CN1940628A - Image-forming lens - Google Patents
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- CN1940628A CN1940628A CN 200610139617 CN200610139617A CN1940628A CN 1940628 A CN1940628 A CN 1940628A CN 200610139617 CN200610139617 CN 200610139617 CN 200610139617 A CN200610139617 A CN 200610139617A CN 1940628 A CN1940628 A CN 1940628A
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- 201000009310 astigmatism Diseases 0.000 description 11
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Abstract
The invention provides an image-forming lens, including: a first lens G1 is a positive lens, whose surface on an object side is formed to be convex; a second lens G2 being a negative meniscus lens whose surface on the object side; and a third lens G3 a positive lens; and a forth lens G4 being a meniscus lens whose surface on the object side is formed to be concave paraxially; and the image-forming lens fully satisfies conditional expression (1)-(5), thereby realize compact and insure high imaging performance. The focal power of the first lens determined by conditional expression (1), dispersion is determined by conditional expression (2) and (3), the focal power of the second lens determined by conditional expression (4), the focal power of the thirrd lens determined by conditional expression (5). Thereby, an image-forming lens with more compact structure but with high imaging performance is provided.
Description
Technical Field
The present invention relates to a fixed focus imaging lens suitable for mounting in a digital camera using an image pickup Device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) or a small image pickup Device such as a camera using a silver salt film.
Background
In recent years, as personal computers have been spread to general homes and the like, digital still cameras (hereinafter, simply referred to as digital cameras) capable of inputting image information such as captured images of scenery and human figures into personal computers have been rapidly spread. With the development of higher functions of mobile phones, there are an increasing number of cases in which image input module cameras (モジユ - ルカメラ: modulecamera) (portable module cameras: モジユ - ルカメラ for carrying) are mounted in mobile phones.
In these imaging devices, imaging elements such as CCDs and CMOSs have been used. In recent years, as the size of an imaging element of such an imaging device has been reduced, the size of the entire device has been extremely reduced. In addition, high pixelation of the image pickup device is also in progress, and high image resolution and high performance are demanded.
As an imaging lens used in such a downsized imaging device, there is a lens described in the following patent document, for example. Patent documents 1 and 2 each describe an imaging lens having a 3-lens structure. Patent documents 3 to 6 each describe an imaging lens having a 4-lens structure. In the imaging lens described in patent document 3, a lens stop is disposed between the 2 nd lens and the 3 rd lens from the object side, and in the imaging lens described in patent document 4, the lens stop is disposed at a position closest to the object side. In the imaging lenses described in patent documents 5 and 6, a lens stop is disposed at a position closest to the object side or between the 1 st lens and the 2 nd lens from the object side.
[ patent document 1] Japanese patent application laid-open No. 10-48516
[ patent document 2] Japanese patent application laid-open No. 2002-221659
[ patent document 3] Japanese patent laid-open publication No. 2004-302057
[ patent document 4] Japanese patent application laid-open No. 2005-245781
[ patent document 5] Japanese patent laid-open No. 2005-4027
[ patent document 6] Japanese patent laid-open No. 2005-4028
Disclosure of Invention
As described above, in recent years, miniaturization and high-pixelation of an image pickup device have been progressing, and along with this, high image resolution performance and structural miniaturization are required particularly for an imaging lens for a digital camera. On the other hand, although there have been demands for an imaging lens of a portable module camera mainly in terms of cost and downsizing, recently, there is a tendency for an imaging element to be higher in pixel even in a portable module camera, and thus demands for performance have been increased.
Therefore, it is desired to develop various lenses that can be improved in a comprehensive manner in terms of cost, imaging performance, and miniaturization, and for example, it is desired to develop a low-cost high-performance imaging lens that has come into sight, is miniaturized to be mounted not only in a portable module camera but also in a digital camera in terms of performance.
