JPH10333027A - Image forming lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming lens whose F number is small and which can form a bright image. SOLUTION: The image forming lens is constituted by arranging a first group G1 including one positive refracting lens 10 in which a diffraction lens surface is formed on the lens surface 10b of an image side and a second group G2 which is provided with parallel flat plates 10 and 21 and which is hardly provided with power in order from an object side. The lens 10 of the group G1 is constituted as a positive meniscus lens whose both surfaces are spherical and which is convex to the object side. Besides, the first surface thereof on the object side is spherical and provided with action for correcting astigmatism. The second surface thereof on the image side is spherical and provided with action for correcting a spherical aberration and the high-level curvature of an image surface. At this time, the lens 10 satisfies the condition of 0.64<r1×r2/ f(n1-1)<2> ×d1<1.60. Provided that, r1 and r2 are the radiuses of the curvature of the first and the second surfaces of the lens 10, (f) is the focal distance of the whole system and n1 and d1 are the refractive index and the lens thickness of the lens 10 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens used as an inexpensive camera photographing lens and the like, and more particularly, to a half angle of view of about 20 DEG combining a single lens and an optical element having almost no power. It relates to an imaging lens.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 1-219813 discloses a photographic lens in which one meniscus lens having an image forming action is combined with an optical element having almost no power. The meniscus lens has an aspheric surface on both surfaces, and the optical element having almost no power is formed as a plane-parallel plate or a curved surface having an aspheric component on one surface.

[0003]

However, in the photographic lens disclosed in the above-mentioned Japanese Patent Laid-Open No. 1-29813, a single meniscus lens bears almost all of the power as an imaging lens. Axial chromatic aberration cannot be corrected satisfactorily.
The axial chromatic aberration generated in proportion to the aperture (by increasing the F number) is made inconspicuous. Therefore, there is a problem that the formed image is dark. The F-number of the photographic lens of the embodiment described in the official gazette is 8.

[0004] The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide an imaging lens capable of forming a bright image having a small F-number.

[0005]

In order to achieve the above object, an imaging lens according to the present invention includes, in order from an object side, a first group including one refracting lens having a positive power; In the imaging lens constituted by arranging the second group having almost no power, the refracting lens is a meniscus lens whose both surfaces are aspherical and convex on the object side.
A diffractive lens surface for correcting chromatic aberration of the refractive lens is formed on at least one surface of the group.

[0006] Since a positive diffractive lens with respect to dispersion is equivalent to a refractive lens having a negative Abbe number, chromatic aberration can be corrected by combining this with a positive refractive lens, and a bright lens having a small F-number can be obtained. Obtainable.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the imaging lens according to the present invention will be described. For example, as shown in FIG. 1, the imaging lens according to the embodiment includes one positive refraction lens 10 having a diffractive lens surface formed on a lens surface 10 a on the object side in order from the object side on the left side in the drawing. A first group G1 and a substantially powerless second
The group G2 is arranged.

The refractive lens 10 of the first group G1 is configured as a positive meniscus lens convex on the object side, and the stop S is disposed on the image side. This configuration is of a type that generates a small amount of astigmatism as a single lens imaging system. The refractive lens 10 is a double-sided aspherical surface. The first group of diffractive lens surfaces is
An optical element 11 having almost no power is formed on the lens surface 10a or 10b of the refractive lens 10 or on the object side of the refractive lens 10 as shown in the example of FIG. It is formed. As the second group G2, a plane-parallel plate or the like is used. The second group G2 may also be used as a low-pass filter, a cover glass, a beam splitter, and the like, and includes a single element or a plurality of elements.

Further, the imaging lens of the embodiment is formed by increasing the distance between the first surface (convex surface) 10a and the second surface (concave surface) 10b of the refractive lens 10, and By making the radius of curvature close, the Petzval sum of the positive lens approaches zero, thereby suppressing the occurrence of field curvature.

If the curvature radii of the first surface 10a and the second surface 10b are exactly the same, the Petzval sum can be made zero, but even if the Petzval sum becomes zero, a higher-order field curvature component and Astigmatism remains. In order to comprehensively suppress the occurrence of these aberrations, it is desirable to set the Petzval sum to a value that takes a positive value slightly larger than 0. For this purpose, the Petzval sum is set so as to satisfy the following condition (1). It is desirable. 0.64 <r1 * r2 / (f (n1-1) ² * d1) <1.60 (1)

Here, r 1 and r 2 are the first values of the refractive lens 10.
The radii of curvature of the surface 10a and the second surface 10b, f is the focal length of the entire system, and n1 and d1 are the refractive index and the lens thickness of the refractive lens 10, respectively. When the value is below the lower limit of the condition (1), the field curvature is overcorrected, and when the value exceeds the upper limit, the field curvature is undercorrected. When the allowable width for aberration is stricter, it is preferable to satisfy more strict condition (2). 0.70 <r1 × r2 / (f (n1-1) ² × d1) <1.25 (2)

In order to make the Petzval sum close to zero without increasing the lens thickness d1, the refractive lens 10
It is desirable that the refractive index n1 is higher, specifically, it is desirable to satisfy the following condition (3). n1> 1.6 ... (3)

Since there is no plastic material having a high refractive index, it is desirable to use glass for the refractive lens 10. When a diffractive lens surface is formed on the lens surface of the refractive lens 10, it is desirable to use a glass mold technique. Forming a positive lens with a glass mold is less affected by changes in the environment such as temperature and humidity. Therefore, it is suitable when a lens with a short focal length is used in a system in which focus cannot be adjusted.

