KR100457967B1 - Optical system for ultrathin visible and infrared broadband camera - Google Patents

Abstract

PURPOSE: An optical system is provided to achieve improved optical performance in both visible band and infrared band, even without performing a focusing operation. CONSTITUTION: An optical system comprises a first lens(10) having a convex surface arranged toward an object and a concave surface arranged upward; a second lens(20) having a convex surface toward the object and a plane surface arranged upward; an iris(60) for selectively converging light from the second lens; a third lens(30) having convex surfaces arranged toward the object and upward, respectively; a fourth lens(40) having convex surfaces arranged toward the object and upward; and a fifth lens(50) having concave surfaces arranged toward the object and upward. The first, second and fifth lenses have negative magnifying powers, and the third and fourth lenses have positive magnifying powers.

Description

OPTICAL SYSTEM FOR ULTRATHIN VISIBLE AND INFRARED BROADBAND CAMERA}

The present invention relates to an optical system for a camera, and more particularly, to an optical system for an ultra-small visible light and an infrared broadband camera, which is suitable for showing excellent optical performance that can be satisfied without additional focus adjustment in both the visible light band and the infrared band. .

In general, an optical system refers to a device for the purpose of making an image of a subject by using phenomena such as reflection and refraction of optical, and a plurality of lenses having a positive and a positive magnification are arranged and assembled, usually 5 sheets or It consists of four lenses.

These optical systems are used in various camera devices such as video phone cameras and CCTV (closed circuit) cameras. In general, CCTV cameras use sunlight during the day and separate lighting devices such as street lamps or incandescent lamps at night. The subject is captured by the camera.

However, at night, as a separate lighting device such as a street lamp, incandescent lamp is used as described above, people may feel that they are being monitored and cause discomfort, and they are not available in places where lighting devices are not installed. There was this.

Thus, to compensate for the shortcomings of the general CCTV cameras as described above, an infrared camera capable of capturing a subject at night without a street lamp or an incandescent lamp has appeared by using an infrared lighting device that is invisible to the human eye. Infrared bands, which are invisible to the eye, can be photographed, so that the subject can be photographed at daytime as well as at night.

Surveillance cameras using such an infrared illuminating device can be used in the visible light band during the day rich in natural light, and a broadband optical system that can be used in the infrared band at night when the natural light is insufficient.

However, optical systems used in surveillance cameras in the prior art have a significant decrease in optical performance in the infrared band, and therefore, subject to subjects in both the visible and infrared bands including the wavelength band of 400 to 940 nm, without additional focus adjustment. There was a problem in that image quality could not be obtained.

Therefore, in the related art, a separate apparatus for autofocusing has to be installed as a means to solve the above problems, which makes it difficult to miniaturize the product and increase the cost and inefficiency in the manufacturing process.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to provide an excellent optical performance that can be satisfied without additional focus adjustment in both the visible light band and the infrared band. And an optical system for an infrared broadband camera.

1 is a state diagram used in the present invention.

Figure 2 is a block diagram showing the arrangement of the optical system for the ultra-small visible light and infrared broadband camera according to the present invention.

3 is a diagram showing aberration characteristics of the optical system for the ultra-small visible light and infrared broadband camera according to the present invention.

4A is an MTF diagram showing the optical performance of the present invention in the visible light band.

4B is an MTF diagram showing the optical performance of the present invention in the infrared band.

* Description of the symbols for the main parts of the drawings *

10: first lens 20: second lens

30: third lens 40: fourth lens

50: fifth lens 60: aperture

70 optical filter 80 imaging device

In order to achieve the above object, the optical system for the ultra-small visible light and infrared broadband camera according to the technical idea of the present invention is a camera optical system in which lenses having a plurality of negative and positive magnifications are sequentially assembled from an object side to an image side. A first lens having a negative magnification having a convex surface on the subject side and a concave surface on the image side, a second lens having a negative magnification having a convex surface on the subject side and a plane on the image side, and from the second lens Aperture and a third lens having positive magnifications having convex surfaces respectively on the subject side and image side, a fourth lens having positive magnifications having convex surfaces on the subject side and image side respectively, and the subject side And a fifth lens, which is a negative magnification having a concave surface and an image side, respectively.

Here, when f is the focal length of the entire lens system and B is the rear focal length,

1.3 ≤ B / f ≤ 1.5

It is desirable to satisfy the phosphorus condition.

Also, when the distance from the first lens surface of the optical system to the last lens surface is T and the focal length of the entire lens system is f,

T / f ≤ 4.5

It is desirable to satisfy the phosphorus condition.

In addition, the first lens, the second lens, the third lens, the fourth lens and the fifth lens preferably form a glass sphere.

In addition, the refractive index and the dispersion coefficient of each of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens preferably correspond to the following ranges.

Refractive index dispersion coefficient

First lens 1.60 ≤ n1 ≤ 1.70 55 ≤ νd ≤ 65

Second lens 1.70 ≤ n2 ≤ 1.90 20 ≤ νd ≤ 30

Third lens 1.50 ≤ n3 ≤ 1.75 50 ≤ νd ≤ 60

Fourth lens 1.50 ≤ n3 ≤ 1.75 50 ≤ νd ≤ 60

Fifth lens 1.70 ≤ n2 ≤ 1.90 20 ≤ vd ≤ 30

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

1 is a state diagram used in the present invention.