For such a demand, for example, it is conceivable to make the number of lenses 3 or 4 for downsizing and cost reduction, and to use an aspherical surface for high performance. In this case, although the aspherical surface contributes to downsizing and high performance, it is disadvantageous in terms of manufacturability and is liable to increase cost, and therefore, it is preferable to use the aspherical surface in consideration of manufacturability. The lenses described in the above patent documents have a configuration in which an aspherical surface is used so as to have a 3-piece or 4-piece configuration, but are insufficient in terms of satisfying both imaging performance and downsizing, for example.
The present invention has been made in view of the above problems, and an object thereof is to provide an imaging lens having a compact structure and capable of obtaining high imaging performance.
An imaging lens of the present invention includes, in order from an object side: a 1 st lens having positive power with a convex surface facing the object side; a 2 nd lens having a negative power with a concave surface facing the object side; a 3 rd lens having a positive refractive power; and a 4 th lens having a meniscus shape with a convex surface facing the object side in the vicinity of the paraxial region; and is configured to satisfy the following conditional expressions (1) to (5).
0.7＜f1/f＜1.1 (1)
1.45＜n1＜1.6 (2)
ν1＞60 (3)
0.8＜|f2/f|＜1.8 (4)
1.9＜f3/f＜20 (5)
Where f1 is a focal length of the 1 st lens, f is an overall focal length, n1 is a refractive index of the 1 st lens with respect to a d-line, ν 1 is an abbe number of the 1 st lens with respect to the d-line, f2 is a focal length of the 2 nd lens, and f3 is a focal length of the 3 rd lens.
The imaging lens of the present invention can be reduced in size by a small number of lenses, such as 4 lenses, and can also achieve imaging performance that is compatible with a digital camera equipped with an image pickup device having 500 ten thousand pixels, for example. Specifically, since the 1 st lens has such refractive power as to satisfy the conditional expression (1), not only an increase in size but also an increase in spherical aberration can be suppressed. Further, the 1 st lens is formed of a lens material satisfying the conditional expressions (2) and (3), and axial chromatic aberration can be reduced. Further, since the configuration satisfies conditional expressions (4) and (5), not only higher order aberrations such as spherical aberration and coma aberration can be corrected well, but also downsizing can be achieved.
In the imaging lens of the present invention, the following conditional expression (6) can be further satisfied.
bf/TL＞0.2 (6)
Where bf is a distance from the image-side surface of the 4 th lens to the image forming surface (air conversion, that is, an actual distance is converted into a distance in an air medium), and TL is a distance from the object-side surface of the 1 st lens to the image forming surface (air conversion). When this conditional expression is satisfied, a more sufficient back-focus (back-focus) can be ensured.
In the imaging lens of the present invention, the following conditional expression (7) can be further satisfied.
TL/(2×Ih)＜1.1 (7)
Where Ih is the maximum image height in the imaging plane. When this conditional expression is satisfied, further miniaturization can be achieved.
In the imaging lens of the present invention, the 1 st lens to the 4 th lens preferably each include at least one aspherical surface. By doing so, high aberration performance can be obtained relatively easily. Further, when the 1 st lens is made of optical glass and the 2 nd to 4 th lenses are all made of a resin material, it is possible to reduce the weight of the lens while reducing aberrations (particularly chromatic aberration).
In the imaging lens of the present invention, a lens stop may be disposed between an object-side surface position on the optical axis of the 1 st lens and an image-side surface position on the optical axis of the 1 st lens. This is advantageous in shortening the overall length.
An imaging lens according to the present invention includes, in order from an object side: a 1 st lens which is a positive lens having a convex surface facing the object side; a 2 nd lens which is a negative lens having a concave surface facing the object side; a 3 rd lens which is a positive lens; and a 4 th lens which is a meniscus-shaped lens with a convex surface facing the object side in the vicinity of the paraxial region; and the imaging lens is configured to fully satisfy the following conditional expressions (1) to (5), whereby not only miniaturization can be achieved but also high imaging performance can be ensured.