In order to correct higher-order field curvature, it is required that light beams transmitted through different positions on the first surface 10a of the refracting lens 10 enter the stop S at different angles. Therefore, the first surface 10 of the refractive lens 10
It is desirable that the chief rays incident on the same position of a at different angles of incidence be guided to different positions on the aspherical second surface 10b. Therefore, the thickness of the refraction lens 10 should be set to a certain value or more. It is required that there be. The following conditions (4)
Is a condition relating to the lens thickness d1 so that the effect of the aspheric surface of the second surface can be sufficiently utilized. 0.17 <d1 / f (4)

When the value falls below the lower limit of the condition (4), the lens thickness d1 is smaller than the focal length f, so that the incident position on the second surface 10b is substantially equal to the incident position on the first surface 10a. The amount of change of the incident position on the second surface 10b according to the incident angle becomes too small as described above,
The independence of the first surface 10a and the second surface 10b with respect to aberration correction is reduced, and high-order field curvature cannot be satisfactorily corrected.

On the other hand, considering the balance with the thickness of the second lens unit G2 and the securing of the back focus, d1 /
It is desirable that the value of f be smaller than the upper limit shown in the following condition (5). d1 / f <0.40 (5)

Since the first lens unit G1 is composed of a single lens having a rear stop, positive distortion remains. This distortion is the second
This can be suppressed by increasing the thickness of the group G2. For this reason, the second group G2 also requires a certain thickness. If the lens thickness d1 of the refractive lens 10 exceeds the condition (5), the correction of the distortion becomes insufficient or the back focus cannot be sufficiently secured.

In a rear stop single lens type imaging lens like this embodiment, when the half angle of view is 10 ° or more, the effect of astigmatism becomes remarkable, and the curvature of field in the meridional direction becomes excessive. There are characteristics. For this reason, in order to configure a lens having a wide angle of view, the refractive lens 1
It is necessary that the 0 aspherical surface has an action to correct astigmatism. In order to correct spherical aberration with a single lens,
An aspheric surface is essential. The aspheric surface for correcting astigmatism has a component in the direction in which the positive power of the lens increases from the center to the periphery, and the aspheric surface for correcting spherical aberration extends from the center to the periphery. Has a component in the direction in which the positive power of becomes weaker.

In order to improve the performance of both astigmatism and spherical aberration with a single aspherical surface, the half field angle is limited to about 15 °. Therefore, the imaging lens of this embodiment is configured so that both surfaces of the meniscus refraction lens 10 are aspherical to correct spherical aberration and astigmatism. That is, the first surface 10a on the object side of the refraction lens 10 is an aspheric surface having an action of correcting astigmatism, and the second surface 10b on the image side
Is designed as an aspherical surface having the function of correcting spherical aberration.

As described above, in order to reduce the occurrence of astigmatism, the stop S is disposed on the image side of the refracting lens 10. On the other hand, since the lens thickness d1 is relatively large, the first
The distance between the surface 10a and the stop S is also relatively large, and the incident position of the principal ray on the first surface 10a greatly changes depending on the angle of view. Therefore, it is desirable that the first surface 10a has a function of correcting particularly high-order astigmatism. The aspherical surface of the first surface 10a is given a sign with positive deviation from the spherical surface defined by the paraxial radius of curvature to the image plane side, and the sag amount is a power series expansion as a function of the height from the optical axis. In this case, at least the fourth-order coefficient is positive, and is defined as a surface having a fourth-order or higher positive coefficient.

On the second surface 10b, the light beam is directed to the first surface 10a.
, The overlap between the on-axis ray and the marginal ray increases, and it is difficult to selectively correct higher-order astigmatism. Therefore, an aspheric surface having an action of correcting spherical aberration is formed on the second surface 10b. Since the incident height of the marginal ray is reduced by the positive power of the first surface 10a, it is necessary to introduce an aspherical component to the second surface 10b at a higher rate than the first surface 10a.

The aspherical component of the concave second surface 10b is:
This is a component whose curvature becomes steeper than the paraxial spherical surface as the distance from the optical axis increases, and acts to weaken the positive power of the refractive lens 10 by increasing the negative power toward the periphery. The aspherical surface of the second surface 10b is given a sign with the deviation from the spherical surface defined by the paraxial radius of curvature to the image surface side being positive, and the sag amount is a power series expansion as a function of the height from the optical axis. In this case, at least the fourth-order coefficient is positive, and this fourth-order coefficient is the fourth coefficient of the first surface 10a.
Defined as a surface with a value greater than

The diffractive lens surfaces included in the first group G1 include:
An effect of mainly correcting axial chromatic aberration is provided. The phase type diffractive lens surface is constituted by a plurality of concentric annular zones centered on the optical axis. A diffractive lens has a dispersion characteristic of the opposite sign to a refractive lens and is equivalent to a refractive lens having a negative Abbe number, so by combining a refractive lens with positive power and a diffractive lens with positive power. Chromatic aberration can be corrected.

When the optical element 11 having almost no power is arranged on the object side of the refractive lens 10 and the diffractive lens surface is formed on the surface 11b of the element 11 as in the example of FIG. Can be constituted by a plane perpendicular to the optical axis. In this case, the macroscopic shape of the diffraction lens surface is concave. Similarly, it is also possible to form a Fresnel lens type diffractive lens surface in which each ring zone is not perpendicular to the optical axis. In this case, the macroscopic shape of the diffraction lens surface is a plane. In any case, the diffractive lens surface should be formed on the image-side (refracting lens 10 side) surface 11b so that the axial chromatic aberration corrected by the diffractive lens surface does not result in overcorrection of lateral chromatic aberration. Is desirable.

