JP2000171697A - Photographing lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photographing lens capable of restraining aberration fluctuation at the time of focusing to be small and obtaining excellent image quality in a wide photographing distance range from long-distance photographing to short-distance photographing by improving the optical system having triplet constitution and appropriately setting the constitution of the lens. SOLUTION: This lens is constituted of four lenses being four groups, that is, a positive meniscus lens G1 whose concave surface faces to an object side, a positive lens G2 whose convex surface faces to the object side, a negative lens G3 whose both surfaces are concave, and a positive lens G4 whose convex surface faces to an image surface side from the object side. When it is assumed that the refractive indexes of the material of the lenses G2, G3 and G4 are N2, N3 and N4, respectively, and the Abbe number thereof are V2, V3 and V4, respectively, the lens satisfies conditions 1.65<(N2+N4)/2<1.9, 1.70<N3<1.95, 35<(V2+V4)/2<60 and 20<V3<30. When it is assumed that the radius of curvature of the surface of the lens G1 on the object side is R and the focal distance of a lens entire system LE is F, the lens satisfies 0.3<|R/F|<0.7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention achieves high image quality in a wide photographing distance range from a photographing distance of infinity to a finite distance having a photographing magnification of about 0.5, particularly for video cameras, digital still cameras, and films. The present invention relates to a camera and a photographing lens suitable as an optical system for a scanner.

[0002]

2. Description of the Related Art As a photographing optical system having a simpler lens configuration than before, there is a triplet lens having a three-group configuration in which three lenses of a positive lens, a negative lens, and a positive lens are arranged from the object side. Gazette, JP-A-7-32525
For example, Japanese Patent Application Laid-Open No. 7-3230035 discloses a scanning optical system proposed in Japanese Patent Application Publication No. 0 and the like and having a relatively small number of lenses.

In recent years, the image pickup device is not limited to general photographing due to its miniaturization and high image quality, but instead of taking a high-sharp image, which has been conventionally performed by a scanning optical system, a small-sized device further captures an image in an area area. It is possible to do.

Accordingly, it is desired that the optical system be small in size with a relatively small number of lenses, with a small change in optical performance over a wide range of object distances corresponding to the object distance from a long distance to a short distance.

[0005]

Generally, when an image pickup system having a small variation in aberration is formed in a wide object distance range from an object at infinity to a close object, the number of lenses increases and the size of the optical system increases.

[0006] The photographing system is based on a specific object distance (often a photographing magnification of 20 to 50 times), and various aberrations are satisfactorily corrected at this distance.

Accordingly, when the photographing magnification deviates greatly from the reference state, for example, when it becomes about 0.5, various aberrations occur, and
Optical performance decreases.

The present invention improves the optical system of the triplet configuration and appropriately sets the lens configuration to suppress fluctuations in aberrations during focusing and to provide good image quality in a wide range of photographing distances from long-distance photography to short-distance photography. It is an object of the present invention to provide a photographic lens capable of obtaining an image.

[0009]

According to a first aspect of the present invention, there is provided a photographic lens comprising a positive meniscus lens Gl having a concave surface facing the object side from the object side, and a positive lens G having a convex surface facing the object side.
2. It is characterized by comprising four groups of four lenses: a negative lens G3 having both concave surfaces and a positive lens G4 having a convex surface facing the image surface side.

According to a second aspect of the present invention, in the first aspect of the invention, the refractive indices of the materials of the lenses G2, G3, and G4 are N2, N3, and N4, respectively, and the Abbe numbers are V2, V3, and V4, respectively. In this case, the following condition is satisfied: 1.65 <(N2 + N4) / 2 <1.9 1.70 <N3 <1.9535 <(V2 + V4) / 2 <6020 <V3 <30

[0011]

1 to 4 are a sectional view of a lens according to a numerical example 1 of the present invention and various aberration diagrams for an object at infinity, a photographing magnification of 0.1 times, and a photographing magnification of 0.5 times.

FIGS. 5 to 8 are a sectional view of a lens according to a second numerical embodiment of the present invention and various aberration diagrams of an object at infinity, a photographing magnification of 0.1 and a photographing magnification of 0.5.

9 to 12 are a sectional view of a lens according to Numerical Example 3 of the present invention and various aberration diagrams of an object at infinity, a photographing magnification of 0.1 and a photographing magnification of 0.5.

