Patent Grant
6927927
This application is based on the following Japanese Patent Applications, the contents of which are hereby incorporated by reference:
1. Field of the Invention
The present invention relates to a taking lens system, and more particularly to a compact taking lens system suitable for use in a digital input device (such as a digital still camera or digital video camera) that takes in an image of a subject by means of a solid-state image sensor.
2. Description of the Prior Art
In recent years, as personal computers and the like become more and more popular, digital still cameras and digital video cameras (hereinafter collectively referred to as “digital cameras”), which permit easy entry of image data into digital equipment, have been becoming more and more popular for personal use among general users. Such digital cameras are expected to become even more widespread in the future.
Solid-state image sensors, such as CCDs (charge-coupled devices), used in digital cameras have been made increasingly small, and accordingly further miniaturization is sought in digital cameras themselves. As a result, miniaturization is eagerly sought also in taking lens systems, which occupy the largest volumes in digital input devices. The easiest way to make a taking lens system smaller is to make a solid-state image sensor smaller. However, this involves making photosensitive elements smaller, and thus makes the solid-state image sensor more difficult to fabricate, and in addition requires higher performance in the taking lens system.
On the other hand, making a taking lens system smaller while keeping the size of a solid-state image sensor unchanged inevitably brings the exit pupil position closer to the image plane. When the exit pupil position is brought closer to the image plane, the off-axial rays exiting from the taking lens system are obliquely incident on the image plane. This makes it impossible to make the most of the light-condensing ability of the microlenses provided in front of the solid-state image sensor, with the result that the obtained image shows extremely uneven brightness between in a central portion and in a peripheral portion thereof. This can be avoided by bringing the exit pupil position of the taking lens system farther away from the image plane, but this inevitably makes the taking lens system as a whole unduly large.
Moreover, in keen competition for lower prices in recent years, lower costs are increasingly eagerly sought in taking lens systems. To meet these requirements, Japanese Patent Application Laid-Open No. H6-88939 proposes a taking lens system composed of one lens element, and Japanese Patent Application Laid-Open No. H1-245211 proposes a taking lens system composed of two lens elements. Moreover, Japanese Patent Application Laid-Open No. 2001-183578 proposes a taking lens system composed of two lens elements for use with a solid-state image sensor. Furthermore, Japanese Patent Applications Laid-Open Nos. 2001-272598, 2002-698889, and H11-52227 propose taking lens systems composed of three lens elements.
These conventional taking lens systems, however, have the following disadvantages. The taking lens system composed of one lens element disclosed in Japanese Patent Application Laid-Open No. H6-88939 has the exit pupil position located far beyond the total length of the taking lens system, but suffers from poor image plane quality, and thus cannot maintain high imaging performance. The taking lens system composed of two lens elements disclosed in Japanese Patent Application Laid-Open No. H1-245211 offers good image plane quality, and thus maintains high imaging performance. However, here, the exit pupil position is located too close, namely at about 6/10 of the total length of the taking lens system. The taking lens system disclosed in Japanese Patent Application Laid-Open No. 2001-183578, in which the first lens element has a negative optical power and the second lens element has a positive optical power, has a long total length and is not compact.
The taking lens system composed of three lens elements disclosed in Japanese Patent Application Laid-Open No. 2001-272598, of which the total length is about three times its focal length, is not compact. The taking lens system disclosed in Japanese Patent Application Laid-Open No. 2002-698889, of which the total length is about twice its focal length, is compact, but uses two glass lens elements, which make it impossible to produce this taking lens system at low costs. The taking lens system disclosed in Japanese Patent Application Laid-Open No. H11-52227, of which the total length is about 2.5 times its focal length, is not compact. Moreover, here, the angle of view is about 40 degrees, which is too narrow to make this taking lens system usable.
