JPH03240010A - Compact photographic lens - Google Patents

Abstract

PURPOSE:To obtain this compact photographic lens by arraying four lens groups which have a positive, a negative, a positive, and a negative refractive indexes in order from an object side in a specific state and satisfying specific conditions. CONSTITUTION:The photographic lens is equipped with the 1st positive meniscus lens I which has a convex surface on the object side, the 2nd biconcave lens II, the 3rd biconvex lens III, and the 4th negative meniscus lens IV which is convex to the image plane side in order from the object side. A diaphragm SP is arranged between the 2nd lens II and 3rd lens III and inequalities I and II are satisfied, where F123 is the composite focal length of the 1st - 3rd groups I - III, F4 is the focal length of the 4th group IV, and F is the focal length of the whole system. The lens is constituted by using only spherical surfaces without using any aspherical surface and off-axis aberrations such as a spherical aberration, distortion of field, and astigmatism are compensated with good balance even for wide-angle photographying while the overall length of the lens is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of use in tlj industry) The present invention relates to a compact photographic lens, and particularly to a telephoto ratio (
Tele ratio) is 0.98! The present invention relates to a compact photographic lens suitable for photographic cameras, still video cameras, etc. with a short lens Ii (distance from the lens surface to the image plane), a short photographing angle of view of 64 degrees, and an F number of about 4.

(Prior Art) Recently, with the miniaturization of cameras, various compact photographic lenses with short overall lens lengths have been proposed. For example, Japanese Patent Laid-Open Nos. 56-59217 and 58-57106 disclose a compact photographing lens with a short overall length of the lens, which has a small ratio of the focal length to the total length of the lens, the so-called telephoto ratio, and has about four lenses. , Japanese Patent Publication No. 59-137
This method has been proposed in Japanese Patent Publication No. 916, Japanese Patent Application Laid-open No. 178419/1980, and the like. The photographic lenses proposed in these publications are, in order from the object side, a positive lens with a convex surface facing the object side, a negative lens with concave surfaces on both lens surfaces, and a triplet system consisting of a positive lens with a convex surface facing the image side at the rear. The lens is a telephoto type consisting of four lenses, with a meniscus-shaped negative lens pointing towards the camera.

(Problems to be Solved by the Invention) In general, when trying to shorten the total length of the lens by reducing the number of lenses to about 4, and at the same time widening the shooting angle of view to 60 degrees or more, higher-order aberrations occur. It appears in the book written by gJl. In particular, distortion aberration and astigmatism worsen, and Tsuma aberration and halo also increase, making it difficult to obtain good optical performance over the entire screen.

For this reason, in the photographic lens proposed in the above-mentioned Tani Publication, some lens surfaces in the lens system are made aspherical to prevent the optical performance from deteriorating as the angle of view becomes wider.

However, using an aspherical lens to achieve a certain optical performance (
In order to do this, a highly accurate aspherical surface is required, and in general, it is very difficult to obtain an aspherical shape with high precision in terms of processing, and large M production is also difficult.

By appropriately setting the lens shapes of the four lenses, the present invention does not use aspherical surfaces, and uses only spherical lenses to achieve an angle of view of 65 degrees, an F number of about 4, and a telephoto ratio of 0.9, resulting in a short overall length of the lens. The objective is to provide a compact photographic lens with high optical performance over the entire screen.

(Means for Solving the Problems) The compact photographic lens of the present invention includes, in order from the object side, a positive meniscus lens with a convex surface facing the object side, a second lens whose lens surface is concave, and a second lens with a concave surface. It has four lenses: a third lens with a convex lens surface, and a meniscus-shaped negative fourth lens with a convex surface facing the image plane, and an aperture is disposed between the second lens and the third lens. , the combined focal length of the first to third groups is F123, and the fourth detailed focal length is F4.
, when the focal length of the entire system is F, 0.4<F123/F<0.6...(1)0,
4<-F4/F<0. 8 ・・・・・・・・・ (2
) is characterized by satisfying the following conditions.

