JPH11142730A - Image pickup lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup lens in which various lens aberrations are excellently corrected and which is low-cost and further is used suitably for a compact CCD camera, etc. SOLUTION: This image pickup lens consists of a 1st lens as a negative lens, a 2nd lens as a positive lens and three or four lenses following them in order from an object side and has at least two negative lenses and three positive lenses as the whole and at least two among the lenses constituting the whole optical system are made of plastic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens, and more particularly, to a wide-angle lens which uses a small CCD as a light receiving element, has a long back focus, and is excellent in correcting various aberrations.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for low cost, high performance and compactness of lenses used in electronic photographing equipment. To meet this demand,
For example, Japanese Patent Application Laid-Open No. Sho 64-61714,
Japanese Patent Publication No. 1008 and Japanese Patent Publication No. Sho 60-26919 propose a wide-angle lens.

[0003]

However, in the above-mentioned prior art, the size of the lens is large, the telecentricity is lacking, and the wide angle of view is not enough. Provision of a compact wide-angle lens was insufficient.

An object of the present invention has been made in view of the above-mentioned problems, and is compact and compact in which various aberrations have been well corrected.
An object of the present invention is to provide an imaging lens which is suitable for use in a CCD camera or the like having good telecentricity.

[0005]

The above object can be achieved by the following means.

[Claim 1] In order from the object side, a first lens which is a negative lens, a second lens which is a positive lens, and three or four lenses subsequent thereto, and at least a negative lens 2 as a whole. And three positive lenses,
An imaging lens, wherein at least two of the lenses constituting the all-optical system are made of plastic.

According to the first aspect of the present invention, since the negative lens and the positive lens are arranged in this order from the object side, a back focus for arranging an infrared cut filter, a low-pass filter, and the like necessary for the lens for the CCD camera. And a low-cost imaging lens can be realized by using a plastic lens. further,
Since the plastic lens can easily use an aspherical surface, the degree of freedom of aberration correction is increased, so that a compact configuration is possible.

[Claim 2] The imaging lens according to claim 1, wherein the two plastic lenses are each a negative lens and a positive lens.

According to the second aspect of the present invention, since the plastic lens is used for the negative lens and the positive lens, it is possible to realize a low-cost imaging lens with less focus change due to temperature change.

[Claim 3] The imaging lens according to claim 1 or 2, further comprising at least one set of cemented lenses after the second lens.

According to the third aspect of the present invention, the use of the bonded lens makes it possible to design the surface with a small curvature, so that the degree of freedom for correcting the lens aberration is wider than that of the single lens. Also, the eccentric sensitivity can be reduced.

[0012] When the total of two [Claim 4] wherein the first lens in the entire optical system and the subsequent one positive lens and a plastic _{lens, 0.5 <f p / | f} 1 | <7. 0... (1) where f _p : a focal length of _one positive lens made of plastic, and f ₁ : a focal length of the first lens. 2
An imaging lens according to item 1.

According to the fourth aspect of the present invention, the conditional expression (1) is a conditional expression for restricting the influence of the temperature change on the plastic lens. If the conditional expression is out of the range, it is difficult to suppress a change in image position or performance due to a temperature change. More preferably, 0.8 <f _p / | f ₁ | <5.0.

[0014] [Claim 5] The imaging lens is _{0.5 <f r /f<5.0 ········· (2} ) 0.5 <| f 1 | / f ····· ... (3) 0.5 <f ₂ / f (4) where f: focal length of all optical systems _fr : composite focal point from the third lens to the last lens 3. The imaging lens according to claim 1, wherein the following conditional expression is satisfied: f ₁ : focal length of the first lens f ₂ : focal length of the second lens

According to the fifth aspect of the present invention, conditional expression (2)
By satisfying both (3) and (4), a compact optical system can be achieved without sacrificing the angle of view, while ensuring a sufficient back focus. In the lens system of the present invention, the first lens is a negative lens and is of a retrofocus type, thereby widening the angle of the entire optical system without shortening the back focus.

