lens and second lens Axial distance between the third lens and the third lens d ₅ : Center thickness of the third lens d ₆ : Axial 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 : The center thickness of the third lens Refractive index for the d-line of the medium of the first lens and the third lens ν ₂ , ν ₃ , ν ₄ : Abbe number of the medium of the second, third, and fourth lenses Furthermore, in addition to this condition, the following conditions This is a compact wide-angle lens that satisfies the following.

(9) r ₅ = | r ₆ | where 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 Each condition of the wide-angle lens according to the present invention will be explained below. Add.

Condition (1) is to maintain good aberrations while keeping the telephoto ratio at about 1.0. If the upper limit is exceeded, the diameter of the fourth lens becomes large and the lens system becomes large. If the lower limit is exceeded, spherical aberration will be overcorrected, making it difficult to correct comatic aberration.

Condition (2) is intended to suppress changes in the image plane during focusing by extending the front group consisting of the first, second, and third lenses. If the upper limit is exceeded, the image plane will be over-corrected at close range, and if the lower limit is exceeded, the image plane will be under-corrected.

Condition (3) is intended to satisfactorily correct positive distortion. Distortion becomes better when the upper limit is exceeded, but
The amount of peripheral light decreases, and in order to prevent this, it is necessary to increase the diameters of the first and second lenses, and if the diameter exceeds the limit, 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 fourth lens, and is a restriction imposed by 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 axial chromatic aberration and off-axis chromatic aberration (chromatic aberration of magnification and chromatic coma) under conditions (4) and (5), and if these conditions are exceeded, At times, it becomes difficult to achieve a good balance between the two chromatic aberrations.

Condition (8) is a condition for maintaining coma aberration well 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 ₅ = |r ₆ |.

This condition (9) is desired mainly from the viewpoint of assembly and processing. That is, in a biconvex lens such as the third lens, when the radii of curvature on both sides are close, if the curvatures on the object side and the image side are made the same, the troublesomeness of discrimination during assembly can be reduced.

Next, examples of the present invention will be shown.

However, ri: Radius of curvature of the i-th lens surface from the object side di: The i-th and (i+1)th lens surfaces from the object side
Distance between the th surfaces ni, νi: refractive index and Atsube number for the d-line of the medium of the ith lens in order from the object side f: focal length of the entire system ω: half angle of view TR: telephoto ratio Also, an aspheric surface The shape is given by the following equation, where the X coordinate is in the optical axis direction, the Y coordinate is in the direction perpendicular to the optical axis, the origin is the intersection of the vertex of the lens surface and the X axis, and r is the paraxial radius of curvature.