FIGS. 13 to 16 are a sectional view of a lens according to a numerical example 4 of the present invention and various aberration diagrams of an object at infinity, a photographing magnification of 0.1 and a photographing magnification of 0.5.

FIGS. 17 to 20 are a sectional view of a lens according to a numerical example 5 of the present invention and various aberration diagrams of an object at infinity, a photographing magnification of 0.1 times, and a photographing magnification of 0.5 times.

FIGS. 21 to 24 are a sectional view of a lens according to Numerical Example 6 of the present invention and various aberration diagrams of an object at infinity, a photographing magnification of 0.1 and a photographing magnification of 0.5.

The taking lens LE of this embodiment is a meniscus positive lens G having a concave surface facing the object side from the object side.
l, a positive lens G2 having a convex surface facing the object side, a negative lens G3 having both lens surfaces concave, and a positive lens G4 having a convex surface facing the image surface side. Is a type in which a meniscus-shaped negative lens is added to the object side having the above lens configuration.

SP denotes an aperture, FSP denotes a fixed aperture (flare cut aperture), GF denotes a glass block such as a face plate or an optical filter, and IP denotes an image plane.

Here, the object-side lens surface of the lens Gl has a concave surface facing the object side, and the lens surface has a negative refractive power. As a result, a large coma aberration and a negative spherical aberration are generated, and at the same time, cancellation is performed on the lens surface on the image plane side of the lens Gl, so that on-axis and off-axis aberrations are well-balanced, and at the same time, high-order aberrations of the entire lens system Is corrected. And lens G2, lens G3, lens G4
Is set as described above, thereby focusing over a wide object distance range by moving the entire lens system LE on the optical axis, thereby achieving high optical performance.

In the present embodiment, with the above configuration,
Although a photographic lens having high optical performance over the entire screen in a wide object distance range is achieved, it is more preferable to satisfy at least one of the following configurations.

(A-1) The lens G2, lens G3,
The refractive index of the material of the lens G4 is set to N2 and N, respectively.
3, N4 and Abbe number are V1, V2, V3 and V4, respectively.
1.65 <(N2 + N4) / 2 <1.9 (1) 1.70 <N3 <1.95 (2) 35 <(V2 + V4) / 2 <60 (3) The condition 20 <V3 <30 (4) is satisfied.

Here, the conditional expressions (1) and (2) are to correct the various aberrations in a well-balanced manner by defining the refractive indexes of the materials of the positive lens and the negative lens in the lens system.

Upper limit of conditional expression (1) or conditional expression (2)
If the lower limit is exceeded, the Betzval sum becomes too small, and large field curvature occurs, which is not good.

If the lower limit of conditional expression (1) is exceeded, the curvature of the lens surface of the positive lens will be too steep to cause a large degree of spherical aberration, and if the upper limit of conditional expression (2) is exceeded, a negative lens will be obtained. The effect of correcting aberration on the lens surface becomes weak, and as a result, it becomes impossible to correct various aberrations in a well-balanced manner.

The conditional expressions (3) and (4) are mainly conditions for satisfactorily correcting chromatic aberration. Exceeding this range makes it difficult to achieve a high-performance optical system.

In the present embodiment, it is more desirable to limit the numerical ranges of the conditional expressions (1) to (4) as follows in order to further improve the optical performance.

1.75 <(N2 + N4) / 2 <1.85 ‥‥‥ (1a) 1.75 <N3 <1.85 ‥‥‥ (2a) 40 <(V2 + V4) / 2 <50 ‥‥‥ ( 3a) 23 <V3 <28 (4a) (A-2) When the radius of curvature of the lens surface on the object side of the lens G1 is R and the focal length of the entire lens system is F, 0.3 <| R / F | <0.7 ‥‥‥ (5)

Conditional expression (5) is intended to satisfactorily correct spherical aberration and coma of the entire lens system by limiting the radius of curvature R of the lens surface of the lens G1 on the object side.

When the radius of curvature R is increased beyond the upper limit of the conditional expression (5), the negative refracting action on the lens surface is reduced, so that the positive spherical aberration generating action is weakened. As a result, in the entire lens system, Large negative spherical aberration occurs,
It becomes difficult to correct it.

On the other hand, when the value exceeds the lower limit, the influence on off-axis aberrations becomes large, and large coma aberrations are not generated.

