JPH07120672A - High performance photographing lens - Google Patents

Abstract

PURPOSE:To downsize a lens system including the outer diameter, and enhance the optical performance up to a screen peripheral part by setting the lens first face and lens final face into concave faces, and satisfying a specified condition. CONSTITUTION:The lens system is formed out of a first lens group having positive refracting power, a second lens group having negative refracting power, a diaphragm, a third lens group having positive refracting power, and a fourth lens group having positive refracting power in the order from an object side, the lens first face and the lens final face are set to concave faces, and the following condition is satisfied: 0.25<fR/fF<1.3, wherein fF is the composed focus distance of the lens groups in the front of the diaphragm, and fR is the composed focus distance of the lens groups in the rear of the diaphragm. When the lens first face is concave rather than convex, the peripheral light quantity is relatively easily ensured. Therefore, when the first face is set to be the concave face, a vicious cycle such that the lens diameter is increased only to ensure the light quantity, can be avoided, the distance from the lens first face to the incident pupil position can be shortened, and the lens system can be reduced in size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a caliber ratio of F / 1.4 to
The present invention relates to a compact and high-performance single-focus photographing lens having an angle of view of about 60 to 75 ° at F / 2.8.

[0002]

2. Description of the Related Art As a conventional example of a taking lens of the same kind as the taking lens of the present invention, a lens system described in Japanese Patent Application Laid-Open No. 5-80252 is known. This conventional shooting lens
From the object side, in order from the object side, a first lens group having a positive refracting power composed of a cemented lens in which a biconcave lens and a biconvex lens are cemented together, and a negative lens having a negative refracting power in which a biconvex lens and a biconcave lens cemented 2 lens groups, diaphragm,
A third lens group having a positive refracting power with a convex surface facing the image side, a fourth lens group having a positive refracting power composed of a cemented lens in which a biconcave lens and a biconvex lens are bonded, and a biconvex lens and a biconcave lens. The fifth lens group having a positive refractive power and made up of cemented cemented lenses, has a very weak power in the front group before the diaphragm, and a relatively strong power in the rear group after the diaphragm. It is a lens configuration.

[0003]

In the above-mentioned conventional taking lens, the power of the front group is very weak and the power of the rear group is relatively strong, so that the correction function of the rear group is burdened in terms of aberration correction. It is large, and in particular, the curvature of field has a large influence, which adversely affects the image. Further, since the configuration length from the first lens surface to the stop is large, the distance from the first lens surface to the entrance pupil position becomes long, and the front lens diameter becomes extremely large in order to secure a sufficient amount of peripheral light. In recent years, the demand for miniaturization has become stronger, and it cannot be said that the lens system meets this demand.

In order to reduce the size of the entire camera, it is possible to use a mechanical method such as collapsing the lens system. However, the outer diameter of the lens system such as the front lens diameter is determined by such a mechanical method. It cannot be used, and it is desired to make the lens system compact by optical design.

The present invention achieves downsizing of the lens system including the outer diameter by appropriately maintaining the lens configuration and power distribution with the minimum number of lenses, and at the same time, the optical performance up to the peripheral portion of the screen. The objective is to provide a good and high-performance shooting lens.

[0006]

The taking lens of the present invention comprises:
A first lens group having positive refractive power in order from the object side;
A second lens group having a negative refractive power, a diaphragm, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, and a lens first surface and a lens final surface The lens system has a concave surface and further satisfies the following condition (1).

(1) 0.25 <f _R / f _F <1.3 where f _F is the composite focal length of the lens group before the diaphragm,
f _R is the combined focal length of the lens group after the stop.

It is relatively easy to secure the peripheral light amount when the first surface of the lens is a concave surface rather than a convex surface. Therefore, if the first surface is a concave surface, the lens diameter is increased only to secure the light amount. It is possible to avoid a vicious circle such as to make it possible to shorten the distance from the first lens surface to the entrance pupil position, and to downsize the lens system.