However, C=1/r K, A ₄ , A ₆ , A ₈ , A ₁₀ are aspherical coefficients Example 1 f=100 FNO=3.5 2ω=63° TR=0.999 r ₁ =30.208 d ₁ =9.398 n ₁ = 1.6968 ν ₁ = 55.46 r ₂ = 89.073 d ₂ = 2.619 r ₃ = −134.109 d ₃ = 2.735 n ₂ = 1.7552 ν ₂ = 27.53 r ₄ = 59.994 d ₄ = 7.245 r ₅ = 75.962 d ₅ =7.74 _n3 =1.72 ν ₃ = 42.02 r ₆ = −91.383 d ₆ = 19.03 r ₇ = −19.791 d ₇ = 4.394 n ₄ = 1.4915 ν ₄ = 57.8 r ₈ = −33.368 Aspheric coefficient (8th surface) K = 0 A ₄ = − 1.481906×10 ^-7 A ₆ = 2.202945×10 ^-9 A ₈ = −1.150907×10 ^-11 A ₁₀ = 1.403118×10 ^-14 Parameter values for conditions (2) and (3) d ₆ / | r ₇ | = 0.962 , d ₄ / (d ₄ + d ₅ ) = 0.483 Example 2 f = 100 FNO = 3.5 2ω = 63° TR = 1.011 r ₁ = 30.832 d ₁ = 9.531 n ₁ = 1.6968 ν ₁ = 55.46 r ₂ = 92.509 d ₂ ＝2.513 r ₃ ＝−126.314 d ₃ ＝2.718 n ₂ ＝1.71736 ν ₂ ＝29.5 r ₄ ＝55.435 d ₄ ＝7.823 r ₅ ＝71.283 d ₅ ＝6.666 n ₃ ＝1.7003 ν ₃ ＝47.84 r ₆ ＝ −89.182 d ₆ ＝19.623 r ₇ ＝−21.029 d ₇ ＝4.856 n ₄ ＝1.491 ν ₄ ＝61.4 r ₈ ＝−35.563 Aspheric coefficient (8th surface) K＝0 A ₄ ＝7.590430×10 ^-7 A ₆ ＝2.107188×10 ^{- -} ₀ A ₈ = -9.343424×10 ^-13 A ₁₀ = 2.606837×10 ^-15 Parameter values for conditions (2) and (3) d ₆ / | r ₇ | = 0.933, d ₄ / (d ₄ + d ₅ ) = 0.54 Example 3 f = 100 FNO = 3.5 2ω = 63° TR = 0.999 r ₁ = 30.203 d ₁ = 9.629 n ₁ = 1.6935 ν ₁ = 53.34 r ₂ = 88.729 d ₂ = 2.735 r ₃ = -131.939 d ₃ = 3 .084 n ₂ = 1.76182 ν ₂ = 26.55 r ₄ = 60.22 d ₄ = 7.244 r ₅ = 72.284 d ₅ = 7.127 n ₃ = 1.70154 ν ₃ = 41.15 r ₆ = −88.433 d ₆ = 18.764 r ₇ = −19.784 _d7 =4.393 n ₄ = 1.4915 ν ₄ = 57.8 r ₈ = −33.348 Aspheric coefficient (8th surface) K = 0 A ₄ = 1.839948×10 ^-7 A ₆ = 3.934060×10 ^-10 A ₈ = −6.571677×10 ^-12 A ₁₀ = 1.031060×10 ^-14 Parameter values of conditions (2) and (3) d ₆ / | r ₇ | = 0.948, d ₄ / (d ₄ + d ₅ ) = 0.504 Example 4 f = 100 FNO = 3.5 2ω = 63゜ TR=0.993 r ₁ = 30.434 d ₁ = 9.652 n ₁ = 1.6968 ν ₁ = 55.46 r ₂ = 103.778 d ₂ = 2.667 r ₃ = −137.679 d ₃ = 2.696 n ₂ = 1.7552 ν ₂ = 27. 53r4= _58.405 d ₄ = 7.884 r ₅ = 85.871 d ₅ = 6.261 n ₃ = 1.70154 ν ₃ = 41.15 r ₆ = −85.871 d ₆ = 19.101 r ₇ = −19.713 d ₇ = 4.377 n ₄ = 1.4915 ν ₄ = 57.8 _r8 =- 32.307 Aspheric coefficient (8th surface) K=-0.325666 A ₄ =-9.664720×10 ^-7 A ₆ =2.915494× ^10-9 A ₈ =-1.363011× ^10-12 A ₁₀ =2.741080× ^10-15 Condition (2 )(3) parameter values d ₆ / | r ₇ | = 0.969, d ₄ / (d ₄ + d ₅ ) = 0.557 Example 5 f = 100 FNO = 3.5 2ω = 63° TR = 0.997 r ₁ = 30.218 d ₁ = 9.64 n ₁ = 1.6935 ν ₁ = 53.34 r ₂ = 90.069 d ₂ = 2.724 r ₃ = −131.811 d ₃ = 3.094 n _{2 = 1.76182 ν 2 =} 26.55 r ₄ = 60.148 d ₄ = 7.198 r ₅ = _72.632d5 =7.265 n ₃ =1.702 ν ₃ =40.2 r ₆ =−88.474 d ₆ =18.77 r ₇ =−19.792 d ₇ =4.395 n ₄ =1.4919 ν ₄ =56.1 r ₈ =−33.571 Aspheric coefficient (8th surface) K =0 A ₄ =1.544712×10 ^-7 A ₆ =3.134751×10 ^-10 A ₈ =−2.690861×10 ^-12 A ₁₀ =3.841679×10 ^-15 Parameter values for conditions (2) and (3) d ₆ / | r ₇ | = 0.948, d ₄ / (d ₄ + d ₅ ) = 0.498 Example 6 f = 100 FNO = 3.5 2ω = 63° TR = 0.995 r ₁ = 29.809 d ₁ = 10.154 n ₁ = 1.6583 ν ₁ = 57.26 r ₂ = 111.127 d ₂ = 2.44 r ₃ = -140.924 d ₃ = 3.09 n ₂ = 1.72825 ν ₂ = 28.32 r ₄ = 