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Digital Camera Patent Abstract
A digital camera imaging lens includes first, second and third lenses
arranged in sequence from an object side toward an imaging surface
side. The first lens is a meniscus lens having a positive power,
whose convex surface faces the object side. The second lens is a
meniscus lens having a negative power, whose concave surface faces
the object side. The third lens is an aspherical lens having an
inflection point on its object-side surface. An aperture stop is
disposed between the first and second lenses. The imaging surface
is defined by an element surface of a photosensor.
Digital Camera Patent Claims
1. A digital camera imaging lens comprising a first lens, a second
lens, and a third lens arranged in sequence from an object side
toward an imaging surface side; wherein the first lens is a meniscus
lens having a positive power, whose convex surface faces the object
side; the second lens is a meniscus lens having a negative power,
whose concave surface faces the object side; the third lens is an
aspherical lens having an inflection point on its object-side surface;
an aperture stop is disposed between the first and second lenses;
and the imaging surface is defined by an element surface of a photosensor.
2. A digital camera imaging lens according to claim 1, wherein
the first lens has at least one lens surface thereof which is aspherical,
and wherein the following condition is satisfied when a total focal
distance of the digital camera imaging lens is f, and a focal distance
of the first lens is f1: 0.5<f1/f<1.5.
3. The digital camera imaging lens according to claim 2, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
4. The digital camera imaging lens according to claim 1, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
5. A digital camera imaging lens comprising a first lens, a second
lens, and a third lens arranged in sequence from an object side
toward an imaging surface side; wherein the first lens is a meniscus
lens having a positive power, whose convex surface faces the object
side; the second lens is a meniscus lens whose concave surface faces
the object side; the third lens is an aspherical lens having an
inflection point on its object-side surface; an aperture stop is
disposed between the first and second lenses; the first lens has
a strong power compared with the second lens; and the imaging surface
is defined by an element surface of a photosensor.
6. A digital camera imaging lens according to claim 5, wherein
the first lens has at least one lens surface thereof which is aspherical,
and wherein the following condition is satisfied when a total focal
distance of the digital camera imaging lens is f, and a focal distance
of the first lens is f1: 0.5<f1/f<1.5.
7. The digital camera imaging lens according to claim 6, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
8. The digital camera imaging lens according to claim 5, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
9. A digital camera imaging lens comprising a first lens, a second
lens, and a third lens arranged in sequence from an object side
toward an imaging surface side; wherein the first lens is a meniscus
lens having a positive power, whose convex surface faces the object
side; the second lens is a meniscus lens whose concave surface faces
the object side; the third lens is an aspherical lens having an
inflection point on its object-side surface; an aperture stop is
disposed between the first and second lenses; and the imaging surface
is defined by an element surface of a photosensor, and wherein the
following condition is satisfied when a total focal distance of
the digital camera imaging lens is f, and a distance from an incident
surface of the first lens on the object side to the imaging surface
is .SIGMA.d: 0.5<.SIGMA.d/f<1.5.
10. A digital camera imaging lens according to claim 9, wherein
the first lens has at least one lens surface thereof which is aspherical,
and wherein the following condition is satisfied when a total focal
distance of the digital camera imaging lens is f, and a focal distance
of the first lens is f1: 0.5<f1/f<1.5.
11. The digital camera imaging lens according to claim 10, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
12. The digital camera imaging lens according to claim 9, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
13. A digital camera imaging lens comprising a first lens, a second
lens, and a third lens arranged in sequence from an object side
toward an imaging surface side; wherein the first lens is a meniscus
lens having a positive power, whose convex surface faces the object
side; the second lens is a meniscus lens whose concave surface faces
the object side; the third lens is an aspherical lens having an
inflection point on its object-side surface; an aperture stop is
disposed between the first and second lenses; the imaging surface
is defined by an element surface of a photosensor, and wherein the
following condition is satisfied when an Abbe number of the second
lens is .nu.d2: 50>.nu.d2.
14. A digital camera imaging lens according to claim 13, wherein
the first lens has at least one lens surface thereof which is aspherical,
and wherein the following condition is satisfied when a total focal
distance of the digital camera imaging lens is f, and a focal distance
of the first lens is f1: 0.5<f1/f<1.5.
15. The digital camera imaging lens according to claim 14, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
16. The digital camera imaging lens according to claim 13, wherein
the third lens has a peripheral portion of its lens surface on the
imaging surface side, the peripheral portion being convex towards
the imaging surface side; and a maximum exit angle of a principal
ray in the digital camera imaging lens is 30 degrees or less.
