KR101002993B1 - Lens - Google Patents

Abstract

Disclosed is a variable magnification pan focus imaging lens. According to an aspect of the present invention, a magnification-variable pan-focus imaging lens that is sequentially arranged along the optical axis from the object side to the image side, comprising: a first lens having a negative refractive power; A second lens spaced apart from the first lens by a predetermined distance in the image-side direction and having a negative refractive power; A first lens group disposed to be spaced apart from the second lens in the image-side direction by a predetermined interval, and including a third lens having positive refractive power and having a negative refractive power as a whole; A fourth lens disposed spaced apart from each other by a predetermined distance in an image side direction, and having a positive refractive power and bonded with an aspheric plastic resin in the image side direction; A fifth lens spaced apart from the fourth lens by a predetermined interval in the image-side direction and having a positive refractive power; A sixth lens positioned in the image-side direction from the fifth lens and having a negative refractive power; A magnification-variable pan-focus imaging lens including a seventh lens that is spaced apart from the sixth lens in the image-side direction by a predetermined interval, and includes a seventh lens having positive refractive power and has a positive refractive power as a whole Is provided.

Variable magnification pan-focus imaging lens, imaging lens, refractive power, temperature, long distance, near field, small size.

Description

Magnification-variable pan focus imaging lens {Lens}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens, and more particularly, to a variable magnification pan focus imaging lens.

Conventionally, in the imaging lens applied to a surveillance camera using a small solid-state image pickup device, a plastic aspherical lens having a predetermined thickness or more is applied to an optical system composed of a spherical lens according to the miniaturization and the high pixel number of the imaging device, thereby responding to the improvement of the performance of the imaging device. . However, when a plastic aspherical lens having a predetermined thickness or more is used, a large decrease in optical performance is likely to occur because the change in refractive index and shape of the plastic aspherical lens increases with increasing temperature. In addition, in the case of an imaging lens applied to a conventional surveillance camera, an optical system design has been made by reducing the F number, which improves the brightness of an image acquired through the imaging lens, but at the same time, makes the depth of field shallow and at a certain distance from the focused object. A satisfactory resolution cannot be obtained for objects that are separated, and since the diameter of the lens units applied to the optical system is increased, the size of the entire optical system is increased.

The present invention aims to provide a variable magnification-type pan-focus imaging lens capable of minimizing fluctuation in focus position due to temperature change and having a small resolution of the lens while having an appropriate resolution for near and far objects.

According to an aspect of the present invention, a magnification-variable pan-focus imaging lens that is sequentially arranged along the optical axis from the object side to the image side, comprising: a first lens having a negative refractive power; A second lens spaced apart from the first lens by a predetermined distance in the image-side direction and having a negative refractive power; A first lens group spaced apart from the second lens in the image-side direction by a predetermined interval, and including a third lens having positive refractive power and having a negative refractive power as a whole; and the image from the third lens An aperture that is spaced apart at a predetermined interval in the lateral direction and blocks a part of incident light of the light emitted from the third lens, and is spaced apart from the aperture at a predetermined interval in the image side direction, and has a positive refractive power A fourth lens in which an aspheric plastic resin is bonded to the image side direction; A fifth lens spaced apart from the fourth lens by a predetermined interval in the image-side direction and having a positive refractive power; A sixth lens positioned in the image-side direction from the fifth lens and having a negative refractive power; A magnification-variable pan-focus imaging lens including a seventh lens that is spaced apart from the sixth lens in the image-side direction by a predetermined interval, and includes a seventh lens having positive refractive power and has a positive refractive power as a whole Is provided.

The infrared blocking filter may be further spaced apart from the seventh lens in the image-side direction and may filter the infrared wavelength emitted from the seventh lens.

In addition, the sixth lens may be bonded to the fifth lens by a bonding resin, and the magnification-variable pan focus imaging lens according to the present embodiment may satisfy the following conditional expression.