If the focal length of the combining system from the third lens to the final lens becomes longer than the upper limit of conditional expression (2), the refractive power of the first lens must be increased in order to obtain a sufficiently wide angle. Disappears, leading to deterioration of various aberrations, particularly distortion. Conversely, if the lower limit is exceeded, it is easy to achieve a wide angle without increasing the load on the first lens, but it is difficult to secure the back focus.

When the focal length of the first lens becomes longer than the upper limit of the conditional expression (3), the distance between the first lens and the second lens must be increased in order to widen the entire optical system. And it leads to an increase in size. Conversely, if the lower limit is exceeded, the distortion generated by the first lens will increase.

If the focal length of the second lens becomes longer than the upper limit of the conditional expression (4), the luminous flux emitted from the second lens becomes a divergent luminous flux. Astigmatism tends to deteriorate. Further, as the distance between the first lens and the second lens is increased, the light flux emitted from the second lens is converged. In this case, the size of the entire optical system is increased. Conversely, if the lower limit is exceeded, the spherical aberration generated by the second lens increases, making it difficult to correct. Preferably 1.0 <f _r /f<3.0 1.0 <| a _{/ f <3.0 1.0 <f 2} /f<4.0 | f 1.

[Claim 6] When the lens closest to the image side is a single lens, -2.0 <f / r _L <2.0 (5) where: f: focal point of all optical systems distance r _L: imaging lens according to claim 1 or 2 a curvature condition: the final surface, characterized in that Mitsurusu.

According to the sixth aspect of the present invention, the conditional expression (5) is for preventing an increase in curvature of field while ensuring good telecentricity. If the convex surface becomes tighter than the lower limit, the Petzval sum increases, which is not preferable. On the other hand, if the concave surface becomes tighter than the upper limit, it becomes difficult to secure telecentricity. Desirably _{-1.0 <f / r L <1.0} .

[Claim 7] The second lens satisfies the following condition: 28 <ν _d <60 (6) where ν _{d is the} Abbe number of the material of the second lens with respect to the d-line. The imaging lens according to claim 1, wherein:

According to the seventh aspect of the present invention, d of the second lens
In conditional expression (6) that defines the Abbe number in the line,
When the stop is disposed between the second lens and the third lens, if the Abbe number is smaller than the lower limit and the Abbe number is reduced, chromatic aberration of magnification occurs and an image of a short wavelength becomes large. Conversely, if the upper limit is exceeded, the opposite result will appear.

[8] The imaging lens according to [1], wherein the two plastic lenses have one or more aspherical shapes.

According to the eighth aspect of the present invention, the use condition of the aspherical surface is specified to simplify the lens configuration while maintaining good optical performance. The effect of the aspheric surface of each lens is as follows. When the first lens has an aspherical surface, distortion and coma can be improved.
The aspherical surface of the lens near the stop has the effect of correcting spherical aberration. The aspherical surface of the positive lens closest to the image is effective in correcting astigmatism and coma.

[Claim 9] At least one surface of the first lens is aspherical.
An imaging lens according to item 1.

According to the ninth aspect of the present invention, the use condition of the aspherical surface is specified similarly to the eighth aspect, thereby simplifying the lens configuration while maintaining good optical performance. The effect of the aspheric surface of each lens is as follows. When the first lens has an aspherical surface, distortion and coma can be improved. The aspherical surface of the lens near the stop has the effect of correcting spherical aberration. The aspherical surface of the positive lens closest to the image is effective in correcting astigmatism and coma.

[Claim 10] When the first lens is a plastic lens and a stop is arranged between the second lens and the third lens, at least one of the two lenses adjacent to the stop is used. 3. The imaging lens according to claim 1, wherein the lens is a positive lens, and the positive lens is an aspheric plastic lens having at least one surface.

According to the tenth aspect, similarly to the seventh aspect, the use condition of the aspherical surface is specified to simplify the lens configuration while maintaining good optical performance.
The effect of the aspheric surface of each lens is as follows. When the first lens has an aspherical surface, distortion and coma can be improved. The aspherical surface of the lens near the stop has the effect of correcting spherical aberration. The aspherical surface of the positive lens closest to the image is effective in correcting astigmatism and coma.

(11) The imaging lens according to (1), (2) or (3), wherein the positive lens closest to the image is a plastic lens, and at least one surface of the positive lens is aspherical.