Next, a description will be given of the setting of a step for each ring zone of the diffraction lens surface and the difference in diffraction efficiency due to the setting. The additional amount of the optical path difference due to the parallel plane plate having a thickness t arranged perpendicular to the optical axis is as follows: wavelength is λ, incident angle to the parallel plane plate is θ, and refraction angle in the parallel plane plate is θ ′. , The refractive index of the medium before entering the plane-parallel plate is n, and the refractive index of the plane-parallel plate is n ′.
As t (n'cosθ'-ncosθ) / λ. The step t1 for providing a phase difference corresponding to the wavelength is represented by the following equation (A). t1 = λ / (n′cosθ′−ncosθ) (A) The step t1 is a step in the normal direction of the surface on which the diffraction grating is formed, and when the diffraction grating is formed on a curved surface. Is the step in the direction of the normal to the curved surface, or the step in the direction of the optical axis when the diffraction grating is formed on a plane perpendicular to the optical axis.

Therefore, when the light beam is incident perpendicularly to the surface, the gap t in the direction of the optical axis between the adjacent orbicular zones is expressed by the following formula: t = blade wavelength λ0, refractive index at lens wavelength λ0 n0 It is determined by λ0 / (n0-1). Thereby, the diffraction efficiency with respect to the light of wavelength λ0 becomes 100%.

When the refraction angle θ ′ in the above equation (A) is replaced with the incident angle θ and approximated, the following equation (B) is obtained. t1 ≒ (λ / (n′−n)) × (1−0.5nθ ² / n ′) (B)

From this equation (B), it can be understood that as the incident angle θ increases, that is, as the angle of view of the incident light beam increases, the step t1 for giving a phase difference corresponding to the wavelength decreases. Therefore, when the diffractive lens surface is arranged in an optical system having an angle of view, in order to increase the diffraction efficiency for each angle of view, it is necessary to make the step smaller than when the incident angle θ is 0. For example, assuming that a light beam having a refractive index of 1.7 and an incident angle range of ± 24 ° is incident on the center of the surface of the diffractive lens, the above equation (A) indicates that the on-axis light beam having an incident angle of 0 ° is obtained. It can be seen that there is a difference of about 5.3% between the optimal step and the optimal step for a marginal ray at an incident angle of 24 °.

In order to increase the average value of the diffraction efficiency over the entire range of the incident angle, assuming a specific reference incident angle θ0, a step is formed so that the diffraction efficiency with respect to the light beam incident at the reference incident angle θ0 is maximized. You only have to decide. As a method for obtaining the reference incident angle θ0, a first method for obtaining a simple average of the incident angles, a second method for obtaining the area occupied on the image plane according to the incident angle, and a formula for determining the step ( B)
Is determined by the square of the incident angle θ, the third value obtained in consideration of the square of the incident angle and the area occupied on the image plane.
The method is conceivable.

Assuming that there is no distortion at a half angle of view w and the screen is circular, in the first method, the absolute value of the incident angle | θ |
Is 0 and the maximum value is w, and the reference incident angle θ0 =
0.5w. In the second method, the product of the incident angle θ and the length 2πθ of the circle on the image plane formed by the rays incident at the incident angle θ is calculated from the incident angle 0 to the maximum angle of view w
By dividing the value obtained by integrating up to the area πw ² of the circle on the image plane formed by the light rays incident at the maximum angle of view w, the reference incident angle θ0 = 0.667w. In the third method, the product of the square of the incident angle θ and the length 2πθ of the circle on the image plane formed by the light rays incident at the incident angle θ is integrated from the incident angle 0 to the maximum angle of view w. Is divided by the area πw ² of the circle on the image plane formed by the light rays incident at the maximum angle of view w, and the square root thereof is obtained to obtain the reference incident angle θ0 = 0.707w. In the second and third methods, the process of the calculation is shown in the following equations (C) and (D), respectively.

[0031]

(Equation 1)

The step t0 of the innermost ring zone according to the first, second, and third methods is obtained by substituting 0.5w, 0.667w, and 0.707w for θ in the following equation (E). Required by t0 = (λ / (n′−1)) × (1−0.5θ ² / n ′) (E)

When the value of θ is reduced, the diffraction efficiency at the center of the screen increases, and when the value is increased, the diffraction efficiency at the periphery increases. Actually, if it is set to 0.45w <θ <w, which is slightly wider than the range of θ obtained by the above three methods,
Sufficient diffraction efficiency can be obtained at each of the central portion and the peripheral portion of the screen. In this case, the relationship between the step and the wavelength satisfies the following condition (6). −0.5 w ² / n ′ <− ¹ + t 0 (n′− ¹⁾ / λ 0 <−0.1 w ² / n ′ (6) The above condition (6) is qualitatively defined as the vicinity of the center of the diffraction lens. Means that when determined in consideration of the angle of view, the value becomes lower than the value t0 = (n-1) / λ0 in the case of normal incidence. The value of the step can be designed independently of numerical values such as the radius of curvature, refractive index, and lens interval of the lens.

When the diffractive lens surface is formed on the curved surface of the refracting lens, the relationship between the apparent pupil position on the entrance side of the diffractive lens surface and the radius of curvature of the lens surface causes the adjacent annular zone to change. There are cases where it is preferable to increase the step as the distance from the optical axis increases, and cases where it is preferable to decrease the step. On the other hand, when the diffraction lens surface is formed on a plane, the average incident angle with respect to the diffraction surface increases as the distance from the optical axis increases. Can be raised.

The second group G2 mainly has a function of correcting axial chromatic aberration, astigmatism, and distortion. Astigmatism is
The correction is made by the aspherical surface of the refractive lens 10 of the meniscus of the first group G1, and is further corrected well when the total thickness of the first group G1 and the second group G2 satisfies the following condition (7). You. 1.0 <(3d1 + d2) / f <2.0 (7) When the value falls below the lower limit of the condition (7), an astigmatism difference in which the meridional image surface becomes under occurs, and when the value exceeds the upper limit, the meridional image surface falls. , An astigmatic difference occurs.