As shown, the optical system 101 for the ultra-small visible and infrared broadband cameras of the present invention can be adopted and used in a variety of camera devices that require excellent optical performance in the visible and infrared bands, infrared, such as infrared LED The illumination device 102 is installed to photograph the subject by natural light during the daytime, and is adopted by the infrared surveillance camera 103 for capturing the subject by the infrared light emitted from the infrared illuminating device 102 at night when the natural light is insufficient. It is suitable to be.

In particular, the optical system of the present invention is configured to exert excellent optical performance in both visible and infrared (near infrared) bands in the wavelength range of 400 to 940 [nm], so that the apparatus for focusing the camera 103 is separately provided. Even if it is not installed, the subject can be captured at high quality anytime during the day and night.

As described above, in order for the optical system of the present invention to exhibit excellent optical performance in both visible and infrared bands, the arrangement state of the lens, the shape and the material of the lens constituting the optical system of the present invention serve as major factors.

Hereinafter, the configuration of the optical system 101 for the ultra-small visible light and infrared broadband camera of the present invention in detail, the present embodiment will be described with an optical system for the effective focal length (3.6mm).

2 is a block diagram showing the arrangement of the optical system for the ultra-small visible light and infrared broadband camera according to the present invention.

As shown in the drawing, the present invention includes a first lens 10, a second lens 20, a third lens 30, a fourth lens 40, and a first lens 10 arranged sequentially from the subject side to the image side. 5 includes a lens 50 and an aperture 60 for selectively converging the light transmitted through the second lens 20 between the second lens 20 and the third lens 30.

Meanwhile, an optical filter 70 (OLPF) and an image pickup device 80 to which image information is input are installed at a position after the fifth lens 50.

Here, the first lens 10 is provided with a magnification ((-) Power) lens having a convex surface on the subject side and a concave surface on the image side.

In addition, the second lens 20 is provided with a magnification ((-) Power) lens having a convex surface on the subject side and an infinite radius value on the plane on the image side.

In addition, the third lens 30 is provided with a positive power lens having a convex surface on the subject side and the image side, respectively.

In addition, like the third lens 30, the fourth lens 40 is provided with a positive (+) Power lens having convex surfaces on the subject side and the image side, respectively.

In addition, the fifth lens 50 is provided with a negative magnification ((-) Power) lens having concave surfaces on the subject side and the image side, respectively.

Here, the first lens 10, the second lens 20 and the third lens 30 are spaced apart from each other by a predetermined distance, but the third lens 30 and the fourth lens 40 The fourth lens 40 and the fifth lens 50 are spaced at a minute interval, and the fourth lens 40 and the fifth lens 50 are also spaced at a minute interval from each other in the center with the outer parts in contact with each other.

As such, when the third lens 30, the fourth lens 40, and the fifth lens 50 are arranged in a finely spaced state from each other, the refractive indices of the lenses and the refractive indices in the spaces in which the medium is air are mutually different. In contrast, this has the effect of improving the performance of the lens group.

In addition, the five lenses (10, 20, 30, 40, 50) is characterized in that all of the high refractive index (n = 1.6 ~ 1.8) of the glass material lens is selected and arranged. As a result, high-resolution resolution can be obtained and the lens arrangement of a form that can be easily processed has the effect of productivity improvement and cost reduction.

In addition, the present invention is configured to have an angle of view (clock angle) of 101 °, an aperture ratio of F / 2.0, and an optical length of approximately 22.17 mm.

Thus, in Table 1 below, the curvature radius, the center interval, the refractive index and the dispersion coefficient of the lens, which are the main values of the components of the present invention, are attached.

However, the focal length measurement of the entire lens system measured by dl [mm] and spherometer using the effective inner diameter measured by the projection measuring instrument (RROFELE PROJECTOR), f is the rear focal length B, the fifth lens from the first lens (10) The distance to the lens 50 is T, the angle of view measurement value measured by the projection inspector is θ, and the aperture ratio between the center CR and the periphery PR of the resolution measurement value is called f / dl (= F / 2.0).

Lens surface Radius of curvature Center interval Refractive index Dispersion Remarks R1 19.80 0.60 1.640 60.2 R2 3.40 2.72 R3 25.53 2.20 1.847 23.8 R4 ∞ 3.50 plane ∞ 1.32 Aperture (60) R5 28.00 1.80 1.697 55.5 R6 -7.72 0.05 R7 7.19 3.20 1.697 55.5 R8 -4.10 0.04 R9 -4.00 1.30 1.847 23.8 R10 70.41 0.4 ∞ 2.35 1.517 OLPF ∞ 2.7221 Image pickup device 80

From the figures in Table 1 above,

1.3 ≤ B / f ≤ 1.5

T / f ≤ 4.5

I can derive the condition that is.

