JPS60218614A - Image forming lens - Google Patents

Abstract

PURPOSE:To obtain a wide-field-angle photographic lens which has various aberrations compensated excellently by isuing two distributed index lenses. CONSTITUTION:This lens consists of two lenses which vary in refractive index continously with the distance from the optical axis. The 1st lens arranged at an object field side is thickest on the optical axis, and becomes thinner and thinner according to the distance from the optical axis, and the refractive index distribution has the largest refractive index on the optical axis and decreases in refractive index according to the distance from the optical axis. The 2nd lens arranged at the image field side is thickest on the optical axis and increases in thickness according to the distance from the optical axis, and its refractive index distribution has the maximum refractive index on the optical axis and decreases in refractive index according to the ditance from the optical axis. The 1st and the 2nd lens both have positive power; and the object-field side surface of the 1st lens is convex to the object field side and the object-field side of the 2nd lens is concave to the object field side.

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the refractive index gradually changes around the optical axis in a plane perpendicular to the optical axis.

The present invention relates to an imaging lens that uses a medium having a so-called refractive index distribution and is suitable for, for example, a photographic lens.

Conventionally, most imaging lenses are constructed using a medium with a uniform refractive index, such as a half-field angle of 25° FNOl, 4
-1.8fj! If (FIHIIy, (a) A configuration with 6 to 7 homogeneous medium lenses as seen in photographic lenses is a must.If it is possible to configure this with a smaller number of lenses, lens processing This is extremely advantageous in that it reduces the labor required for manufacturing, simplifies the lens holding mechanism, and reduces the number of intervening factors such as eccentricity and other manufacturing errors.

However, with the prior art, it is extremely difficult to reduce the number of lenses compared to the current state while maintaining good optical performance.

On the other hand, in recent years, gradient index lenses have attracted attention as a new optical technology, such as play lenses used as positive and vertical equal-magnification collimation elements, t-collimator lenses that take into account only near-on-axis imaging, and optical disc lenses. Many applications have been proposed for pickup lenses, etc., and the paper by Atklnson et al.
(1982)).

Application to photographic lenses has been reported. This photographic lens is composed of two graded refractive index lenses.On the object side, there is a surface that is thinnest on the optical axis, increases in thickness as it moves away from the optical axis, and is convex toward the object side. The first lens has a nine-meniscus shape and has a refractive index distribution in which the refractive index is highest on the optical axis and the refractive index value decreases continuously as it moves away from the optical axis. It has the thinnest wall thickness on the optical axis and increases in thickness as it moves away from the optical axis, and has a meniscus shape with a convex surface facing the image field side.It also has the highest refractive index on the optical axis and moves away from the optical axis. A second lens having a refractive index distribution in which the refractive index value continuously decreases according to -21 is arranged, and with this configuration, a standard lens of 11 to 2 is obtained. The number of lenses is significantly reduced compared to that of the original model.

Other than this report, there are hardly any examples of applying a gradient index lens to an imaging lens having a relatively large angle of view.

An object of the present invention is to provide an imaging lens that uses a medium with a refractive index distribution, and that has aberrations well corrected despite being composed of an extremely small number of lenses, and that has a wide angle of view that can be applied to photographic lenses, etc. It is said to provide.

In the imaging lens system according to the present invention, the distance from the optical axis @
It is formed by two lenses made of a medium whose refractive index continuously changes according to the change in refractive index. The shape of the first lun arranged on the material world side is such that the maximum wall thickness is thick on the optical axis, and the wall thickness decreases as it moves away from the optical axis (hereinafter, in this specification, such a shape will be referred to as The refractive index distribution has the smallest refractive index on the optical axis, and the refractive index value increases as it moves away from the optical axis (hereinafter referred to as a refractive index with negative refractive power). rate distribution). On the other hand, the second
The shape of the lens is such that it is thinnest on the optical axis and increases in thickness as it moves away from the optical axis (hereinafter, such a shape is referred to as a concave shape), and its refractive index distribution is as follows: It has a distribution in which the refractive index is highest on the optical axis and decreases as it moves away from the optical axis (hereinafter referred to as a refractive index distribution with positive refractive power). ,.