According to the eleventh aspect, the use condition of the aspherical surface is specified as in the eighth aspect, thereby simplifying the lens configuration while maintaining good optical performance.
The effect of the aspheric surface of each lens is as follows. When the first lens has an aspherical surface, distortion and coma can be improved. The aspherical surface of the lens near the stop has the effect of correcting spherical aberration. The aspherical surface of the positive lens closest to the image is effective in correcting astigmatism and coma.

[Claim 12] The first lens has a concave surface on the object side, and −0.7 <(r ₂ + r ₁ ) / (r ₂ −r ₁ ) <5.0... (7) The imaging lens according to claim 1, wherein r ₁ : a radius of curvature of a side surface of the first lens object, and r ₂ : a radius of curvature of a side surface of the first lens image.

According to the twelfth aspect of the present invention, the conditional expression (7)
Is related to the shape of the first lens, and the lower limit is to make the lens system more compact while obtaining a sufficient back focus. If r ₁ becomes a strongly concave surface exceeding the upper limit, the image surface of the meridian oil becomes too over. In addition, negative distortion becomes large. Further, the eccentric sensitivity also increases.

[Claim 13] In order from the object side, a first lens which is a negative lens, a second lens which is a positive lens, a third lens which is a negative lens, a fourth lens which is a positive lens, and a positive lens A lens system composed of five groups and five lenses including a fifth lens, wherein a diaphragm is arranged between the second lens and the third lens, and at least one lens surface of the first lens is An imaging lens comprising an aspherical surface and satisfying the following conditions.

0.4 ≦ | f ₁ /f|≦4.0 (8) 1.1 ≦ | f ₁ / f ₃ | ≦ 1.9 ( ₁ ) ... (9) where, f: composite focal length of all optical systems f ₁ : focal length of first lens f ₃ : focal length of third lens According to the invention of claim 13, negative from the object side ,positive and negative,
By adopting a retrofocus type that is arranged in the positive and positive order, the back focus is secured to arrange the infrared cut filter, low pass filter, etc. necessary for the imaging lens for the CCD camera in addition to widening the angle, and further, the rear of the aperture Is negative, positive, and positive, so that the sub-system after the stop becomes a retrofocus type, and the back focus can be made sufficiently long.At the same time, the luminous flux emitted toward the image plane is suppressed by the positive lens behind the stop. Bending in the direction of the optical axis also has the effect of making the chief ray substantially parallel to the optical axis, that is, improving the so-called telecentricity. In addition, the configuration in which one negative lens is disposed before and after the stop has an effect of correcting distortion by power distribution between the front and rear negative lenses. Further, the use of the aspherical lens increases the degree of freedom of aberration correction, and accordingly, a compact configuration with a wide angle of view is possible.

If the focal length of the first lens becomes longer than the upper limit of conditional expression (8), the back focus cannot be made sufficiently long. If the lower limit is exceeded, the negative distortion generated in the first lens increases, and the influence of manufacturing errors such as eccentricity of the first lens increases.

If the upper limit of conditional expression (9) is exceeded, the focal length of the first lens will be long, the focal length of the third lens will be short, and the divergence behind the diaphragm will be strong, thus deteriorating the telecentricity. If the lower limit is exceeded, the negative distortion generated in the first lens becomes large, and the correction of the third lens, which should be corrected, becomes weak. In particular, the deterioration of the distortion becomes large. Preferably, 0.8 ≦ | f ₁ /f|≦2.0.

[14] The apparatus according to [13], wherein the first lens is an aspherical lens, and at least one of the fourth lens and the fifth lens is formed by an aspherical surface. Imaging lens.

According to the fourteenth aspect of the invention, in addition to the first lens being an aspherical lens, at least one of the fourth lens and the fifth lens is made aspherical, so that the aperture of the diaphragm can be reduced. By providing aspherical surfaces on the front side and the rear side, the degree of freedom of aberration correction such as correction of coma flare is increased, and it is possible to satisfactorily correct asymmetric aberration regardless of the retrofocus type so-called asymmetric lens configuration. .

