KR100896634B1 - Auto focus Optical System - Google Patents

Abstract

Provides auto focusing optics.

According to an exemplary embodiment of the present invention, a liquid crystal lens having a curvature of an interface formed between different liquids contained therein according to an applied voltage is changed from an object side and the interface acting as a surface of a lens, and at least one refractive surface is an aspherical surface. A first lens group having a phosphor lens and having negative refractive power; A second lens group having at least one refractive surface aspherical and having positive refractive power; At least one refractive surface is an aspherical surface, and has a negative refractive power; And a fourth lens group having at least one refractive surface aspherical and having negative refractive power; It includes.

According to the present invention, miniaturization is possible and high resolution is obtained. When the compact camera module is required, power can be concentrated to maximize the efficiency of the optical system and to shorten the length of the entire optical system and consume less power. .

Liquid crystal, liquid crystal lens, optical system, aspherical surface, auto focus, high resolution, miniaturization

Description

Auto Focus Optical System

The present invention relates to an auto focusing optical system, and more particularly, to an auto focusing optical system that can obtain a compact and high resolution by using a liquid crystal lens whose phase difference changes according to an applied voltage.

Generally, a camera has a plurality of lenses and is configured to adjust the optical focal length by moving each lens to change its relative distance. Recently, a mobile communication terminal equipped with a camera has been introduced to enable recording of still images and videos, and the performance of the camera is gradually being improved for high resolution and high quality shooting.

However, the conventional camera module mounted in the mobile communication terminal adopts a fixed focus method, which makes it impossible to adjust the focus at a specific distance, thereby causing a problem in that there is a limit in the sharpness of image quality. Therefore, focusing is indispensable for camera modules larger than megapixels.

To this end, the necessity of applying a camera module having an automatic focusing device, a macro device and an optical zoom device to a mobile phone has emerged. However, a conventionally manufactured camera module has been difficult to mount in a small mobile phone.

That is, the conventional method uses a DC motor as a driving source of the focusing and / or zooming function by changing the relative distance between the image sensor and the lens. However, the response is because the relative distance between the lenses is changed by connecting a plurality of reduction gears. Due to the lowering of the speed and the deviation of the rotational speed, accurate position control for precisely adjusting the focus is difficult. Moreover, there is a problem that it is difficult to implement a focusing function in an extremely limited space in a small optical device such as a mobile phone because of its bulky and complex device.

In addition, in order to obtain a high resolution, a large number of lenses are used, and a manufacturing cost is high, and there is a problem that power consumption is large because mechanical driving is required.

In order to solve this problem, a method of implementing auto focusing using a liquid crystal lens has been proposed.

FIG. 1 is a schematic configuration diagram illustrating a general liquid crystal lens, in which a spacer 130 is disposed between two glass substrates 110 and 120 to form a chamber having a predetermined size, and the liquid crystal layer 113 in the chamber. Formed.

An indium-tin oxide (ITO) electrode layer 114 for voltage driving is formed on the upper surface of the lower glass 120, and the liquid crystal alignment is formed on the upper surface of the electrode layer 114 and the lower surface of the upper glass substrate 110. PI layers 115a and 115b are formed of polyimide, respectively, and an electrode pattern 116 printed on a metal material such as aluminum, chromium, and nickel is formed on the upper surface of the upper glass substrate 110. Equipped.

The electrode pattern 116 has an aperture area that transmits circular or elliptical light so as to serve as a stop for controlling the amount of light, and a driving voltage for driving the liquid crystal layer 113 is applied.

Accordingly, when the voltage is driven only in the range other than the aperture region through the electrode pattern, the potential difference P is formed to be gradient, thereby controlling the orientation of the liquid crystal molecules of the liquid crystal layer, thereby generating a position difference and collecting the light. Will be

Due to the distribution of the potential difference P shown in FIG. 1, a phase difference of light occurs as shown in FIG. 2A, and the phase difference corresponds to an optical path phase difference of light, which is the same as the optical path difference of a general glass lens. You have a principle.