Digital Camera Patent Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Ser. No. 10/532,382,
filed Apr. 21, 2005, which is incorporated herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to a small, lightweight imaging
lens used in an automobile-mounted camera, a surveillance camera,
a digital camera, a camera installed in a mobile telephone, or the
like that uses a CCD, CMOS, or other photosensor.
BACKGROUND ART
[0003] It is desired that an imaging lens installed in surveillance
cameras, digital cameras, and other devices that use CCD, CMOS,
or other photosensors be provided with the ability to faithfully
reproduce the subject. CCDs themselves or CCD cameras have also
been made smaller in recent years, which has been accompanied by
an inevitable increase in the demand for miniaturization and compact
design of the imaging lenses incorporated therein. CCD and other
photosensors have also been provided with high resolution on the
order of millions of pixels in contrast with CCD miniaturization.
It has inevitably become necessary for the imaging lenses used in
cameras having such sensors to also be capable of demonstrating
high optical performance. In the past, in order to demonstrate high
optical performance, aberration had been corrected using large numbers
of lens elements.
[0004] A characteristic of a CCD, CMOS, or other photosensor is
that the ray angle of each pixel incorporated therein is limited.
In a camera equipped with an optical system that ignores this characteristic,
the peripheral light intensity is reduced, and shading occurs. In
order to compensate for these effects, methods have been employed
whereby an electrical correction circuit is provided, or a microlens
array that forms a pair with the photosensor is mounted or the like,
and the angle at which light is received on the surface of the element
is enlarged or the like. Alternatively, configurations have been
adopted whereby the exit pupil is positioned as far away as possible
from the image surface.
[0005] On the other hand, there must be a space between the imaging
lens and the CCD in which a low-pass filter, infrared-blocking filter,
or the like is inserted. A limitation therefore exists in that the
back focus of the imaging lens must be lengthened to a certain degree.
[0006] An imaging lens having high resolution, a small number of
lens elements, and a compact structure is disclosed in JP-A 2002-228922.
The imaging lens disclosed therein is composed of four elements
in three groups, and the second and third lens groups therein are
composed of single lenses. An aspherical surface that contains an
inflection point is also employed as the lens surface.
DISCLOSURE OF THE INVENTION
[0007] An object of the present invention is to provide a lightweight,
compact imaging lens whereby the maximum exit angle with respect
to the element surface of the photosensor can be made smaller than
the angle of view in order to prevent shading, and aberration can
be corrected in order to adapt to high resolutions of millions of
pixels.
[0008] Another object of the present invention is to provide a
lightweight, compact imaging lens in which an aspherical surface
not containing an inflection point is employed in the lens surface,
in which aberration can be corrected in order to adapt to high resolutions
of millions of pixels, which is advantageous to produce, and which
has a small number of constituent lens elements.
[0009] In order to achieve the abovementioned objects, the imaging
lens according to a first invention of the present application comprises
three elements in three groups, wherein a first lens with a positive
meniscus whose convex surface faces an object side, a subsequently
positioned second lens whose meniscus has a negative power, and
a third lens with positive or negative power are arranged sequentially
from the object side, and the second and third lenses function as
correction lenses. The first lens also has a stronger power compared
with the second and third lenses. Furthermore, among the first,
second, and third lenses, both surfaces of at least the second lens
and third lens are aspherical. Also, at least one aspherical inflection
point is formed at the aspherical surface of the third lens.
[0010] In this arrangement, at least one of the lens surfaces among
the lens surfaces on both sides of the aforementioned first lens
can be an aspherical surface.
[0011] It is preferred in the imaging lens of the present invention
that when a total focal distance of the imaging lens is f, a focal
distance of the first lens is f1, a distance from an incident surface
on the object side to an imaging surface of the first lens is .SIGMA.d,
and an Abbe number of the second lens is .nu.d2, the following conditional
expressions are satisfied. 0.50<f1/f<1.5 (1) 0.50<.SIGMA.d/f<1.5(2)
50>.nu.d2(3)
[0012] Conditional expression (1) is a condition for ensuring that
spherical aberration is kept stable and that the lens system as
a whole is compact. If the lower limit is exceeded, the lens system
can be made compact, but it becomes difficult to correct spherical
aberration. If the upper limit is exceeded, spherical aberration
becomes easy to correct, but it becomes impossible to keep the lens
system as a whole compact. By satisfying this conditional expression,
the lens system can be made compact while a satisfactory state of
spherical aberration is maintained.