In order to correct the positive distortion generated in the first lens unit G1 as described above, it is necessary to increase the thickness of the second lens unit G2 to some extent. It is desirable that the thickness d2 of the second group be set so as to satisfy the following condition (8). 0.6 <d2 / f <1.2 (8)

When the value goes below the lower limit of the condition (8), the distortion generated by the refractive lens 10 of the first lens unit G1 cannot be satisfactorily corrected. When the value exceeds the upper limit of the condition (8), the working distance is reduced. It is difficult to secure.

On the other hand, focusing on the chromatic aberration of magnification, the first group G
In the case where the first lens surface is provided with a diffractive lens surface, when the axial chromatic aberration is corrected by the diffractive lens surface, the chromatic aberration of magnification generated by the positive meniscus lens due to the effect is substantially corrected in the first lens unit. Therefore, in order to prevent the chromatic aberration of magnification of the entire system from being overcorrected, it is necessary to set the chromatic aberration of magnification correction effect of the second group G2 so as not to be too large. The action of correcting the chromatic aberration of magnification of the second group G2 is smaller when the dispersion of the optical element is small and the thickness is small. Therefore, it is desirable to satisfy the following condition (9). Σd2 / Σ (ν / d2)> 50.0 (9) If this condition (9) is not satisfied, the chromatic aberration of magnification of the entire system will be overcorrected.

When a diffractive lens surface is provided on the second surface of the first lens unit G1, lateral chromatic aberration remains even if axial chromatic aberration is corrected by the diffractive lens surface. Therefore, in this case, the second diffraction lens surface is compared with the case of one diffraction lens surface.
It is desirable to use a high-dispersion and thicker optical element for the group G2. Since high-dispersion glass generally has a high refractive index, using high-dispersion glass as the second group G2 also increases the refractive index of the second group G2. When a parallel plane plate is used as the second group G2, the parallel plane plate disposed in the convergent light has an action of moving the convergence point away, and the action becomes larger as the refractive index becomes higher. Second
Forming the plane-parallel plates of the group G2 is advantageous in securing the back focus.

When a color CCD is used as an image pickup device, it is required that the principal ray of the incident light is perpendicular to the optical axis, that is, it is required that the image side be telecentric on the image side. As described above, the meniscus positive lens is used. If the stop S is arranged after the first group G1, it is difficult to form a telecentric system on the image side. Therefore, when a color CCD is used, it is desirable to use a CCD with a lens array that makes the entrance pupil a finite distance. In this case, it is desirable that the imaging lens satisfies the following performance. 0.50 <ENP / f <0.70 (10) where ENP is the distance from the exit pupil of the imaging lens to the image plane, and f is the focal length of the imaging lens not including the microlens array. The entrance pupil of the microlens array desirably matches the exit pupil of the imaging lens. In that case, ENP is equal to the distance from the entrance pupil of the microlens array to the image plane. However, when the entrance pupil diameter of the microlens array is larger than the exit pupil diameter of the imaging lens, it is not necessary to completely match.

[0041]

EXAMPLES Next, 13 specific examples based on the above-described embodiment will be presented. In the following embodiments, the diffractive lens surface is represented by a macroscopic radius of curvature and a coefficient of an optical path difference function indicating the additional amount of the optical path length that the diffractive lens should have as a function of the height h from the optical axis. You. The optical path difference added by the diffraction lens △ φ (h) is, △ φ (h) = ( P2h 2 + P4h 4 + P6h 6 + P8h 8) × represented by lambda. P2, P4, P6, and P8 are second, fourth, and sixth respectively
Next, an eighth-order coefficient. In this expression, when the coefficient P2 of the term h2 is negative, it means that the power has paraxially positive power. When the coefficient P4 of the term h4 is positive, the negative power increases toward the periphery.

The actual microscopic shape of the lens is determined so as to have a Fresnel lens-shaped additional optical path length △ φ ′ in which a component of an integral multiple of the wavelength of the optical path length is eliminated. △ φ '(h) = ( MOD (P2h 2 + P4h 4 + P6h 6 + P8h 8 + Const,
l) −Const) × λ The constant term Const is a constant for setting the phase of the boundary position of the annular zone, and takes an arbitrary number from 0 to 1. MOD (X, Y) is a function that gives the remainder of X divided by Y. ^{MOD (P2h 2 + P4h 4 +} ...
The point of h where the value of + Const, 1) becomes 0 is the boundary of the ring zone. A gradient and a step are set on the base shape so as to have an optical path difference of △ φ ′ (h). In the embodiments described below,
Const = 0.5.

[0043]

First Embodiment FIG. 1 shows an imaging lens according to a first embodiment. In the imaging lens of Example 1, a first group G1 composed of a meniscus refracting lens 10 and a second group G2 composed of two parallel plane plates 20, 21 are arranged in order from the object side. Be composed. The stop S is disposed between the first and second units. In this embodiment, a diffractive lens surface is formed on the first surface 10a of the refractive lens 10.

Table 1 shows a specific numerical configuration of the imaging lens of the first embodiment. Surface numbers 1 and 2 indicate the refractive lens 10 of the first group G1, and surface numbers 3 to 6 indicate the parallel plane plates 20 and 21 of the second group G2. The column of the surface number of the surface on which the diffraction lens surface is formed is marked with “*”. In the table, FN
o. is the F number, f is the focal length of the whole system (unit: mm), w is the half angle of view (unit: degree), fB is the back focus, and r is the macroscopic radius of curvature of each lens surface (unit: mm) ), D is the lens thickness or lens interval (unit: mm), n is the d line of each lens (588n
m) is the Abbe number of each lens.