Drawings
Fig. 1 is a diagram showing a 1 st configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 1.
Fig. 2 is a view showing a configuration example 2 of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 2.
Fig. 3 is a diagram showing a configuration example 3 of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 3.
Fig. 4 is a diagram showing a 4 th configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 4.
Fig. 5 is a diagram showing a 5 th configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 5.
Fig. 6 is a view showing a 6 th configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 6.
Fig. 7 is a diagram showing a 7 th configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 7.
Fig. 8 is a diagram showing an 8 th configuration example of an imaging lens according to an embodiment of the present invention, and is a cross-sectional view corresponding to example 8.
Fig. 9 is a view showing a 9 th configuration example of an imaging lens according to an embodiment of the present invention, and is a sectional view corresponding to example 9.
Fig. 10 is an explanatory diagram showing basic lens data in the imaging lens of example 1.
Fig. 11 is an explanatory diagram showing data on an aspherical surface in the imaging lens of example 1.
Fig. 12 is an explanatory diagram showing basic lens data in the imaging lens of example 2.
Fig. 13 is an explanatory diagram showing data on aspherical surfaces in the imaging lens of example 2.
Fig. 14 is an explanatory diagram showing basic lens data in the imaging lens of example 3.
Fig. 15 is an explanatory diagram showing data on an aspherical surface in the imaging lens of example 3.
Fig. 16 is an explanatory diagram showing basic lens data in the imaging lens of example 4.
Fig. 17 is an explanatory diagram showing data on aspherical surfaces in the imaging lens of example 4.
Fig. 18 is an explanatory diagram showing basic lens data in the imaging lens of example 5.
Fig. 19 is an explanatory diagram showing data on aspherical surfaces in the imaging lens of example 5.
Fig. 20 is an explanatory diagram showing basic lens data in the imaging lens of example 6.
Fig. 21 is an explanatory diagram showing data on an aspherical surface in the imaging lens of example 6.
Fig. 22 is an explanatory diagram showing basic lens data in the imaging lens of example 7.
Fig. 23 is an explanatory diagram showing data on aspherical surfaces in the imaging lens of example 7.
Fig. 24 is an explanatory diagram showing basic lens data in the imaging lens of example 8.
Fig. 25 is an explanatory diagram showing data on an aspherical surface in the imaging lens of example 8.
Fig. 26 is an explanatory diagram showing basic lens data in the imaging lens of example 9.
Fig. 27 is an explanatory diagram showing data on aspherical surfaces in the imaging lens of example 9.
Fig. 28 is an explanatory diagram showing numerical values corresponding to expressions (1) to (7) in each imaging lens of examples 1 to 9.
Fig. 29 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 1.
Fig. 30 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 2.
Fig. 31 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 3.
Fig. 32 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 4.
Fig. 33 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 5.
Fig. 34 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 6.
Fig. 35 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 7.
Fig. 36 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 8.
Fig. 37 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the imaging lens of example 9.