58.652 d ₄ = 8.259 r ₅ = 91.193 d ₅ = 5.802 n ₃ = 1.72 ν ₃ = _42.02r6 = −91.193 d ₆ = 17.836 r ₇ = −19.855 d ₇ = 4.381 n ₄ = 1.4915 ν ₄ = 57.8 r ₈ = −32.617 Aspheric coefficient (8th surface) K = −0.404266 A ₄ = −5.917351×10 ^-7 A ₆ = −5.216908×10 ^-9 A ₈ =4.784520×10 ^-12 A ₁₀ = −8.755808×10 ^-15 Parameter values of conditions (2) and (3) d ₆ / | r ₇ | = 0.898, d ₄ / (d ₄ + d ₅ ) = 0.587 Example 7 f = 100 FNO = 3.5 2ω = 63° TR = 0.996 r ₁ = 29.75 d ₁ = 10.175 n ₁ = 1.6583 ν ₁ = 57.26 r ₂ = 90.299 d ₂ = 2.578 r ₃ ＝−115.751 d ₃ ＝2.927 n ₂ ＝1.72825 ν ₂ ＝28.32 r ₄ ＝62.244 d ₄ ＝8.008 r ₅ ＝66.501 d ₅ ＝5.931 n ₃ ＝1.66892 ν ₃ ＝44.91 r ₆ ＝−82.871 d ₆ = 17.741 r ₇ =-20.631 d ₇ =4.4 n ₄ =1.491 ν ₄ =61.4 r ₈ =-37.474 Aspheric coefficient (8th surface) K=0 A ₄ =1.159728×10 ^-6 A ₆ =-9.768563×10 ^-10 A ₈ = 9.653485×10 ^-13 A ₁₀ = 2.784667×10 ^-15 Parameter values for conditions (2) and (3) d ₆ / | r ₇ | = 0.860, d ₄ / (d ₄ + d ₅ ) = 0.575 Effect Explanation above As mentioned above, the wide-angle lens according to the present invention has a simple configuration of 4 elements in 4 groups, has only one aspherical surface that is difficult to process, and has an extremely small number of aspherical surfaces, and even has a telephoto ratio of 1.01.
It is small in size, and even if a simple distance adjustment method in which only the front group is advanced is used, the change in the image plane due to focusing is small, so it is satisfactory. In addition, coma aberration and off-axis chromatic aberration are excellent even at high angles of view.

[Brief explanation of the drawing]

FIG. 1 shows Example 1 of a 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 an aberration diagram of the lens according to Fig. 1 when the imaging magnification is -1/40x. , FIG. 4 to FIG. 9 are aberration diagrams for an object at infinity in Examples 2 to 7, respectively.

Claims (1)

[Claims] 1. In order from the object side, the first lens is a positive meniscus lens with the 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 facing the object side. A compact wide-angle lens consisting of 4 elements in 4 groups, characterized in that the fourth lens is made of resin and has an aspherical surface on the image surface side, and satisfies the following conditions: lens. (1) 0.17f＜d ₆ ＜0.2f (2) 0.8＜d ₆ ／｜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: Combined focal length of the entire system d ₄ : Second lens and second lens Axial distance between the third lens and the third lens d ₅ : Center thickness of the third lens d ₆ : Axial 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 : Refractive index for the d-line of the medium of the first lens and the third lens ν ₂ , ν ₃ , ν ₄ : Atsube number 2 of the medium of the second, third, and fourth lenses In addition to the conditions of claim 1 , the compact wide-angle lens (9) according to claim 1, characterized in that it further satisfies the following conditions: r ₅ = | r ₆ | where r ₅ is the 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.