That is, the phase difference distribution value generated in the liquid crystal layer may correspond to a general lens shape as shown in FIG. 2 (b), and the optical characteristics of the lens may be geometrically determined using this.

Here, FIG. 2 (a) is not limited to the values disclosed as data applied for explaining the operation of the liquid crystal lens, and FIG. 2 (b) is data obtained when the normal lens is assumed to be a convex lens having a refractive index of 1.52. As shown in FIG. 2 (a), the liquid crystal lens having the phase difference distributed as shown in FIG. 2 (b) has the same optical characteristics as the block lens having a refractive index of 1.52 having a radius of curvature of -100 mm.

As described above, the liquid crystal lens has an advantage of miniaturization compared to the conventional method of adjusting the focus through the mechanical driving of the lens. However, when using only the liquid crystal lens, the resolution remains at approximately 300,000 pixels, so high resolution cannot be obtained. There is a limit to apply to mecha pixel camera. In order to solve this problem, there is a need for an auto focusing optical system capable of miniaturization and high resolution.

Accordingly, an object of the present invention is to provide an autofocus optical system capable of miniaturization and high resolution.

In particular, it is an object of the present invention to provide an auto focusing optical system capable of maximizing the efficiency of the optical system and shortening the length of the entire optical system by concentrating power when a compact camera module such as a camera phone is required.

It is also an object of the present invention to provide an autofocus optical system with low power consumption.

As a specific means for achieving the above object, the present invention in order from the object side, the phase difference distribution is formed in the liquid crystal contained therein according to the applied voltage is changed the curvature of the boundary surface formed between the body and the boundary surface of the lens A first lens group having a liquid crystal lens serving as a surface, and a lens in which at least one refractive surface is an aspherical surface, and having positive refractive power; A second lens group having at least one refractive surface aspherical and having negative refractive power; At least one refractive surface is an aspherical surface, and has a third lens group having positive refractive power; And a fourth lens group having at least one refractive surface aspherical and having negative refractive power; It provides an auto focusing optical system comprising a.

Preferably, the following Conditional Expression 1 is satisfied with respect to the refractive power of the liquid crystal lens.

(Condition 1)

0 ≤ D ≤ 20

Here, D is a refractive power (unit: diopter) of the plane in which the focal length of the lens changes due to the phase difference change of the liquid crystal lens.

More preferably, the following Conditional Expression 2 is further satisfied with respect to the optical axis direction dimension of the entire lens group.

(Condition 2)

1.0 <TTL / f <1.5

TTL is the distance from the aperture stop to the image plane, and f is the combined focal length of the optical system.

More preferably, the following Conditional Expression 3 is further satisfied with respect to the power of the first lens group.

(Condition 3)

0.5 <f1 / f <0.8

Here, f1 is the combined focal length of the first lens group.

More preferably, the following Conditional Expression 4 and Conditional Expression 5 further satisfy the shape of the first lens group.

(Condition 4)

0.4 <r2 / f <0.7

Here, r2 is the radius of curvature of the object-side surface of the first lens group.

(Condition 5)

0.7 <| r6 | / f <0.9

Here, r6 is the radius of curvature of the image-side surface of the first lens group.

More preferably, the following Conditional Expression 6 is further satisfied with respect to the power of the second lens group.

(Condition 6)

0.7 <| f2 | / f <1.1

Here, f2 is a combined focal length of the second lens group.

More preferably, the following Conditional Expression 7 is further satisfied with the shape of the second lens group.

(Condition 7)

0.7 〈r8 / f 〈1.0

Here, r8: is the radius of curvature of the image-side surface of the second lens group.

More preferably, the following Conditional Expression 8 is further satisfied with respect to the power of the third lens group.

(Condition 8)

1.0 <f3 / f <3.0

Here, f3 is a combined focal length of the third lens group.

More preferably, the following conditional expression 9 is further satisfied with the power of the third lens group.

(Condition 9)

0.1 <r10 / f <0.5

Here, r10 is the radius of curvature of the image-side surface of the third lens group.

More preferably, the following conditional expression 10 is further satisfied with respect to the shape of the third lens group.