[0013] In the present invention, a total length of the imaging
lens can be reduced by making the first lens into a lens with a
positive meniscus whose convex surface faces the object side, and
satisfying conditional expression (1).
[0014] Conditional expression (2) is also a condition for ensuring
that the lens system as a whole is more compact. Particularly in
the case of an imaging lens employed in a camera installed in a
mobile telephone, it is necessary to reduce the size of the lens
system as a whole while at the same time reducing the total length
of the lens system. The optical system is preferably designed so
as to satisfy conditional expression (2) in order to satisfy these
requirements. Below the lower limit of conditional expression (2),
the lens system can be made compact, but various types of aberration
become difficult to correct. Exceeding the upper limit is also not
preferred, because the lens system increases in size.
[0015] Conditional expression (3) is a condition for making the
Abbe number of the second lens equal to 50 or less, and ensuring
that the on-axis chromatic aberration and the off-axis chromatic
aberration are kept stable.
[0016] It is also preferred that the third lens in the imaging
lens of the present invention be configured so that a peripheral
portion of a lens surface thereof on the image side is convex towards
the image surface, and that a lens surface thereof on an object
side and a lens surface thereof on the image side are provided with
one or a plurality of aspherical inflection points. By forming the
lens surface in this manner, coma aberration and astigmatic aberration
can be satisfactorily corrected, and distortion can also be satisfactorily
corrected.
[0017] As a characteristic feature of a case in which the imaging
surface is a CCD or CMOS, the ray angle incorporated into each pixel
is limited, and the ray angle increases towards the periphery of
the image. It is also preferred to mitigate this phenomenon that
a configuration be adopted whereby the periphery of the lens surface
of the third lens on the image side is an inflected aspherical surface
whose convex side faces the image surface, and that a maximum exit
angle of a principal ray is 30 degrees or less. Aspherical correction
whereby shading is prevented from occurring in the periphery of
the image is thereby obtained.
[0018] An imaging lens according to a second invention of the present
application comprises three elements in three groups, wherein a
first lens whose meniscus has a positive power and whose convex
surface faces an object side, a second lens whose meniscus has positive
or negative power and whose concave surface faces the object side,
and a third lens with positive power are arranged sequentially from
the object side.
[0019] Among surfaces of the first, second, and third lenses, the
shape of at least one lens surface is defined by an aspherical shape
in which an inflection point does not occur in an effective lens
surface region thereof.
[0020] Thus, since the imaging lens of the present invention is
a lens system comprised of three elements in three groups, and the
first lens positioned on the object side is configured as a lens
with a positive meniscus whose convex surface faces the object side,
the total length of the lens system can be reduced. By also making
the lens surface of the second lens on the object side concave,
the position of the exit pupil can be lengthened, whereby shading
can be prevented. Furthermore, since an aspherical shape having
no inflection point is employed in the lens surface, loss of resolution
due to lens machining error or assembly error can be minimized,
and production is facilitated.
[0021] In the imaging lens of the present invention herein, when
a total focal distance of the imaging lens is f, a back focus thereof
is BF, a focal distance of the first lens is f1, a curvature of
the lens surface of the third lens on the object side is Ra, and
a curvature of the lens surface of the third lens on the image side
is Rb, it is preferred that conditional expressions (A) through
(C) be satisfied. 0.5<f1/f<1.5 (A) 0.25<BF/f<1.0 (B)
1.0<|Rb/Ra| (C)
[0022] Conditional expression (A) is a condition for ensuring that
spherical aberration is stable and that the lens system as a whole
is compact. Below its lower limit, the lens system can be made compact,
but spherical aberration becomes difficult to correct. If, conversely,
its upper limit is exceeded, spherical aberration becomes easy to
correct, but it becomes impossible to keep the lens system as a
whole compact. By satisfying this conditional expression, the lens
system can be made compact while a satisfactory state of spherical
aberration is maintained.
[0023] In the present invention, the total length of the imaging
lens can be reduced by making the first lens into a lens with a
positive meniscus whose convex surface faces the object side, and
satisfying conditional expression (A).
