JP2010117669A - Single focus lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single focus lens that sufficiently satisfies a demand for the entire length of an optical system, a demand for high image quality and a demand for a low cost. <P>SOLUTION: The single focus lens includes, in order from the object side: a meniscus-shaped first lens of positive power, the object side face of which is convex; and a second lens that is aspherical on both sides such that its shape near the center is convex on the object side and has positive power, and the shape of the peripheral part is concave on the object side and has negative power following the gradual decrease in positive power toward the periphery. The single focus lens satisfies conditional expressions: (1) 1.65<L/Ih<1.89; and (2) 0.88<¾h1/h2¾; wherein L is the entire length of the optical system; Ih is the radii of an image circle; h1 is the height of the inflection point of the object side face of the second lens from an optical axis; and h2 is the height of the inflection point of the image side face of the second lens from the optical axis. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a single-focus lens, and more particularly to a single-focus lens that forms an object image on an imaging surface of a solid-state imaging device such as a CCD or CMOS mounted in a mobile phone or a portable computer equipped with a camera module. .

  In recent years, for example, mobile phones and portable computers equipped with a camera module using a solid-state imaging device such as a CCD or CMOS have been rapidly reduced in size and cost. Along with this, further miniaturization and cost reduction are required for imaging lenses mounted on them. As such an imaging lens, a single lens system using a single lens has been conventionally used.

JP 2007-156031 A JP 2004-170460 A

  However, with a single lens system, it is possible to reduce the size and cost, but it is difficult to correct each aberration in order to sufficiently display the resolution of a recent solid-state imaging device. Therefore, recently, an optical system using two or more lenses has been proposed. For example, the optical systems described in Patent Document 1 and Patent Document 2 are examples in which two lenses are used.

  However, in the optical systems described in Patent Document 1 and Patent Document 2, if the total length of the optical system is shortened in accordance with the current request, various aberrations increase, and it becomes impossible to meet the demand for high image quality. There is a problem. In addition, although an optical system using three or more lenses is easy to obtain good optical performance, there is a problem that it is more difficult than an optical system having two lenses from the viewpoint of shortening the overall length.

  The present invention has been made under the above-described background, and an object of the present invention is to provide a single focus lens that can sufficiently satisfy the demand for the total length of the optical system, the demand for high image quality, and the demand for low cost. To do.

Means for solving the above-described problems are as follows.
In order from the object side, a meniscus first lens having a positive power with the object-side surface convex,
Both sides are aspherical, the shape near the center with the convex surface facing the object with positive power, and the positive power gradually weakens toward the periphery, with the concave surface facing the object side with negative power at the periphery A second lens having a shape,
In addition, the single focus lens is configured to satisfy the following conditional expressions (1) and (2).
1.65 <L / Ih <1.89 (1)
0.88 <| h1 / h2 | (2)
However,
L: Optical total length Ih: Image circle radius h1: Height from the optical axis of the inflection point on the object side surface of the second lens h2: Height from the optical axis of the inflection point on the image side surface of the second lens

According to the above means, each aberration can be suppressed at the same time while keeping the entire length of the optical system short.
That is, by configuring both the first lens and the second lens with positive lenses, the total length of the lens can be reduced. In the positive / negative configuration, power is concentrated on the positive lens in order to shorten the overall length. However, by using the positive / negative configuration, bias in power distribution can be avoided and manufacturing errors can be reduced. In addition, the second lens is a positive lens having a convex surface facing the object side, both surfaces are aspherical, and the positive power gradually decreases from the center of the lens to the periphery, and has a negative power at the periphery. By using this positive lens, it is possible to effectively utilize the negative power at the peripheral portion, align the image plane and make it flat, and it is suitable for aberration correction.
If the second lens has a positive power over the entire area, the image plane falls to the object side and the optical performance deteriorates. However, effective aberration correction is possible by using the above shape.
In addition, in an optical system having a very short total lens length such as a single focus lens according to the above means, the incident angle to the image pickup device is large. However, the second lens has a positive power at the center and a peripheral portion. Since the shape is such that the positive power is gradually weakened as it goes, and the peripheral portion has negative power, an effect of reducing the incident angle to the image sensor can be obtained. In particular, the second lens has a shape in which both surfaces have inflection points, the image side surface mainly serves to reduce the incident angle to the image sensor, and the object side surface mainly includes the second surface. It is considered that it plays the role of adjusting the amount of negative power at the periphery of the lens and the role of assisting the image side surface, and in the following conditional expression (1), the second lens satisfies the conditional expression (2). It is preferable that
1.66 <L / Ih <1.89 (1)
0.88 <h1 / h2 (2)
As described above, the smaller the optical system, the larger the incident angle to the image sensor. Therefore, the image side surface alone is sufficient to reduce the incident angle to the image sensor on the image side surface of the second lens. The effect cannot be obtained. Therefore, it is necessary to bend the light beam slightly toward the optical axis on the object side surface as an aid to the image side surface, and the above conditional expression is used to correct the tilt of the image surface while slightly bending the light beam toward the optical axis. By setting as in (2), it is possible to reduce the incident angle to the image sensor sufficiently and sufficiently on the object side surface, and to obtain the best negative power for correcting various aberrations.
However, when h1 / h2 in the above conditional expression (2) is smaller than 0.88, H1 is relatively closer to the optical axis than H2, and the best negative for correcting the image plane in the peripheral portion. Power cannot be obtained, and correction of various aberrations including astigmatism becomes difficult.
That is, when h1 / h2 is 0.88 or more, the light beam is bent slightly on the object side surface, and the light beam is bent largely on the original image side surface that lowers the incident angle to the image sensor. However, when h1 / h2 is 0.88 or less, the light ray is greatly bent on the object side surface, the original role cannot be achieved on the image side surface, and the role of bending the light beam is weakened. In addition, since the roles that the image side and the object side should have are lost, the balance of the negative power in the periphery is lost, and aberration correction becomes difficult.