(Condition 10)

1.0 <f4 / f <4.0

Here, f4 is a combined focal length of the fourth lens group.

More preferably, the following conditional expression 11 is further satisfied with the shape of the fourth lens group.

(Condition 11)

0.1 <r12 / f <0.4

Here, r12 is the radius of curvature of the image-side surface of the fourth lens group.

More preferably, an aperture stop for removing unnecessary light at the front end of the first lens group; It includes.

As described above, according to the present invention, the auto focusing optical system including the liquid crystal lens can be miniaturized and high resolution can be obtained.

In particular, by including the liquid crystal lens in the first lens group, the power of the first lens group can be increased to maximize the efficiency of the optical system and to shorten the length of the entire optical system. Therefore, it is applied to a small camera module such as a camera phone. This has the beneficial effect of doing it.

In addition, the present invention is less power consumption than the conventional mechanical driving method by using the liquid crystal lens, close-up photography is possible to benefit the code service (code service), and furthermore can be applied to the scanning function or optical function Will be.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a configuration diagram of a lens showing an embodiment of an autofocus optical system according to the present invention. In the drawings, the thickness, size, and shape of the lens are somewhat exaggerated for the sake of explanation, and in particular, the shapes of the spherical and aspherical surfaces shown in the drawings are provided as an example and are not limited thereto.

As shown in Fig. 3, the auto focusing optical system according to the embodiment of the present invention arranges the aperture stop 1 for removing unnecessary light closest to the object side, and then is applied in order from the object side. The liquid crystal lens 120 has a phase difference in the liquid crystal contained therein according to the voltage to change the curvature, and the liquid crystal lens 120 serves as the surface of the lens, and the lenses 110 and 130 have at least one refractive surface aspherical. And a first lens group LG1 having positive refractive power, at least one refractive surface is an aspherical surface, a second lens group LG2 having a negative refractive power, at least one refractive surface is an aspherical surface, and having a positive refractive power. The third lens group LG3 and at least one refractive surface are aspherical surfaces, and are composed of the fourth lens group LG4 having negative refractive power.

Here, chromatic aberration can be corrected through the first lens group LG1 having a strong positive refractive power and the second lens group LG2 having a strong negative refractive power, and a small optical system can be realized at a small F number. .

In addition, by arranging the third lens group LG3 to have a weak positive refractive power and the fourth lens group LG4 to have a weak negative refractive power, the third aberration such as spherical aberration, distortion aberration and coma aberration is corrected. This improves telecentricity and reduces the size of the entire lens system.

By arranging the aperture 1 of the optical system in front of the first lens group LG1 as the curvature changing unit, the curvature change in the first lens group LG1 for auto focusing according to the change in the position of the subject is displayed in the entire field. This will minimize the amount of defocus that will be incurred.

On the other hand, the first lens group LG1 has, in order from the object side, the first lens 110 and the object side surface 3 which have positive refractive power, the object side surface 2 is convex, and the image side surface 3 is flat. The second lens 120 having a liquid crystal layer and a negative refractive power, and the object side surface 5 is flat and the image side surface 6 is planar, and the image side surface 4 is convex, and the curvature varies between them. ) Includes the convex third lens 130.

Preferably, the second lens 120 has a liquid crystal in which a phase difference is formed in the liquid crystal contained therein according to the applied voltage, and thus the curvature changes so that the boundary surface serves as a surface of the lens. It consists of a lens.

That is, the second lens 120 made of a liquid crystal lens is divided into two lenses with the front and rear of an interface, and the liquid crystal layer 113 provided between the upper and lower glass substrates 110 and 120 is applied as shown in FIG. 1. The phase difference is generated according to the voltage, and the auto focusing is performed by changing the curvature of the boundary surface.

In this case, the first lens 110 and the third lens 130 may form a cover portion of the second lens 120.

By introducing the second lens 120, which is a liquid crystal lens, focus adjustment may be automatically performed according to an applied voltage.

On the other hand, by including the second lens 120, which is a liquid crystal lens whose focus changes due to a phase difference that changes when voltage is applied, to the first lens group LG1, the power of the first lens group is increased to increase the optical system as described later. It is possible to maximize the power of and shorten the length of the entire optical system, which is advantageous in that the auto focus can be performed in a small camera module.