[0024] Conditional expression (B) is also a condition for ensuring
that the lens system as a whole is more compact. Particularly in
the case of an imaging lens employed in a camera installed in a
mobile telephone, it is necessary to reduce the size of the lens
system as a whole while at the same time reducing the total length
of the lens system. The optical system is preferably designed so
as to satisfy conditional expression (B) in order to satisfy these
requirements. Below the lower limit of conditional expression (B),
the lens system can be made compact, but the organic space between
the lens system and the CCD or other imaging surface is lost, and
various types of aberration become difficult to correct. Exceeding
its upper limit is also not preferred, because the lens system increases
in size.
[0025] Conditional expression (C) relates to the exit pupil and
the back focus, and a condition in which the absolute value of the
curvature Ra is equal to or greater than the absolute value of the
curvature Rb is not preferred, because the exit pupil and the back
focus are shortened.
[0026] Next, when the imaging surface is a CCD, CMOS, or the like,
a limit is placed on the ray angle incorporated into each pixel
in order to ensure substantial aperture efficiency. To mitigate
this phenomenon, it is preferred that the exit pupil be lengthened
and that the maximum exit angle of the principal ray be corrected
to 30 degrees or less. Shading can thereby be prevented from occurring
in the periphery of the image surface. Distortion can also be satisfactorily
corrected by appropriately designing the aspherical shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a structural diagram of the imaging lens according
to Example 1 in which the first invention of the present application
is applied;
[0028] FIG. 2 is a structural diagram of the imaging lens according
to Example 2 in which the first invention of the present application
is applied;
[0029] FIG. 3 is an aberration diagram of the imaging lens of Example
1 shown in FIG. 1;
[0030] FIG. 4 is an aberration diagram of the imaging lens of Example
2 shown in FIG. 2;
[0031] FIG. 5 is a structural diagram of the imaging lens according
to Examples 3 and 5 in which the first invention of the present
application is applied;
[0032] FIG. 6 is a structural diagram of the imaging lens according
to Example 4 in which the first invention of the present application
is applied;
[0033] FIG. 7 is an aberration diagram of the imaging lens of Example
3 shown in FIG. 5;
[0034] FIG. 8 is an aberration diagram of the imaging lens of Example
4 shown in FIG. 6;
[0035] FIG. 9 is an aberration diagram of the imaging lens of Example
5 shown in FIG. 5;
[0036] FIG. 10 is a structural diagram of the imaging lens of Example
A in which the second invention of the present application is applied;
[0037] FIG. 11 is an aberration diagram of the imaging lens of
Example A shown in FIG. 10;
[0038] FIG. 12 is a structural diagram of the imaging lens of Examples
B and C in which the second invention of the present application
is applied;
[0039] FIG. 13 is an aberration diagram of the imaging lens of
Example B shown in FIG. 12; and
[0040] FIG. 14 is an aberration diagram of the imaging lens of
Example C in which the second invention of the present application
is applied.
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] Examples of the imaging lens having a three-group, three-element
structure according to the present invention will be described hereinafter
with reference to the drawings.
EXAMPLE 1
[0042] An imaging lens according to Example 1 in which the first
invention of the present application is applied is depicted in FIG.
1. An imaging lens 100 of the present example has, arranged in sequence
from an object side towards an imaging surface 6, a first lens 1
whose meniscus has a positive power and whose convex surface faces
the object side; a second lens 2 whose meniscus has a negative power
and whose concave surface faces the object side, positioned subsequently
via an aperture 4; and a third lens 3 having a positive power; and
the second and third lenses function as correction lenses. In the
present example, all of the lens surfaces on both sides of lenses
1, 2, and 3 are aspherical. In the present example, a cover glass
5 is mounted between the second lens surface R6 of the third lens
3 and the imaging surface 6.
[0043] In the third lens 3, an aspherical inflection point is provided
in the location of substantially 50% of the aperture diameter in
the first lens surface R5, and an aspherical inflection point is
provided in the vicinity of substantially 25% of the aperture diameter
in the second lens surface R6. The annular zone of the lens periphery
of the third lens 3 thereby forms a convex surface towards the imaging
surface side, and the maximum exit angle of the principal ray is
adjusted to 22 degrees with respect to the total angle of view of
63 degrees.
[0044] The lens data for the entire optical system of the imaging
lens 100 of the present example are as follows.