An object of the present invention is to provide a high-optical-performance, low-cost, compact taking lens system for use with a solid-state image sensor
To achieve the above object, according to one aspect of the present invention, a two-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a positive lens element; and a meniscus lens element convex to the image side. Moreover, the following condition is fulfilled:
0.4<D/f<1.9 (1)
where
According to another aspect of the present invention, a three-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a first lens element having a weak optical power; an aperture stop; a second lens element having a positive optical power; and a third lens element having a concave surface on the image side thereof and having a negative optical power. Moreover, the following conditions are fulfilled:
|f/f1|<0.6 (A0)
−2.2<f/f3<−0.79 (A1)
where
According to another aspect of the present invention, a three-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a first lens element having a positive optical power; an aperture stop; a second lens element having a positive optical power; and a third lens element having a negative optical power. Moreover, the following condition is fulfilled:
−2.6<f3/f1<−0.15 (A2)
where
According to another aspect of the present invention, a three-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a first lens element having a positive optical power; an aperture stop; a second lens element having a meniscus shape with a convex surface on the image side thereof and having a positive optical power; and a third lens element having a meniscus shape with a concave surface on the image side thereof and having a negative optical power. Moreover, the following condition is fulfilled:
0.05<T6/f<0.5 (A3)
where
According to another aspect of the present invention, a three-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a first lens element having a positive optical power; an aperture stop; a second lens element having a positive optical power; and a third lens element having a positive optical power. Moreover, the following condition is fulfilled:
0.2<f/f3<0.4 (B1)
where
According to another aspect of the present invention, a three-lens-element taking lens system for forming an image on a solid-state image sensor provided with, from the object side: a first lens element having a meniscus shape with a convex surface on the object side thereof and having a positive optical power; an aperture stop; a second lens element having a meniscus shape with a convex surface on the image side thereof and having a positive optical power; and a third lens element having a meniscus shape with a convex surface on the image side thereof and having a positive optical power. Moreover, the following conditions are fulfilled:
0.05<T6/f<0.4 (B3)
where
According to another aspect of the present invention, a two-lens-element taking lens system for forming an image on a solid-state image sensor is provided with, from the object side: a first lens element having a meniscus shape with a convex surface on the object side thereof and having a positive optical power; and a second lens element having a meniscus shape with a concave surface on the image side thereof Moreover, the following condition is fulfilled:
|f2|/f1<25 (I)
where
According to another aspect of the present invention, a two-lens-element taking lens system for forming an image on a solid-state image sensor, comprising, from the object side: a first lens element having a meniscus shape with a convex surface on the object side thereof and having a positive optical power; and a second lens element having a meniscus shape with a concave surface on the image side thereof Moreover, the following condition is fulfilled:
0.1<T1/f<0.5 (II)
where
This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanying drawings in which:
Hereinafter, taking lens systems embodying the present invention will be described with reference to the drawings.
First, a first to a ninth embodiment of the invention will be described.
In a taking lens system of the type composed of two lens elements, namely, from the object side, a positive lens element L1 and a meniscus lens element L2 convex to the image side, by adopting a characteristic optical construction as will be described below, as in the first to ninth embodiments, it is possible to strike a proper balance among the exit pupil position, optical performance, costs, and compactness required in a taking lens system for a solid-state image sensor. For example, with respect to the exit pupil position, it is preferable that, as in the first to ninth embodiments, the aperture stop ST be disposed on the object side of the positive lens element L1. Disposing the aperture stop ST on the object side of the positive lens element L1 makes it possible to locate the exit pupil farther away. Moreover, it is preferable that the lens element L1 have a convex surface on the image side. Giving the lens element L1 a convex surface on the image side is also effective in locating the exit pupil position farther away.
It is preferable that the positive lens element L1 and the meniscus lens element L2 be both plastic lens elements. Using plastic lens elements as both of the lens elements L1 and L2 is effective in reducing the costs of the taking lens system. It is preferable that the positive lens element L1 and the meniscus lens element L2 each have at least one aspherical surface. Giving each of the lens elements L1 and L2 at least one aspherical surface is highly effective in reducing spherical aberration, coma aberration, and distortion. More specifically, giving the positive lens element L1 an aspherical surface makes possible effective correction of spherical aberration and distortion, and giving the meniscus lens element L2 an aspherical surface makes possible effective correction of coma aberration.