In addition, the second lens group LG2 has a negative refractive power, the object-side surface 7 is flat, and the image-side surface 8 is concave. The third lens group LG3 has a positive refractive power. And the object side surface 9 is concave and the image side surface 10 is convex, while the fourth lens group LG4 has negative refractive power and the object side surface 11 is convex and the image side surface ( 12) is provided with a concave lens.

On the other hand, when the optical filter (OF) consisting of an infrared filter, cover glass, etc. is provided between the third lens (L3) and the image surface (IP), the image surface (IP) is an image formed by the lens in the CCD sensor, CMOS sensor, etc. It is a photosensitive surface which receives.

The optical system according to the embodiment of the present invention having such characteristics satisfies the following conditions.

(Condition 1)

0 ≤ D ≤ 20

Here, D is a refractive power of the surface in which the focal length of the lens changes due to the phase difference change of the liquid crystal lens, and the unit is a diopter.

Condition 1 above relates to the power of the optical system. If the upper limit is exceeded without satisfying Condition 1, the power arrangement of the optical system is not properly performed. Thus, the second lens group LG2 and the third lens The power arrangement of the group LG3 is changed so that the aberration characteristic for proximity is not good.

(Condition 2)

1.0 <TTL / f <1.5

Here, TTL is the distance from the aperture stop 1 to the image surface IP, and f is the combined focal length of the optical system.

The conditional expression 2 above relates to the optical axis direction dimension of the entire lens group and is a condition regarding miniaturization.

In other words, the deviation from the upper limit of Conditional Expression 2 is advantageous in terms of aberration correction, while the length of the optical system is so long that it cannot be mounted on a small optical device such as a camera phone or a PDA. However, the optical system length becomes too short, making it difficult to satisfy the desired optical characteristics.

(Condition 3)

0.5 <f1 / f <0.8

Here, f1 is a combined focal length of the first lens group LG1.

The conditional expression 3 above is related to the power of the first lens group, and is effective in correcting spherical aberration by giving the power of the first lens group LG1, which is the curvature change part, to be similar to the total power.

If f1 is longer than the upper limit value, the chromatic aberration increases because the power of the second lens group LG2, the third lens group LG3, and the fourth lens group LG4 must also be increased. On the contrary, when f1 is smaller than the lower limit value, the power of the first lens group LG1 becomes excessive, so that spherical aberration and coma aberration become large, and the radius of curvature of the lens spherical surface constituting the first lens group LG1 is reduced and processed. This becomes difficult.

(Condition 4)

0.4 <r2 / f <0.7

Here, r2 is the radius of curvature of the object-side surface 2 of the first lens group LG1.

(Condition 5)

0.7 <| r6 | / f <0.9

Here, r6 is the radius of curvature of the image-side surface of the first lens group.

Conditional Expressions 4 and 5 above relate to the shape of the first lens group LG1. If the upper and lower limit values deviate, the aberrations are excessively generated and cannot be corrected in other lens groups.

(Condition 6)

0.7 <| f2 | / f <1.1

Here, f2 is a combined focal length of the second lens group LG2.

The conditional expression 6 above relates to the power of the second lens group LG2. The second lens group mainly serves to correct aberrations occurring on the axis, and in particular, interacts with the first lens group LG1 to provide chromatic aberration. To compensate.

If it is out of the upper limit, chromatic aberration correction becomes difficult, and if it is out of the lower limit, the radius of curvature of the lens becomes small, making machining difficult.

(Condition 7)

0.7 〈r8 / f 〈1.0

Here, r8: is the radius of curvature of the image surface 8 of the second lens group LG2.

The above Conditional Expression 7 relates to the shape of the second lens group LG2. If the upper limit and the lower limit are out of range, the conditional expression 7 adversely affects spherical aberration, coma aberration, and distortion aberration. It is disadvantageous to, and beyond the lower limit, lens processing becomes difficult.

(Condition 8)

1.0 <f3 / f <3.1

Here, f3 is a combined focal length of the third lens group LG3.