(Example) FIG. 1 is a sectional view of a lens according to a numerical embodiment of the present invention.

In the figure, ■ is a meniscus-shaped positive lens with a convex surface facing the object side, I+ is a negative second lens with both concave lens surfaces, ■ is a positive third lens with both lens surfaces convex, and ■ is an image A meniscus-shaped negative fourth lens SP with a convex surface facing the front side is a diaphragm, and is arranged between the second group (2) and the third group m.

In this example, as shown in Fig. 1, the aperture SP is placed between the second and third groups, and the effective diameters of the lenses of the first and fourth groups are approximately the same, thereby achieving a wide angle of view. This effectively prevents the overall size of the lens system from increasing.

The first lens group eliminates spherical aberration, field curvature, astigmatism, and other off-axis aberrations that often occur when a photographic lens is configured with only a spherical system without using an aspherical surface to achieve a wide angle of view. Combined focal length up to the 3rd group 1IIF123 and focal length of the 4th group @F
By setting 4 as in conditional expressions (1) and (2), the overall lens length can be shortened and corrected in a well-balanced manner.

In other words, the entire lens system is a telephoto type, the overall length of the lens is shortened, and the refractive power of each lens group is appropriately set to minimize the amount of off-axis aberrations generated when widening the angle of view. ing.

Conditional expression (1) appropriately sets the combined refractive power of the first to third groups, and together with conditional expression (2), the entire lens length is adjusted so that the entire lens system becomes a telephoto type with an appropriate refractive power arrangement. This is mainly to correct for spherical aberration and off-axis aberration, while shortening the time.

From the first group to the third group beyond 1IlthI under conditional expression (1)
If the combined refractive power from the first group to the third group becomes too strong, the overall length of the lens will be shortened, but the spherical aberration will be insufficiently corrected. If the angle of view increases, the curvature of field will increase, which is not good.

Conditional expression (2) is used to appropriately set the refractive power of the fourth lens group, and, together with conditional expression (1), is used to reduce the overall length of the lens and to satisfactorily correct off-axis aberrations.

If the negative refractive power of the fourth group becomes too strong by exceeding the lower limit A1 of conditional expression (2), the lens will become a telephoto type, and the overall length of the lens will become shorter, or the aberration change due to the difference in eccentricity in the lens assembly will increase. Therefore, it is not good, and if the negative refractive power of the 4th group exceeds the upper limit and becomes weaker, the overall length of the lens will increase, and the Petzval sum will increase in the positive direction, causing a curve to the image plane in the middle of the screen. It is not good if it increases in a negative direction.

In addition, in this embodiment, in order to effectively correct astigmatism and field curvature, the radius of curvature of the first lens surface counted from the object side should be R1! <lR3/F|<1.7 It is preferable to satisfy the following condition (3).

Conditional expression (3) relates to the radius of curvature of the object-side lens surface of the second lens, and is intended to correct spherical aberration and astigmatism in a well-balanced manner at t. If the radius of curvature becomes too strong by setting the lower limit A [^], coma flare will occur from the intermediate angle of view to the periphery of the screen, and if the radius of curvature becomes too weak by setting the F limit, astigmatism will become negative. This is not good because it increases the thickness in the direction of , and IE becomes insufficient to compensate for spherical aberration.

Conditional expression (4) relates to the lens shape of the fourth lens and is intended to satisfactorily correct field curvature to 1-.

If the radius of curvature of the lens surface on the object side becomes too loose after exceeding the limit I^, the Petzval sum will increase in the positive direction, and the field curve will become negative. limit fI
If the curvature r'-radius R7 of the lens surface on the object side becomes too strong beyond rL, the Petzval sum will conversely increase in the negative direction, and the field curvature will increase in the positive direction, which is not good.

In the present invention, focusing may be performed by extending the entire lens system, or by extending the T1 group to the third group as one unit, or by moving only the fourth group.

