KR101175873B1 - Compact optical system - Google Patents

Abstract

A compact imaging optical system according to the present invention.
An optical system for a camera of the present invention includes: a first lens having positive refractive power and having a convex shape toward an object side; A second lens having negative refractive power and shaped concave toward the object side; A third lens having a meniscus shape having positive refractive power and convex toward the image on the paraxial axis; And a fourth lens having a negative refractive power and having an aspheric shape having a concave surface on the paraxial axis, and having an advantage in that it is possible to implement a compact camera optical system that can be easily applied to a mobile communication terminal by improving design freedom. have.

Description

Compact optical system

The present invention relates to a compact imaging optical system, and more particularly, a diaphragm is disposed in front, consisting of four lenses having a positive, negative, positive, and negative refractive power in sequence, and shorten the overall length of the mobile phone or the like. The present invention relates to a compact imaging optical system that can be mounted on a portable terminal.

In recent years, mobile communication means such as mobile communication terminals, PDAs, and smart phones have been equipped with various types of additional functions in addition to basic communication functions as their usage increases and various services provided through communication technologies are diversified.

Among them, a camera module is essentially mounted in a mobile communication means for capturing or transmitting an image and making a video call, and various services are provided or new services are continuously developed using images captured through the camera module.

In particular, in recent years, miniaturization, weight reduction, and cost reduction are required for optical systems composed of lens groups mounted on a camera module, and as the pixel size of an image sensor composed of CCD and CMOS is gradually reduced, high resolution and high quality optical systems are required. It is true.

In order to maintain the high resolution of the optical system, a plurality of lenses should be used, and it is preferable to construct the optical system using glass lenses having high light transmittance and high refractive index, but due to the characteristics of the optical system mounted on the mobile communication means, The same optical system design has a problem that it is difficult to satisfy the conditions of miniaturization and low cost.

Therefore, the optical system mounted on the mobile communication means should use a plastic lens that is easy to mold and reduce the number of lenses possible for miniaturization and manufacturing cost reduction. However, since the optical performance uses a plastic lens whose optical performance is lower than that of the glass lens, the general optical system It is difficult to satisfy the optical performance by the design, and the design freedom of the optical system is reduced due to the reduction of the number of lenses.

In order to solve these disadvantages, the conventional optical system adopts an optical system in which a glass lens and a plastic lens are mixed to improve the performance of the optical system and correct aberration, but it is difficult to correct aberration and difficult to apply aspherical surface. Due to the characteristics of the lens, it is difficult to design an optical system having a short length due to the optical design, and it is difficult to reduce the manufacturing cost by using a glass lens.

Accordingly, the present invention was devised to solve the above-mentioned disadvantages and problems in the conventional optical system, and all four lenses are composed of aspherical plastic lenses, and the object-side surface of the second lens is concave. It is an object of the present invention to provide a small-capacity optical system that can be easily employed in a small portable terminal such as a mobile phone by minimizing the production cost while minimizing the length of the overall length.

The object of the present invention, the first lens having a positive refractive power and of the convex shape on the object side; A second lens having negative refractive power and concave toward the object side; A third lens of a meniscus shape having positive refractive power; And a fourth lens having an aspheric shape having negative refractive power.

The third lens may be configured as a surface convex toward the image side on the paraxial axis and concave toward the object side.

In addition, the fourth lens may be configured as a surface concave toward the object side on the paraxial axis.

In addition, the optical system of the present invention may satisfy the following Conditional Expression 1 with respect to the optical axis direction dimension and the following Conditional Expression 2 with respect to the radius of curvature of the second lens.

[Condition 1] 0.4 <f1 / f <1.0

[Condition 2] -4 <(R3 + R4) / (R3-R4) <-1

Here, f1: focal length of the first lens

          f: effective focal length of the whole optical system

         R3: paraxial curvature radius on the object side of the second lens

R4: Image paraxial curvature radius of the second lens

In addition, in the optical system of the present invention, both surfaces of the first to fourth lenses are preferably composed of aspherical surfaces.

