KR20050118139A - Optical system for security camera using aspheric surface - Google Patents

Abstract

The present invention relates to an optical system for surveillance cameras using an aspherical surface to increase brightness and resolution by complementing an existing spherical optical system through the use of aspherical surfaces, and having a convex surface on an object side and a concave surface on an image side. A first lens which is a magnification lens of; A second magnification lens having a convex surface on the object side and a convex surface on the image side, and an aspherical lens having both aspherical surfaces on both sides; A third lens having a positive magnification lens having convex surfaces on both the object side and the image side, wherein the object side convex surface forms an aspherical surface; A fourth lens which is a negative magnification lens having a concave surface on the object side and a flat or convex surface on the image side; The technical configuration is characterized by consisting of an aperture that selectively converges the light incident from the first lens.

According to the present invention, it is possible to reduce the size of the optical system and to facilitate the installation of the optical system in a narrow space as well as to expand the application range and to increase the resolution by implementing the miniaturization of the optical system by the appropriate aspherical design In addition to enabling megapixel performance, it also enables the construction of a lens optical system for each field of view characteristic, and has the effect of correcting aberrations and eliminating the difference in brightness between the center and the periphery of the lens.

Description

Optical system for surveillance camera using aspherical surface {OPTICAL SYSTEM FOR SECURITY CAMERA USING ASPHERIC SURFACE}

The present invention relates to an optical system for a surveillance camera that maintains a proper line angle and focuses on improving image quality, and more particularly, facilitates mounting in a narrow space and secures an amount of ambient light. The present invention relates to an optical system for surveillance cameras using an aspherical surface to enhance brightness and resolution by complementing existing spherical optical systems.

Existing low-cost surveillance cameras have been mainly used in closed spaces such as parking lots and elevators in apartments or in places where people such as factories are not suitable for direct monitoring.

Lenses used in such surveillance cameras are usually made of glass material, thereby causing a cost increase. In addition, there is a problem of deterioration of optical performance due to the remarkably lowered ambient light amount of less than 30% to less than 60%, and easy to produce image curvature or distortion, in particular, CMOS camera should use a lens with an ambient light amount of 70% or more. Not only was it difficult to apply, but a lens suitable for a CMOS camera has not been developed until now.

In addition, the market is growing rapidly, and according to the diversification of application fields, the market is demanding a camera with better optical performance as well as an improvement in image sensor technology. I'm asking.

The present invention has been made to solve the problems described above, the purpose is to reduce the size of the optical system by using an aspherical surface to facilitate mounting in a narrow space and to enlarge the application range It is to provide an optical system for surveillance camera using.

In addition, the present invention is designed to form an ambient light ratio of 90% or more to solve the difference in brightness between the center and the surrounding of the lens and to provide an optical system for surveillance cameras using aspherical surface to be used in CCD and CMOS cameras. have.

Furthermore, the present invention provides an aspherical surface that can achieve mega-pixel performance through the design of an aspherical surface so as to overcome the problem that the resolution of the conventional surveillance camera optical system mainly consists of only a spherical surface. It is to provide an optical system for surveillance cameras used.

The present invention for achieving the above object is a first lens which is a negative magnification lens having a convex surface on the object side and a concave surface on the image side; A second magnification lens having a convex surface on the object side and a convex surface on the image side, and an aspherical lens having both aspherical surfaces on both sides; A third lens having a positive magnification lens having convex surfaces on both the object side and the image side, wherein the object side convex surface forms an aspherical surface; A fourth lens which is a negative magnification lens having a concave surface on the object side and a flat or convex surface on the image side; The technical feature is a configuration including an aperture for selectively converging light incident from the first lens.

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

1 to 3 are views showing the arrangement state according to the angle of view characteristics of the optical system for surveillance cameras using the aspherical surface according to the present invention.

As shown in Figures 1 to 3, the optical system for surveillance cameras using the aspherical surface according to the present invention is configured to have the identity of the components, the angle of view (clock angle) by adjusting the design parameters of the components including the aspherical surface It is an optical system made to have a difference in processing.