The conditional expression 8 above relates to the power of the third lens group, and the third lens group LG3 has a weak positive power and serves to correct out-of-axis aberration, and if out of the upper limit, it becomes difficult to correct out-of-axis aberration. Outside of this, the chromatic aberration becomes large and the off-axis performance deteriorates.

(Condition 9)

0.1 <r10 / f <0.5

Here, r10 is a radius of curvature of the image side surface 10 of the third lens group LG3.

The conditional expression 9 above relates to the shape of the third lens group LG3. When the upper limit value is out of the range, the angle of the off-axis ray is lowered so that the correction is impossible in the fourth lens group. The surface telecentric property is improved, but the optical property is deteriorated due to the increase in the off-axis aberration.

(Condition 10)

1.0 <f4 / f <4.0

Here, f4 is a combined focal length of the fourth lens group LG4.

Conditional Expression 4 above relates to the power of the fourth lens group LG4. The fourth lens has a weak negative power and reduces the angle of the chief rays to reduce the difference in color sensitivity between the center and the periphery of the image. If it is out of the upper limit, the refractive power becomes smaller, making it difficult to miniaturize. If it is out of the lower limit, it is advantageous for miniaturization, but the peripheral color sensitivity is not good and distortion aberration increases.

(Condition 11)

0.1 <r12 / f <0.4

Here, r12 is the radius of curvature of the image surface 12 of the fourth lens group LG4.

The conditional expression 11 above relates to the shape of the fourth lens group LG4, and it is difficult to miniaturize if it is outside the upper limit value. Not only quality but also lens processing becomes difficult.

Hereinafter, a first embodiment and a second embodiment of the present invention implemented to satisfy the conditional expressions 1 to 11 will be described.

<First Embodiment>

The F number F _NO of the autofocus lens according to the first embodiment of the present invention is 2.6, the focal length f has a value of 3.9 mm, the field angle (2ω) is 60 °, and the total optical system length TTL. Has a value of 4.8 mm.

Table 1 describes exemplary values of each lens constituting the lens according to the exemplary embodiment of the present invention.

Here, r represents a radius of curvature of the lens surface, t represents a thickness of the lens or a distance between the lens surfaces, and n represents a refractive index. In addition, the unit of the value which shows a length is mm.

In Table 1, * denotes a surface whose curvature is variable, and the radius of curvature of the fourth surface according to the distance of the object is shown in Table 2 below.

As shown in Table 2, when the liquid crystal lens is used, the phase shift of the liquid crystal lens plays the same role as the change in the radius of curvature so that auto focusing is performed, thereby allowing super close-up photography. Therefore, there is an advantage that the fingerprint recognition or character recognition is possible through the camera module mounted on the mobile phone.

In other words, it is possible to further develop a code service (a service in which relevant information is displayed on a mobile phone when a camera is placed on a special character that looks like a barcode in a newspaper or a magazine). Furthermore, a scanner function or an optical zoom function can be implemented.

In Table 1, * denotes an aspherical surface, and an equation for aspherical surface coefficient is as follows.

Z: Distance from the vertex 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 at the vertex of the lens (1 / R)

K: Conic constant

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

Aspheric coefficients according to the first embodiment of the present invention calculated according to Equation 1 are shown in Table 2 below. In the above-described embodiment shown in FIG. 3, the first lens group LG1 and the first lens ( The object side surface 2 of the first lens group LG1, the image side surface 6 of the third lens 130, and the object side surface 9 and the image side surface 10 of the third lens group LG3 of 110. And the object-side surface 11 and the image-side surface 12 of the fourth lens group LG4 are aspherical surfaces.

On the other hand, the aspherical surface used in each of the following examples is obtained from the known equation (1), 'E and subsequent numbers' used for the Conic constant (K) and the aspherical surface coefficient represents a power of 10. For example, E + 01 represents 10 ¹ and E-02 represents 10 ⁻² .

Figure 4 shows the characteristics of spherical aberration, astigmatism and distortion according to the first embodiment of the present invention made of such an embodiment value, "S" in the astigmatism graph, "T" is a burnt Represents a tangential.