The first surface 10a and the second surface 10b of the refracting lens 10 are aspherical, and their shapes are on the optical axis of the aspherical coordinate point on the aspherical surface whose height from the optical axis is h. Is the distance from the tangent plane (sag amount) at X, the curvature (1 / r) on the optical axis of the aspherical surface is C, and the cone coefficient is K, the fourth, sixth, eighth, and tenth order.
The following aspheric coefficients are represented by the following equation (F), where A4, A6, A8, and A10 are set. The radius of curvature of the aspheric surface in Table 1 is the radius of curvature on the optical axis, and the conical coefficient and the aspheric surface coefficient are shown in Table 2. The notation E in the table represents a power with radix 10 as an exponent and the number to the right of E as an exponent. For example, the value "-1.25E + 1" of the coefficient P2 of the optical path difference function in Table 1 is "-12 .
The value of “5.” and the coefficient P8 “−1.76E-3” mean “−0.00176”. ^{X = Ch 2 / (1 +} √ (1- (1 + K) C 2 h 2)) + A4h 4 + A6h 6 + A8h 8 + A10h 10 ... (F)

[0046]

[Table 1] FNo. 1: 2.8 f = 10.00mm w = 23.6 ゜ fB = 0.11mm P2 = -1.25E + 1 P4 = -2.91E-1 P6 = -9.13E-3 P8 = -1.76E-3 Number rdn ν 1 * 3.297 2.000 1.80518 25.4 2 3.615 1.600 3 ∞ 5.500 1.69680 55.5 4 ∞ 0.200 5 ∞ 3.000 1.51633 64.1 6 ∞

[0047]

[Table 2]

FIG. 2 shows various aberrations of the imaging lens of the first embodiment. FIG. 2A shows the spherical aberration SA and the sine condition SC at the d-line, and FIG. 2B shows the chromatic aberration represented by the spherical aberration at each wavelength of the d-line, g-line (436 nm) and C-line (656 nm). Indicates chromatic aberration of magnification at g-line and C-line based on d-line, (D) indicates astigmatism (S: sagittal, M: meridional), and (E) indicates distortion. The vertical axes of the graphs (A) and (B) are F numbers, (C),
The vertical axes of (D) and (E) are half angles of view. The abscissa indicates the amount of occurrence of each aberration, and the unit is percent (%) in (E) and mm in other graphs indicating the amount of distortion.

[0049]

Second Embodiment FIG. 3 shows an imaging lens according to a second embodiment. The imaging lens according to the second embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 10
Is formed on the first surface 10a. Table 3 shows a specific numerical configuration of the second embodiment. First of the refractive lens 10
Table 4 shows conic coefficients and aspheric coefficients of the surface 10a and the second surface 10b.
Is shown in FIG. 4 shows various aberrations of the imaging lens of the second embodiment.

[0050]

[Table 3] FNo. 1: 2.8 f = 10.00mm w = 23.1 ゜ fB = 0.60mm P2 = -6.518 P4 = -1.24E-1 P6 = -1.58E-3 P8 = -6.07E-4 Surface number rdn ν 1 * 3.705 3.600 1.59551 39.2 2 5.399 0.800 3 ∞ 7.280 1.51633 64.1 4 ∞

[0051]

[Table 4]

[0052]

Third Embodiment FIG. 5 shows an imaging lens according to a third embodiment. The imaging lens according to the third embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 10
Is formed on the first surface 10a. The specific numerical configuration of the third embodiment is shown in Table 5. First of the refractive lens 10
Table 6 shows the conical coefficient and the aspheric coefficient of the surface 10a and the second surface 10b.
Is shown in FIG. 6 shows various aberrations of the imaging lens of the third embodiment.

[0053]

[Table 5] FNo.1: 2.8 f = 10.00mm w = 23.6 ゜ fB = 0.55mm P2 = -8.289 P4 = -2.00E-1 P6 = -6.22E-3 P8 = -1.32E-3 Surface number rdn ν 1 * 3.246 2.000 1.80 100 35.0 2 3.659 1.400 3 ∞ 8.600 1.65 160 58.5 4 ∞

[0054]

[Table 6]

[0055]

Fourth Embodiment FIG. 7 shows an imaging lens according to a fourth embodiment. The imaging lens according to the fourth embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 10
Is formed on the first surface 10a. Table 7 shows a specific numerical configuration of the fourth embodiment. First of the refractive lens 10
Table 8 shows the conical coefficient and aspheric coefficient of the surface 10a and the second surface 10b.
Is shown in FIG. 8 shows various aberrations of the imaging lens of the fourth embodiment.

[0056]

[Table 7] FNo. 1: 2.8 f = 10.00mm w = 22.3 ゜ fB = 1.83mm P2 = -1.07E + 1 P4 = -2.53E-1 P6 = -6.30E-3 P8 = -1.72E-3 Number rdn ν 1 * 3.300 2.540 1.80 100 35.0 2 3.300 1.400 3 ∞ 4.800 1.51633 64.1 4 ∞

[0057]

[Table 8]

[0058]

FIG. 9 shows an imaging lens according to a fifth embodiment. The imaging lens of the fifth embodiment is configured such that a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 are arranged in order from the object side. The diffractive lens surface is a refractive lens 10
Is formed on the first surface 10a. Table 9 shows a specific numerical configuration of the fifth embodiment. First of the refractive lens 10
Table 1 shows the conical coefficient and aspheric coefficient of the surface 10a and the second surface 10b.
0 is shown. FIG. 10 shows various aberrations of the imaging lens of the fifth embodiment.