The optical system of the present invention comprises a first lens 10 which is a negative ((-) Power) magnification lens having a convex surface R1 on the object side and a concave surface R2 on the image side; A second lens 20 which is a positive ((+) Power) magnification lens having a convex surface R3 on the object side and a convex surface R4 on the image side, and an aspherical lens having both aspherical surfaces on both sides; A third lens 30 having a positive [(+) Power] magnification lens having convex surfaces R5 and R6 on both the object side and the image side, wherein the object side convex surface R5 forms an aspherical surface; A fourth lens 40 which is a negative ((-) Power) magnification lens having a concave surface R7 on the object side and a planar or convex surface R8 on the image side; The diaphragm includes an aperture 50 that selectively converges the light incident from the first lens 10.

At this time, the image side surface R8 of the fourth lens 40 has a plane in the configuration of Fig. 1 (view angle 78 degrees) and Fig. 2 (view angle 92 degrees), and is convex in the configuration of Fig. 3 (view angle 120 degrees). It is configured to have a face.

In front of the image of the fourth lens 40, a window glass 60 for protecting the image pickup device and preventing foreign matters from entering the image lens and an image pickup device 70 for inputting image information are sequentially disposed. 70 includes a CCD sensor or a CMOS sensor.

Here, the first lens 10 and the second lens 20 are arranged to be spaced apart at regular intervals with the aperture 50 therebetween, and the third lens 30 and the fourth lens 40 are mutually It is configured to correct the junction chromatic aberration by abutting to be in contact with the surface contact, the chromatic aberration by adjusting the combination of the aspherical surface and the second lens 20 and the third lens 30 and their design parameters It is designed to be minimized.

By aspherizing the second lens 20 and the third lens 30 is configured to improve optical aberration, such as correction of spherical aberration, in the existing spherical optical system by actively using the aspherical degree of freedom along with such aspherical configuration The use of a lens corresponding to the arrangement of the second lens and the third lens as an expensive lens is configured to have a low-cost lens configuration.

In other words, the optical system of the present invention combines two spherical lenses 10 and 40 and two aspherical lenses 20 and 30 in combination, and at the appropriate magnification distribution and selection of a productive lens. It is to improve mass productivity and to make good aberration correction by making full use of two aspherical second lens 20 and third lens 30, especially correcting spherical aberration and tangential field curvature The state was made good.

The optical system according to the present invention having such a configuration is designed to form a total length of 20.4mm, an aperture ratio F / 2.5, and an angle of view (clock angle) of 78 degrees, 92 degrees, and 120 degrees while satisfying the following conditions.

[Condition 1]

1.2 ≤ B / f ≤ 2.4

Here, the focal length of the entire lens system is f, and the back focal length from the image side surface R8 of the fourth lens 40 to the focal point is B.

[Condition 2]

T / f ≤ 4.5

Here, the distance from the first first lens 10 of the optical system to the last fourth lens 40 is T, and the focal length of the entire lens system is f.

[Condition 3]

Xo1-Xa1 <0 [First surface R3 of aspherical second lens]

Xo2-Xa2> 0 [second surface R4 of the aspherical second lens]

Xo3-Xa3> 0 [first surface R5 of the aspherical third lens]

Herein, when the object-side convex surface R3 of the second lens 20 is an aspherical surface, the sag of the reference spherical surface is referred to as Xo1 and the sag by the aspherical surface is referred to as Xa1.

When R4, the image-side convex surface of the second lens 20, is an aspherical surface, the sag of the reference spherical surface is called Xo2, and the sag by the aspherical surface is Xa2.

When R5, the object-side convex surface of the third lens 30, is an aspherical surface, the sag of the reference spherical surface is called Xo3 and the sag by the aspherical surface is called Xa3. Satisfies the absolute value and the calculated values satisfy the real value.)

[Condition 4]

1.48≤n≤1.80, 35≤v≤65 [First Lens]

1.48≤n≤1.80, 45≤v≤85 [second lens]

1.48≤n≤1.80, 45≤v≤85 [Third Lens]

1.58≤n≤1.93, 18≤v≤30 [Fourth Lens]

Where n is the refractive index of the lens and v is the dispersion of the lens.