Fw <3.0 (1)

Ft / Fw> 2.7 (2)

0.85 <| Ff / Fr | <1.0 (3)

2.6 <D6t + D7t <3.0 (4)

FNOw> 1.95 (5)

0.04 <ASPct <0.08 (6)

Here, Fw: focal length of the imaging lens in a wide position, Ft: focal length of the imaging lens in a tele position, Ff: focal length of the first lens group, Fr: the Focal length of the second lens group, BFLw: Back light point distance of the imaging lens in wide position, BFLt: Back light point distance of the imaging lens in tele position, D6t: The image side surface of the third lens when in tele position Center distance between the directional surface and the aperture, D7t: center distance between the image side direction surface of the fourth lens and the aperture when in the tele position, FNOw: F number in the wide position, FNOt: tele position F number in Ep, ASPct: center thickness of the plastic resin bonded to the fourth lens.

The variable magnification-type pan-focus imaging lens may be an imaging lens for a surveillance camera applied to CCD and CMOS imaging devices, and the first lens may have a meniscus shape convex toward the object side and concave toward the image side.

In addition, both surfaces of the second lens and the sixth lens are concave, and the third lens, the fourth lens, the fifth lens, and the seventh lens are both convex, and the first lens group and the second lens are convex. The group may be movable along the optical axis.

Other aspects, features, and advantages other than those described above will become apparent from the following drawings, claims, and detailed description of the invention.

The variable magnification-type pan-focus imaging lens according to the present invention has the effect of minimizing the fluctuation of the focus position due to temperature change and having a proper resolution for a subject located near and far, and at the same time miniaturizing the lens size.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. And / or &lt; / RTI &gt; includes any combination of a plurality of related listed items or any of a plurality of related listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. In the following description of the present invention, if it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a variable magnification-type pan-focus imaging lens, and more particularly, to an imaging lens in which the optical magnification is variable in a group of seven elements. The present invention can be applied to a surveillance camera using a solid-state imaging device such as a small CCD, CMOS, etc., the optical performance is very small due to the temperature change of the surrounding environment, and the depth of field is deep. In addition, the present invention compacts the overall length and diameter of the lens in the imaging lens, guarantees the image performance for the space between the object located at a distance and the object located at a distance from the imaging lens, and suppress the fluctuation of the focus position according to the temperature change can do. In addition, the present invention is applicable to a recent image pickup device regardless of the kind of overall aberration generated in the optical system.

FIG. 1 illustrates a configuration of a lens in wide, middle, and tele operations according to zoom positions according to the present invention. The variable magnification-type pan-focus imaging lens according to the present embodiment is composed of a first lens group having a negative refractive power and a second lens group having a positive refractive power, sequentially from the object side. Since the distance between the two lens groups is variable, the magnification is also variable.

The lens according to the present invention includes a first lens group including first to third lenses 110 to 130 having negative refractive power as a whole in an image side direction where an image is formed on an object side and a fourth having overall positive refractive power. A second lens group including the seventh lens (110 to 170), the aperture 180 is located between the first lens group and the second lens group. Each lens group is moved along the optical axis in a position not invading the region of the aperture 180 to change the magnification.

In addition, the magnification-variable pan-focus imaging lens according to the present invention has a meniscus-type first lens having negative refractive power in order from the object side to the image side direction, and the object side surface being convex and the image side surface concave. 110), the second lens 120 having a negative refractive power and the object side and the image side are both concave, and the third lens 130 having the positive refractive power and both the object side and the image side are convex. The first lens group and the first lens group are spaced apart by a predetermined distance in the image-side direction, have a positive refractive power, and both the object side and the image side are convex, and the plastic resin defined as an aspherical surface is bonded to the image side. When the fourth lens 140, the fifth lens 150 having positive refractive power and both convex sides, and the bonding resin are injected into the image side surface of the fifth lens and bonded to each other, the fourth lens 140 has negative refractive power and both surfaces are concave. 6 lenses (160), positive It has a refractive power of the two-sided convex shape claim 7 and a second lens group consisting of a lens 170. In addition, an infrared blocking filter 190 is disposed spaced apart from the seventh lens 170 by a predetermined interval and filters the infrared wavelength incident on the optical system. In addition, an aperture for adjusting the amount of unnecessary rays and light incident on the interior of the optical system in the space between the image side surface of the third lens 130 of the first lens group and the object side surface of the fourth lens 140 of the second lens group ( 180 is additionally included. In the variable magnification-type pan-focus imaging lens according to the present exemplary embodiment, all lens surfaces except the plastic resin bonded to the upper surface of the fourth lens 140 defined as aspherical surfaces are defined in the form of spherical surfaces, refractive power, types of materials, The spacing between the lenses is properly arranged to have a long depth of field, and the optical system can be compactly constructed.