5 and 6 show the optical system MTF characteristics according to the embodiment of the present invention made up of these exemplary values. FIG. 5 shows the MTF characteristics for the long distance and FIG.

5 and 6 show the MTF change of spatial frequency per millimeter when the image height (distance from the center of the lens) is 0, and the space per millimeter when 0.5 fields, 0.7 fields, 0.9 and 1.0 fields The MTF change of frequency is shown, respectively. T represents a tangential MTF and R represents a MTF on a radiation source.

Here, MTF (Modulation Transfer Function) depends on the spatial frequency of the cycle per millimeter, and is a value defined by the following equation (2) between the maximum intensity (Max) and the minimum intensity (Min) of light.

In other words, when the MTF is 1, it is most ideal. The resolution decreases as the MTF value decreases.

As shown in FIG. 5 and FIG. 6, it can be seen that the MTF characteristics of the long distance and the short distance are excellent, and the autofocus type micro optical system capable of realizing high resolution using a liquid crystal lens can be implemented.

Second Embodiment

The F number F _NO of the autofocus lens according to the second exemplary embodiment of the present invention is 2.6, the focal length f has a value of 3.9 mm, the field angle (2ω) is 60 °, and the total optical system length TTL. Has a value of 4.8 mm.

Table 4 shows the example values of each lens constituting the lens according to the second embodiment of the present invention.

Here, r represents a radius of curvature of the lens surface, t represents a thickness of the lens or a distance between the lens surfaces, and n represents a refractive index. In addition, the unit of the value which shows a length is mm.

In Table 4, * denotes a surface having a variable curvature, denotes an aspherical surface, and the radius of curvature of the fourth surface according to the distance of the object is shown in Table 5 below.

As shown in Table 5, when the liquid crystal lens is used, the phase difference change of the liquid crystal lens plays the same role as the change in the radius of curvature so that auto focusing is performed, thereby allowing super close-up photography. Therefore, there is an advantage that the fingerprint recognition or character recognition is possible through the camera module mounted on the mobile phone.

That is, the code service (a service in which related information is displayed on a mobile phone when a camera is placed on a special character like a barcode in a newspaper or a magazine) can be further developed. Furthermore, a scanner function or an optical zoom function can be implemented.

In addition, each aspherical coefficient according to the second embodiment of the present invention calculated according to Equation 1 is shown in Table 6 below. In the second embodiment, like the first embodiment, the first lens group LG1 is first. The object side surface 2 of the lens 110, the image side surface 6 of the first lens group LG1, the third lens 130, and the object side surface 9 and the image side surface of the third lens group LG3 ( 10) and the object-side surface 11 and the image-side surface 12 of the fourth lens group LG4 are aspherical surfaces.

Fig. 7 shows the characteristics of spherical aberration, astigmatism, and distortion according to the second embodiment of the present invention, which is composed of such embodiment values. In the astigmatism graph, "S" is sagittal and "T" is burnt. Represents a tangential.

8 and 9 show the optical system MTF characteristics according to the second embodiment of the present invention, which is composed of such embodiment values, and FIG. 8 shows the MTF characteristics for the long distance and FIG.

8 and 9 show the MTF change of spatial frequency per millimeter when the image height (distance from the center of the lens) is 0, and the space per millimeter when 0.5 fields, 0.7 fields, 0.9 and 1.0 fields The MTF change of frequency is shown, respectively. T represents a tangential MTF and R represents a MTF on a radiation source.

Here, the MTF (Modulation Transfer Function) is a value defined by Equation 2 between the maximum intensity Max and the minimum intensity Min of the light, depending on the spatial frequency of the cycle per millimeter.

In other words, when the MTF is 1, it is most ideal. The resolution decreases as the MTF value decreases.

As shown in Figures 8 and 9, it can be seen that the MTF characteristics of the remote and short distance is excellent, and the autofocus type micro-optical system capable of realizing high resolution using the liquid crystal lens can be implemented.

On the other hand, the values of the conditional expressions 1 to 11 for the first embodiment and the second embodiment are shown in Table 7 below.