Now, the conditions of which the fulfillment is preferable in the taking lens systems of the first to ninth embodiments will be described. It is to be noted, however, that, in any of these embodiments, it is not necessary that all of the conditions described below be fulfilled simultaneously; that is, the fulfillment of whichever of those conditions are appropriate in a given optical construction provides the corresponding benefits and advantages. Needless to say, from the viewpoint of optical performance, miniaturization, assembly, and other factors, it is preferable that as many of the conditions as possible be fulfilled.
It is preferable that condition (1) below be fulfilled.
0.4<D/f<1.9 (1)
where
Condition (1) defines the range within which the distance D from the first lens surface r2 to the last lens surface r5 along the optical axis AX needs to be kept mainly to strike a proper balance between the total length and the aberrations produced. If the upper limit of condition (1) is transgressed, it is easy to correct aberrations, but the total length is unduly long. By contrast, if the lower limit of condition (1) is transgressed, it is easy to shorten the total length, but the aberrations produced, in particular distortion and curvature of field, are unduly large.
It is preferable that condition (2) below be fulfilled, and it is further preferable that condition (2a) below be fulfilled.
0.2<(R1+R2)/(R1−R2)<1.7 (2)
0.5<(R1+R2)/(R1−R2)<1.7 (2a)
where
Conditions (2) and (2a) define the ranges of which one needs to be observed with respect to the positive lens element L1 mainly to strike a proper balance of coma aberration. If the lower limit of condition (2) is transgressed, coma aberration is so large as to adversely affect lateral chromatic aberration. By contrast, if the upper limit of condition (2) is transgressed, coma aberration is so large as to adversely affect astigmatism.
It is preferable that condition (3) below be fulfilled, and it is further preferable that condition (3a) below be fulfilled.
−10<(R3+R4)/(R3−R4)<−1 (3)
−9<(R3+R4)/(R3−R4)<−2 (3a)
where
Conditions (3) and (3a) define the ranges of which one needs to be observed with respect to the meniscus lens element L2 mainly to strike a proper balance of coma aberration. If the lower limit of condition (3) is transgressed, coma aberration is so large as to adversely affect lateral chromatic aberration. By contrast, if the upper limit of condition (3) is transgressed, coma aberration is so large as to adversely affect astigmatism.
It is preferable that condition (4) below be fulfilled, and it is further preferable that condition (4a) below be fulfilled.
1.05<f/f1<1.9 (4)
1.1<f/f1<1.9 (4a)
where
Conditions (4) and (4a) define the ranges of which one needs to be observed with respect to the positive lens element L1 mainly to achieve proper correction of distortion and curvature of filed. If the upper limit of condition (4) is transgressed, positive distortion is unduly large, and the inclination of the image plane toward the over side is unduly sharp. In addition to these inconveniences, the exit pupil position is located unduly close. By contrast, if the lower limit of condition (4) is transgressed, negative distortion is unduly large, and the inclination of the image plane toward the under side is unduly sharp. This makes the taking lens system practically unusable.
It is preferable that condition (5) below be fulfilled, and it is further preferable that condition (5a) below be fulfilled.
−1.5<f/f2<0.5 (5)
−0.4<f/f2<0.3 (5a)
where
Conditions (5) and (5a) define the ranges of which one needs to be observed with respect to the meniscus lens element L2 mainly to achieve proper correction of distortion and curvature of filed. If the lower limit of condition (5) is transgressed, positive distortion is unduly large, and the inclination of the image plane toward the over side is unduly sharp. In addition to these inconveniences, the exit pupil position is located unduly close. By contrast, if the upper limit of condition (5) is transgressed, negative distortion is unduly large, and the inclination of the image plane toward the under side is unduly sharp. This makes the taking lens system practically unusable.
Next, a tenth to a twenty-first embodiment of the invention will be described.
In the tenth to fourteenth embodiments (
Lens Type A (Negative/Positive-positive-negative)
In the tenth to twelfth embodiments (
In the thirteenth and fourteenth embodiments (
In the fifteenth and seventeenth embodiments (
Now, the conditions of which the fulfillment is preferable in taking lens systems of lens type A will be described. It is to be noted, however, that, in any given optical construction, it is not necessary that all of the conditions described below be fulfilled simultaneously; that is, the fulfillment of whichever of those conditions are appropriate in a given optical construction provides the corresponding benefits and advantages. Needless to say, from the viewpoint of optical performance, miniaturization, assembly, and other factors, it is preferable that as many of the conditions as possible be fulfilled.