In order to realize a sufficient wide-angle area at a wide position, the first lens group may have a negative refractive power and the second lens group may have a retro focus type. In order to compact the length and the outer diameter of the full length, at least two or more lenses may be formed of a glass material having a high refractive index. In order to prevent the deterioration of resolution performance due to the compactness of the optical system and the temperature change, a resin-bonded aspherical lens having a very small thickness may be used as compared to a plastic aspherical lens having a certain size and thickness. In addition, the F-number in a wide position may be restricted to implement a deep depth of field focus function.

The variable magnification-type pan-focus imaging lens according to the embodiment of the present invention made as described above satisfies the following conditions.

Fw <3.0 (1)

Fw in Equation (1) represents the focal length of the entire lens at the wide position. The unit is mm.

2.7 <Ft / Fw <2.8 (2)

Fw and Ft in Equation (2) refer to the focal lengths of the entire lens at the wide position and the tele position, respectively, and represent the ratio between the maximum and minimum magnifications of the entire lens.

When the upper limit value of Equation (2) is exceeded, the resolution performance is reduced within the limited lens length, the distortion aberration is difficult to correct, and when the lower limit value is exceeded, the range of magnification change is reduced, thereby degrading the value as a product.

0.85 <| Ff / Fr | <1.0 (3)

Ff and Fr represent focal lengths of the first and second lens groups, respectively.

Equation (3) is for equally distributing the refractive power between the first lens group and the second lens group. If the equation (3) is not satisfied, the shapes of the lenses are easily disadvantageous for processing. In this case, the refraction may be concentrated on one side, resulting in resolution degradation due to aberration.

2.6 <D6t + D7t <3.0 (4)

The D6t is the center distance between the image side direction surface of the third lens 130 belonging to the first lens group in the tele position and the aperture 180, and the D7t belongs to the second lens group in the tele position. The center distance between the image-side direction surface of the fourth lens 140 and the aperture 180 is shown.

Equation (4) is to secure the interval at which the aperture 180 between the first lens group and the second lens group can operate. When the upper limit value is exceeded, the position of the aperture 180 is increased. And there is no problem in applying the aperture 180 to the optical system is secure enough space to operate, but aberration correction is difficult. On the other hand, when the lower limit value is exceeded, the aberration correction is relatively easy, so that the resolution performance is improved, but since the space for positioning the aperture 180 is not secured, the aperture 180 may not be applied to the optical system.

1.95 <FNOw <2.1 (5)

The FNOw represents the F number FNO of the optical system in the wide position.

Equation (5) is a condition for deepening the depth of field so that the distant object and the near object at the same time to form a clear image at the same time, if the upper limit is exceeded, the depth of field becomes deeper but passes through the lens to enter the image plane When the amount of light to be reduced is reduced, the acquired image becomes dark overall, and when the upper limit value is exceeded, the image becomes relatively bright overall but the depth of field becomes shallow, so that a long distance object and a near object cannot be clearly seen simultaneously.

0.04 <ASPct <0.08 (6)

The ASPct represents the center thickness of the resin-bonded aspherical surface bonded to the image-oriented surface of the fourth lens 140 belonging to the second lens group.

Equation (6) is for minimizing the change in the focus position according to the temperature change by minimizing the volume of the plastic material which has a significant effect on the degradation of the resolution performance according to the temperature change, if the upper limit exceeds the focus The change of position becomes large and resolution performance falls, and when exceeding a lower limit, manufacture and measurement of an actual resin bonding aspherical surface become disadvantageous.

Optical characteristics of the variable magnification-type pan-focus imaging lens according to the exemplary embodiment of the present invention are shown in Table 1 below.

Unit: mm Wide Middle Tele Focal Length 2.99 4.79 8.20 Back focus distance 6 7.8 11.5 F number 1.99 2.32 3.45 Magnification 0.0010 0.0016 0.0027 Battlefield
(Lens first surface-imaging surface) 40.9 33.5 30.6 Angle of view (diagonal / 2) 60.2 35.9 20.7

Here, the imaging surface means the surface of the image sensor in the image side direction.