[Claim 15] In order from the object side, a first lens which is a negative lens, a second lens which is a positive lens, a third lens which is a negative lens, a fourth lens which is a positive lens, and a positive lens is constituted by the fifth lens is a lens, also a non-spherical surface with at least one surface in the entire system, and _{0.3 <f B / f <1} ················ (10) where, f: lens focal length f _B of: an image pickup lens and satisfies the back focus becomes conditional expression.

According to the fifteenth aspect, the conditional expression (1)
0) is a conditional expression for securing a back focus required for a lens for a CCD camera while maintaining various aberrations favorably. When the back focus becomes longer than the upper limit of the conditional expression, the power of the first lens needs to be increased, which causes deterioration of distortion. Further, when the back focus is shorter than the lower limit, a sufficient space for disposing an infrared cut filter, a low-pass filter, and the like necessary for a lens for a CCD camera is lost. Preferably, 0.7 <f _B / f <1.

[Claim 16] The imaging lens according to claim 15, wherein the third lens which is a negative lens and the fourth lens which is a positive lens are cemented lenses.

According to the sixteenth aspect of the present invention, the use of the cemented lens makes it possible to design the surface with a small curvature, and thus has a greater degree of freedom for correcting aberrations than a single lens. Also, the eccentric sensitivity can be kept small.

[0043]

Embodiments Embodiments 1 to 14 of the present invention will be described below. The symbols used in the table are as follows. f is the focal length of the entire optical system, F _no is the F number, ω is the half angle of view, r is the radius of curvature, d is the axial top surface interval, _nd is the refractive index for the d line,
ν _d is the Abbe number. In the table, “Δf _B at + 30 ° C.” indicates a shift amount of the back focus at normal temperature + 30 ° C. f _B
Indicates a back focus calculated by adding the filter unit to the air conversion length and adding the calculated values.

In addition, “* 1” and “*” described in n _d in the table
"2" and "* 3" indicate plastic lenses, and the change in the refractive index due to each temperature change is as shown in Table 1.

[0045]

[Table 1]

The surface No. Indicates an aspheric surface. Further, the aspherical surface is represented by the expression of “Equation 1”.

[0047]

(Equation 1)

In an orthogonal coordinate system having the vertex as the origin and the optical axis direction as the X axis in Equation 1, the vertex curvature C, the conic constant K, and the aspheric coefficient are Ai (i = 4, 6, 8, 10, 10). 1
2) is shown.

(Embodiment 1) An embodiment corresponding to claims 1 to 9 and 11, wherein the first lens is a plastic negative lens using an aspheric surface, the second lens is a positive lens, an aperture,
A laminated lens and a plastic positive lens using an aspheric surface are arranged in this order.

FIG. 1 is a sectional view of an optical system of a lens system corresponding to the first embodiment, and FIG. 2 shows spherical aberration, astigmatism, and distortion corresponding to the first embodiment. Tables 2 and 3 show lens data.

[0051]

[Table 2]

[0052]

[Table 3]

(Embodiment 2) An embodiment corresponding to the first to ninth and eleventh embodiments. In the second embodiment, similarly to the first embodiment, the first lens is a plastic negative lens using an aspherical surface, and the second lens is a positive lens. A lens, an aperture, a cemented lens, and a plastic positive lens using an aspheric surface are arranged in this order.

FIG. 3 is a sectional view of an optical system of a lens system corresponding to the second embodiment, and FIG. 4 shows spherical aberration, astigmatism, and distortion corresponding to the second embodiment. Tables 4 and 5 show lens data.

[0055]

[Table 4]

[0056]

[Table 5]

(Embodiment 3) Claims 1 to 5, 7 to 10
In the third embodiment, the first lens is a plastic negative lens using an aspheric surface, the second lens is a positive lens,
An aperture, a plastic positive lens using an aspheric surface, and a cemented lens are arranged in this order.

FIG. 5 is a sectional view of an optical system of a lens system corresponding to the third embodiment. FIG. 6 shows spherical aberration, astigmatism, and distortion corresponding to the third embodiment. Tables 6 and 7 show lens data.