Next will be described the operation of the optical system for the surveillance camera using the aspherical surface according to the present invention implemented to satisfy the above conditions (Conditions 1 to 4).

Fig. 4 shows a sag Xa and a spherical surface in an aspherical surface in the optical system for a surveillance camera according to the present invention, when the height of the optical is Y in the plane where the curvature on the optical axis of the reference sphere is C (= 1 / R). As a graph showing Sag Xo in, comparing Sag Xa in an aspherical lens and Sag Xo in an aspherical lens, Equation 1 (for spherical lens) and Equation 2 (for aspheric lens) It can be represented by.

[Equation 1]

[Equation 2]

Where C is the curvature (C = 1 / R; R is the radius of the lens), Y is the height, K is the conic constant, and AD / AE / AF / AG represents the aspherical coefficient, respectively.

When the above conditions 1 to 3 are satisfied through this equation, the optical system of the present invention forms an optical field of 20.4 mm, an aperture ratio (f / dl) F / 2.5, and an angle of view (clock angle) of 78 degrees / 92 degrees / 120 degrees. You can do it.

In addition, Tables 1 to 3 show the optical system data according to the angle of view characteristics, and show the curvature radius of the lens, the center interval, the refractive index of the lens, and the dispersion coefficient of the lens.

[Table 1] Optical system data having a 78 degree view angle characteristic of the present invention

Lens surface Radius of curvature (r) Interval (d) Refractive index (n) Dispersion rate (v) Remarks First side (R1) 1.8283 0.1808 1.5688 56.04 2nd side (R2) 0.6502 1.0492 - - 0.4294 iris Page 3 (R3) * 1.8600 0.4226 1.4900 57.88 Aspheric surface Page 4 (R4) * -1.4532 0.0113 Aspheric surface Page 5 (R5) * 1.1119 0.6622 1.4900 57.88 Aspheric surface Page 6 (R6) -0.8588 0.1017 1.8467 23.78 Joint surface Page 7 (R7) -0.8588 0.1017 1.8467 23.78 Joint surface 8th page (R8) ∞ 0.6780 - - 0.1695 1.5168 64.20 Window glass - - 0.4533 Image pickup device

Here, each of the data is a value normalized to 1.0 mm of effective focal length (EFL).

K = 0.0, AD = 1.740343E-01, AE = 8.173637E-02, AF = 0.00000E-00, AG = 0.00000E-00 on the third side R3,

K = 0.0, AD = 1.174459E-01, AE = 1.537304E-01, AF = 0.00000E-00, AG = 0.00000E-00 of the fourth side (R4),

K = 0.0, AD = -4.875410E-02, AE = 7.507458E-03, AF = 0.00000E-00, and AG = 0.00000E-00 on the fifth surface R5.

[Table 2] Optical system data having a 92-degree field of view characteristic of the present invention

Lens surface Radius of curvature interval Refractive index (n) Dispersion rate (v) Remarks First side (R1) 2.5147 0.2118 1.6400 60.20 2nd side (R2) 0.7518 1.2035 - - 0.5917 iris Page 3 (R3) * 1.9853 0.4950 1.4900 57.88 Aspheric surface Page 4 (R4) * -1.6703 0.0132 Aspheric surface Page 5 (R5) * 1.3024 0.7756 1.4900 57.88 Aspheric surface Page 6 (R6) -1.0059 0.1191 1.8467 23.78 Joint surface Page 7 (R7) -1.0059 0.1191 1.8467 23.78 Joint surface 8th page (R8) ∞ 0.7941 10 - 0.1985 1.5168 64.20 Window glass 11 - 0.5000 Image pickup device

Here, each of the data is a value normalized to 1.0 mm of effective focal length (EFL).

K = 0.0, AD = 7.708711E-02, AE = 4.019489E-02, AF = 0.00000E-00, AG = 0.00000E-00 on the third side R3,

K = 0.0, AD = 6.073482E-02, AE = 6.638648E-02, AF = 0.00000E-00, AG = 0.00000E-00 of the fourth side (R4),

K = 0.0, AD = -2.536310E-03, AE = 3.405738E-03, AF = 0.00000E-00, AG = 0.00000E-00 on the fifth surface R5.