[0059]

[Table 9] FNo.1: 2.8 f = 10.00mm w = 22.0 ゜ fB = 2.33mm P2 = -8.084 P4 = -2.07E-1 P6 = -5.31E-3 P8 = -1.68E-3 Surface number rdn ν 1 * 3.172 2.714 1.74400 44.8 2 3.203 1.300 3 ∞ 3.900 1.51633 64.1 4 ∞

[0060]

[Table 10]

[0061]

Sixth Embodiment FIG. 11 shows an imaging lens according to a sixth embodiment. The imaging lens according to the sixth embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 1
0 is formed on the first surface 10a. Table 11 shows a specific numerical configuration of the sixth embodiment. Table 12 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 12 shows various aberrations of the imaging lens of the sixth embodiment.

[0062]

[Table 11] FNo.1: 2.8 f = 10.00mm w = 21.8 ゜ fB = 2.13mm P2 = -8.195 P4 = -2.16E-1 P6 = -1.87E-3 P8 = -2.17E-3 Surface number rdn ν 1 * 3.302 2.977 1.74400 44.8 2 3.302 1.300 3 ∞ 3.880 1.51633 64.1 4 ∞

[0063]

[Table 12]

[0064]

Seventh Embodiment FIG. 13 shows an imaging lens according to a seventh embodiment. The imaging lens according to the seventh embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 1
0 is formed on the first surface 10a. Table 13 shows a specific numerical configuration of the seventh embodiment. Table 14 shows the conical coefficients and the aspherical coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 14 shows various aberrations of the imaging lens of the seventh embodiment.

[0065]

[Table 13] FNo.1: 2.8 f = 10.00mm w = 21.7 ゜ fB = 2.86mm P2 = -6.578 P4 = -1.92E-1 P6 = 5.78E-3 P8 = -2.72E-3 Surface number rdn ν 1 * 3.132 3.592 1.54358 55.6 2 3.867 1.300 3 ∞ 2.455 1.51633 64.1 4 ∞

[0066]

[Table 14]

[0067]

Eighth Embodiment FIG. 15 shows an imaging lens according to the eighth embodiment. The imaging lens of Example 8 is configured by arranging a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 in order from the object side. The diffractive lens surface is a refractive lens 1
0 is formed on the first surface 10a. Table 15 shows a specific numerical configuration of the eighth embodiment. Table 16 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 16 shows various aberrations of the imaging lens of the eighth embodiment.

[0068]

[Table 15] FNo.1: 2.8 f = 10.00mm w = 21.6 ゜ fB = 2.73mm P2 = -6.127 P4 = -1.59E-1 P6 = -1.80E-5 P8 = -1.64E-3 Surface number rdn ν 1 * 3.217 3.285 1.63854 55.4 2 3.550 1.300 3 ∞ 2.800 1.51633 64.1 4 ∞

[0069]

[Table 16]

[0070]

Ninth Embodiment FIG. 17 shows an imaging lens according to the ninth embodiment. The imaging lens according to the ninth embodiment includes a first group G1 including a meniscus refracting lens 10 and a second group G2 including a parallel plane plate 20 arranged in order from the object side. The diffractive lens surface is a refractive lens 1
0 is formed on the second surface 10b. Table 17 shows a specific numerical configuration of the ninth embodiment. Table 18 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 18 shows various aberrations of the imaging lens of the ninth embodiment.

[0071]

[Table 17] FNo.1: 2.8 f = 10.00mm w = 23.0 ゜ fB = 0.63mm P2 = -1.921E + 1 P4 = -2.39E-1 P6 = 0.000 P8 = 0.000 Surface number rdn ν 1 4.125 3.600 1.80 100 35.0 2 * 4.539 1.000 3 ∞ 8.100 1.80518 25.4 4 ∞

[0072]

[Table 18]

[0073]

FIG. 19 shows an imaging lens according to the tenth embodiment. The imaging lens according to the tenth embodiment includes a first group G1 including a meniscus refracting lens 10.
And a second group G2 composed of parallel plane plates 20 are arranged in order from the object side. The diffractive lens surface is formed on the second surface 10b of the refractive lens 10. Example 1
The specific numerical configuration of 0 is shown in Table 19. Table 20 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 20 shows various aberrations of the imaging lens of the tenth embodiment.

[0074]

[Table 19] FNo.1: 2.8 f = 10.00mm w = 23.3 ゜ fB = 0.98mm P2 = -1.525E + 1 P4 = -3.70E-1 P6 = 0.000 P8 = 0.000 Surface number rdn ν 1 2.986 1.935 1.74400 44.8 2 * 3.320 1.868 3 ∞ 7.000 1.59551 39.2 4 ∞

[0075]

[Table 20]

[0076]

[Embodiment 11] FIG. 21 shows an imaging lens according to an eleventh embodiment. The imaging lens of the eleventh embodiment has a first group G1 composed of a meniscus refracting lens 10.
And a second group G2 composed of parallel plane plates 20 are arranged in order from the object side. The diffractive lens surface is formed on the second surface 10b of the refractive lens 10. Example 1
The specific numerical configuration of 1 is shown in Table 21. Table 22 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 22 shows various aberrations of the imaging lens of the eleventh embodiment.