[0059]

[Table 6]

[0060]

[Table 7]

(Embodiment 4) Claims 1 to 5, 7 to 1
In the fourth embodiment, the first lens is a plastic negative lens using an aspheric surface, and the second lens is a positive lens, an aperture, and the plastic positive lens using an aspheric surface, as in the third embodiment. The lens and the laminated lens are arranged in this order.

FIG. 7 is a sectional view of an optical system of a lens system corresponding to the fourth embodiment, and FIG. 8 shows spherical aberration, astigmatism, and distortion corresponding to the fourth embodiment. Tables 8 and 9 show lens data.

[0063]

[Table 8]

[0064]

[Table 9]

(Embodiment 5) Claims 1 to 5, 7 to 10
In Example 5, the first lens is a plastic negative lens using an aspherical surface, the second lens is a plastic positive lens, an aperture, the third lens is a negative lens, the fourth lens is a positive lens, and the bonding is performed. The lenses are arranged in order.

FIG. 9 is a sectional view of an optical system of a lens system corresponding to the fifth embodiment, and FIG. 10 shows spherical aberration, astigmatism, and distortion corresponding to the fifth embodiment. Tables 10 and 11 show lens data.

[0067]

[Table 10]

[0068]

[Table 11]

(Embodiment 6) Claims 1 to 5, 7 to 10
The sixth embodiment is similar to the fifth embodiment in that the first
Plastic negative lens using aspherical lens, 2nd
The lens is a plastic positive lens, a diaphragm, a third lens is a negative lens, a fourth lens is a positive lens, and a cemented lens is arranged in this order.

FIG. 11 is a sectional view of an optical system of a lens system corresponding to the sixth embodiment, and FIG.
Astigmatism and distortion are shown respectively. Tables 12 and 13 show lens data.

[0071]

[Table 12]

[0072]

[Table 13]

(Embodiment 7) An embodiment corresponding to the first to ninth and eleventh embodiments will be described. In the seventh embodiment, similarly to the first embodiment, the first lens is a plastic negative lens using an aspherical surface, and the second lens is a positive lens. A lens, an aperture, a cemented lens, and a plastic positive lens using an aspheric surface are arranged in this order.

FIG. 13 is a sectional view of an optical system of a lens system corresponding to the seventh embodiment, and FIG.
Astigmatism and distortion are shown respectively. Tables 14 and 15 show lens data.

[0075]

[Table 14]

[0076]

[Table 15]

(Embodiment 8) Claims 1, 2, 4 to 9,
Embodiment 8 is an embodiment corresponding to 1. In Embodiment 8, a first lens is a plastic negative lens using an aspherical surface, a second lens is a positive lens, an aperture, a third lens is a negative lens, a fourth lens is a positive lens, and a fifth lens. Are arranged in the order of a plastic positive lens using an aspheric surface.

FIG. 15 is a sectional view of an optical system of a lens system corresponding to the eighth embodiment, and FIG.
Astigmatism and distortion are shown respectively. Tables 16 and 17 show lens data.

[0079]

[Table 16]

[0080]

[Table 17]

(Embodiment 9) Claims 1 to 5, 7 to 10
In Example 9, the first lens is a plastic negative lens using an aspherical surface, the second lens is a plastic positive lens using an aspherical surface, an aperture, the third lens is a negative lens, and the fourth lens is a negative lens. The positive lens and the cemented lens are arranged in this order.

FIG. 17 is a sectional view of an optical system of a lens system corresponding to the ninth embodiment. FIG.
Astigmatism and distortion are shown respectively. Tables 18 and 19 show lens data.

[0083]

[Table 18]

[0084]

[Table 19]

(Embodiment 10) Claims 1 to 9, 11, 1
In the tenth embodiment, the first lens uses a plastic negative lens using an aspherical surface, and the second lens uses a positive lens, an aperture, a cemented lens, and an aspherical surface, as in the first embodiment. They are arranged in the order of the plastic positive lenses.

FIG. 19 is a sectional view of an optical system of a lens system corresponding to the tenth embodiment, and FIG. 20 shows spherical aberration, astigmatism, and distortion corresponding to the tenth embodiment. Tables 20 and 21 show lens data.