In the tenth to fourteenth embodiments, the first lens element L1 has a weak optical power. It is preferable that this weak optical power fulfill condition (A0) below:
|f/f1|<0.6 (A0)
where
Condition (A0) defines the range that needs to be observed with respect to the first lens element L1 having a weak optical power mainly to minimize degradation in optical performance ascribable to fabrication-associated errors. When condition (A0) is not fulfilled, the optical power of the first lens element L1 is so strong that the large aberrations produced by the first lens element L1 needs to be corrected by the second L2 and following lens elements. This aggravates degradation in optical performance ascribable to fabrication-associated errors.
With respect to the third lens element L3, it is preferable that condition (A1) below be fulfilled, and it is further preferable that this condition be fulfilled together with condition (A0) noted above.
−2.2<f/f3<−0.79 (A1)
where
Condition (A1) defines the range that needs to be observed with respect to the third lens element L3 mainly to strike a proper balance of coma aberration. If the lower limit of condition (A1) is transgressed, coma aberration is so large as to adversely affect lateral chromatic aberration. By contrast, if the upper limit of condition (A1) is transgressed, coma aberration is so large as to adversely affect astigmatism.
In an optical construction of lens type A having a positive-positive-negative (+, +, −) power arrangement, as in the thirteenth to seventeenth embodiments, with respect to the first and third lens elements L1 and L3, it is preferable that condition (A2) below be fulfilled, and it is further preferable that condition (A2a) below be fulfilled. It is particularly preferable that condition (A2b) below be fulfilled.
−2.6<f3/f1<−0.15 (A2)
−1.1<f3/f1<−0.15 (A2a)
−0.35<f3/f1<−0.15 (A2b)
where
Conditions (A2), (A2a), and (A2b) define the ranges of which one needs to be observed mainly to strike a proper balance between the total length and the aberrations produced. If the upper limit of condition (A2) is transgressed, it is easy to correct aberrations, but the total length is unduly long. By contrast, if the lower limit of condition (A2) is transgressed, it is easy to shorten the total length, but the aberrations produced, in particular distortion and curvature of field, are unduly large.
With respect to the third lens element L3, it is preferable that condition (A3) below be fulfilled, and it is further preferable that condition (A3a) below be fulfilled. It is particularly preferable that one of these conditions be fulfilled together with at least one of conditions (A0), (A1), (A2), (A2a), and (A2b) noted above. In an optical construction of lens type A having a positive-positive-negative (+, +, −) power arrangement, as in the thirteenth to seventeenth embodiments, it is preferable that the second lens element L2 have a positive meniscus shape with a convex surface on the image side, that the third lens element L3 have a negative meniscus shape with a concave surface on the image side, and in addition that condition (A3) below be fulfilled. In this case, it is further preferable that condition (A3a) below be fulfilled.
0.05<T6/f<0.5 (A3)
0.05<T6/f<0.4 (A3a)
where
Conditions (A3) and (A3a) define the ranges of which one needs to be observed with respect to the third lens element L3 mainly to strike a proper balance between the lateral chromatic aberration produced and the manufacturability of the lens element. If the upper limit of condition (A3) is transgressed, it is difficult to correct lateral chromatic aberration properly. By contrast, if the lower limit of condition (A3) is transgressed, the lens element is too thin to be manufactured easily.
Lens Type B (Positive-positive-positive)
In the eighteenth to twenty-first embodiments (
Now, the conditions of which the fulfillment is preferable in taking lens systems of lens type B will be described. It is to be noted, however, that, in any given optical construction, it is not necessary that all of the conditions described below be fulfilled simultaneously; that is, the fulfillment of whichever of those conditions are appropriate in a given optical construction provides the corresponding benefits and advantages. Needless to say, from the viewpoint of optical performance, miniaturization, assembly, and other factors, it is preferable that as many of the conditions as possible be fulfilled.
With respect to the third lens element L3, it is preferable that condition (B1) below be fulfilled.