[Table 3] Optical system data having a 120 degree angle of view characteristic of the present invention

Lens surface Radius of curvature (r) Interval (d) Refractive index (n) Dispersion rate (v) Remarks First side (R1) 10.668 0.1801 1.5168 64.20 2nd side (R2) 0.8527 1.4235 - - 0.6538 iris Page 3 (R3) * 2.1318 0.6005 1.4900 57.88 Aspheric surface Page 4 (R4) * -2.0387 0.0150 Aspheric surface Page 5 (R5) * 1.4772 0.8797 1.4900 57.88 Aspheric surface Page 6 (R6) -1.1409 0.1351 1.8467 23.78 Joint surface Page 7 (R7) -1.1409 0.1351 1.8467 23.78 Joint surface Page 8 (R7) -16.514 0.9007 - - 0.2252 1.5168 64.20 Window glass - - 0.5060 Image pickup device

Here, each of the data is a value normalized to 1.0 mm of effective focal length (EFL).

K = 0.0, AD = 5.048711E-02, AE = 2.254509E-02, AF = 0.00000E-00, AG = 0.00000E-00 on the third side (R3),

K = 0.0, AD = 3.949785E-02, AE = 3.559711E-02, AF = 0.00000E-00, AG = 0.00000E-00 on the fourth side (R4),

K = 0.0, AD = -1.737992E-03, AE = 1.813929E-03, AF = 0.00000E-00, and AG = 0.00000E-00 on the fifth surface R5.

The present invention is an effective diameter (dl: mm), spherometer (measured by measuring the inner diameter in the projection measuring instrument (RROFELE PROJECTOR), the focal length measurement value of the entire lens system f, the rear focal length B, the first first lens of the optical system ( 10), the distance from the last fourth lens 40 to T, the angle of view measured value θ by the projection inspector, the center (CR) and the periphery (PR) of the resolution measured value (f / dl = F / 2.5), the second When the sag of the reference spherical surface of the lens 20 and the third lens 30 is Xa, and the sag by the aspherical surface is Xo, the lens shape and the lens arrangement of the optical system according to the present invention are as described above. , 3 and 4 are satisfied.

That is, [condition 1]

1.2 ≤ B / f ≤ 2.4,

[Condition 2]

With T / f ≤ 4.5,

[Condition 3]

Xo1-Xa1 <0 [First surface R3 of aspherical second lens]

Xo2-Xa2> 0 [second surface R4 of the aspherical second lens]

Xo3-Xa3> 0 [first surface R5 of the aspherical third lens],

[Condition 4]

1.48≤n≤1.80, 35≤v≤65 [First Lens]

1.48≤n≤1.80, 45≤v≤85 [second lens]

1.48≤n≤1.80, 45≤v≤85 [Third Lens]

1.58? N? 1.93, 18? V? 30 [Fourth lens] are satisfied.

Therefore, the optical system for surveillance cameras using the aspherical surface according to the present invention exhibits an optical performance having an optical field of 20.4 mm, an aspect ratio F / 2.5, and an angle of view (clock angle) of 78 degrees / 92 degrees / 120 degrees, and is an extremely small optical system. In addition, since two lenses of the four lenses are manufactured as the lenses 20 and 30 having aspherical surfaces, the number of lenses can be reduced and the aberration of the optical system can be minimized.

5A to 7D are graphs illustrating aberration characteristics of an optical system for a surveillance camera using an aspherical surface having different angle of view characteristics of 78 degrees, 92 degrees, and 120 degrees in the present invention.

5A, 6A, and 7A show meridian aberrations and spherical aberrations in regions 0, 0.7, and 1.0 on the optical axis, respectively, and FIGS. 5B, 6B, and 7B illustrate tangential field curvature (T). A) and astigmatism of the sagittal field curvature (S), and FIGS. 5C, 6C, and 7C show distortion, and FIGS. 5D, 6D, and 7D show chromatic aberration. Lateral Aberration). At this time, in FIG. 5B, FIG. 6B, and FIG. 7B, the curved surface curvature S is a line which has (x) mark, and the meridional surface curve T is a line which has (-) mark.