[0045] F-number: 3.5
[0046] Focal distance: f=5.7 mm
[0047] Total length: .SIGMA.d=7.06 mm
[0048] The lens data for the lens surfaces of the imaging lens
100 of the present example are shown in Table 1A; and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
are shown in Table 1B. TABLE-US-00001 TABLE 1A FNo.: 3.5; f = 5.7
mm; .SIGMA.d = 7.06 mm i R d Nd .nu.d 1* 1.73 1.0 1.5247 56.2 2*
4.46 0.15 3 0.00 0.4 4 0.00 0.5 5* -1.052 0.8 1.585 29.0 6* -1.50
0.1 7* 5.75 1.2 1.5247 56.2 8* 15.25 1.336 9 0.00 0.6 1.51633 64.2
10 0.00 0.9779 11 (*indicates an aspherical shape)
[0049] TABLE-US-00002 TABLE 1B i k A B C D 1 4.740865 .times. 10.sup.-2
5.067696 .times. 10.sup.-3 4.581707 .times. 10.sup.-3 -6.222765
.times. 10.sup.-3 3.890559 .times. 10.sup.-3 2 3.767275 .times.
10.sup.-1 3.143529 .times. 10.sup.-3 -1.939397 .times. 10.sup.-2
9.886734 .times. 10.sup.-2 -9.132532 .times. 10.sup.-2 5 -3.275267
.times. 10.sup.-1 1.603653 .times. 10.sup.-2 6.356242 .times. 10.sup.-2
2.087871 .times. 10.sup.-5 -3.891845 .times. 10.sup.-2 6 -1.071306
-7.703536 .times. 10.sup.-3 1.776501 .times. 10.sup.-2 7 2.361313
-1.916465 .times. 10.sup.-2 6.266366 .times. 10.sup.-4 5.086988
.times. 10.sup.-6 6.795863 .times. 10.sup.-7 8 0.00 -2.213400 .times.
10.sup.-2 7.502348 .times. 10.sup.-4 -3.884072 .times. 10.sup.-5
-1.070020 .times. 10.sup.-5
[0050] In Table 1A, i indicates the sequence of lens surfaces counted
from the object side; R indicates the curvature of each of the lens
surfaces; d indicates the distance between lens surfaces; Nd indicates
the refractive index of each of the lenses; and .nu.d indicates
the Abbe number of the lenses. An asterisk (*) by the i of a lens
surface indicates that the lens surface is aspherical.
[0051] When the axis in the optical axis direction is X, the height
in the direction perpendicular to the optical axis is H, the conical
coefficient is k, and the aspherical coefficients are A, B, C, and
D, the aspherical shape employed in the lens surface is indicated
by the following equation. X = H 2 R 1 + 1 - ( k - 1 ) .times. (
H R ) 2 + AH 4 + BH 6 + CH 8 + DH 10
[0052] The meanings of the symbols and the equations for indicating
the aspherical shapes are the same in Examples 2, 3, 4, and 5. In
the present example, since f1/f=0.84, .SIGMA.d/f=1.24, and .nu.d2=29,
conditional expressions (1) through (3) are satisfied.
[0053] FIG. 3 is an aberration diagram showing aberrations in the
imaging lens 100 of Example 1. In the diagram, SA indicates the
spherical aberration, OSC indicates the sine condition, AS indicates
the astigmatic aberration, and DIST indicates the distortion. The
T in the astigmatic aberration AS indicates a tangential image surface,
and the S indicates a sagittal image surface. The aberration diagram
at the bottom of the figure shows the lateral aberration, and in
the figure, DX indicates the laterally directed X aberration relating
to the X pupil coordinate; and DY indicates the laterally directed
Y aberration relating to the Y pupil coordinate. The meanings of
these symbols are also the same in the aberration diagrams showing
the aberration in Examples 2, 3, 4, and 5.
EXAMPLE 2
[0054] FIG. 2 is a structural diagram of an imaging lens according
to Example 2 in which the first invention of the present application
is applied. In an imaging lens 110 of the present example, a first
lens 11 with a positive meniscus whose convex surface faces an object
side, a second lens 12 with a negative meniscus whose concave surface
faces the object side, positioned via an aperture 14, and a third
lens 13 that is a biconvex lens are arranged in sequence from the
object side towards an imaging surface 16. An aspherical inflection
point is provided in the location of substantially 48% of the lens
aperture diameter in the first lens surface R5 of the third lens
13 on the object side. The second lens surface R6 thereof on the
image side is formed as an extension of the convex surface. Forming
the lens surface of the third lens 13 in this manner allows the
maximum exit angle of the principal ray to be 23.5 degrees with
respect to the total angle of view of 63 degrees. The lens surfaces
of the first lens 11, second lens 12, and third lens 13 of the present
example are also all aspherical. A cover glass 15 is also mounted
in the present example between the second lens surface R6 of the
third lens 13 and the imaging surface 16.