In this case, all of the first to fourth lenses may be formed of plastic lenses.

In addition, the front of the first lens may be provided with an aperture stop for blocking unnecessary light from the light passing through the optical system of the present invention.

On the other hand, the optical system of the present invention satisfies the following Conditional Expression 3 with respect to the optical axis direction dimension.

[Condition 3] TTL / f <1.4

Here, TTL: distance from the object-side surface of the first lens to the image surface

f: effective focal length of the whole optical system

As described above, the optical system for a camera according to the present invention comprises four aspherical plastic lenses while applying four lenses, thereby improving design freedom and making it easy to apply a mobile communication terminal. There is an advantage to implement the optical system for.

1 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a first embodiment of the present invention.
2A to 2C are spherical aberration, astigmatism, and distortion aberration of the optical system shown in Table 1 and FIG. 1, respectively.
3A to 3D are field-specific coma aberration diagrams of the first embodiment.
4 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a second embodiment of the present invention.
5A to 5C are spherical aberration, astigmatism, and distortion aberration of the optical system shown in Tables 3 and 4, respectively.
6A to 6D are field-specific coma aberration diagrams of the second embodiment.
7 is a lens diagram illustrating a lens arrangement of an optical system for a camera according to a third exemplary embodiment of the present invention.
8A to 8B are spherical aberration, astigmatism, and distortion aberration of the optical system shown in Tables 5 and 7, respectively.
9A to 9D are field-specific coma aberration diagrams of the third embodiment.

Matters relating to the operational effects including the technical configuration for the above object of the compact imaging optical system according to the present invention will be clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention.

However, the thickness, size, and shape of the lenses in the lens configuration diagrams of the following embodiments are somewhat exaggerated for the detailed description of the present invention. In particular, the shape of the spherical or aspherical surface shown in the lens configuration is merely an example. It is not limited to a shape.

1 is a lens configuration diagram showing a first embodiment of an optical system for a camera according to the present invention. As shown in FIG. 1, the compact imaging optical system according to the present invention has a positive shape in a convex shape from the object side to the object side in order. A first lens L1 having refractive power, a second lens L2 concave toward the object side and a negative refractive power, a third lens L3 having positive refractive power in an image-convex meniscus shape, and The fourth lens L4 may have a negative refractive power, and the aperture diaphragm AS may be installed in front of the first lens L1.

In addition, between the fourth lens (L4) and the image surface 11, the optical filter (OF) consisting of a cover glass coated with an infrared filter or an infrared filter for blocking excessive infrared rays in the light passing through the optical system It may be provided.

The compact imaging optical system according to the present invention places the diaphragm AS in front of the first lens L1 so as to easily secure the amount of light and to block the light that can flow through the first lens L1 as much as possible. By making it possible, it is possible to configure an ultra-compact optical system while using four lenses.

In addition, since the fourth lens L4 is configured in a shape having an aspherical surface concave toward the object on the optical axis, the fourth lens L4 may converge luminous flux to provide an appropriate focal length. 11) The distortion aberration at the end can be controlled.

On the other hand, the first lens (L1) to the fourth lens (L4) employed in the present invention in consideration of the configuration of a compact imaging optical system mainly employed in the mobile communication terminal, the first lens (L1), the second lens ( Since the L2), the third lens L3 and the fourth lens L4 are all formed of a plastic lens which is easy to process the lens, the optical system can be reduced in weight and workability and the manufacturing cost can be reduced.

In addition, the first lens L1 to the fourth lens L4 may form an aspherical surface of each lens to facilitate correction of various aberrations, and may improve design freedom of the lens.

Therefore, in the optical system for a camera of the present invention, the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are disposed to have positive, negative, positive, and negative refractive power, respectively. In addition, the refractive surface of each lens is an aspherical surface which is easy to mold, thereby improving the resolution of the optical system, improving astigmatism and distortion characteristics, and placing the aperture AS in front of the first lens L1. It is possible to form a small optical system by reducing the size of L1).