Further, it is desirable that the ratio of the radius of curvature between the first lens surface and the last lens surface is determined so as to satisfy the following condition (2).

(2) 1 <| r _a / r _b | <3.5 where r _a is the radius of curvature of the first lens surface and r _b is the radius of curvature of the final lens surface.

The condition (1) defines the ratio of the focal lengths of the lens groups before and after the stop, and by appropriately adjusting the power distribution before and after the stop, various aberrations up to the peripheral portion of the screen can be obtained. This is for making a well-balanced correction and reducing the size of the lens system.

When the upper limit of 1.3 of the condition (1) is exceeded, various aberrations can be corrected in a well-balanced manner, but in this case, in order to reduce the occurrence of off-axis aberrations such as coma aberration, the final lens surface should be reduced. Inevitably, the shape of is a convex surface with respect to the image side, in which case the total length of the lens system becomes long, which is contrary to the object of the present invention.

When the lower limit of 0.25 of condition (1) is exceeded,
The power of the rear group (the entire lens group on the image side of the diaphragm) becomes extremely strong, the amount of aberration generated on each lens surface of the rear group becomes large, and it becomes difficult to secure good optical performance. Also,
The air gap between the front group and the rear group tends to increase, which is against the miniaturization of the lens system.

By keeping the value of | r _a / r _b | within the range of the condition (2), the overall length of the lens system, the size of the front lens diameter, the amount of peripheral light, etc. are properly balanced, and a compact photographing lens is provided. Will be easier to obtain.

If the upper limit of condition (2) is exceeded, the first lens
The radius of curvature of the surface becomes relatively gentle, and the effects of securing the peripheral light amount and shortening the entrance pupil distance as described above are diminished. Therefore, there is a possibility that the diameter of the front lens is increased.

When the value goes below the lower limit of the condition (2), the radius of curvature of the final lens surface becomes relatively gentle, and good performance can be secured, but the total length of the lens system becomes long. In order to achieve the object of the present invention, it is preferable that the second lens group having a negative refractive power is composed of one negative lens.

As described above, the constituent length of the front unit of the lens unit before the aperture greatly affects the diameter of the front lens, so it is desirable to keep the number of lenses to the minimum within a range that does not deteriorate the optical performance. For that purpose, it is preferable that the second lens group is a single lens, and the second lens group is configured such that the optical system is as symmetrical as possible with respect to the diaphragm. The meniscus lens having the convex surface facing the object side is the second lens group. Is desirable.

The above negative lens is also important for keeping the Petzval sum of the lens system at an appropriate value. For that purpose, the focal length f ₂ of the second lens group is the following condition (3). It is desirable to satisfy

(3) 1.5f <| f ₂ | <4.5f where f is the focal length of the entire system.

Exceeding either the upper limit of 4.5f or the lower limit of 1.5f of the above condition (3) is not preferable for setting the Petzval sum of the lens system to an appropriate value.

Further, in the condition (1) regarding the value of f _R / f _F , it is more preferable to set the lower limit to 0.4 in order to correct various aberrations in a photographing lens having a large aperture ratio in a well-balanced manner. That is, it is more desirable to satisfy the following condition (1-a).

(1-a) 0.4 <f _R / f _F <1.3 Under the condition (1-a), when the lower limit of 0.4 is exceeded, the influence of spherical aberration and coma becomes particularly strong, and It becomes difficult to keep a high-performance shooting lens with high performance.

Further, regarding the upper limit of the condition (1), setting it to 1.0 is effective in further improving the aberration correction action, and particularly effective in preventing image deterioration due to field curvature. That is, it is more preferable to satisfy the following condition (1-b).