0.2<f/f3<0.4 (B1)
where
Condition (B1) defines the range that needs to be observed with respect to the third lens element L3 mainly to strike a proper balance of coma aberration. If the lower limit of condition (B1) is transgressed, coma aberration is so large as to adversely affect lateral chromatic aberration. By contrast, if the upper limit of condition (B1) is transgressed, coma aberration is so large as to adversely affect astigmatism.
With respect to the first and third lens elements L1 and L3, it is preferable that condition (B2) below be fulfilled.
0.5<f3/f1<2.6 (B2)
where
Condition (B2) defines the range that needs to be observed mainly to strike a proper balance between the total length and the aberrations produced. If the upper limit of condition (B2) is transgressed, it is easy to correct aberrations, but the total length is unduly long. By contrast, if the lower limit of condition (B2) is transgressed, it is easy to shorten the total length, but the aberrations produced, in particular distortion and curvature of field, are unduly large.
With respect to the third lens element L3, it is preferable that condition (B3) below be fulfilled. It is further preferable that condition (B3) below be fulfilled in a three-lens-element construction of lens type B in which the first lens element L1 is a positive meniscus lens element with a convex surface on the object side, the second lens element L2 is a positive lens element with a convex surface on the image side, and the third lens element L3 is a positive meniscus lens element with a convex surface on the image side.
0.05<T6/f<0.4 (B3)
where
Condition (B3) defines the range that needs to be observed with respect to the third lens element L3 mainly to strike a proper balance between the lateral chromatic aberration produced and the manufacturability of the lens element. If the upper limit of condition (B3) is transgressed, it is difficult to correct lateral chromatic aberration properly. By contrast, if the lower limit of condition (B3) is transgressed, the lens element is too thin to be manufactured easily.
Features Preferable in Both Lens Types A and B
As described earlier, in the tenth to twenty-first embodiments, the first to third lens elements L1 to L3 are all plastic lens elements, and all the lens surfaces r1, r2, and r4 to r7 are aspherical surfaces. In this way, it is preferable that all the lens elements L1 to L3 be plastic lens elements, and that each of the lens elements L1 to L3 is given at least one aspherical surface. Using plastic lens elements as all of the lens elements L1 to L3 is effective in reducing the costs of the taking lens system. On the other hand, giving each of the lens elements L1 to L3 at least one aspherical surface is highly effective in reducing spherical aberration, coma aberration, and distortion.
Next, a twenty-second to a twenty-fifth embodiment of the invention will be described.
Thus, in the twenty-second to twenty-fifth embodiments, a taking lens system having a positive-positive/negative (+, +/−) power arrangement (here, the optical power is the quantity defined as the reciprocal of the focal length, and “/” signifies “or”) is built by arranging two lens elements, namely, from the object side, a positive meniscus lens element L1 with a convex surface on the object side and then a meniscus lens element with a concave surface on the image side. In this way, it is possible to strike a proper balance among the exit pupil position, optical performance, costs, and compactness required in a taking lens system for a solid-state image sensor. Specifically, that can be achieved effectively when the conditions described below are fulfilled.
Now, the conditions that need to be fulfilled in the taking lens systems of the twenty-second to twenty-fifth embodiments, i.e., the conditions of which the fulfillment is preferable in taking lens systems of the types like those of the twenty-second to twenty-fifth embodiments, will be described. It is to be noted, however, that, in any of these embodiments, it is not necessary that all of the conditions described below be fulfilled simultaneously; that is, the fulfillment of whichever of those conditions are appropriate in a given optical construction provides the corresponding benefits and advantages. Needless to say, from the viewpoint of optical performance, miniaturization, assembly, and other factors, it is preferable that as many of the conditions as possible be fulfilled.
It is preferable that condition (I) below be fulfilled.
|f2|/f1<25 (I)
where
Condition (I) defines the range that needs to be observed mainly to strike a proper balance between the total length and the aberrations produced. If the upper limit of condition (I) is transgressed, the optical power of the second lens element L2 is so weak that, while it is easy to correct aberrations, the total length is unduly long.
It is preferable that condition (II) below be fulfilled.