In the figure: G1-G4-1 st to 4 th lenses, CG-cover glass, Si-i lens surface from the object side, Ri-curvature radius of i lens surface from the object side, Di-surface interval of i lens surface and i +1 th lens surface from the object side, and Z1-optical axis.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Fig. 1 shows a 1 st configuration example of an imaging lens according to an embodiment of the present invention. This structural example corresponds to the lens structure of numerical example 1 (fig. 10 and 11) described later. Fig. 2 to 9 show 2 nd to 9 th configuration examples in the present embodiment, respectively. The 2 nd configuration example corresponds to a lens structure of the 2 nd numerical embodiment (fig. 12, 13) described later, the 3 rd configuration example corresponds to a lens structure of the 3 rd numerical embodiment (fig. 14, 15) described later, the 4 th configuration example corresponds to a lens structure of the 4 th numerical embodiment (fig. 16, 17) described later, the 5 th configuration example corresponds to a lens structure of the 5 th numerical embodiment (fig. 18, 19) described later, the 6 th configuration example corresponds to a lens structure of the 6 th numerical embodiment (fig. 20, 21) described later, the 7 th configuration example corresponds to a lens structure of the 7 th numerical embodiment (fig. 22, 23) described later, the 8 th configuration example corresponds to a lens structure of the 8 th numerical embodiment (fig. 24, 25) described later, and the 9 th configuration example corresponds to a lens structure of the 9 th numerical embodiment (fig. 26, 27) described later. In fig. 1 to 9, symbol Si denotes the ith surface to which reference numeral i is added so that the surface of the component closest to the object side is the 1 st surface and increases sequentially toward the image side (image forming side). The symbol Ri represents the radius of curvature of the surface Si. Symbol Di denotes a surface interval between the i-th surface Si and the i + 1-th surface Si +1 on the optical axis Z1. Since the basic configurations of the respective configuration examples are the same, the following description will be made based on the configuration example of the imaging lens shown in fig. 1, and the configuration examples of fig. 2 to 9 will also be described as necessary.
The imaging lens can be used in, for example, a portable module camera or a digital camera using an imaging device such as a CCD or a CMOS. The imaging lens is configured to be arranged in order from the object side along an optical axis Z1: a lens stop St, a 1 St lens G1, a 2 nd lens G2, a 3 rd lens G3, and a 4 th lens G4. On an imaging surface (imaging surface) S of the imaging lensimgAn image pickup device (not shown) such as a CCD is disposed thereon. A cover glass CG for protecting an image formation surface of the image pickup element is disposed in the vicinity of the image formation surface. Between the 4 th lens G4 and the image forming surface (image forming surface), other optical members such as an infrared cut filter and a low-pass filter may be disposed in addition to the cover glass CG.
The 1 st lens G1, which is formed in a meniscus shape with a convex surface toward the object side near the paraxial region (near the optical axis) and has positive power. However, the 1 st lens G1 may be biconvex near the paraxial region, as in the 6 th and 9 th configuration examples. For example, in the 1 st lens G1, at least one of the object-side surface S1 and the image-side surface S2 is preferably aspheric, and particularly, both surfaces S1 and S2 are preferably aspheric. The 1 st lens G1 is made of optical glass with low chromatic dispersion. Further, the lens stop St is advantageously disposed at a position as close to the object side as possible in order to reduce the incident angle to the image pickup device. On the other hand, when the lens stop St is located on the object side than the surface S1, the total of the components (the distance between the lens stop St and the surface S1) is taken as the optical path length, which is disadvantageous in terms of downsizing of the entire structure (thinning: low back (ていせいか)). For these reasons, the lens stop St is preferably disposed between the surface S1 and the surface S2 on the optical axis Z1.
The 2 nd lens G2, formed in a meniscus shape with a concave surface facing the object side in the vicinity of the paraxial region, has negative power. However, as in the 9 th configuration example, the 2 nd lens G2 may be formed in a biconcave shape near the paraxial region. For example, in the 2 nd lens G2, at least one of the object-side surface S3 and the image-side surface S4 is preferably aspheric, and particularly, both surfaces S3 and S4 are preferably aspheric.
The 3 rd lens G3, formed in a meniscus shape with the convex surface facing the object side near the paraxial region, has positive power. For example, in the 3 rd lens G3, at least one of the object-side surface S5 and the image-side surface S6 is preferably aspheric. In particular, in the effective diameter range, the surface S5 is preferably an aspherical shape whose power becomes weaker as closer to the positive power of the periphery, and the surface S6 is preferably an aspherical shape whose power becomes weaker as closer to the negative power of the periphery. That is, the object-side surface S5 is preferably an aspherical surface which is convex in the vicinity of the paraxial region but concave in the peripheral region, and the image-side surface S6 is preferably an aspherical surface which is concave in the vicinity of the paraxial region but convex in the peripheral region.