[0077]

[Table 21] FNo.1: 2.8 f = 10.00mm w = 23.6 ゜ fB = 0.49mm P2 = -1.231E + 1 P4 = -2.18E-1 P6 = 0.000 P8 = 0.000 Surface number rdn ν 1 3.359 2.334 1.77250 49.6 2 * 3.845 1.300 3 ∞ 8.700 1.67790 55.3 4 ∞

[0078]

[Table 22]

[0079]

Twelfth Embodiment FIG. 23 shows an imaging lens according to the twelfth embodiment. The imaging lens of the twelfth embodiment is composed of a meniscus refracting lens 10 and an optical element 11 having almost no power and disposed on the object side thereof.
The group G1 and the second group G2 composed of the parallel plane plate 20 are arranged in order from the object side. Diffractive lens surface
The optical element 11 is formed on an image-side surface 11b. A specific numerical configuration of the twelfth embodiment is shown in Table 23. Table 24 shows the conical coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 24 shows the first embodiment.
2 shows various aberrations of the imaging lens of No. 2;

[0080]

[Table 23] FNo. 1: 2.8 f = 10.00mm w = 21.7 ゜ fB = 2.21mm P2 = -5.106 P4 = 0.000 P6 = 0.000 P8 = 0.000 Surface number rdn ν 1 ∞ 2.000 1.54358 55.6 2 * ∞ 0.400 3 3.217 3.285 1.63854 55.4 4 3.613 1.300 5 ∞ 3.600 1.51633 64.1 6 ∞

[0081]

[Table 24]

[0082]

[Thirteenth Embodiment] FIG. 25 shows an imaging lens according to the thirteenth embodiment. The imaging lens of the thirteenth embodiment is composed of a meniscus refracting lens 10 and an almost powerless optical element 11 disposed on the object side thereof.
The group G1 and the second group G2 composed of the parallel plane plate 20 are arranged in order from the object side. Diffractive lens surface
The optical element 11 is formed on an image-side surface 11b. Table 25 shows the specific numerical configuration of the thirteenth embodiment. Table 26 shows the conic coefficients and aspheric coefficients of the first surface 10a and the second surface 10b of the refractive lens 10. FIG. 26 shows the first embodiment.
3 shows various aberrations of the imaging lens of No. 3;

[0083]

[Table 25] FNo.1: 2.8 f = 10.00mm w = 22.0 ゜ fB = 2.28mm P2 = -5.106 P4 = 0.000 P6 = 0.000 P8 = 0.000 Surface number rdn ν 1 ∞ 2.000 1.54358 55.6 2 * 90.596 0.400 3 3.217 3.285 1.63854 55.4 4 3.903 1.300 5 ∞ 3.700 1.51633 64.1 6 ∞

[0084]

[Table 26]

Next, the correspondence between the above-described conditional expressions and the above-described embodiments will be described with numerical values. Table 27 and Table 2
8 shows a calculation result when the numerical value of each embodiment is applied to the numerical expression of each conditional expression. As for the condition (6), as described above, its value can be arbitrarily determined independently of other numerical values.

[0086]

[Table 27] Example Condition (1) (2) Condition (3) Condition (4) (5) 1 0.92 1.80518 0.200 2 1.57 1.59551 0.360 3 0.93 1.80 100 0.200 4 0.67 1.80 100 0.254 5 0.68 1.74400 0.271 6 0.66 1.74400 0.298 7 1.14 1.54358 0.359 8 0.85 1.63854 0.329 9 0.81 1.80 100 0.360 10 0.93 1.74400 0.194 11 0.93 1.77250 0.233 12 0.87 1.63854 0.329 13 0.94 1.63854 0.329

[0087]

[Table 28] Example Condition (7) Condition (8) Condition (9) Condition (10) 1 1.450 0.850 58.3 0.613 2 1.808 0.728 64.1 0.580 3 1.460 0.860 58.5 0.645 4 1.242 0.480 64.1 0.570 5 1.204 0.390 64.1 0.560 6 1.281 0.388 64.1 0.539 7 1.323 0.246 64.1 0.518 8 1.266 0.280 64.1 0.528 9 1.890 0.810-0.552 10 1.281 0.700-0.624 11 1.570 0.870-0.627 12 1.346 0.360-0.529 13 1.356 0.370-0.529

[0088]

As described above, according to the present invention, it is possible to provide a bright imaging lens having a small F-number by correcting aberrations by combining a refractive lens and a diffractive lens.

[Brief description of the drawings]

FIG. 1 is a lens diagram of an imaging lens according to a first embodiment.

FIG. 2 is a diagram illustrating various aberrations of the imaging lens according to the first example;

FIG. 3 is a lens diagram of an imaging lens according to Example 2;

FIG. 4 is a diagram of various aberrations of the imaging lens according to Example 2;

FIG. 5 is a lens diagram of an imaging lens according to Example 3;

FIG. 6 is a diagram illustrating various aberrations of the imaging lens according to the third example;

FIG. 7 is a lens diagram of an imaging lens according to Example 4;

FIG. 8 is a diagram of various aberrations of the imaging lens according to Example 4;

FIG. 9 is a lens diagram of an imaging lens according to Example 5;

FIG. 10 is a diagram illustrating various aberrations of the imaging lens according to the fifth example;

FIG. 11 is a lens diagram of an imaging lens according to Example 6;

FIG. 12 is a diagram illustrating various aberrations of the imaging lens according to Example 6;

FIG. 13 is a lens diagram of an imaging lens according to Example 7;

FIG. 14 is a diagram of various aberrations of the imaging lens according to Example 7;

FIG. 15 is a lens diagram of an imaging lens according to Example 8;

FIG. 16 is a diagram illustrating various aberrations of the imaging lens according to Example 8;

FIG. 17 is a lens diagram of an imaging lens according to Example 9;

FIG. 18 is a diagram of various aberrations of the imaging lens according to Example 9;

FIG. 19 is a lens diagram of an imaging lens according to Example 10;