0.1<T1/f<0.5 (II)
where
Condition (II) defines the range that needs to be observed with respect to the first lens element L1 mainly to strike a proper balance between the lateral chromatic aberration produced and the manufacturability of the lens element. If the upper limit of condition (II) is transgressed, it is difficult to correct lateral chromatic aberration properly. By contrast, if the lower limit of condition (II) is transgressed, the lens element is too thin at the edge to be manufactured easily.
It is preferable that condition (III) below be fulfilled, and it is further preferable that this condition be fulfilled together with at least one of conditions (I) and (II) noted above.
1.4<f/Y′<1.9 (III)
where
Condition (III) defines the range that needs to be observed to strike a proper balance between the total length of the taking lens system and the front lens diameter. If the lower limit of condition (III) is transgressed, the front lens diameter is so large that the dimension, in the diametrical direction, of the taking lens device incorporating the taking lens system is unduly large and that it is difficult to correct distortion. By contrast, if the upper limit of condition (III) is transgressed, the total length of the taking lens system is so long that the dimension, in the axial (AX) direction, of the taking lens device incorporating the taking lens system is unduly large.
It is preferable that condition (IV) below be fulfilled, and it is further preferable that this condition be fulfilled together with at least one of conditions (I) to (III) noted above.
V2<40 (IV)
where
Condition (IV) defines the range that needs to be observed with respect to the correction of chromatic aberration by the second lens element L2. If condition (IV) is not fulfilled, the correction of chromatic aberration by the second lens element L2 is unsatisfactory, aggravating the chromatic aberration produced through the taking lens system as a whole.
It is preferable that condition (V) below be fulfilled, and it is further preferable that this condition be fulfilled together with at least one of conditions (I) to (IV) noted above.
0.13<TA/f<0.41 (V)
where
Condition (V) defines the range that needs to be observed to strike a proper balance between the total length and the aberrations produced. If the upper limit of condition (V) is transgressed, it is easy to correct aberrations, but the total length is unduly long. By contrast, if the lower limit of condition (V) is transgressed, it is easy to shorten the total length, but the aberrations produced, in particular distortion and curvature of field, are unduly large.
It is preferable that, as in the twenty-second to twenty-fifth embodiments, the aperture stop ST be disposed on the object side of the first lens element L1. Disposing the aperture stop ST on the object side of the first lens element L1 makes it possible to locate the exit pupil farther away. Moreover, in the twenty-second to twenty-fifth embodiments, plastic lens elements and aspherical surfaces are used. Here, it is preferable that the first and second lens elements L1 and L2 be both plastic lens elements, and that the first and second lens elements L1 and L2 each have at least one aspherical surface. Using plastic lens elements as both of the lens elements L1 and L2 is effective in reducing the costs of the taking lens system. Giving each of the lens elements L1 and L2 at least one aspherical surface is highly effective in reducing spherical aberration, coma aberration, and distortion.
In any of the first to twenty-fifth embodiments, the taking lens system is composed solely of refractive lens elements, which deflect incident light by refraction (i.e. lens elements of the type in which light deflects at the interface between two media having different refractive indices). It is possible, however, to replace any of these lens elements with a lens element of any other type, for example, a diffractive lens element, which deflects incident light by diffraction, or a refractive/diffractive hybrid lens element, which deflects incident light by diffraction and refraction combined together, or a gradient index lens element, which deflects incident light with varying refractive indices distributed within a medium. Among these types, gradient index lens elements, which have varying refractive indices distributed within a medium, are expensive because of the complicated fabrication process they require. Therefore, in a taking lens system embodying the invention, it is preferable to use lens elements formed out of a uniform material as both of the lens elements L1 and L2 where two lens elements are provided and as all of the lens elements L1 to L3 where three lens elements are provided.
In any of the first to twenty-fifth embodiments, a surface having no optical power (for example, a reflective, refractive, or diffractive surface) may be disposed in the optical path so that the optical path is bent in front of, behind, or in the middle of the taking lens system. Where to bend the optical path may be determined to suit particular needs. By bending the optical path appropriately, it is possible to make the digital input device (such as a digital camera) incorporating the taking lens system apparently slim and compact.