The 4 th lens G4 is formed in a meniscus shape with a convex surface facing the object side in the vicinity of the paraxial region, and has, for example, positive power. For example, in the 4 th lens G4, at least one of the object-side surface S7 and the image-side surface S8 is preferably aspheric. In particular, in the effective diameter range, the surface S7 is preferably an aspherical shape whose power becomes weaker as closer to the positive power of the periphery, and the surface S8 is preferably an aspherical shape whose power becomes weaker as closer to the negative power of the periphery. That is, the object-side surface S7 is preferably an aspherical surface which is convex in the vicinity of the paraxial region but concave in the peripheral region, and the image-side surface S8 is preferably an aspherical surface which is concave in the vicinity of the paraxial region but convex in the peripheral region.
The 2 nd lens G2 to the 4 th lens G4, which have a shape more complicated than that of the 1 st lens G1 and are larger in size, are all made of a resin material. Therefore, not only can a complicated aspherical shape be formed with high accuracy, but also the entire imaging lens can be reduced in weight.
Further, the imaging lens is configured to satisfy the following conditional expressions (1) to (5).
0.7＜f1/f＜1.1 (1)
1.45＜n1＜1.6 (2)
ν1＞60 (3)
0.8＜|f2/f|＜1.8 (4)
1.9＜f3/f＜20 (5)
Where f1 is the focal length of the 1 st lens G1, f is the focal length of the whole, n1 is the refractive index of the 1 st lens G1 with respect to the d-line, ν 1 is the abbe number of the 1 st lens with respect to the d-line, f2 is the focal length of the 2 nd lens G2, and f3 is the focal length of the 3 rd lens G3.
In the imaging lens, the following conditional expression (6) may be further satisfied.
bf/TL＞0.2 (6)
Bf is from the surface S7 on the image side of the 4 th lens G4 to the imaging surface SimgTL is the distance from the object side surface S1 of the 1 st lens G1 to the image forming surface S (air conversion)imgDistance to (air conversion).
In the imaging lens, the following conditional expression (7) may be further satisfied.
TL/(2×Ih)＜1.1 (7)
Where Ih is the maximum image height in the imaging plane.
The operation and effect of the imaging lens of the present embodiment configured as described above will be described below.
In the imaging lens of the present invention, by forming each lens surface of the 1 st lens G1 to the 4 th lens G4 to be an aspherical shape defined by even-numbered and odd-numbered aspherical coefficients, not only can the size be reduced by a small number of lenses such as 4 lenses, but also imaging performance corresponding to a digital camera equipped with an image pickup device having 500 ten thousand pixels, for example, can be obtained. Specifically, the 1 st lens G1 has such refractive power as to satisfy the conditional expression (1), and thus not only can increase in size be suppressed, but also increase in spherical aberration can be suppressed. Further, since the 1 st lens G1 is formed of optical glass satisfying the conditional expressions (2) and (3), axial chromatic aberration can be reduced. Further, since the configuration satisfies conditional expressions (4) and (5), not only higher order aberrations such as spherical aberration and coma aberration can be corrected well, but also downsizing can be facilitated. Further, when the configuration satisfies the conditional expressions (6) and (7), not only a sufficient back focus is secured but also further downsizing is achieved. Further, since the lens stop St is disposed at a position between the surface S1 and the surface S2 on the optical axis Z1, the overall length can be further reduced. The meanings of conditional expressions (1) to (7) will be described in detail below.
The conditional expression (1) is an expression representing an appropriate range of the amount (f1/f), and the amount (f1/f) is an amount representing the magnitude of the power (1/f1) of the 1 st lens G1 with respect to the power (1/f) of the entire system. By rationalizing the power distribution of the 1 st lens G1, it is possible to perform correction of each aberration and sufficient securing of the back focal length in a well-balanced manner. Here, if the positive power of the 1 st lens G1 becomes too strong below the lower limit of the conditional expression (1), the correction of the spherical aberration is not sufficient, and the entire system becomes large. On the other hand, if the positive power of the 1 st lens G1 is too weak beyond the upper limit of the conditional expression (1), the back focal length cannot be sufficiently secured.