[0055] The lens data for the entire optical system of the imaging
lens 110 of the present example are as follows.
[0056] F-number: 3.5
[0057] Focal distance: f=5.7 mm
[0058] Total length: .SIGMA.d=6.985 mm
[0059] The lens data for the lens surfaces of the imaging lens
110 of the present example are shown in Table 2A; and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
are shown in Table 2B. In the present example, since f1/f=0.70,
.SIGMA.d/f=1.23, and .nu.d2=29, conditional expressions (1) through
(3) are satisfied. The aberration diagram thereof is shown in FIG.
4. TABLE-US-00003 TABLE 2A FNo.: 3.5; f = 5.7 mm; .SIGMA.d = 6.985
mm i R d Nd .nu.d 1* 1.386 1.0 1.5247 56.2 2* 3.087 0.15 3 0.00
0.18 4 0.00 0.47 5* -0.953 0.9 1.585 29.0 6* -2.016 0.1 7* 6.57
1.2 1.5247 56.2 8* -6.15 1.336 9 0.00 0.6 1.51633 64.2 10 0.00 1.0489
11 (*indicates an aspherical shape)
[0060] TABLE-US-00004 TABLE 2B i k A B C D 1 -2.414289 .times.
10.sup.-1 1.704389 .times. 10.sup.-2 -7.630913 .times. 10.sup.-4
1.397945 .times. 10.sup.-2 -5.89427 .times. 10.sup.-3 2 7.215993
.times. 10.sup.-1 -3.474378 .times. 10.sup.-3 -7.800064 .times.
10.sup.-2 9.886734 .times. 10.sup.-2 -9.132532 .times. 10.sup.-2
5 5.484851 .times. 10.sup.-1 1.097456 .times. 10.sup.-1 -2.023164
.times. 10.sup.-1 5.6317100 .times. 10.sup.-1 -5.506715 .times.
10.sup.-1 6 -1.456663 -2.197336 .times. 10.sup.-2 -1.003731 .times.
10.sup.-2 7 -3.168123 -1.446476 .times. 10.sup.-2 1.192514 .times.
10.sup.-3 3.793835 .times. 10.sup.-5 -7.112863 .times. 10.sup.-6
8 0.00 -1.342604 .times. 10.sup.-3 -1.088183 .times. 10.sup.-3 -8.566835
.times. 10.sup.-6 7.766112 .times. 10.sup.-6
[0061] In the imaging lenses 100 and 110 of Examples 1 and 2 above,
lenses having aspherical surfaces on both sides are used as the
first lenses 1 and 11 on the object side, but lenses having spherical
surfaces on both sides, or lenses in which at least one of the two
surfaces is aspherical may also be used for the first lenses.
EXAMPLE 3
[0062] An imaging lens according to Example 3 in which the first
invention of the present application is applied is shown in FIG.
5. An imaging lens 120 of the present example has, arranged in sequence
from an object side towards an imaging surface 26, a first lens
21 whose meniscus has a positive power and whose convex surface
faces the object side; a second lens 22 whose meniscus has a negative
power and whose concave surface faces the object side, positioned
subsequently via an aperture 24; and a third lens 23 having a negative
power; and the second and third lenses function as correction lenses.
A cover glass 25 is mounted between the third lens 23 and the imaging
surface 26. In the third lens 23, the second lens surface R6 on
the side of the imaging surface is formed so that the annular zone
of the lens periphery forms a convex surface towards the imaging
surface side, and the maximum exit angle of the principal ray is
adjusted to 24 degrees or less.
[0063] In the present example, the both lens surfaces of the first
lens 21 among the lenses 21, 22, and 23 are spherical. The lens
surfaces on the both sides of the second and third lenses 22 and
23 are aspherical, the same as in Examples 1 and 2.
[0064] The lens data for the entire optical system of the imaging
lens 120 of the present example are as follows.
[0065] F-number: 3.5
[0066] Focal distance: f=5.7 mm
[0067] Total length: .nu.d=6.46 mm
[0068] The lens data for the lens surfaces of the imaging lens
120 of the present example are shown in Table 3A; and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
are shown in Table 3B. In the present example, since f1/f=0.73,
.SIGMA.d/f=1.13, and .nu.d2=29, conditional expressions (1) through
(3) are satisfied. The aberration diagram thereof is shown in FIG.