The taking lens systems of the first to twenty-fifth embodiments are all suitable as compact taking lens systems for use in digital input devices, and, by combining one of those taking lens systems with an optical low-pass filter and a solid-state image sensor, it is possible to build a taking lens device that takes in an image of a subject optically and outputs it as an electrical signal. A taking lens device is used as the main component of a camera (for example, a digital camera, video camera, or camera incorporated in or externally fitted to a digital video unit, personal computer, mobile computer, pen-type scanner, cellular phone, personal digital assistant (PDA), or the like) that is used to take a still or moving picture of a subject. A taking lens device is composed of, for example, from the object (subject) side, a taking lens system for forming an optical image of a subject, an optical low-pass filter, and a solid-state image sensor for converting the optical image formed by the taking lens system into an electrical signal.
Thus, the first to twenty-fifth embodiments described hereinbefore include inventions (i) to (xvii) having features as noted below, and, with those features, it is possible to realize high-optical-performance, low-cost, compact taking lens devices. By incorporating such a taking lens device in a digital camera or the like, it is possible to enhance the performance and functionality of the camera, and to reduce the costs and size of the camera.
Covered by the first to ninth embodiments are these inventions:
Covered by the tenth to twenty-first embodiments are these inventions:
Covered by the twenty-second to twenty-fifth embodiments are these inventions:
Used as the solid-state image sensor is a CCD, CMOS (complementary metal oxide semiconductor) sensor, or the like having, for example, a plurality of pixels. The optical image formed by the taking lens system is converted into an electrical signal by the solid-state image sensor. The optical image to be formed by the taking lens system passes through the optical low-pass filter having a predetermined cutoff frequency characteristic that depends on the pixel pitch of the solid-state image sensor, and meanwhile the optical image has its spatial frequency characteristic so adjusted as to minimize so-called aliasing noise generated when the optical image is converted into an electric signal. The signal produced by the solid-state image sensor is subjected to predetermined digital image processing, image compression processing, and the like as required, and is recorded in a memory (such as a semiconductor memory or an optical disk) as a digital video signal; in some cases, the signal is transferred to another device through a cable or after being converted into an infrared signal.
In the first to twenty-fifth embodiments, a glass filter GF is used as the optical low-pass filter disposed between the last surface of the taking lens system and the solid-state image sensor. It is possible, however, to use instead an optical low-pass filter of any other type that suits the digital input device in which the taking lens system is incorporated. For example, it is possible to use a birefringence-type low-pass filter made of quartz or the like having an appropriately aligned crystal axis, a phase-type low-pass filter that achieves the required optical cut-off frequency characteristics by exploiting diffraction, or a low-pass filter of any other type.
Hereinafter, practical examples of the present invention will be presented with reference to their construction data and other data. Tables 1 to 25 show the construction data of Examples 1 to 25, respectively. Examples 1 to 25 correspond to the first to twenty-fifth embodiments described hereinabove. Thus, the lens construction diagrams (
A surface of which the radius of curvature ri is marked with an asterisk (*) is a refractive optical surface having an aspherical shape or a surface that exerts a refractive effect equivalent to that of an aspherical surface. The surface shape of such an aspherical surface is defined by formula (AS) below. The aspherical surface data of the aspherical surfaces used in each example are also shown together with the other data mentioned above.
X(H)=(C0·H2)/(1+√{square root over (1−ε·C02·H2)})+Σ(Ai·H1) (AS)
where
As described above, according to the present invention, it is possible to realize a high-optical-performance, low-cost, compact taking lens system for use with a solid-state image sensor. By incorporating a taking lens system according to the invention in a digital input device such as a digital camera, it is possible to enhance the performance and functionality of the camera, and to reduce the costs and size of the camera.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-361363 | Nov 2001 | JP | national |
| 2002-220692 | Jul 2002 | JP | national |
| 2002-220699 | Jul 2002 | JP | national |
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| 11-052227 | Feb 1999 | JP |
| 2001-183578 | Jul 2001 | JP |
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| Number | Date | Country | |
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| 20030210341 A1 | Nov 2003 | US |