[0087]

[Table 20]

[0088]

[Table 21]

(Embodiment 11) Claims 1 to 9, 11, 1
Embodiment 11 is an embodiment corresponding to Embodiments 5 and 16. In Embodiment 11, as in Embodiment 1, the first lens uses a plastic negative lens using an aspheric surface, and the second lens uses a positive lens, an aperture, a bonded lens, and an aspheric surface. They are arranged in the order of the plastic positive lenses.

FIG. 21 is a sectional view of an optical system of a lens system corresponding to the eleventh embodiment. FIG. 22 shows spherical aberration, astigmatism, and distortion corresponding to the eleventh embodiment. Tables 22 and 23 show lens data.

[0091]

[Table 22]

[0092]

[Table 23]

(Embodiment 12) Claims 1 to 9, 11, and 1
Embodiment 12 is an embodiment corresponding to Embodiments 5 and 16. In Embodiment 12, as in Embodiment 1, the first lens uses a plastic negative lens using an aspheric surface, and the second lens uses a positive lens, an aperture, a bonded lens, and an aspheric surface. They are arranged in the order of the plastic positive lenses.

FIG. 23 is a sectional view of an optical system of a lens system corresponding to the twelfth embodiment. FIG. 24 shows spherical aberration, astigmatism, and distortion corresponding to the twelfth embodiment. Tables 24 and 25 show lens data.

[0095]

[Table 24]

[0096]

[Table 25]

(Embodiment 13) An embodiment corresponding to claims 13 and 14 will be described. FIG. 25 shows an optical system sectional view of a lens system corresponding to Example 13, and FIG. 26 shows spherical aberration, astigmatism, and distortion corresponding to Example 13. Tables 26 and 27 show lens data.

[0098]

[Table 26]

[0099]

[Table 27]

(Embodiment 14) An embodiment corresponding to claims 13 and 14. FIG. 27 is a sectional view of an optical system of a lens system corresponding to Example 14, and FIG. 28 shows spherical aberration, astigmatism, and distortion corresponding to Example 14. Tables 28 and 29 show lens data.

[0101]

[Table 28]

[0102]

[Table 29]

Table 30 shows the specification values of each embodiment, and Table 31 shows the numerical values of the conditional expressions (1) to (10).

[0104]

[Table 30]

[0105]

[Table 31]

As shown in Table 31, all the values satisfy the numerical values of the conditional expressions.

[0107]

As described above, a compact imaging lens suitable for use in a CCD camera or the like having a good correction of various aberrations and having good telecentricity can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical system of a lens system corresponding to a first embodiment.

FIG. 2 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 1.

FIG. 3 is an optical system sectional view of a lens system corresponding to a second embodiment.

FIG. 4 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 2.

FIG. 5 is an optical system sectional view of a lens system corresponding to a third embodiment.

FIG. 6 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 3.

FIG. 7 is an optical system sectional view of a lens system corresponding to Example 4.

FIG. 8 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 4.

FIG. 9 is an optical system sectional view of a lens system corresponding to Example 5.

FIG. 10 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 5.

FIG. 11 is an optical system sectional view of a lens system corresponding to Example 6.

FIG. 12 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 6.

FIG. 13 is an optical system sectional view of a lens system corresponding to Example 7.

14 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 7. FIG.

FIG. 15 is an optical system sectional view of a lens system corresponding to Example 8.

FIG. 16 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 8.

FIG. 17 is an optical system sectional view of a lens system corresponding to Example 9;

FIG. 18 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 9.

FIG. 19 is an optical system sectional view of a lens system corresponding to Example 10.

FIG. 20 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 10.

FIG. 21 is an optical system sectional view of a lens system corresponding to Example 11;

FIG. 22 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 11;

FIG. 23 is an optical system sectional view of a lens system corresponding to Example 12;

FIG. 24 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 12.

FIG. 25 is an optical system sectional view of a lens system corresponding to Example 13.

FIG. 26 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 13.

FIG. 27 is an optical system sectional view of a lens system corresponding to Example 14;

FIG. 28 is a graph of spherical aberration, astigmatism, and distortion corresponding to Example 14.