Let us look at in more detail with respect to the effect of the following Conditional Expressions 1 to 6 under the optical system of the present invention having such a configuration.

[Condition 1] 0.4 <f1 / f <1.0

Here, f1 is the focal length of the first lens,

        f is the effective focal length of the whole optical system.

Conditional Expression 1 defines the optical axis direction dimension of the entire optical system and is a condition for miniaturization of the optical system.

In other words, if the optical power of the first lens is too large to deviate from the lower limit of Conditional Expression 1, it is difficult to correct spherical aberration and coma aberration, and if it is out of the upper limit of Conditional Expression 1, it may be advantageous in terms of correction of the aberration. The overall length in the optical axis direction is long, which is contrary to the miniaturization aspect, which is a technical feature of the small imaging optical system mainly employed in the mobile communication terminal.

[Condition 2] -4 <(R3 + R4) / (R3-R4) <-1

Where R3 is the object-side curvature radius with respect to the paraxial axis of the second lens,

        R4 is an image curvature radius with respect to the paraxial axis of the second lens.

Conditional Expression 2 defines the dimension of the radius of curvature of the second lens and is a condition for miniaturization similarly to Conditional Expression 1.

That is, when the deviation from the lower limit of Conditional Expression 1 is exceeded, the curvature of the object-side surface, which is the first surface of the second lens, may become excessively large. Therefore, it is difficult to correct chromatic aberration on the paraxial axis (optical axis). Since the effective diameter of the lens must be large (why is the effective diameter large?) , It is difficult to construct an optical system that pursues miniaturization as a whole.

[Condition 3] TTL / f <1.4

Here, TTL: distance from the object-side surface of the first lens to the image surface

          f: Effective focal length of the whole optical system.

Conditional Expression 3 is a condition for defining the full length of the entire optical system.

Hereinafter, the optical system of the present invention will be described in more detail through specific numerical examples.

As described above, the following first to third embodiments all have a first lens L1 having positive refractive power in a convex shape from the object side to the object side in order, and a negative refractive power having a concave shape toward the object side. A second lens (L2) having a positive lens, a third lens (L3) having positive refractive power in a meniscus shape convex toward the image, and a fourth lens (L4) having negative refractive power, and including a first lens ( In front of L1), an aperture stop AS is provided.

In addition, an optical filter OF including an infrared filter or a cover glass coated with an infrared filter is provided between the fourth lens L4 and the image surface 11.

On the other hand, the aspherical surface used in each of the following examples is obtained from a known equation (1), 'E used for the conic constant (K) and aspherical coefficients (A, B, C, D, E, F) And the number following it represents a power of ten. For example, E + 02 represents 10 ² and E-02 represents 10 ⁻² .

Where Z is the distance from the apex of the lens to the optical axis direction

Y: Distance in the direction perpendicular to the optical axis

c: inverse of the radius of curvature r at the vertex of the lens

K: Conic constant

A, B, C, D, E, F: Aspheric coefficient

[First Embodiment]

Table 1 below shows numerical examples according to the first embodiment of the present invention.

In addition, Figure 1 is a lens configuration showing the lens arrangement of the optical system for the camera according to the first embodiment of the present invention, Figures 2a, 2b and 2c is a spherical aberration of the optical system shown in Table 1 and 1, respectively Astigmatism and distortion aberrations are shown, and FIGS. 3A to 3D are field-based coma aberration diagrams of the first embodiment.

In the case of the first embodiment, the distance TL from the object-side surface 1 to the image surface of the first lens L1 is 4.152 mm, and the effective focal length f of the whole optical system is 3.884 mm. In addition, all of the first to fourth lenses L1 to L4 are made of plastic lenses.

In Table 1, the * in front of the surface number denotes an aspherical surface, and in the first embodiment, all surfaces of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4. Is aspherical.

In addition, the values of the aspherical coefficients of the first embodiment according to Equation 1 are shown in Table 2 below.