The □power level of the above-mentioned gradient index lens is determined by the mutual relationship between the state of the refractive index distribution and the lens shape. □It is desirable that both of the second lenses have positive power. Further, as for the shape, it is desirable that the surface of the second lens on the material world side be convex toward the material world side, and that the surface of the second lens on the material world side be concave toward the material world side.

The present invention will be explained in detail below. □ □The refractive index N (r) of a so-called radial gradient lens, which forms the imaging lens of the present invention and whose refractive index N changes depending on the distance #rK from the optical axis, such as the y-z element, is (r) mH0+H, r"4-M, r'+Hsr"
It is expressed as +---□. However, N. e'1 #N
鵞e "I..." is a constant, and "R" represents the distance from the optical axis. A lens with such a distribution has the following characteristics.

(1) The refractive index distribution itself has refractive power, so there is a large degree of freedom in design in the paraxial region.

(2) The refractive index distribution has a contribution to the Petzval sum. When a positive refractive power is added to the refractive index distribution, its contribution to the Petzval sum is small compared to when the refractive surface has an equivalent refractive power. year.

It is relatively easy to correct the surface curvature.

(3) It has an aberration-correcting effect similar to that of an aspherical surface. That is, it is possible to control the gambling aberration within a certain range by using the fourth-order or higher distribution coefficients (M, , N, . . . ) without affecting the paraxial tK.

(4) Has an achromatic effect. That is, since the wavelength dependence of the second-order coefficient Mm has four effects on the chromatic aberration coefficient, it is possible to control nine chromatic aberrations.

The line of the present invention takes advantage of these features and adopts a first-order configuration.That is, the shape of the first lun on the material world side is convex, the shape of the concave lens on the information world side is concave, and The refractive power of the refractive index distribution of the second lens is negative, and the refractive power of the refractive index distribution of the second lens is positive.

As already mentioned, it is more advantageous for correcting the curvature of field to share positive refractive power with the outer refractive index cloth.

Therefore, in the present invention, the refractive index distribution of the second lens is given a strong positive refractive power to reduce the positive contribution to the Petzval sum. Furthermore, by making the shape of the second lens concave,
In addition to correcting the field curvature by waiting for its negative contribution to the Petzval sum, other aberrations such as spherical aberration are also corrected.

In this case, in order to correct off-axis aberrations, it is preferable to make the surface on the object world side a concave surface, and in order to correct spherical aberrations etc. by the aspherical effect of the distribution, the fourth-order distribution coefficient N, It is desirable to have a positive value.

In general, since the second lens has a relatively strong positive refractive power as a whole, spherical aberration can be prevented from being under-corrected. This is corrected by the outer refractive index distribution of the negative refractive power of the second lens. In this case, for aberration correction, it is desirable to set the fourth-order distribution coefficient N to a positive value.

In order to perform even better aberration correction, it is desirable that the following conditions be satisfied.

1≦r 1 / f≦2.9 (1) −042≦r, / f≦−o, s s (2) 0.5
≦t1. /f≦o,s (3)0.28≦(1,/f
≦0.55 (4) In particular, the focal length of the entire fl-i system, r
t+rs is the 1st radius of the first WEB surface as counted from the object side, that is, r.

is the radius of curvature of the object-world side of the second lens, r is the radius of curvature of the object-world side of the second lens, al is the axial thickness of the second lens, and d is the axial thickness of the second lens.

When r@/f exceeds the lower limit of conditional expression (1), the spherical aberration generated on the object-world side surface of the #11 lens becomes large9, making it difficult to correct it in the entire system. 5 of off-axis rays when the upper limit is exceeded.
[The refraction on the surface of the lens on the object side increases9, and off-axis aberrations worsen.

When r, /f exceeds the lower limit of (2), the Petzval sum becomes large, making it difficult to correct field curvature. The occurrence is large, especially spherical aberration, coma conditional expressions (5), (4)
is a condition regarding lens thickness.

If a, , a3 exceeds the lower limit of conditional expressions (5) and (4), the refractive power distribution of each lens will be strong, 9 various aberrations will worsen, and it will be difficult to manufacture the medium. 3), (
If the upper limit of 4) is exceeded, the entire system will become larger.

Table 1 shows the lens data of the first to seventh embodiments of the present invention. Each embodiment has a half angle of view of 24°, and Example 1°2 has an F' angle of 1.
．． 8. In other embodiments, the FA is 1.4 and the focal length is normalized to 1.