FIG. 20 is a diagram of various aberrations of the imaging lens according to Example 10;

FIG. 21 is a lens diagram of an imaging lens according to Example 11;

FIG. 22 is a diagram of various aberrations of the imaging lens according to Example 11;

FIG. 23 is a lens diagram of an imaging lens according to Example 12;

FIG. 24 is a diagram of various aberrations of the imaging lens according to Example 12;

FIG. 25 is a lens diagram of an imaging lens according to Example 13;

FIG. 26 is a diagram illustrating various aberrations of the imaging lens according to Example 13;

[Explanation of symbols]

 G1 First group G2 Second group 10 Positive lens 20,21 Parallel plane plate

Claims (19)

[Claims] 1. An imaging lens comprising, in order from an object side, a first group including one refracting lens having a positive power, an aperture, and a second group having substantially no power. The refracting lens is a meniscus lens having both aspheric surfaces on both sides and convex on the object side, and a diffractive lens surface for correcting chromatic aberration of the refracting lens is formed on at least one surface of the first group. Imaging lens. 2. The image forming apparatus according to claim 1, wherein the first group includes the refractive lens alone, and the diffractive lens surface is formed on one lens surface of the refractive lens. lens. 3. The imaging lens according to claim 2, wherein the diffractive lens surface is formed on an object-side lens surface of the refractive lens. 4. The imaging lens according to claim 2, wherein the diffractive lens surface is formed on an image-side lens surface of the refraction lens. 5. The first group includes the refractive lens and an optical element having almost no power disposed on the object side of the refractive lens, and the diffractive lens surface is formed on the optical element. The imaging lens according to claim 1, wherein: 6. The imaging lens according to claim 5, wherein the diffraction lens surface is formed on an image-side surface of the optical element. 7. An object-side first surface of the refracting lens is an aspheric surface having an action of correcting astigmatism, and an image-side second surface is provided.
The imaging lens according to claim 1, wherein the surface is an aspheric surface having an action of correcting spherical aberration and higher-order field curvature. 8. The imaging lens according to claim 1, wherein the refractive lens satisfies the following condition (1). 0.64 <r1 * r2 / (f (n1-1) ² * d1) <1.60 (1) where r1 and r2 are the radii of curvature of the first surface and the second surface of the refractive lens, and f is the total. The focal lengths of the system, n1 and d1, are the refractive index and lens thickness of the refractive lens, respectively. 9. The imaging lens according to claim 1, wherein the refractive lens satisfies the following condition (2). 0.70 <r1 × r2 / (f (n1-1) ² × d1) <1.25 (2) where r1 and r2 are the radii of curvature of the first surface and the second surface of the refractive lens, and f is all The focal lengths of the system, n1 and d1, are the refractive index and lens thickness of the refractive lens, respectively. 10. The imaging lens according to claim 1, wherein the refractive lens is a glass lens whose refractive index n1 satisfies the following condition (3). n1> 1.6 ... (3) 11. The imaging lens according to claim 1, wherein the refractive lens satisfies the following condition (4). 0.17 <d1 / f (4) where f is the focal length of the entire system, and d1 is the lens thickness of the refractive lens. 12. The imaging lens according to claim 1, wherein the refractive lens satisfies the following condition (5). d1 / f <0.40 (5) where f is the focal length of the entire system, and d1 is the lens thickness of the refractive lens. 13. The object-side first surface of the refractive lens,
When the shift from the spherical surface to the image plane side defined by the paraxial curvature radius is given a positive sign, and the sag amount is subjected to a power series expansion as a function of the height from the optical axis, at least a fourth-order coefficient is obtained. The imaging lens according to claim 7, wherein is defined as a surface having a positive coefficient of fourth order or higher. 14. The object-side second surface of the refractive lens,
When the shift from the spherical surface to the image plane side defined by the paraxial curvature radius is given a positive sign, and the sag amount is subjected to a power series expansion as a function of the height from the optical axis, at least a fourth-order coefficient is obtained. 14. The imaging lens of claim 13, wherein is positive and the fourth order coefficient is defined as a surface having a value greater than a fourth order coefficient of the function defining the first surface. 15. The step t0 of the innermost annular zone of the diffractive lens surface is defined as w [unit: rad.] Of the half angle of view of the entire system, and n 'as the refractive index of the element on which the diffractive lens surface is formed. 2. The imaging lens according to claim 1, wherein the following condition (6) is satisfied, where λ0 is the reference wavelength. −0.5 w ² / n ′ <− ¹ + t 0 (n′− ¹⁾ / λ 0 <−0.1 w ² / n ′ (6) 16. The imaging lens according to claim 1, wherein the thickness d1 of the first group and the thickness d2 of the second group satisfy the following condition (7). 1.0 <(3d1 + d2) / f <2.0 (7) 17. The imaging lens according to claim 1, wherein the second group satisfies the following condition (8), where d2 is the thickness and f is the focal length of the entire system. 0.6 <d2 / f <1.2 (8) 18. The second group has the following conditions, where d2 is the thickness of the optical element constituting the second group, and ν is the Abbe number.
The imaging lens according to claim 1, wherein (9) is satisfied. Σd2 / (d2 / ν)> 50.0 (9) 19. The imaging lens according to claim 1, further comprising: an imaging element provided substantially coincident with an image plane of the imaging lens; and an imaging element arranged between the imaging lens and the imaging element. An imaging optical system comprising: a lens array for setting a position of an entrance pupil of an element to a finite distance; and satisfying the following condition (10). 0.50 <ENP / f <0.70 (10) where E
NP is the distance from the exit pupil of the imaging lens to the image plane, and f is the focal length of the imaging lens not including the microlens array.