  FIG. 1 is a diagram illustrating a configuration of a single focus lens according to the first embodiment, FIG. 2 is an explanatory diagram of the second lens in FIG. 1, and FIG. 3 is a diagram illustrating each aberration of the single focus lens according to the first embodiment. is there. The single focus lens according to the first embodiment will be described below with reference to these drawings.

As shown in FIG. 1, the single focus lens according to the first embodiment includes the first lens 1, the second lens 2, the optical member 3, and the imaging surface 4 in order from the object side to the image plane side. It is arranged on O. The first lens 1 is an aspheric meniscus lens having a positive power with a convex surface facing the object side. The second lens 2 is a positive region in which the object side surface is a convex surface on the object side and the image surface side is a concave surface on the image surface side in a certain region including at least the region from the lens center toward the periphery. The lens. The positive power gradually decreases from the lens center to the periphery, and the lens is an aspheric lens having negative power at the periphery.

  The optical member 3 has a transparent thin plate shape, and in this embodiment, an IR cut filter that cuts infrared light from transmitted light is used. The imaging surface 4 is a light receiving surface of an imaging element such as a CCD or CMOS. In addition to the IR filter, the optical member 3 may be a cover glass, a low-pass filter, or the like.

  Here, as shown in FIG. 1, the surfaces of the first lens 1, the second lens 2, the optical member 3, the imaging surface 4, and the distances between the surfaces are as follows. That is, the object side surface of the first lens 1 is M1, and the image side surface is M2. The object side surface of the second lens 2 is M3, and the image side surface is M4. Further, the object side surface of the optical member 3 is M5, and the image side surface is M6.

Further, the distance between the surfaces M1 and M2 is d1. Here, the distance between the surfaces M1 and M2 is the distance between the points 11 and 12 when the intersections of the optical axis O of the first lens 1 and the surfaces M1 and M2 are 11 and 12, respectively. Okay, this is also the center thickness of the first lens. Similarly, the distance between the surfaces M2 and M3 (the distance between the points 12 and 21; the air space between the lenses) is d2, and the distance between the surfaces M3 and M4 (the distance between the points 21 and 22; the second). Lens center thickness) is d3
And the distance between the surfaces M4 and M5 (the distance between the points 22 and 31; the air space between the lenses)) is d4.
And the distance between the surfaces M5 and M6 (the distance between the points 31 and 32; the center thickness of the optical member 3) is d5.
And a distance between the surface M6 and the imaging surface 4 (a distance between the point 32 and the point 41; an air interval between the optical member 3 and the imaging surface 4) is d6.

Further, when the radii of curvature of the surfaces M1 to M6 are r1 to r6, the refractive index of d-line of each lens or the like is nd, and the Abbe number is νd, the optical system according to the first example is shown in Table 1. Have a value.

And the surface shape of each surface M1-M6 is represented by the following aspherical formulas.
Z = Ch ² / [1+ (1-KC ² h ² ) ^1/2 ] + A ₄ h ⁴
+ A ₆ h ⁶ + A ₈ h ⁸ + A ₁₀ h ¹⁰ + A ₁₂ h ¹² (4)
However,
Z is the length of a vertical line drawn from a point on the aspheric surface at a height h from the optical axis O to the tangential plane at the apex of the aspheric surface,
C is the curvature (1 / r),
h is the height from the optical axis,
K is the conic constant,
A ₄ , A ₆ , A ₈ , A ₁₀ , and A ₁₂ are _fourth , _sixth , _eighth , _tenth , and _twelfth -order aspheric coefficients.