Data of the optical system according to the above embodiment is shown in Table 2 below.

Unit: mm Face number Surface properties Bending Radius (R) Thickness, thickness Refractive index (nd) Abbe number (Vd) One Sphere 22.2084 0.5 1.914656 21.7 2 Sphere 5.4574 3.4405 3 Sphere -14.3257 0.6003 1.767025 50.0 4 Sphere 13.069 0.1 5 Sphere 11.5753 2.4824 1.923 20.9 6 Sphere -32.9465 11.6486 STOP Sphere 0 6.7855 8 Sphere 8.2343 3.1803 1.795564 44.0 9 Sphere -112.1962 0.0645 1.517 52.0 10 Asphere -47.3368 0.4159 11 Sphere 10.3405 2.7037 1.668431 56.7 12 Sphere -8.4486 0.5 1.850159 25.6 13 Sphere 5.5193 0.4319 14 Sphere 10.0508 2.0664 1.51729 66.9 15 Sphere -9.3954 0.1 16 Sphere 0 3.14 1.5168 64.2 17 Sphere 0 3.8 18 Sphere 0 0

Table 3 is a table showing the eccentricity and aspheric coefficient value of the resin bonding aspherical surface (surface number 10) according to the embodiment. The aspherical shape is represented by the following equation, where k is an eccentricity and A, B, .., E are aspherical coefficients of 4th, 6th, 8th, 10th and 12th order. Z (r) represents the horizontal distance from the apex of the aspherical surface to the height r, and c represents the curvature (1 / R).

(7)

(7)

k 103.422 A 0.0007 B 8.29E-06 C -7.87E-07 D 3.45E-08 E -7.03E-17

Referring to FIG. 2 (FIGS. 2A to 2C), longitudinal spherical aberration, astigmatism field curve, and distortion aberration for the wide, middle, and tele positions are shown in order from the left. The astigmatic field curve aberrations for the sagittal and tangential top surfaces are shown. In these aberration diagrams, the y axis represents the height of the upper surface. The y-axis notation of the longitudinal spherical aberration diagram is expressed by converting the maximum image height, 3mm, into 1.0, and the y-axis notation in the astigmatism field and the distortion aberration diagram indicates the height of the plane as mm. The x-axis in the longitudinal spherical aberration and the astigmatism field aberration is indicated in mm units to indicate the position of the optical axis in the upper surface as 0.0, indicating the occurrence of aberration, and the x-axis of the distortion aberration is a percentage. Is displayed.

As can be seen from the aberration diagram of FIG. 2, in the case of the longitudinal aberration, all of the wide-angle magnification (wide), middle magnification (middle) and telephoto magnification position (tele) are all 0.07 from the reference wavelength (587.6 nm, expressed in blue). In the case of non-point field aberration, the difference in focus between the upper surface of the sagittal indicated by the solid line and the upper surface of the tangential shown by the dotted line is within 0.05 mm. As shown in the distortion aberration diagram, it can be seen that the distortion of the general form appears from the center of the top surface to the outside of the top surface without a sudden change of the distortion.

 As is clear from these aberration diagrams, according to the imaging lens of the embodiment, each of the above-described aberrations can be corrected well.

3 (FIG. 3A to FIG. 3C) show the performance of MTF (modulation transfer function) at each of the wide-angle magnification (wide), middle magnification (middle), and telephoto magnification (tele: tele) positions. The spatial frequency of unit is cycle / mm, and the y-axis represents the MTF value by spatial spatial frequency, with 1.0 being the maximum value of transmitting the spatial frequency.

In FIG. 3, the black dotted line represents the diffraction limit of the optical system according to the embodiment, and the MTF characteristics when the half angle of view of the optical system increases in the order of red-lime green-blue-pink are shown, except for the black dotted line and the red solid line. Represents a tangential direction MTF, and a dotted line represents a sagittal direction MTF. Referring to FIG. 3, it can be seen that the imaging lens of the present embodiment has sufficient MTF performance to be applied to an imaging device for surveillance cameras, which is generally used, 1/3 inch VGA CCD, CMOS, and the like.