In addition, the present invention has excellent optical performance in both visible and infrared bands while having the resources of effective focal length f = 3.7mm, angle of view 101 °, and optical full length of 22.17mm when the above conditions are satisfied. Hereinafter, the aberration characteristics and the MTF characteristics of the present invention will be described.

First, Figure 3 is a diagram showing the aberration characteristics of the optical system for ultra-small visible light and infrared broadband camera according to the present invention.

As shown, due to meridian surface curvature (T: Tangential Field Curvature, or Meridional Field Curvature), nodular phase curvature (S: Sagittal Field Curvature) and percent distortion in the band 0, 0.5, 0.7, 1.0 on the optical axis The aberration characteristics of the present invention are shown.

Here, aberration refers to a phenomenon in which light from one point when an image is formed in an optical system, such as a lens, passes through the optical system, and then the image appears colored or distorted without being collected at one point. The distortion aberration is minimized when the image distance and the object distance are similar. Therefore, in the general optical system, distortion aberration is corrected by adjusting the shape of the lens, the arrangement of the refractive power, and the position of the aperture.

In the present invention, by arranging the high refractive glass spherical lenses 10, 20, 30, 40, and 50 having positive and negative refractive powers, as shown in FIG. The correction state is good and is suitable for improving the brightness of the surroundings as well as the center.

Next, the optical performance of the present invention in the visible and infrared bands through the MTF diagram.

For reference, the MTF (Modulation Transfer Function) diagram is briefly described. After passing through the lens, light from two adjacent points on the subject surface undergoes deformation and some overlap occurs in the image pickup surface. The numerical value indicating the degree of overlap is a value called modulation. How faithfully the lens delivers the subject's image to the imaging surface can be seen by comparing the modulation of the subject and the modulation of the image (ie, the imaging surface) to each other. TransferFunction). Therefore, in the ideal case, the MTF value should be '1', but the actual lens will have a smaller value due to the aforementioned factors.

4A is an MTF diagram showing the optical performance of the present invention in the visible light band, and FIG. 4B is an MTF diagram showing the optical performance of the present invention in the infrared band.

As shown, the present invention provides excellent optical performance with MTF value of '0.4' or more in both visible and infrared bands, resolution of 30.0 [cycle / mm] or less, and a distance within ± 0.040 [mm] from the lens center. It can be seen that the MTF value is quite high in the range of.

Especially noteworthy is that when comparing Fig. 4A showing optical performance in the visible light band and Fig. 4B showing optical performance in the infrared band, the optical performance in the visible light band is also superior, but the optical performance in the infrared band is Is better.

As such, the optical system of the present invention can be used in all camera apparatuses requiring such performance because it exhibits excellent optical performance that can be satisfied in both the visible light band and the infrared band.

In particular, in the case of a camera apparatus for capturing a subject by infrared light emission at night, if the present invention is adopted, high quality imaging is possible from the subject without a separate apparatus for focusing.

The preferred embodiment of the present invention has been described above. The present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

As described above, the optical system for the ultra-small visible light and infrared broadband camera according to the present invention has excellent optical performance without additional focus adjustment in the visible light and infrared bands so that it can be actively employed in a camera using infrared light at night. do.

In addition, the present invention does not require a separate focusing device and easy lens processing has the effect of miniaturization of the product as well as the production cost.

In addition, the present invention can eliminate the difference in brightness between the center of the lens and the surroundings while ensuring an ambient light ratio of 80% or more, thereby obtaining a clearer image from the subject.

Claims (5)

In the optical system for a camera in which a lens having a plurality of negative and positive magnification are sequentially assembled from the subject side to the image side, A first lens having a negative magnification having a convex surface on the subject side and a concave surface on the image side; A second lens having a negative magnification having a convex surface on a subject side and a plane on an image side; An aperture to selectively converge light from the second lens; A third lens having a positive magnification having a convex surface on the subject side and the image side, respectively; A fourth lens having a positive magnification having a convex surface on the subject side and the image side, respectively; And a fifth lens having a negative magnification having a concave surface on a subject side and an image side, respectively. The method of claim 1, When f is the focal length of the entire lens system and B is the rear focal length, 1.3 ≤ B / f ≤ 1.5 Optical system for ultra-small visible and infrared broadband cameras, characterized by satisfying phosphorus conditions. The method of claim 1, When the distance from the first lens surface of the optical system to the last lens surface is T and the focal length of the entire lens system is f, T / f ≤ 4.5 Optical system for ultra-small visible and infrared broadband cameras, characterized by satisfying phosphorus conditions. In claim 1, And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens form a glass spherical surface. The method of claim 1, The refractive index and the dispersion coefficient of each of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are in the following ranges. Refractive index dispersion coefficient First lens 1.60 ≤ n1 ≤ 1.70 55 ≤ νd ≤ 65 Second lens 1.70 ≤ n2 ≤ 1.90 20 ≤ νd ≤ 30 Third lens 1.50 ≤ n3 ≤ 1.75 50 ≤ νd ≤ 60 Fourth lens 1.50 ≤ n3 ≤ 1.75 50 ≤ νd ≤ 60 Fifth lens 1.70 ≤ n2 ≤ 1.90 20 ≤ vd ≤ 30