7. TABLE-US-00005 TABLE 3A FNo.: 3.5; f = 5.7 mm; .SIGMA.d = 6.46
mm i R d Nd .nu.d 1 1.621 1.0 1.5247 56.2 2 5.009 0.15 3 0.00 0.4
4 0.00 0.5 5* -1.207 0.8 1.585 29.0 6* -1.644 0.1 7* 10.993 1.2
1.5247 56.2 8* 7.773 1.336 9 0.00 0.6 1.51633 64.2 10 0.00 0.3726
11 (*indicates an aspherical shape)
[0069] TABLE-US-00006 TABLE 3B i k A B C D 5 -2.567837 .times.
10.sup.-1 3.208279 .times. 10.sup.-2 -1.916911 .times. 10.sup.-1
3.791361 .times. 10.sup.-1 -3.067684 .times. 10.sup.-1 6 -9.161619
.times. 10.sup.-1 -2.732818 .times. 10.sup.-3 1.984030 .times. 10.sup.-2
7 6.274432 -2.566783 .times. 10.sup.-2 3.344091 .times. 10.sup.-3
8.712945 .times. 10.sup.-5 -2.670618 .times. 10.sup.-5 8 0.00 -3.171232
.times. 10.sup.-2 1.875582 .times. 10.sup.-3 -2.705621 .times. 10.sup.-4
1.570770 .times. 10.sup.-5
EXAMPLE 4
[0070] FIG. 6 is a structural diagram of an imaging lens according
to Example 4 in which the first invention of the present application
is applied. In an imaging lens 130 of the present example, a first
lens 31 with a positive meniscus whose convex surface faces an object
side, a second lens 32 with a negative meniscus whose concave surface
faces the object side via an aperture 34, and a third lens 33 having
a positive power are arranged in sequence from the object side towards
an imaging surface 36. A cover glass 35 is mounted between the third
lens 33 and the imaging surface 36. In the third lens 33, the second
lens surface R6 is formed so that the annular zone of the lens periphery
forms a convex surface towards the imaging surface side, and the
maximum exit angle of the principal ray is adjusted to 24 degrees
or less.
[0071] In the present example, the both lens surfaces of the first
lens 31 among the lenses 31, 32, and 33 are spherical. The lens
surfaces on the both sides of the second and third lenses 32 and
33 are aspherical, the same as in Examples 1, 2 and 3.
[0072] The lens data for the entire optical system of the imaging
lens 130 of the present example are as follows.
[0073] F-number: 3.5
[0074] Focal distance: f=5.7 mm
[0075] Total length: .SIGMA.d=6.66 mm
[0076] The lens data for the lens surfaces of the imaging lens
130 of the present example are shown in Table 4A; and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
are shown in Table 4B. In the present example, since f1/f=0.77,
.SIGMA.d/f=1.17, and .nu.d2=29, conditional expressions (1) through
(3) are satisfied. The aberration diagram thereof is shown in FIG.
8. TABLE-US-00007 TABLE 4A FNo.: 3.5; f = 5.7 mm; .SIGMA.d = 6.66
mm i R d Nd .nu.d 1 1.626 1.2 1.4970 81.6 2 4.76 0.15 3 0.00 0.4
4 0.00 0.5 5* -1.036 0.8 1.585 29.0 6* -1.51 0.1 7* 4.90 1.1 1.5247
56.2 8* 6.80 0.81 9 0.00 0.6 1.51633 64.2 10 0.00 1.0 11 (*indicates
an aspherical shape)
[0077] TABLE-US-00008 TABLE 4B i k A B C D 5 -6.210503 .times.
10.sup.-1 3.611876 .times. 10.sup.-2 -2.806078 .times. 10.sup.-1
5.465960 .times. 10.sup.-1 -4.831922 .times. 10.sup.-1 6 -1.143408
4.811894 .times. 10.sup.-3 1.896129 .times. 10.sup.-3 7 1.531998
-2.174083 .times. 10.sup.-2 2.450461 .times. 10.sup.-3 -2.581896
.times. 10.sup.-4 1.113489 .times. 10.sup.-5 8 0.00 -3.318003 .times.