4 (FIG. 4A to FIG. 4C) show spot diagrams at each of a wide-angle magnification (wide), a middle magnification (middle) and a telephoto magnification (tele). The x-axis represents the focus position on the optical axis in mm, the y-axis represents the half angle of view, and a scale bar is set at 0.05 mm as a measure for measuring the spot size at the bottom right. As can be seen from the spot diagram of FIG. 4, it can be seen that the aberration is well corrected so that the size of the spots displayed at the designated points on the diagram is 0.05 mm or less.

In the foregoing description, the variable magnification-type pan-focus imaging lens according to the exemplary embodiment of the present invention has described the number and configuration of the lenses according to an exemplary embodiment, but the present invention is not necessarily limited thereto. In the case of the addition, if there is no difference in the overall operation and effect, such other configuration may be included in the scope of the present invention, and those skilled in the art, the spirit and scope of the present invention described in the claims It will be understood that various modifications and variations can be made in the present invention without departing from the scope thereof.

1 is a lens configuration for each zoom position of a variable-magnification variable-focused focus lens according to an embodiment of the present invention.

2A to 2C are field aberration diagrams for each zoom position of a variable focus pan focus lens according to an exemplary embodiment of the present invention.

3A to 3C are MTF diagrams according to zoom positions of the variable focus pan focus lens according to the exemplary embodiment of the present invention.

4A to 4C are spot diagrams for each zoom position of a variable focus pan focus lens according to an exemplary embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

110 to 170: first to seventh lenses

180: Aperture

190: infrared cut filter

Claims (8)

In the magnification-variable pan-focus imaging lens arranged sequentially along the optical axis from the object side to the image side where the image is formed, A first lens having negative refractive power; A second lens spaced apart from the first lens by a predetermined distance in the image-side direction and having a negative refractive power; A first lens group disposed to be spaced apart from the second lens in the image-side direction by a predetermined interval, and including a third lens having a positive refractive power and having a negative refractive power as a whole; An aperture stop disposed at a predetermined interval from the third lens in the image-side direction and blocking a part of incident light of the light emitted from the third lens; A fourth lens disposed spaced apart from the aperture in the image-side direction by a predetermined interval, and having a positive refractive ability, wherein an aspheric plastic resin is bonded to one surface of the fourth lens in the image-side direction; A fifth lens spaced apart from the fourth lens by a predetermined interval in the image-side direction and having a positive refractive power; A sixth lens positioned in the image-side direction from the fifth lens and having a negative refractive power; A magnification-variable pan-focus imaging lens including a seventh lens that is spaced apart from the sixth lens in the image-side direction by a predetermined interval, and includes a seventh lens having positive refractive power and has a positive refractive power as a whole . The method of claim 1, The variable magnification-focused focus lens of claim 7, further comprising an infrared cut-off filter disposed to be spaced apart from the seventh lens in the image-side direction by a predetermined interval, and to filter infrared wavelengths emitted from the seventh lens. The method of claim 1, And the sixth lens is bonded to the fifth lens by a bonding resin. The method of claim 1, A variable magnification-type pan focus imaging lens, which satisfies the following conditional expression. Fw <3.0 (1) Ft / Fw> 2.7 (2) 0.85 <| Ff / Fr | <1.0 (3) 2.6 <D6t + D7t <3.0 (4) FNOw> 1.95 (5) 0.04 <ASPct <0.08 (6) Fw: focal length of the imaging lens in a wide position Ft: focal length of the imaging lens in the tele position Ff: focal length of the first lens group Fr: focal length of the second lens group D6t: center distance between the image side direction surface of the third lens and the aperture when in the tele position D7t: center distance between the image side surface of the fourth lens and the aperture when in the tele position FNOw: F number in wide position ASPct: center thickness of the plastic resin bonded to the fourth lens. The method of claim 1, And the imaging lens is an imaging lens for a surveillance camera applied to a CCD and a CMOS imaging device. The method of claim 1, The first lens has a meniscus shape in which the first lens is convex toward the object and concave to the image side surface. The method of claim 1, Both surfaces of the second lens and the sixth lens are concave, The third lens, the fourth lens, the fifth lens, and the seventh lens are convex on both sides thereof. The method of claim 1, And the first lens group and the second lens group are movable along the optical axis.

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