The conditional expressions (2) and (3) define dispersion of the optical glass used for the 1 st lens G1 with respect to the d-line. By satisfying conditional expressions (2) and (3), dispersion can be suppressed, and axial chromatic aberration can be reduced.
The conditional expression (4) is an expression representing an appropriate range of the amount (f2/f), and the amount (f2/f) is an amount representing the magnitude of the power (1/f2) of the 2 nd lens G2 with respect to the power (1/f) of the entire system. By rationalizing the power distribution of the 2 nd lens G2, each aberration can be corrected well. If the negative power of the 2 nd lens G2 is too strong below the lower limit of the conditional expression (4), the higher-order aberration increases. On the other hand, when the negative power of the 2 nd lens G2 is too weak beyond the upper limit of the conditional expression (2), correction of the main terrestrial aberration or coma becomes difficult. In particular, when the imaging lens satisfies the following conditional expression (8), it is possible to perform more preferable aberration correction.
0.9＜|f2/f|＜1.1 (8)
The conditional expression (5) is an expression representing an appropriate range of the amount (f3/f), and the amount (f3/f) is an amount representing the magnitude of the power (1/f3) of the 3 rd lens G3 with respect to the power (1/f) of the entire system. By rationalizing the power distribution of the 3 rd lens G3, it is possible to perform correction of each aberration and sufficient securing of the back focal length in a well-balanced manner. Here, if the positive power of the 3 rd lens G3 becomes too strong below the lower limit of conditional expression (5), the back focal length cannot be sufficiently secured. On the other hand, if the positive power of the 3 rd lens G3 is too weak beyond the upper limit of the conditional expression (5), sufficient aberration correction becomes difficult. In particular, when the following conditional expression (9) is satisfied, sufficient securing of the back focus and good aberration correction can be performed in a well-balanced manner.
3.0＜f3/f＜10 (9)
Conditional expressions (6) and (7) prescribe downsizing of the entire imaging lens. Satisfying the condition (6) can ensure a more sufficient back focus. In particular, when the following conditional expression (10) is satisfied, a larger back focus can be secured. Further, satisfying the condition (7) enables further downsizing. In particular, when the following conditional expression (11) is satisfied, further miniaturization can be achieved.
bf/TL＞0.23 (10)
TL/(2×Ih)＜1.0 (11)
As described above, according to the imaging lens of the present embodiment, the 1 st lens G1 to the 4 th lens G4 are configured as described above and satisfy the predetermined conditional expressions, thereby making it possible to achieve not only miniaturization but also high imaging performance.
Next, a specific numerical example of the imaging lens according to the present embodiment will be described. Hereinafter, numerical examples 1 to 9 (examples 1 to 9) will be described in general based on numerical example 1.
Fig. 10 and 11 show specific lens data (example 1) corresponding to the imaging lens configuration shown in fig. 1. Fig. 10 shows basic lens data, and fig. 11 shows data relating to an aspherical shape. Similarly, fig. 12 and 13 show specific lens data (example 2) corresponding to configuration example 2 (fig. 2). Similarly, fig. 14 and 15 show specific lens data (example 3) corresponding to configuration example 3 (fig. 3). Similarly, fig. 16 and 17 show specific lens data (example 4) corresponding to the 4 th configuration example (fig. 4). Similarly, fig. 18 and 19 show specific lens data (example 5) corresponding to configuration example 5 (fig. 5). Similarly, fig. 20 and 21 show specific lens data (example 6) corresponding to configuration example 6 (fig. 6). Similarly, fig. 22 and 23 show specific lens data (example 7) corresponding to the 7 th configuration example (fig. 7). Similarly, fig. 24 and 25 show specific lens data (example 8) corresponding to the 8 th configuration example (fig. 8). Similarly, fig. 26 and 27 show specific lens data (example 9) corresponding to the 9 th configuration example (fig. 9).