[Second Embodiment]

Table 3 below shows numerical examples according to the second embodiment of the present invention.

In addition, Figure 4 is a lens configuration showing the lens arrangement of the optical system for a camera according to a second embodiment of the present invention, Figures 5a and 5c are spherical and astigmatism of the optical system shown in Table 3 and 4, respectively And distortion aberrations, and FIGS. 6A to 6D are comma aberration diagrams for each field of the second embodiment.

In the case of the second embodiment, the distance TL from the object-side surface 1 to the image surface of the first lens L1 is 4.122 mm, and the effective focal length f of the entire optical system is 3.850 mm. In addition, all of the first to fourth lenses L1 to L4 are made of plastic lenses.

In Table 3, the * in front of the surface number denotes an aspherical surface, and in the second embodiment, all surfaces of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4. Is aspherical.

In addition, the values of the aspherical coefficients of the second embodiment according to Equation 1 are shown in Table 4 below.

Third Embodiment

Table 5 below shows a numerical example according to the third embodiment of the present invention.

7 is a lens configuration diagram showing the lens arrangement of the optical system for a camera according to the third embodiment of the present invention, and FIGS. 8A to 8C are spherical aberration and astigmatism of the optical system shown in Tables 5 and 7, respectively. 9A to 9D show the coma aberration for each field of the third embodiment.

In the third embodiment, the distance TL from the object-side surface 1 to the image surface of the first lens L1 is 4.116 mm, and the effective focal length f of the entire optical system is 3.850 mm. In addition, all of the first to fourth lenses L1 to L4 are made of plastic lenses.

In Table 5, the * in front of the surface number denotes an aspherical surface, and in the third embodiment, all surfaces of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4. Is aspherical.

In addition, the values of the aspherical coefficients of the third embodiment according to Equation 1 are shown in Table 6 below.

2, 3, 5, 6, 8, and 9, the optical system having excellent characteristics of the aberration can be obtained by using the above embodiments.

Meanwhile, the values of Conditional Expressions 1 to 3 for the first to third embodiments are shown in Table 7 below.

As shown in Table 7, it can be seen that the first to third embodiments of the present invention satisfy conditional expressions 1 to 3.

Preferred embodiments of the present invention described above are disclosed for the purpose of illustration, and various substitutions, modifications, and changes within the scope without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It will be possible, but such substitutions, changes and the like should be regarded as belonging to the following claims.

L1. First lens L2. Second lens
L3. Third lens L4. Fourth lens
AS. Aperture aperture OF. Optical filter
1, 2, 3, 4 ... 9, 10, 11. Face number

Claims (6)

A first lens having positive refractive power and shaped convex toward the object;
A second lens having negative refractive power and shaped concave toward the object side;
A third lens having a meniscus shape having positive refractive power and convex toward the image on the paraxial axis; And
And a fourth lens having a negative refractive power and having an aspherical surface with a concave surface formed on the paraxial axis.
The first to fourth lenses are composed of a plastic lens,
A compact imaging optical system that satisfies the following conditional expression for the radius of curvature of the second lens and the optical axis direction dimension of the optical system.
[Condition Expression] -4 <(R3 + R4) / (R3-R4) <-1
Here, R3: paraxial curvature radius on the object side of the second lens
R4: Image paraxial curvature radius of the second lens
[Condition Expression] TTL / f <1.4
Here, TTL: distance from the object-side surface of the first lens to the image surface
f: effective focal length of the whole optical system
The method of claim 1,
And the optical system satisfies the following conditional expression with respect to the optical axis dimension.
[Condition Expression] 0.4 <f1 / f <1.0
Here, f1: focal length of the first lens
f: effective focal length of the whole optical system
delete The method of claim 1,
The first to fourth lenses, the both sides of the compact imaging optical system consisting of an aspherical surface.
delete The method of claim 1,
A small imaging optical system having an aperture diaphragm for blocking unnecessary light flowing through the first lens in front of the first lens.

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