As shown in the analysis graph of FIGS. 5A to 7D, the optical system for the surveillance camera using the aspherical surface according to the present invention shows the values of the images adjacent to the axis in almost all fields, such as spherical aberration, meridian surface aberration, percent distortion, The correction state of chromatic aberration is in good condition, and it indicates that a very effective design is made to improve the brightness of the surroundings as well as the center.

In addition, in view of the fact that the distortion aberration in the optical system is minimized when the image distance and the object distance are similar, the conventional optical system corrects the distortion aberration by adjusting the shape of the lens, the arrangement of the refractive power, and the position of the aperture. In the present invention, two aspherical lenses having a positive refractive power (20, 30) are arranged immediately after the aperture forming the overall optical center, thereby correcting the spherical aberration and the meridian aberration. Therefore, it is possible to improve the brightness of the surroundings as well as the center.

As described above, according to the optical system for surveillance cameras using the aspherical surface according to the present invention, it is possible to reduce the size of the optical system by implementing the miniaturization of the optical system by the design of the appropriate aspherical surface, thereby mounting the optical system in a narrow space In addition to facilitating a wide range of applications.

In addition, by the aspherical design to achieve the mega-pixel (mega-pixel) performance by increasing the resolution, it is possible to configure a lens optical system for each view angle characteristic.

In addition, it is possible to form an ambient light ratio of 90% or more with good correction of aberration, thereby eliminating the difference in brightness between the center and the periphery of the lens, which can be used throughout CCD and CMOS cameras.

1 is a view showing an optical system characterized by an angle of view of 78 degrees of the arrangement of the optical system for surveillance cameras according to the present invention.

2 is a view showing an optical system characterized by an angle of view of 92 degrees of the array state of the optical system for surveillance cameras according to the present invention.

3 is a view showing an optical system characterized by an angle of view of 120 degrees of the arrangement of the optical system for surveillance cameras according to the present invention.

4 is a view showing a sag related to an aspherical lens of the optical system for surveillance camera according to the present invention.

5A to 5D are diagrams showing aberration characteristics of an optical system characterized by an angle of view of 78 degrees shown in FIG.

6A to 6D are diagrams showing aberration characteristics of an optical system characterized by a 92 degree angle of view shown in FIG.

7A to 7D are diagrams showing aberration characteristics of the optical system characterized by the 120-degree field of view shown in FIG.

Explanation of symbols on the main parts of the drawings

10: first lens 20: second lens

30: third lens 40: fourth lens

50: aperture 60: window glass

70: imaging device

Claims (4)

A first lens having a convex surface on the object side and a negative magnification lens having a concave surface on the image side; A second magnification lens having a convex surface on the object side and a convex surface on the image side, and an aspherical lens having both aspherical surfaces on both sides; A third lens having a positive magnification lens having convex surfaces on both the object side and the image side, wherein the object side convex surface forms an aspherical surface; A fourth lens which is a negative magnification lens having a concave surface on the object side and a flat or convex surface on the image side; An optical system for surveillance cameras using an aspherical surface comprising a diaphragm for selectively converging light incident from a first lens. The method of claim 1, When f is the focal length of the entire lens system and B is the rear focal length, 1.2 ≤ B / f ≤ 2.4 Surveillance camera optical system using an aspherical surface characterized by satisfying the phosphorus conditions. The method of claim 1, When the distance from the first lens plane of the optical system to the last lens plane is T and the focal length of the entire lens system is f, T / f ≤ 4.5 Surveillance camera optical system using an aspherical surface characterized by satisfying the phosphorus conditions. The method of claim 1, The first to fourth lenses, 1.48≤n≤1.80, 35≤v≤65 [First Lens] 1.48≤n≤1.80, 45≤v≤85 [second lens] 1.48≤n≤1.80, 45≤v≤85 [Third Lens] 1.58≤n≤1.93, 18≤v≤30 [Fourth Lens] An optical system for a surveillance camera using an aspherical surface, which satisfies the refractive index (n) and dispersion (v) conditions.