KR100662237B1 - Compact Shooting Optical System - Google Patents

Abstract

 The present invention includes a first lens, an aperture, a second lens, and a third lens in order from an object side, wherein the first lens is a positive refractive lens having a meniscus shape in which the object side is convex, and the second lens Is a lens of negative refractive power having a meniscus shape in which an image side is convex, and the third lens relates to a photographing optical system, wherein the third lens has positive or negative refractive power.

According to the present invention, it is possible to realize a microscopic imaging optical system having a resolution and image incidence angle applicable to the MEGA class and having an optical length shorter than the diagonal size of the sensor.

In particular, since the second lens L2 has negative refractive power, the optical electric field is shortened, thereby minimizing the size of the optical system, reducing the incident angle of the chief ray incident on the image sensor, and despite the short electric field, the back focal length (bfl). ) Can be secured.

Description

Small photographing optical system

 1A and 1B are diagrams illustrating a configuration diagram and aberration diagram of the optical system according to the first embodiment of the present invention, respectively.

 2A and 2B are diagrams illustrating a configuration diagram and aberration diagram of the optical system according to the second embodiment of the present invention, respectively.

 3A and 3B are diagrams illustrating a configuration diagram and aberration diagram of the optical system according to the third embodiment of the present invention, respectively.

* Explanation of symbols for main parts of drawings *

L1: first lens L2: second lens

L3: Third Lens LF: FILTER

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing optical system for use in a digital photographing apparatus such as a digital still camera, a surveillance camera, a PC camera, a mobile phone camera, and the like. It is about.

Recently, as the spread of digital still cameras and mobile phone cameras has increased significantly, and miniaturization and light weight of devices have been pursued, opposing technical matters such as miniaturization and high performance are required for the lens optical system used therein.

In addition, in the past, the optical system used in such a device is often composed of one or two lenses, but in recent years, more than three lenses are used to secure high performance through aberration correction.

The structure of the compact photographing optical system including three lenses is also disclosed in US Patent Publications US2003 / 210475 and US2004 / 246598.

Looking at this, the optical system described in US2003 / 210475 has the refractive power of each lens in the order of positive, positive, and negative from the object side, and realizes high performance, but in terms of size, the optical length (image on the first side of the first lens) The distance to the plane is 1.26 times larger than the diagonal size of the image sensor.

The optical system described in US2004 / 246598 also has a refractive power distribution in the order of positive, positive, and negative, and also realizes a high performance, but the optical length is 1.1 to 1.42 times the diagonal size of the image sensor.

However, in the recent compact photographing optical system, since the optical length of a very short length is required for miniaturization, there is a problem in that the compact optical system of the above-described configuration is increasingly difficult to apply to the microscopic optical system.

The present invention has been made to solve such a problem, and has an object of providing a method of significantly reducing the size of a photographing optical system by minimizing an optical electric field while having a high performance that is applicable to a MEGA class.

In order to achieve the above object, the present invention includes a first lens, an aperture, a second lens, and a third lens in order from an object side, and the first lens has a positive refractive power having a meniscus shape in which the object side is convex. A lens, wherein the second lens is a lens of negative refractive power having a meniscus shape of which the image side is convex, and the third lens provides a positive or negative refractive power.

In this case, all the lens surfaces of the first lens, the second lens, and the third lens are preferably aspherical surfaces.

In addition, it is preferable that the third lens has a concave shape, and the peripheral portion of the lens effective mirror has positive refractive power.

In addition, the photographing optical system satisfies the condition of 0.65 <TTL / 2Y <0.95 when TTL is a distance from the first surface of the first lens to the image plane and Y is the highest image height in the image plane. .

In addition, the photographing optical system preferably satisfies the condition of -1.5 <f / f2 <0 when f is the total focal length of the lens system and f2 is the focal length of the second lens.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention;

Lens optical system according to an embodiment of the present invention includes three lenses, basically as shown in Figure 1a, 2a or 3a to distribute the lens refractive power to the telephoto type (telephoto type), each lens It is characterized by shortening the overall length by configuring the power of refraction in the order of positive, negative, positive or positive, negative, negative from the object side.

That is, from the object side, the first lens L1 has a positive refractive power as a meniscus shape in which the object side is convex, and the second lens L2 has a negative refractive power as a meniscus shape in which the image side is convex and has a third refractive index. L3) has a positive or negative refractive power.

In particular, when the second lens L2 has negative refractive power, the following effects may be obtained.

First, the effect of shortening the optical length can be obtained.

Second, it is possible to reduce the incident angle to the image by increasing the effective height of the center ray to the surrounding field.

Third, in spite of the short length, the lens has a free rear focusing distance (bfl), which increases the degree of freedom in mechanical design. The post focal length bfl means the distance from the last lens surface of the optical system to the image surface.

On the other hand, the third lens (L3) uses a lens having a positive refractive power in the peripheral portion of the effective diameter in order to reduce the incident angle of the chief ray incident on the image plane and to increase the resolution of the lens.