In the column of the surface number Si in the basic lens data shown in fig. 10, the number of the i-th (i is 1 to 10) surface to which the number increases in order toward the image side, with the surface of the component element closest to the object side except the lens stop St as the 1 St surface, corresponding to the symbol Si of the imaging lens shown in fig. 1. In the column of the radius of curvature Ri, a value of the radius of curvature of the i-th surface from the object side corresponding to the symbol Ri shown in fig. 1 is shown. The column for the plane separation Di also indicates what is appended in correspondence with FIG. 1Symbol, i-th surface Si and i + 1-th surface Si +1 from the object side are separated on the optical axis. The values of the radius of curvature Ri and the face separation Di are in millimeters (mm). Columns Ndj and vdj indicate refractive index and abbe number of the j-th (j is 1 to 5) lens element from the object side including the cover glass CG, respectively, with respect to the d-line (wavelength 587.6 nm). The curvature radii R9 and R10 on both sides of the cover glass CG are 0 (zero), indicating a flat surface. In the column of the surface interval Di of the lens stop, the distance (mm) between the surface S1 on the optical axis and the lens stop St is shown. A negative sign means that the lens stop St is closer to the image side than the surface S1. In the outer panel of fig. 10, the focal length F (mm), F Number (FNO), back focal length bf (mm), and the distance from the object-side surface S1 of the 1 st lens G1 to the image S of the entire system are shown as dataimgThe distance to the imaging plane (air conversion) TL (mm) and the maximum image height in the imaging plane ih (mm).
In fig. 10, the symbol "+" attached to the left side of the surface number Si indicates that the lens surface is an aspherical shape. In each of the embodiments, all of the two surfaces of the 1 st lens G1 to the 4 th lens G4 have aspherical shapes. The basic lens data indicates the numerical value of the curvature radius in the vicinity of the optical axis (in the vicinity of the paraxial region) as the curvature radius of each aspherical surface.
In the numerical values of the aspherical surface data in fig. 11, the symbol "E" indicates that the data following the symbol "E" is a "power exponent" with a base 10, and indicates that the numerical value represented by an exponential function with a base 10 is multiplied by the numerical value before "E". For example, if it is "1.0E-02", it means "1.0X 10-2"is used herein.
The aspherical surface data includes values of coefficients Ai and K in an expression of an aspherical surface shape represented by the following expression (ASP). More specifically, Z represents the length (mm) of a perpendicular line from a point on the aspheric surface at a position having a height h from the optical axis to a tangential plane (plane perpendicular to the optical axis) to the apex of the aspheric surface.
Z＝C·h2/{1+(1-K·C2·h2)1/2}+∑Ai·hi (ASP)
Wherein,
z: depth of aspheric surface (mm)
h: distance (height) (mm) from optical axis to lens surface
K: eccentricity of a rotor
C: paraxial curvature of 1/R
(R: paraxial radius of curvature)
Ai: the i-th aspheric coefficient (i is an integer of 3 or more)
In any of examples 1 to 9, all surfaces of the 1 st lens G1 to the 4 th lens G4 have aspherical shapes. Further, the aspherical surface coefficient A isiThe coefficient A of 3 rd to 10 th order can be effectively used3～A10. However, the coefficients a of 3 rd to 16 th order in the 3 rd to 8 th planes of example 6 and the coefficients a of 2 nd to 8 th planes of example 7 can be effectively used3～A16。
Fig. 28 shows values corresponding to the conditional expressions (1) to (7) in general for each example. As shown in fig. 28, the values of the examples fall within the numerical ranges of all the conditional expressions (1) to (7).
