JPS5885410A - Photographic lens having small total length - Google Patents

Abstract

PURPOSE:To obtain a compact lens system having a small total length, 4.5- 5.6 F number, 61.4 deg. angle of view and about 0.84-0.86 tele photo ratio by using 4 lenses so as to satisfy prescribed conditions. CONSTITUTION:A lens system is composed of the 1st positive meniscus lens having the convex surface at the object side, the 2nd negative lens, the 3rd positive lens and the 4th nonspherical negative meniscus lens having the concave surface at the object side, the lenses are arranged in order from the object side, and conditions 1-3 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact photographic lens that has a longer overall length (from the first lens gap to the focal plane) of the lens system.

In recent years, with the miniaturization of cameras, there has been a demand for compact lenses with short overall lengths. In particular, in order to make the total Jk of the lens system less than 1 times the focal length, it is desirable to configure the Ai1 group of the lens system to have positive refractive power and the rear group to have negative refractive power. Such a refractive power arrangement has conventionally been frequently used in long focal length lenses with a relatively narrow photographing angle of view.

However, although it is 1-7, the overall length of lens systems has become shorter recently, and the angle of view is 60.
It has also been applied to wide-angle lenses such as
Several proposals have been made, including No. 7 and Japanese Patent Application Laid-open No. 56-94317. Although these lenses achieve a telephoto ratio of less than 1x (the ratio of the total length of the lens system to the focal length), they have a telephoto ratio of 1. ff1to is not enough.

This lens was proposed in Japanese Patent Application Laid-open No. 56-99314 as a compact lens for garden use (about 0.86 in telephoto), but this lens is composed of 5 elements in 5 groups, and has 44I1 in 4 groups.
The objective of the present invention is to provide an extremely short and compact lens with 4 elements in 4 groups and an extremely short total -r+.
υVF number in the examples described later]: 4.5. For a lens with an angle of view of 61.4°, the telephoto ratio is 0.86. F number 1: 5.6. The lens has an angle of view of 614° and has a telephoto ratio of 0.84 and 0.85, making it a wide-angle and compact lens.

The features of the lens configuration for achieving the purpose of the present invention are a positive meniscus-shaped first lens with a convex surface facing the object from the object side, a negative second lens, a positive third lens, and a concave surface facing the object side. A fourth lens with an aspherical negative meniscus shape is arranged, and the focal length of the entire system is 1, and the object of the fourth lens is +1.
1! The radius of curvature of the lens surface of 1 is 1 (1, the near-I curvature radius (radius of curvature that contributes to determining the focal length) of the object-side lens surface of the fourth lens is R7, the third lens and the When the air distance with the fourth lens is 1)6, uJ O,13(I + / f < 0.21
(2n -0,16 (J too? / f <
-0,07 (3) 0.05 (1) a/f
< 0.2 Kume 171: is satisfied.

In order to make the telephoto ratio as small as possible in a lens with a refractive power arrangement like that of the present invention, it is necessary to
It is necessary to reduce the refractive power of the front group consisting of lenses and the rear group of the fourth lens.

When increasing the refractive power of the front group, the lens surface R1 on the object side of the second lens, where the off-axis light beam passes through the position with the highest incident height among both lenses, is set to the aperture position 1 [t (second It is preferable to set the radius of curvature of the lens surface so that the center of curvature is located near the lens (located between the lens and the third lens (not shown)) in order to correct various aberrations other than +ll+. 'l
! It is preferable to perform an IF to prevent the zagittal ioplane from being over-corrected in the U direction.

(In this case, when the lens curve is 1, extremely large spherical aberration occurs due to the strong convergence effect of the curve. In order to compensate for this spherical aberration, in the present invention, the object of the fourth lens The radius of curvature is set so that the center of curvature is near the aperture position (a), and at the same time as off-axis aberration correction, a large positive spherical aberration is generated due to a strong divergence effect during one processing step. This balances out the large negative taste I aberration that occurred in R4.

For this reason, if the upper limit of conditional expression (1) is exceeded, the refractive power of the first lens is insufficient (-, the back focus is extended, the overall length of the lens is increased, and it is difficult to achieve a compact size.
Once the limit is exceeded, it becomes difficult to adequately compensate for spherical aberration in the rear group.

Conditional expression (2) is based on the aspheric surface of the rear group. /This is related to the lens surface, and if the limit value of -I- in conditional expression (2) is exceeded, large positive spherical aberration will occur, making it difficult to properly correct it with the +itJ group lens; if the lower limit value is exceeded, the lens The overall length increases, making it difficult to achieve a compact lens.

-ffi If you try to make the nonce thread more compact beyond the F limit of 3), the spherical IMi group will be overcorrected at the peripheral angle of view, and the spherical image plane will be undercorrected at the intermediate angle of view. , even the astigmatism point is violated, and an introverted frame occurs. If the upper limit is exceeded, spherical aberration will be under-corrected and a significantly large halo will occur.Is it possible to achieve the photographic lens aimed at by the present invention with the above configuration, and can further correct various aberrations well? In order to do so, it is preferable to satisfy the following conditions. That is, when the radius of curvature of the lens surface on the image plane side of the first lens is R2, and the focal length of the air lens constituted by the opposing lens surfaces of the second lens and the second lens is fA, then 025 < d? ,,z/f<t,o
(4)-0,5(fh
/ f (-03(5)).

If the upper limit of conditional expression (4) is exceeded, or if the lower limit of conditional expression (5) is exceeded, the sphere will become under-corrected, and the astigmatism will also increase. A sexual piece occurs, and the inclusion bias of the magnification increases in the negative direction, which is favorable.
,+L< nai. Also, conditional expression (4) ノ[IYN +m
'c, or if the upper limit of conditional expression (5) is exceeded, the spherical defective image surface will be overcorrected, the astigmatism will also increase, and strong no-low will occur (~, and the chromatic aberration will also be negative). The PC is getting bigger (not 7).