The values of the constants K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ in the formula (4) for each surface M1 to M4 are as shown in Table 2.

In the optical system, the focal length f1 of the first lens 1, the power P1 of the first lens 1, the focal length f2 of the second lens 2, the power P2 of the second lens 2, the total length L, F number of the optical system, the optical system The respective values of the overall focal length f, the image circle radius Ih, and L / Ih are as follows.
f1; 1.72 mm
P1; 0.58
f2; 3.92 mm
P2; 0.25
L; 1.53mm
F number: 2.80
f; 1.31 mm
Ih; 0.90
L / Ih = 1.7 (satisfy 1.65 <L / Ih <1.89)

Here, as shown in FIG. 2, the second lens 2 has inflection points H1 and H2 on the object side surface M3 and the image side surface M4, respectively. Assuming distances h1 and h2 from the inflection points H1 and H2 to the optical axis O, the values of h1, h2, and h1 / h2 are as follows.
h1; 0.35 mm
h2; 0.38 mm
h1 / h2; 0.91 (0.88 <| h1 / h2 | is satisfied)

  Thus, by providing inflection points on the object side surface and the image surface side surface of the second lens 2 and changing the curvature from positive to negative at the inflection point, the incident angle on the imaging surface 4 is suppressed as small as possible. It becomes possible. At the same time, negative power can be given to the periphery, and the image surface that has fallen to the image side can be returned to a flat shape by the positive / positive lens construction.

Table 3 shows the position of the chief ray passing through the second lens 2 in the optical system according to the first embodiment as the image height, and the incident angle of the chief ray on the imaging surface at each image height. .

  FIG. 4 is a graph in which the horizontal axis represents the position where the principal ray passes through the second lens 2 in the optical system according to the first embodiment as the image height, and the vertical axis represents the incident angle to the imaging surface. From this graph, it can be seen that the increase in incident angle is suppressed (28 ° or less) around the lens where the image height is high.

  Furthermore, the spherical aberration, astigmatism, and distortion of the optical system according to the first embodiment are as shown in FIG. This satisfies the conditions that the spherical aberration is within ± 0.1 mm, the astigmatism is within ± 0.1 mm, and the distortion is within 5%. In addition, since it is composed of two positive lenses, it is possible to obtain a large power for shortening the overall length and to avoid biasing the power to one lens. This facilitates the production of the lens and enables the production cost to be reduced. Further, since the first lens 1 is convex on the object side, it is possible to obtain a small F number (bright lens).

  FIG. 5 is a diagram showing an optical system having a conventional positive / positive lens configuration shown as a first comparative example. As shown in FIG. 5, in this optical system, the first lens 101, the second lens 102, the optical member 103, and the imaging surface 104 are arranged on the optical axis O in order from the object side to the image plane side. It is a thing. The fundamental difference from the first embodiment is that the second lens 102 is a normal meniscus lens.

Table 4 shows, in the optical system according to the first comparative example, the position where the chief ray passes through the second lens 102 as an image height, and the incident angle of the chief ray on the imaging surface at each image height.

  FIG. 6 is a graph in the optical system according to the first comparative example, in which the horizontal axis is the position where the principal ray passes through the second lens 102 as the image height, and the incident angle to the imaging surface is the vertical axis. From this graph, it can be seen that as the image height increases, the incident angle increases almost linearly and exceeds 30 ° in the peripheral portion. Further, the image plane is greatly tilted to the image side.

Next, single focus lenses according to second to fourth embodiments of the present invention will be described. The single focus lenses according to the second to fourth embodiments have the same basic arrangement and configuration of the lenses as the single focus lenses according to the first embodiment, but differ in specific lens surface shapes, surface intervals, and the like. Table 5 is a table showing rm (r1 to r6), dm (d1 to d6), nd, and νd in the single focus lens according to the second embodiment.

Table 6 is a table showing the values of the constants K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ of the formula (4) for the surfaces M1 to M4 in the single focus lens according to the second embodiment. It is.