(1-b) 0.25 <f _R / f _F <1.0 A desirable configuration of the taking lens of the present invention is as follows. That is, from the object side, one biconcave lens and one
From a first lens group composed of one biconvex lens, a second lens group consisting of one negative meniscus lens with a convex surface facing the object side, and a cemented lens in which a biconcave lens and a biconvex lens are bonded together It is preferable that the second lens group is composed of a third lens group and a fourth lens group of a cemented lens in which a biconvex lens and a biconcave lens are cemented together.

[0025]

EXAMPLES Examples of high-performance taking lenses according to the present invention will be described below. Example 1 f = 36.00mm, F / 2.88,2ω = 63.2 °, f B = 30.04mm r 1 = -37.9763 d 1 = 1.000 n 1 = 1.53256 ν 1 = 45.91 r 2 = 22.5199 d 2 = 0.100 r 3 = 16.5729 (aspherical surface) d ₃ = 3.975 n ₂ = 1.78650 ν ₂ = 50.00 r ₄ = -51.5406 d ₄ = 0.100 r ₅ = 13.9701 d ₅ = 1.000 n ₃ = 1.62374 ν ₃ = 47.10 r ₆ = 10.8113 d ₆ = 3.370 r ₇ = ∞ _{(stop) d 7 = 2.577 r 8 =} -14.6718 d 8 = 1.000 n 4 = 1.68893 ν 4 = 31.08 r 9 = 54.6154 d 9 = 3.197 n 5 = 1.77250 ν 5 = 49.66 r 10 = -16.3614 d _{10 = 0.100 r 11 = 52.9164 d} 11 = 2.765 n 6 = 1.83481 ν 6 = 42.72 r 12 = -27.4284 d 12 = 1.000 n 7 = 1.54072 ν 7 = 47.20 r 13 = 29.9742 ( aspherical) aspherical coefficients (third Surface) A ₄ = -0.34430 x 10 ^-4 , A ₆ = -0.81137 x 10
^-7 A ₈ = -0.36683 x 10 ^-9 , A ₁₀ = 0.32507 x 10 ^-11 (13th surface) A ₄ = 0.13923 x 10 ^-4 , A ₆ = -0.64905 x
10 ^-7 A ₈ = 0.23589 × 10 ^-9 , A ₁₀ = -0.13877 × 10 ^-11 f _R / f _F = 0.871, f ₂ = -87.27 mm, f ₂ /f=-2.4 | r _a / r _b | _{= | r 1 / r 13 |} = 1.27

Example 2 f = 36.00 mm, F / 1.85, 2ω = 62.4 °, f _B = 24.77 mm r ₁ = -79.9547 d ₁ = 4.034 n ₁ = 1.53256 ν ₁ = 45.91 r ₂ = 26.7201 d ₂ = 0.100 r ₃ = 18.6977 _{(aspherical) d 3 = 7.062 n 2 =} 1.78650 ν 2 = 50.00 r 4 = -98.6469 d 4 = 0.100 r 5 = 17.6483 d 5 = 1.500 n 3 = 1.62374 ν 3 = 47.10 r 6 = 12.4473 d ₆ = 4.810 r ₇ = ∞ _{(stop) d 7 = 3.254 r 8 =} -20.2572 d 8 = 1.000 n 4 = 1.68893 ν 4 = 31.08 r 9 = 23.2955 d 9 = 5.970 n 5 = 1.77250 ν 5 = 49.66 r 10 = _{-22.0958 d 10 = 0.100 r 11 =} 34.0591 d 11 = 5.139 n 6 = 1.83481 ν 6 = 42.72 r 12 = -43.7842 d 12 = 2.000 n 7 = 1.54072 ν 7 = 47.20 r 13 = 23.6790 ( aspherical) aspheric coefficients (Third surface) A ₄ = -0.19163 × 10 ^-4 , A ₆ = -0.46899 × 10
^-7 A ₈ = 0.35187 × 10 ^-11 , A ₁₀ = -0.25979 × 10 ^-12 (13th surface) A ₄ = 0.15219 × 10 ^-4 , A ₆ = -0.28391 ×
10 ^-8 A ₈ = -0.23584 × 10 ^-10 , A ₁₀ = 0.61377 × 10 ^-12 f _R / f _F = 0.573, f ₂ = -76.15 mm, f ₂ /f=-2.1 | r _a / r _b | _{= | r 1 / r 13 |} = 3.38