As shown in Table 7, it can be seen that the first and second embodiments of the present invention satisfy conditional expressions 1 to 11.

1 is a schematic diagram illustrating a general liquid crystal lens.

2 (a) is a graph showing the optical characteristics of the liquid crystal lens.

2B is a graph showing the optical characteristics of the optical lens.

3 is a block diagram of a lens showing the auto focus optical system according to the present invention.

4 is a graph showing characteristics of spherical aberration, astigmatism, and distortion of the optical system according to the first embodiment of the present invention.

FIG. 5 is a graph showing MTF characteristics of a long distance of an optical system according to a first embodiment of the present invention.

FIG. 6 is a graph illustrating MTF characteristics of a short range of an optical system according to a first exemplary embodiment of the present invention.

7 is a graph showing the characteristics of spherical aberration, astigmatism, and distortion of the optical system according to the second embodiment of the present invention.

8 is a graph showing the MTF characteristics over a long distance of the optical system according to a second embodiment of the present invention.

9 is a graph illustrating MTF characteristics of a short range of an optical system according to a second exemplary embodiment of the present invention.

Claims (12)

In order from the object side, A liquid crystal lens in which a phase difference distribution is formed in the liquid crystal contained therein according to the applied voltage, and the curvature changes, and the boundary surface serves as the surface of the lens, and at least one refractive surface is an aspherical lens. A first lens group having positive refractive power; A second lens group having at least one refractive surface aspherical and having negative refractive power; At least one refractive surface is an aspherical surface, and has a third lens group having positive refractive power; And A fourth lens group having at least one refractive surface aspherical and having negative refractive power; Auto focusing optical system comprising a. The method of claim 1, An autofocusing optical system that satisfies the following Conditional Expression 1 regarding the refractive power of the liquid crystal lens. (Condition 1) 0 ≤ D ≤ 20 D: refractive power (unit: diopter) of the plane in which the focal length of the lens changes due to the phase shift of the liquid crystal lens The optical focusing optical system according to claim 2, wherein the following Conditional Expression 2 is further satisfied with respect to the optical axis direction dimension of the entire lens group. (Condition 2) 1.0 <TTL / f <1.5 TTL: Distance from the dog stop to the top f: composite focal length of optical system The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 3 is further satisfied with respect to power of the first lens group. (Condition 3) 0.5 <f1 / f <0.8 f1: composite focal length of the first lens group 4. The autofocus optical system according to claim 2 or 3, wherein the following conditional expressions 4 and 5 are further satisfied with the shape of the first lens group. (Condition 4) 0.4 <r2 / f <0.7 r2: radius of curvature of the object-side surface of the first lens group (Condition 5) 0.7 <| r6 | / f <0.9 r6: radius of curvature of the image-side surface of the first lens group The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 6 is further satisfied with respect to the power of the second lens group. (Condition 6) 0.7 <| f2 | / f <1.1 f2: composite focal length of the second lens group 4. The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 7 is further satisfied with the shape of the second lens group. (Condition 7) 0.7 〈r8 / f 〈1.0 r8: radius of curvature of the image-side surface of the second lens group The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 8 is further satisfied with respect to power of the third lens group. (Condition 8) 1.0 <f3 / f <3.0 f3: composite focal length of the third lens group The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 9 is further satisfied with the shape of the third lens group. (Condition 9) 0.1 <r10 / f <0.5 r10: radius of curvature of the image-side surface of the third lens group The autofocus optical system according to claim 2 or 3, wherein the following conditional expression 10 is further satisfied with respect to power of the fourth lens group. (Condition 10) 1.0 <f4 / f <4.0 f4: composite focal length of the fourth lens group The optical focusing optical system according to claim 2 or 3, wherein the following conditional expression 11 is further satisfied with the shape of the fourth lens group. (Condition 11) 0.1 <r12 / f <0.4 r12: radius of curvature of the image-side surface of the fourth lens group An aperture stop according to any one of claims 1 to 3, further comprising: an aperture stop for removing unnecessary light at the front end of the first lens group; Auto focusing optical system comprising a.

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