In the optical system of the second embodiment, the focal length f1 of the first lens 1, the power P1 of the first lens 1, the focal length f2 of the second lens 2, the power P2 of the second lens 2, the total length L of the optical system,
The values of the F number, the focal length f of the entire optical system, the image circle radius Ih, L / Ih, h1, h2, and h1 / h2 are as follows.

f1; 1.77 mm
P1; 0.56
f2; 3.60 mm
P2; 0.28
L; 1.52mm
F number: 2.80
f; 1.32 mm
Ih; 0.90
L / Ih = 1.7 (satisfy 1.65 <L / Ih <1.89)
h1; 0.37 mm
h2; 0.40 mm
h1 / h2; 0.93 (0.88 <| h1 / h2 | is satisfied)

  Furthermore, the spherical aberration, astigmatism, and distortion of the optical system according to the second embodiment are as shown in FIG. It satisfies the conditions that the spherical aberration is within ± 0.1 mm, the astigmatism is within ± 0.1 mm, and the distortion is within 5%.

Table 7 is a table showing rm (r1 to r6), dm (d1 to d6), nd, and νd in the single focus lens according to the third embodiment.

Table 8 is a table showing the values of the constants K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ of the formula (4) for the surfaces M1 to M4 in the single focus lens according to the third embodiment. It is.

  In the optical system of the third embodiment, the focal length f1 of the first lens 1, the power P1 of the first lens 1, the focal length f2 of the second lens 2, the power P2 of the second lens 2, the total length L of the optical system, The values of the F number, the focal length f of the entire optical system, the image circle radius Ih, L / Ih, h1, h2, and h1 / h2 are as follows.

f1; 1.73 mm
P1; 0.58
f2; 3.83 mm
P2; 0.26
L; 1.51mm
F number: 2.80
f; 1.31 mm
Ih; 0.90
L / Ih = 1.68 (satisfy 1.65 <L / Ih <1.89)
h1; 0.36 mm
h2; 0.40mm
h1 / h2; 0.90 (0.88 <| h1 / h2 | is satisfied)

  Furthermore, the spherical aberration, astigmatism, and distortion of the optical system according to the third embodiment are as shown in FIG. It satisfies the conditions that the spherical aberration is within ± 0.1 mm, the astigmatism is within ± 0.1 mm, and the distortion is within 5%.

Table 9 is a table showing rm (r1 to r6), dm (d1 to d6), nd, and νd in the single focus lens according to the fourth embodiment.

Table 10 is a table showing the values of the constants K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ of the formula (4) for the surfaces M1 to M4 in the single focus lens according to the fourth embodiment. It is.

  In the optical system of the fourth embodiment, the focal length f1 of the first lens 1, the power P1 of the first lens 1, the focal length f2 of the second lens 2, the power P2 of the second lens 2, the total length L of the optical system, The values of the F number, the focal length f of the entire optical system, the image circle radius Ih, L / Ih, h1, h2, and h1 / h2 are as follows.

f1; 1.73 mm
P1; 0.58
f2; 4.20mm
P2; 0.24
L; 1.69mm
F number: 2.80
f; 1.40 mm
Ih; 0.90
L / Ih = 1.88 (satisfy 1.65 <L / Ih <1.89)
h1; 0.31 mm
h2: 0.30 mm
h1 / h2; 1.02 (0.88 <| h1 / h2 | is satisfied)

  Furthermore, the spherical aberration, astigmatism, and distortion of the optical system according to the fourth embodiment are as shown in FIG. It satisfies the conditions that the spherical aberration is within ± 0.1 mm, the astigmatism is within ± 0.1 mm, and the distortion is within 5%.

The present inventor has verified the present invention for a number of similar examples in addition to the above-described first to fourth embodiments, and some of the examples are listed as Examples 1 to 13 and Comparative Examples A to F. For these examples, the values of h1, h2, h1 / h2, L, and L / Ih are listed in Table 11 and FIG. 10, and these various aberrations are listed in FIGS.

  As is clear from Table 11 and FIG. 10 and FIGS. 11 to 17, the examples listed as Comparative Examples A to F are 0.88 <| h1 / h2 | and 1.65 <L / Ih <1. .89, any one or more of the conditions is not satisfied, and the examples listed as Examples 1 to 13 are 0.88 <| h1 / h2 | and 1.65 <L / Ih <1. This is an example in which various aberrations can be kept within a desired range while keeping the total length short by satisfying both of the conditions of 89.

FIG. 18 is an explanatory diagram of the object side ray emission angle (A) and the image side ray emission angle (B). FIG. 19 shows variations in the light exit angle near the inflection point on the second lens image side surface and variations in the light exit angle near the inflection point on the second lens object side surface in Example 9 and Comparative Example D. FIG. Example 12 and Comparative Example B are variations in the light exit angle near the inflection point on the second lens image side surface and variations in the light exit angle near the inflection point on the second lens object side surface. FIG. And for Comparative Example F, the variation in the light exit angle near the inflection point on the side surface of the second lens image and the variation in the light exit angle near the inflection point on the side surface of the second lens object.