(A-3) The focal length of the lens G1 is F
1. When the focal length of the entire lens system is F, the condition 0.05 <F / F1 <0.35 (6) is satisfied.

Conditional expression (6) is for appropriately setting the refractive power of the lens G1, and thereby correcting various on-axis and off-axis aberrations in a well-balanced manner.

If conditional expression (6) is not satisfied, it becomes difficult to satisfactorily correct various on-axis and off-axis aberrations.

(A-4) At least one of the lens systems
Preferably, the two lens surfaces are aspherical or diffractive optical element surfaces. Further, at least one lens may be a refractive power distribution type lens.

According to this, higher optical performance can be easily obtained.

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 spacing 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.

[0038]

[Outside 1]

[0039]

[Outside 2]

[0040]

[Table 1]

[0041]

As described above, according to the present invention, by appropriately setting the lens configuration, fluctuations in aberrations during focusing can be suppressed, and good image quality can be obtained in a wide shooting distance range from long-distance shooting to short-distance shooting. The resulting taking lens can be achieved.

[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 for an object at infinity according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an aberration diagram at a photographing magnification of 0.1 times in Numerical Example 1 of the present invention.

FIG. 4 is an aberration diagram when a photographing magnification is 0.5 × in Numerical Embodiment 1 of the present invention.

FIG. 5 is a sectional view of a lens according to a second numerical embodiment of the present invention;

FIG. 6 is an aberration diagram for an object at infinity according to Numerical Embodiment 2 of the present invention.

FIG. 7 is an aberration diagram at a photographing magnification of 0.1 in Numerical Example 2 of the present invention;

FIG. 8 is an aberration diagram when a photographing magnification of 0.5 is set in Numerical Example 2 of the present invention;

FIG. 9 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 10 is an aberration diagram for an infinitely distant object according to Numerical Example 3 of the present invention.

FIG. 11 is an aberration diagram at a photographing magnification of 0.1 in Numerical Example 3 of the present invention;

FIG. 12 is an aberration diagram at a photographing magnification of 0.5 × in Numerical Example 3 of the present invention.

FIG. 13 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 14 is an aberration diagram for an infinitely distant object according to Numerical Embodiment 4 of the present invention.

FIG. 15 is an aberration diagram at the time of a photographing magnification of 0.1 times in Numerical Example 4 of the present invention.

FIG. 16 is an aberration diagram at a photographing magnification of 0.5 in Numerical Example 4 of the present invention.

FIG. 17 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 18 is an aberration diagram for an infinitely distant object according to Numerical Example 5 of the present invention.

FIG. 19 is an aberration diagram at a photographing magnification of 0.1 × in Numerical Example 5 of the present invention.

FIG. 20 is an aberration diagram at a photographing magnification of 0.5 in Numerical Example 5 of the present invention;

FIG. 21 is a sectional view of a lens according to a numerical example 6 of the present invention.

FIG. 22 is an aberration diagram for an infinitely distant object according to Numerical Example 6 of the present invention.

FIG. 23 is an aberration diagram at a photographing magnification of 0.1 × in Numerical Example 6 of the present invention.

FIG. 24 is an aberration diagram at a photographing magnification of 0.5 in Numerical Example 6 of the present invention;

[Explanation of symbols]

 G1 to G4 Lens SP Aperture d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane FSP Fixed aperture IP image plane

Claims (4)

[Claims] 1. A positive meniscus lens G1 having a concave surface facing the object side from the object side, a positive lens G2 having a convex surface facing the object side, a negative lens G3 having both lens surfaces concave, and a A photographic lens comprising four groups of four positive lenses G4 having convex surfaces. 2. The materials of the lenses G2, G3 and G4 have refractive indices N2, N3 and N4, respectively.
When the Abbe numbers are V2, V3, and V4, respectively, 1.65 <(N2 + N4) / 2 <1.9 1.70 <N3 <1.9535 <(V2 + V4) / 2 <6020 <V3 <30 2. The photographing lens according to claim 1, wherein a condition is satisfied. 3. Assuming that the radius of curvature of the lens surface on the object side of the lens G1 is R and the focal length of the entire lens system is F, the following condition is satisfied: 0.3 <| R / F | <0.7. 3. The photographing lens according to claim 1, wherein: 4. When the focal length of the lens G1 is F1 and the focal length of the entire lens system is F, the condition of 0.05 <F / F1 <0.35 is satisfied. Shooting lens.