Fig. 29(a) to 29(C) show spherical aberration, astigmatism, and distortion (distortion aberration) in the imaging lens of example 1. In each aberration diagram, the aberration with the d-line as the reference wavelength is shown, but in the spherical aberration diagram, the aberration for the F-line (wavelength 486.1nm) and the C-line (wavelength 656.3nm) is also shown. In the astigmatism diagrams, the solid line indicates the aberration in the radial direction, and the broken line indicates the aberration in the tangential direction. Similarly, fig. 30(a) to 30(C) show the respective aberrations in example 2. Similarly, fig. 31(a) to 31(C) show the respective aberrations in example 3. Similarly, fig. 32(a) to 32(C) show the respective aberrations in example 4. Similarly, fig. 33(a) to 33(C) show the respective aberrations in example 5. Similarly, fig. 34(a) to 34(C) show the respective aberrations in example 6. Similarly, fig. 35(a) to 35(C) show the respective aberrations associated with example 7. Similarly, fig. 36(a) to 36(C) show the respective aberrations in example 8. Similarly, fig. 37(a) to 37(C) show the respective aberrations in example 9.
As is clear from the above lens data and aberration diagrams, excellent aberration performance can be exhibited with respect to the respective embodiments. Further, the entire length can be reduced in size.
The present invention has been described above by referring to the embodiments and examples, but the present invention is not limited to the embodiments and examples described above, and various modifications can be made. For example, the values of the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the numerical examples described above, and other values may be used. In the above-described embodiments and examples, both surfaces of the 1 st to 4 th lenses are aspherical surfaces, but the present invention is not limited thereto.
Claims (8)
1. An imaging lens characterized in that,
the object side sequentially comprises:
a 1 st lens having a positive refractive power with a convex surface facing the object side;
a 2 nd lens having a negative power with a concave surface facing the object side;
a 3 rd lens having a positive optical power; and
a meniscus-shaped 4 th lens having a convex surface facing the object side in the vicinity of the paraxial region;
and the imaging lens is configured to satisfy the following conditional expressions (1) to (5):
0.7＜f1/f＜1.1 (1)
1.45＜n1＜1.6 (2)
ν1＞60 (3)
0.8＜|f2/f|＜1.8 (4)
1.9＜f3/f＜20 (5)
wherein,
f 1: the focal length of the 1 st lens is,
f: the overall focal length of the lens is as a whole,
n 1: the refractive index of the 1 st lens with respect to the d-line,
v 1: abbe number of the 1 st lens with respect to d-line,
f 2: the focal length of the 2 nd lens,
f 3: focal length of lens 3.
2. The imaging lens of claim 1,
the following conditional expression (6) is further satisfied:
bf/TL＞0.2 (6)
wherein,
bf: the distance from the image-side surface of the 4 th lens element to the image formation surface (air conversion),
TL: distance (air conversion) from the object-side surface of the 1 st lens to the image forming surface.
3. The imaging lens according to claim 1 or claim 2,
the following conditional expression (7) is further satisfied:
TL/(2×Ih)＜1.1 (7)
wherein,
ih: maximum image height in the imaging plane.
4. The imaging lens according to any one of claims 1 to 3,
the 2 nd lens to the 4 th lens respectively comprise at least one aspheric surface.
5. The imaging lens according to any one of claims 1 to 4,
the 1 st lens includes at least one aspherical surface.
6. The imaging lens according to any one of claims 1 to 5,
the 2 nd lens to the 4 th lens are all made of resin materials.
7. The imaging lens according to any one of claims 1 to 6,
the 1 st lens is made of optical glass.
8. The imaging lens according to any one of claims 1 to 7,
further, a lens stop is disposed between an object-side surface position on the optical axis of the 1 st lens and an image-side surface position on the optical axis of the 1 st lens.
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| JP2005283947 | 2005-09-29 | ||
| JP2005283947 | 2005-09-29 | ||
| JP2006163875 | 2006-06-13 |
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Also Published As
| Publication number | Publication date |
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| CN100476491C (en) | 2009-04-08 |
| JP2011221561A (en) | 2011-11-04 |
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