  In FIGS. 19 to 21, Examples 9, 12, and 13 are examples that satisfy both the conditions of 0.88 <| h1 / h2 | and 1.65 <L / Ih <1.89. Comparative Examples B, D, and F are examples in which the condition of 1.65 <L / Ih <1.89 is satisfied but the condition of 0.88 <| h1 / h2 | is not satisfied. As is clear from these figures, in Examples 9, 12, and 13, the inflection point on the image side is responsible for adjusting the incident angle to the imaging surface 4, and the light beam is bent greatly. In addition, the inflection point on the object side serves as an auxiliary role for the image side inflection point, and it only needs to bend the light beam slightly. By placing a lot of weight on the negative power adjustment, which is the main role, the negative power Balance is achieved, and various aberrations can be corrected.

  On the other hand, in the case of Comparative Examples B, D, and F, the inflection point on the image side is responsible for adjusting the incident angle on the imaging surface 4 and the light beam should be bent greatly. It can be seen that the image side inflection point has lost its original role and hardly bent the light beam. The main role of the inflection point on the object side is to adjust the negative power, but it plays many roles in bending the light beam, the negative power balance is lost, and it is difficult to correct various aberrations.

  The single-focus lens according to the present invention is used as a single-focus lens for forming an object image on an imaging surface of a solid-state imaging device such as a CCD or CMOS mounted on a mobile phone or a portable computer equipped with a camera module. can do.

It is a figure which shows the structure of the single focus lens concerning 1st Embodiment. It is explanatory drawing of the 2nd lens in FIG. It is a figure which shows each aberration of the single focus lens concerning 1st Embodiment. In the optical system according to the first embodiment, the horizontal axis represents the position where the principal ray passes through the second lens 2 as the image height, and the vertical axis represents the incident angle to the imaging surface. It is a figure which shows the optical system of the conventional positive / positive lens structure shown as a 1st comparative example. In the optical system according to the first comparative example, the horizontal axis represents the position where the principal ray passes through the second lens 2 as the image height, and the vertical axis represents the incident angle to the imaging surface. It is a figure which shows each aberration of the single focus lens concerning 2nd Embodiment. It is a figure which shows each aberration of the single focus lens concerning 3rd Embodiment. It is a figure which shows each aberration of the single focus lens concerning 4th Embodiment. It is the figure which plotted the value of h / h2 on the vertical axis | shaft and the value of L / Ih was plotted on the horizontal axis about Examples 1-13 and Comparative Examples AF. It is a figure which shows the various aberrations of Comparative Examples A to C. It is a figure which shows the various aberrations of Comparative Examples D to F. It is a figure which shows the various aberrations of Examples 1-3. It is a figure which shows the various aberrations of Examples 4-6. It is a figure which shows the various aberrations of Examples 7-9. It is a figure which shows the various aberrations of Examples 10-12. It is a figure which shows the various aberrations of Example 13. It is explanatory drawing of the object side light ray emission angle (A) and image side light ray emission angle (B) of a 2nd lens. FIG. 10 is a diagram illustrating a variation in the light exit angle near the inflection point on the second lens image side surface and a variation in the light exit angle near the inflection point on the second lens object side surface for Example 9 and Comparative Example D. FIG. 14 is a diagram showing a variation in the light emission angle near the inflection point on the second lens image side surface and a variation in the light emission angle near the inflection point on the second lens object side surface in Example 12 and Comparative Example B. FIG. 14 is a diagram illustrating a variation in the light exit angle near the inflection point on the second lens image side surface and a variation in the light exit angle near the inflection point on the second lens object side surface for Example 13 and Comparative Example F.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 Optical member 4 Imaging surface

Claims (1)

In order from the object side, a meniscus first lens having a positive power with the object-side surface convex,
Both sides are aspherical, the shape near the center with the convex surface facing the object with positive power, and the positive power gradually weakens toward the periphery, with the concave surface facing the object side with negative power at the periphery A second lens having a shape,
In addition, the single focus lens is configured to satisfy the following conditional expressions (1) and (2).
1.65 <L / Ih <1.89 (1)
0.88 <| h1 / h2 | (2)
However,
L: Optical total length Ih: Image circle radius h1: Height from the optical axis of the inflection point on the object side surface of the second lens h2: Height from the optical axis of the inflection point on the image side surface of the second lens

Images