The values of the third-order spherical aberration coefficient 1, coma aberration coefficient 1, astigmatism coefficient value, Petzval sum P, and distortion aberration coefficient V at high speed are shown. As seen in the table, the speech aberration coefficients of each example are well corrected.

1st. In the third and fourth embodiments, the shape of the second lens is a biconvex shape, the shape of the second lens is a meniscus shape with a concave surface facing the object world side, and #! In the second example, the shape of the second lens is a meniscus shape with a convex surface facing the material world, and the shape of the second lens is a plano-concave shape with a concave surface facing the material world. The shape is a biconvex shape, the shape of the second lens is a plano-concave shape with a concave surface facing the object world side, and in the sixth embodiment, the shape of the second lens is a plano-convex shape with a convex surface facing the object world side. ! The shape of the second lens is a plano-concave T-shape with the concave surface facing the object world side. In the seventh embodiment, the shape of the second lens is a biconvex shape, and the shape of the ls2 and y lenses is a plano-concave T-shape with the concave surface facing the object world side. It has a sinusoidal shape. When processing a medium with a refractive index distribution into a spherical surface, the processing must be performed without eccentricity with respect to the light determined by the outer refractive index distribution, which is harsher than the conventional spherical processing of a homogeneous medium. Therefore, it can be said that the second, fifth and sixth embodiments, in which one side of the lens is flat, are highly effective in terms of mass production.

Table 1 I91 Fifth license fee II! 4th Example 5th Example 6th Example m7 Example 1 Table 3 shows the lens data of *-8-Example of the present invention, and Table 4 shows the lens data of 3. The values of the following various aberration coefficients and longitudinal chromatic aberration coefficient 1x chromatic aberration coefficient T are postulated.This example is an example in which chromatic aberration is corrected.
The order aberration coefficient and the QK chromatic aberration coefficient l are also well corrected. Fig. 1 shows a cross-sectional view of the lens of this eighth embodiment, and Fig. 2 (
A) The refraction main st corresponding to the d@ and g@ of the first runes,
M 2 Figure (B) JCg 2. v y Sf) d4I
, g @lc showed the corresponding refractive index distribution, and the third
The figure is a diagram showing various aberrations of the eighth embodiment, and it can be seen that aberrations are well corrected up to high orders.

Table 2 Furthermore, when correcting chromatic aberration, since the chromatic aberration caused by refraction of one surface is corrected by adjusting the refractive index distribution, it is desirable that the following conditions be satisfied.

``IGI 1'') < ``l G 1 (g)''1(1
2('')〉N+Gz (g) However, ' IGI ('')-'' lG2 (g) is 1 each
141. Represents the quadratic distribution coefficient of the refractive index distribution of the luns for gllK, '+,z(''), NIC,2(g
) represents the quadratic distribution coefficient of the refractive index distribution of the second lens for the d-line and 1g-line, respectively.

As explained above, in the present invention, by using a medium having a radial gradient, a condensing elephant lens with excellent correction of various aberrations can be realized with an extremely small number of lens components of 2. We were able to.

[Brief explanation of the drawing]

FIG. 1 is a lens cross-sectional view of one embodiment of the Yuri lens according to the present invention, and FIGS. 2 (A) and (B) respectively show the refraction of each lens forming the YURIN lens shown in FIG. The diagram showing the rate distribution, Figure @3, is the conclusion shown in Figure 1. Diagrams of various aberrations of the monk lens. γ1... Radius of curvature of the first lens surface counting from the object world side d1... Axial thickness or axial air gap between the first lens surface and the 1st+1st lens surface 80 ...Sine condition dissatisfaction amount M..., meridional my side S00. Sagittal image surface R

Claims (1)

[Claims] (1) The refractive index changes continuously according to the distance from the optical axis.
It is formed by two lenses made of a changing medium, and the first lens placed on the object world side has a refractive index distribution in which the refractive index increases as it moves away from the optical axis, and its shape is similar to the optical axis -
It has a shape in which the wall thickness □ is the thickest in H, and the thickness decreases as it moves away from the optical axis, and the second lens placed on the outside side has a refractive index distribution whose refractive index decreases as it moves away from the optical axis. An imaging lens having a shape that is thinnest on the optical axis and increases in thickness as it moves away from the optical axis.