[Explanation of symbols]

 Reference Signs List 1 1st surface 2 2nd surface 3 3rd surface 4 4th surface 5 5th surface 6 6th surface 7 7th surface 8 8th surface 9 9th surface 10 10th surface 11 11th surface 12 12th surface 13th Thirteen

Claims (16)

[Claims] 1. A first lens which is a negative lens, a second lens which is a positive lens, and three or four lenses subsequent to the first lens, and at least two negative lenses and a positive lens are arranged in order from the object side. An imaging lens having three lenses, wherein at least two of the lenses constituting the entire optical system are made of plastic. 2. The imaging lens according to claim 1, wherein each of the two plastic lenses is a negative lens and a positive lens. 3. The apparatus according to claim 1, further comprising at least one set of cemented lenses subsequent to said second lens.
Or the imaging lens according to 2. 4. The first lens and a subsequent 1 lens in an all-optical system.
The when the plastic lens meter two positive _{lenses, 0.5 <f p / | f} 1 | <7.0 where, f _p: focus of one positive lens made of plastic distance f _1: the The focal length of one lens satisfies the following conditional expression.
An imaging lens according to item 1. 5. The imaging lens _{0.5 <f r /f<5.0 0.5 <|} f 1 | / f 0.5 <f 2 / f where, f: focal length f _r of the entire optical system synthesis of the third lens to the final lens focal length f _1: the focal point of the first lens distance f _2: the image pickup according to claim 1 or 2 the focal length condition: the second lens, wherein the Mitsurusu lens. When 6. the most image-side lens is a single _{lens, -2.0 <f / r L <} 2.0 where, f: total focal point of the optical system distance r _L: the final surface curvature becomes conditional expression The imaging lens according to claim 1 or 2, wherein the following condition is satisfied. 7. The method according to claim 1, wherein the second lens satisfies the following condition: 28 <ν _d <60, where ν _{d is the} Abbe number of the material of the second lens with respect to d-line. Imaging lens. 8. The imaging lens according to claim 1, wherein two plastic lenses have one or more aspherical shapes. 9. The imaging lens according to claim 1, wherein at least one surface of the first lens is an aspheric surface. 10. When the first lens is a plastic lens and a stop is arranged between the second lens and the third lens, at least one of two lenses adjacent to the stop is provided.
The lenses are positive lenses and the positive lens is at least one
The imaging lens according to claim 1, wherein the imaging lens is an aspheric plastic lens having a surface or more. 11. The imaging lens according to claim 1, wherein the positive lens closest to the image side is a plastic lens, and at least one surface of the positive lens is an aspherical surface. 12. The first lens has a concave surface on the object side, and −0.7 <(r ₂ + r ₁ ) / (r ₂ −r ₁ ) <5.0, where r _{1 is} the first lens. 4. The imaging lens according to claim 1, wherein the following conditional expression is satisfied: radius of curvature of the object side surface r ₂ : radius of curvature of the first lens image side surface. 13. A first lens, which is a negative lens, in order from the object side.
A lens system composed of five groups of five lenses including a lens, a second lens that is a positive lens, a third lens that is a negative lens, a fourth lens that is a positive lens, and a fifth lens that is a positive lens. An imaging lens, wherein an aperture is arranged between the second lens and the third lens, and at least one lens surface of the first lens is formed of an aspheric surface, and satisfies the following condition. 0.4 ≦ | f ₁ /f|≦4.0 1.1 ≦ | f ₁ / f ₃ | ≦ 1.9 where f is the combined focal length of all optical systems f _{1 is} the focal length of the first lens f ₃ : Focal length of the third lens 14. The imaging lens according to claim 13, wherein the first lens is an aspheric lens, and at least one of the fourth lens and the fifth lens is formed of an aspheric surface. . 15. A first lens, which is a negative lens, in order from the object side.
The lens system includes a lens, a second lens that is a positive lens, a third lens that is a negative lens, a fourth lens that is a positive lens, and a fifth lens that is a positive lens. using one side, and 0.3 <f _B / f <1 where, f: lens focal length f _B of: an image pickup lens and satisfies the back focus becomes conditional expression. 16. The imaging lens according to claim 15, wherein the third lens that is a negative lens and the fourth lens that is a positive lens are cemented lenses.