In addition, in the present invention, all six lens surfaces of the three lenses constituting the optical system are aspherical, and through this, they may have high performance despite a short overall length. Aspheric shape may be expressed by the following equation (1).

<Equation 1>

Where Z is the distance from the vertex of the lens to the optical axis direction, R is the distance in the direction perpendicular to the optical axis, C is the inverse of the radius of curvature at the vertex of the lens, a1 is the Conic constant, a4, a6, a8, a10, and a12 are aspherical surface coefficients, respectively.

On the other hand, the optical system according to the embodiment of the present invention must satisfy the following two conditions in addition to configuring the lens in the manner described above.

1. First condition

0.65 <TTL / 2Y <0.95

Where TTL: distance from the lens front face to the image plane (optical overall length)

          2Y: Sensor diagonal size in image

           Y: Highest height in image.

The first condition is for miniaturizing the size of the optical system according to the embodiment of the present invention.

If the TTL / 2Y exceeds the upper limit of the first condition, the overall length becomes too long to realize miniaturization of the optical system, which is the object of the present invention. It is hard to get.

2. Second condition

-1.5 <f / f2 <0

Where f is the total focal length of the lens system

       f2: focal length of the second lens,

The second condition defines the degree of negative refractive power of the second lens L2. When the refractive power exceeds the upper limit, since the second lens L2 has positive refractive power, the optical lens becomes difficult to shorten since the second lens L2 is out of the basic configuration of the present invention.

If the refractive power is smaller than the lower limit, the negative refractive power of the second lens L2 becomes so large that the refractive power burden of the first lens L1 and the third lens L3 becomes large, and thus, aberration correction becomes difficult, resulting in difficulty in obtaining high performance. Lose.

Here, the two conditions are not meaningful by themselves, and only when the three lenses have positive, negative, positive or positive, negative and negative refractive powers from the object side, the optical system having a predetermined size or more and having a microminiature performance Condition that can be implemented.

Table 1 below shows the design specifications for any of the three embodiments that meet both the above-described lens configuration and condition 1 and condition 2.

TABLE 1

The above three embodiments are all data of the lens system in which the image height Y value is 1 (that is, the size of the image diagonal is 2).

Where f is the focal length of the optical system, view angle is the angle of view of the lens, f1 is the focal length of the first lens (L1), f2 is the focal length of the second lens (L2), f3 is the focal length of the third lens (L3) , TTL / 2Y is the numerical value of condition 1, f / f2 is the numerical value of condition 2.

Data of the first, second, and third embodiments are as follows, and specific shapes of the optical system according to the above embodiments are shown in FIGS. 1A, 2A, and 3A.

Where R is the radius of curvature of the lens, D is the thickness or air spacing of the lens, Nd is the refractive index of the d-line of the lens, and νd is the Abbe's number of the lens.

<First Embodiment>

Second Embodiment

Third Embodiment

Meanwhile, FIGS. 1B, 2B, and 3B show aberration diagrams of the optical system according to the first and second embodiments, respectively, through which the spherical aberration, the astigmatism, and the distortion aberration are good in each embodiment.

In the astigmatism diagram, the tangential represents the astigmatism curve in the direction parallel to the object and the optical axis, and the sagital represents the astigmatism curve in the direction in which the object and the optical axis are perpendicular.

According to the present invention, it is possible to realize a microscopic imaging optical system having a resolution and image incidence angle applicable to the MEGA class and having an optical length shorter than the diagonal size of the sensor.

In particular, since the second lens L2 has negative refractive power, the optical electric field is shortened, thereby minimizing the size of the optical system, reducing the incident angle of the chief ray incident on the image sensor, and despite the short electric field, the back focal length (bfl). ) Can be secured.

In addition, the third lens L3 may have a positive refractive index at the peripheral portion of the lens effective mirror to improve resolution and reduce an incident angle of chief rays formed on the image sensor.

In addition, by assembling the front surface of the component lens can exhibit high performance despite the short length.

Claims (5)

A first lens, an iris, a second lens, and a third lens are sequentially provided from an object side, and the first lens is a positive refractive lens having a meniscus shape in which the object side is convex. In the photographing optical system having a negative refractive power lens having a convex meniscus shape, the third lens has a positive or negative refractive power, When f is the total focal length of the lens system and f2 is the focal length of the second lens, the shooting optical system is satisfied. -1.5 <f / f2 <0 The method of claim 1. All lens surfaces of the first lens, the second lens, and the third lens are aspherical surfaces. The method of claim 1, The third lens has a concave shape at the image side, and a photographing optical system characterized in that the peripheral portion of the lens effective mirror has a positive refractive power. The method of claim 1, TTL is the distance from the first surface of the first lens to the image plane, and when Y is the highest image height in the image plane, the shooting optical system is satisfied. 0.65 <TTL / 2Y <0.95 delete

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