Example 3 f = 28.51 mm, F / 2.88, 2ω = 73.6 °, f _B = 21.62 mm r ₁ = -39.1331 d ₁ = 1.000 n ₁ = 1.54814 ν ₁ = 45.78 r ₂ = 16.5650 d ₂ = 0.100 r ₃ = 14.1361 _{(aspherical) d 3 = 4.804 n 2 =} 1.78650 ν 2 = 50.00 r 4 = -40.4301 d 4 = 0.100 r 5 = 13.2827 d 5 = 1.000 n 3 = 1.62374 ν 3 = 47.10 r 6 = 9.9256 d ₆ = 2.997 r ₇ = ∞ _{(stop) d 7 = 2.997 r 8 =} -17.3974 d 8 = 1.000 n 4 = 1.67741 ν 4 = 28.52 r 9 = 26.8634 d 9 = 4.280 n 5 = 1.78650 ν 5 = 50.00 r 10 = _{-17.2924 d 10 = 0.100 r 11 =} 36.9784 d 11 = 3.729 n 6 = 1.88300 ν 6 = 40.78 r 12 = -28.6091 d 12 = 1.000 n 7 = 1.54814 ν 7 = 45.78 r 13 = 18.8953 ( aspherical) aspheric coefficients (Third surface) A ₄ = -0.51912 × 10 ^-4 , A ₆ = -0.22098 × 10
^-6 A ₈ = 0.19546 × 10 ^-9 , A ₁₀ = -0.31807 × 10 ^-12 (13th surface) A ₄ = 0.16710 × 10 ^-4 , A ₆ = -0.24854 ×
10 ⁻⁷ A ₈ = −0.24711 × 10 ⁻⁹ , A ₁₀ = 0.22013 × 10 ⁻¹¹ f _R / f _F = 0.613, f ₂ = −71.10 mm, f ₂ /f=−2.5 | r _a / r _b | _{= | r 1 / r 13 |} = 2.23

Example 4 f = 36.03 mm, F / 1.44, 2ω = 62.2 °, f _B = 23.94 mm r ₁ = -49.5585 d ₁ = 0.992 n ₁ = 1.53256 ν ₁ = 45.91 r ₂ = 37.6853 d ₂ = 0.100 r ₃ = 25.4653 _{(aspherical) d 3 = 6.952 n 2 =} 1.78650 ν 2 = 50.00 r 4 = -57.5064 d 4 = 0.100 r 5 = 20.6431 d 5 = 2.997 n 3 = 1.62374 ν 3 = 47.10 r 6 = 14.8765 d ₆ = 5.449 r ₇ = ∞ _{(stop) d 7 = 3.618 r 8 =} -22.8849 d 8 = 1.990 n 4 = 1.68893 ν 4 = 31.08 r 9 = 28.9776 d 9 = 6.650 n 5 = 1.77250 ν 5 = 49.66 r 10 = _{-23.7098 d 10 = 1.182 r 11 =} 28.7068 d 11 = 4.481 n 6 = 1.83481 ν 6 = 42.72 r 12 = -81.4475 d 12 = 1.594 n 7 = 1.54072 ν 7 = 47.20 r 13 = 22.1814 ( aspherical) aspheric coefficients (Third surface) A ₄ = -0.12266 × 10 ^-4 , A ₆ = -0.29341 × 10
^-7 A ₈ = 0.56800 × 10 ^-10 , A ₁₀ = -0.62395 × 10 ^-13 (13th surface) A ₄ = 0.18445 × 10 ^-4 , A ₆ = -0.24748 ×
10 ^-7 A ₈ = 0.64803 × 10 ^-10 , A ₁₀ = 0.44126 × 10 ^-12 f _R / f _F = 0.530, f ₂ = -106.678 mm, f ₂ / f =-
3.0 | r _a / r _b | = | r ₁ / r ₁₃ | = 2.07 where r ₁ , r ₂ , ... Are the radii of curvature of each lens surface, d
₁ , d ₂ , ... Is the thickness of each lens and the lens interval, n
₁ , n ₂ , ... Is the refractive index of each lens, ν ₁ , ν ₂ ,.
Is the Abbe number of each lens, and f _B is the back focus.