Next, numerical examples of the present invention will be shown.
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and ν1 are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Several fth embodiment 1 f-34, mouth 1 FNO=4, 1 2ω-64, 9' R1= 211 3- 4- 5- 6- R 8 depth 8, 691 23, 909 -43.509: 11. 757 18, 471 -28.087 -6, 147 -12.641 DI- 2.560 D 2- 1.041 D 3- 1.088 D4 double 2.87 D 5- 2.089 D6 haze 5.032 D 7- 0.847 N 1-1.622992 N 2-1.846658 N : l-1.592701 N4 虞1.540720 ν t- 58.15 ν 2- 23.89 ν 3- 35.30 ν 4 ．． 47.23 F123/F- 1F4/F- IR3/Fl depth 0, 572 0, 682 1, 28 Tele ratio - 0, 93 Numerical example 2 f section 33.99 FNO-4, 02ω-65,
0" Numerical Example 3 f-34, OFNO-4, 0 2ω proverb 64.9" 9.657 27.439 1:15. ]52 28.732 19.442 -26.315 -6.750 -11.703 2.736 1.247 0.850 :1.038 1.860 5.860 0.967 1.1i96797 1.846658 1. 664459 1.816000 ν0 55.53 2:1.89 :lS, 81 46, 62 9.266 zs, 5oa -45,862 25, 670 18,682 -27,958 -6,545 -11,508 2, 831 1,089 1,0:10 2.978 2.175 5.094 +, 08O 1,696797 1,846658 1,636:+58 1.772499 νD 55,53 23.89 35, :18 49.60 FI23 /F-0,564 -F4/F-0,6:t.

IR3/Fl-1,040 FI23/F-0,561 -F4/F-0,638 1R3/Fl-1,:1lI9 Tele ratio -0,93 Tele ratio -0,933 Several 1tl Example f-33, 99 FNO Snow 4.0 9.606 24.580 -55.497 22.459 18.081 -28.884 -6.521 -11.419 F121/F-0,585 -F4/F 0.711 1R3 /Fl-1,633 Tele ratio ~ 0.94 2ω-65,0' 2.352 1.030 1.082 3.068 1.761 5,936 1fi5 1.772499 0 49.6 1.846658 23.89 1.595509 39.21 1.696797 55, 53 (5F, bright effect) According to Unreleased 11, the shape of the four lenses, the aperture, and the refractive power of each lens should be appropriately set as described above. As a result, it is possible to achieve a compact photographic lens suitable for photographic cameras, still video cameras, etc., which has a shooting angle of view of about 64 degrees, a telephoto ratio of about 0.9, a short overall lens length, and good optical performance over the entire screen. can.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention, and FIGS. 2 to 5 are aberration diagrams of Numerical Examples 1 to 4 of the present invention. In the diagram! is the first lens, ■ is the second lens, m is the third lens,
■ is #I4 lens, SP is aperture, d is d line, g is g line,
S is a sagittal image surface, and 1M is a meridional image surface.

Claims (1)

[Claims] (1) A meniscus-shaped positive first lens with a convex surface facing the object side in order from the object side, a second lens with both lens surfaces concave,
It has four lenses: a third lens whose both lens surfaces are convex, and a meniscus-shaped negative fourth lens whose convex surface faces the image plane side, and an aperture is arranged between the second lens and the third lens. Then, the combined focal length from the first group to the third group is F123.
, when the focal length of the fourth group is F4 and the focal length of the entire system is F, the following conditions are satisfied: 0.4<F123/F<0.6 0.4<-F4/F<0.8 A compact photographic lens featuring (2) When the radius of curvature of the i-th lens surface counting from the object side is Ri, 1<|R3/F|<1.7 0.26<|(R7-R8)/(R7+R8)|<0 ．．
2. The compact photographic lens according to claim 1, wherein the compact photographic lens satisfies the following condition: 38.