In addition, in the present invention, in order to achieve compact and excellent aberration correction, it is preferable to determine the shape of the aspherical surface of the fourth lens so as to satisfy the following conditional expression.

The X axis is in the direction of the optical axis, the Y axis is in the direction perpendicular to the optical axis, and the traveling direction of light is positive, and the intersection of the vertex of the lens and X1lII is taken as the origin, and the aspheric surface of the fourth lens and the focal length are determined. The difference in the X-axis direction from the contributing spherical surface is △X, 1t1
Represent the aspheric surface by an expansion formula where is the radius, al is the aspheric 1^ coefficient, and bl is the aspheric compatibility coefficient, and △X at the height of Y coordinates R,X O,7 is △X[0,7Rtl , R7X O,5
When △X at the height of is △X CO, 5R7], (6) I X 1o"<L/\x CO, 7R
7) l < I X 10-2- 1△x (o, 1tt711 (7) I X 10-'<
The conditional expression (l x 1.0-3f) is satisfied.

Conditional expression (6) U: Particularly relates to aberration correction in the peripheral angle of view.

In a lens of the type in which a negative meniscus lens is placed at the rear of the lens system as in the present invention, astigmatism worsens in the negative direction due to this tjt meniscus lens (7 positive distortion, introverted coma, A halo occurs. Conditional expression (6)
This corrects deterioration of astigmatism, positive distortion, introverted coma, and curvature. That is, 1△xCo,
If qR7]/f1 exceeds the lower limit, positive distortion and halo can be corrected, but the spherical defect 1 phenomenon becomes overcorrected and a strong introverted coma also occurs. If the upper limit of 4 is exceeded, positive distortion cannot be sufficiently corrected even if the frame can be reduced. Therefore, conditional expression (6) is important in order to satisfactorily correct the aberration of the peripheral angle of view.

Conditional expression (7) particularly relates to aberration correction at intermediate angles of view.

That is, if 1Δx CO,5R71/fl exceeds the lower limit value, the meridional image plane will be insufficiently corrected at intermediate angles of view, the astigmatism difference will increase, and a strong introverted coma will occur. Moreover, when the upper limit is exceeded, spherical aberration becomes insufficiently corrected, and a halo occurs at intermediate angles of view. Therefore, conditional expression (7) is essential for good aberration correction at intermediate angles of view.

Note that if the aspherical lens of the fourth lens group is manufactured from a synthetic resin material, an inexpensive photographic lens can be provided.

In the invention, since the first surface of the fourth lens using an aspherical surface is placed relatively close to the image plane, the area through which the light flux corresponding to each image point passes through the fourth lens surface is relatively small. It's getting smaller.

For this reason, the surface M degree of the fourth lens surface is considerably relaxed, so that the fourth lens can be finished inexpensively by using a plastic molded product instead of glass fiber.

Focusing may be performed by extending the entire lens, which is generally done, or by fixing the fourth lens and extending the third lens 1 from the third lens.

By determining the lens configuration as described above, it is possible to achieve a compact photographic lens with a short overall lens length and with excellent aberration correction.

Next, examples of the present invention will be shown. In the examples Ri 11
, the radius of curvature of the lens 1)+i is the first lens thickness and air distance in order from the object side, Ni and νi ij: the first lens in order from the object side, respectively. are the refractive index and Atsube number of the lens glass.

aI is an aspheric coefficient, and biI'I' is an aspheric coefficient.

/ 1'/ 111''' /- / Kaji value
15

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a cross-sectional view of a lens corresponding to Example 1 of the present invention.
Figure 2 is an aberration curve diagram. FIG. 3 is an aberration curve diagram of Example 2, and FIG. 4 is an aberration curve diagram of Example 3. In the figure, △trt (ri meridional image plane, △sp is the zagital image plane. Patent applicant Gyanon Co., Ltd.)
(%n positive Yumio Takumi (Igyu)

Claims (1)

[Claims] (1) In order from the object side, a positive meniscus-shaped lens with a convex surface facing the object, and a negative second lens. A fourth lens with an aspherical negative meniscus shape with a concave curve facing the object side is arranged in the positive third lens 1-7, and the focal length of the entire system is set to When the radius of curvature is 1 mo 1 and the paraxial radius of curvature of the object side lens surface of the fourth lens in Mfi is 0.13 (I +/f<0.2i -0,16<Rtr/f<−0,07o,os<
A photographic lens with a short overall length, characterized by satisfying the condition: D6 /f < 02. (2) The radius of curvature of the lens surface on the image side of the lens is R2,
When the focal length of the air lens constituted by the opposing lens surfaces of the first lens and the second lens is f, 0.25 < R, 2/ f < i. -0,5<fA/f<-0,3.
A photographic lens with a short overall length as described in the section. (3) X axis in the optical axis direction, Y l1l in the direction perpendicular to the optical axis
l. With the traveling direction of light as positive and taking the intersection of the apex of the lens and the X-axis as the origin, the difference in the X-axis direction between the aspherical surface of the fourth lens and the extended spherical surface that contributes to determining the focal length. △X,
l is the radius of curvature of the single surface + at is the even coefficient of the aspherical surface + bl is the non-spherical
− Spherical odd coefficient and (− Express the aspheric surface by the expansion formula L=, Y coordinate &×07 height, △X[0,7R7], R7X0.5 height ([ Claim 1 is characterized in that it satisfies the following condition, when ΔX is ΔX CO,5Ry ”]
No. 1 Item 1: Self-mounted photographic lens with a short overall length.