Example 1 has a configuration as shown in FIG. 1, and has a first lens group having a positive refracting power as a whole, which is composed of a biconcave lens and a biconvex lens in order from the object side, and has a convex surface directed toward the object side. The second lens group of the negative meniscus lens, the diaphragm, the third lens group having a positive refracting power as a whole by the cemented lens in which the biconcave lens and the biconvex lens are cemented, and the biconvex lens and the biconcave lens are cemented The cemented lens is composed of a fourth lens group having a positive refracting power as a whole.

The taking lens of Example 1 has a focal length of 36 mm and an F number of 2.88. In addition, in Example 1,
The aberration situation at the object point at infinity is as shown in FIG. 5, the optical performance is very good up to the peripheral portion of the screen, and the total length is 50.2 mm, and the length from the first surface to the final surface of the lens system is large. It is a small photographic lens with a length Σd of 20.2 mm.

The second embodiment has the configuration shown in FIG.
It has the same configuration as. In the second embodiment, the focal length is 36.
It is a photographic lens with an mm and F number of 1.85.

The second embodiment is shown in FIG. 6 at the object point at infinity.
In the aberration condition as shown in, the optical performance is very good up to the peripheral part of the screen, and the total length is 59.8 mm, Σd
Is a small shooting lens of 35.1 mm.

The third embodiment has the configuration shown in FIG.
With a lens system of the same configuration as the, focal length is 28.5 mm, F
It is a lens system with a number of 2.88.

In the third embodiment, the aberration condition at the object point at infinity is as shown in FIG. 76, the optical performance is good up to the peripheral portion of the screen, and the total length is 44.7 mm, Σd.
Is a small shooting lens of 25.3 mm.

Example 4 is a lens system having a configuration as shown in FIG. 4 and the same configuration as Example 1, with a focal length of 36 mm and an F number of 1.44.

In the fourth embodiment, the aberration at the object point at infinity is as shown in FIG. 8 and the optical performance is good up to the peripheral portion of the screen, and the total length is 60.0 mm and Σd is 36.
It is a compact 1mm lens.

The shape of the aspherical surface used in each of these examples is expressed by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis.

X = y ² / [r + r {1- (y / r) ² } ^1/2 ] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + ... where r is an aspherical surface Radius of curvature on the optical axis of A ₄ , A ₆ ,
A ₈ , A _10, ... Are aspherical coefficients.

[0039]

The present invention can realize an unprecedented high-performance and compact photographing lens by appropriately adjusting the lens structure, diaphragm, front and rear power distribution, and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is an aberration curve diagram of Example 1 of the present invention.

FIG. 6 is an aberration curve diagram of Example 2 of the present invention.

FIG. 7 is an aberration curve diagram of Example 3 of the present invention.

FIG. 8 is an aberration curve diagram of Example 4 of the present invention.

Claims (2)

[Claims] 1. A first lens element having a positive refractive power in order from the object side.
The first lens surface is composed of a lens group, a second lens group having a negative refractive power, a diaphragm, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. A high-performance shooting lens that has the concave surface on the lens and the final surface, and satisfies the following conditions. 0.25 <f _R / f _F <1.3 where f _F is the combined focal length of the lens group before the aperture,
f _R is the combined focal length of the lens group after the diaphragm. 2. The high-performance taking lens according to claim 1, wherein the second lens group is a negative single lens.