10.sup.-2 4.413864 .times. 10.sup.-3 -5.477590 .times. 10.sup.-4
2.739709 .times. 10.sup.-5
EXAMPLE 5
[0078] Referring again to FIG. 5, an imaging lens 140 will be described
wherein instead of the first lens 21 in which the both lens surfaces
are spherical in the imaging lens 120 of Example 3, a first lens
41 is used in which one lens surface is formed with an aspherical
surface, and the other lens surface is formed with a spherical surface.
In FIG. 5, symbols indicating the imaging lens 140 and the first
lens 41 are enclosed in parentheses, the configuration of the other
parts thereof is the same as in Example 3, and a description will
therefore be given using the same symbols.
[0079] The imaging lens 140 of the present example has, arranged
in sequence from an object side towards an imaging surface 26, the
first lens 41 whose meniscus has a positive power and whose convex
surface faces the object side; a second lens 22 whose meniscus has
a negative power and whose concave surface faces the object side
via an aperture 24; and a third lens 23 having a positive power;
and the second and third lenses function as correction lenses. A
cover glass 25 is mounted between the third lens 23 and the imaging
surface 26. In the third lens 23, the second lens surface R6 is
formed so that the annular zone of the lens periphery forms a convex
surface towards the imaging surface, and the maximum exit angle
of the principal ray is adjusted to 24 degrees or less.
[0080] In the present example, of the two lens surfaces of the
first lens 41 among the lenses 41, 22, and 23, the first lens surface
R1 on the object side thereof is aspherical, and the second lens
surface R2 on the imaging surface side thereof is spherical. The
lens surfaces on the both sides of the second and third lenses 22
and 23 are aspherical.
[0081] The lens data for the entire optical system of the imaging
lens 140 of the present example are as follows.
[0082] F-number: 3.5
[0083] Focal distance: f=5.7 mm
[0084] Total length: .SIGMA.d=7.07 mm
[0085] The lens data for the lens surfaces of the imaging lens
140 of the present example are shown in Table 5A; and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
are shown in Table 5B. In the present example, since f1/f=0.83,
.SIGMA.d/f=1.24, and .nu.d2=29, conditional expressions (1) through
(3) are satisfied. The aberration diagram thereof is shown in FIG.
9. TABLE-US-00009 TABLE 5A FNo.: 3.5; f = 5.7 mm; .SIGMA.d = 7.07
mm i R d Nd .nu.d 1* 1.77 1.0 1.5247 56.2 2 4.973 0.15 3 0.00 0.4
4 0.00 0.5 5* -1.074 0.8 1.5850 29.0 6* -1.584 0.1 7* 5.516 1.2
1.5247 56.2 8* 19.41 1.336 9 0.00 0.6 1.51633 64.2 10 0.00 0.985
11 (*indicates an aspherical shape)
[0086] TABLE-US-00010 TABLE 5B i K A B C D 1 -4.356005 .times.
10.sup.-2 8.423055 .times. 10.sup.-3 -4.071931 .times. 10.sup.-3
4.637228 .times. 10.sup.-3 -1.088690 .times. 10.sup.-3 5 -3.998108
.times. 10.sup.-1 3.950244 .times. 10.sup.-2 -4.246316 .times. 10.sup.-2
1.535713 .times. 10.sup.-1 -1.460498 .times. 10.sup.-1 6 -1.324467
-1.748017 .times. 10.sup.-3 1.297864 .times. 10.sup.-2 7 3.313169
-2.172623 .times. 10.sup.-2 1.551952 .times. 10.sup.-3 -2.195645
.times. 10.sup.-5 -1.380375 .times. 10.sup.-5 8 0.00 -2.288283 .times.
10.sup.-2 1.359618 .times. 10.sup.-3 -1.163401 .times. 10.sup.-4
1.446310 .times. 10.sup.-6
EXAMPLE A
[0087] FIG. 10 is a structural diagram of an imaging lens according
to Example A in which the second invention of the present application
is applied. In an imaging lens 200, a first lens 201 whose meniscus
has a positive power and whose convex surface faces an object side,
an aperture 204, a second lens 202 whose meniscus has a negative
power and whose concave surface faces the object side, and a third
lens 203 having a positive power are arranged in sequence from the
object side towards an imaging surface 206. A cover glass 205 is
mounted between the second surface 203b of the third lens 203 and
the imaging surface 206.
[0088] In this arrangement, the lens surfaces 201a and 201b on
both sides of the first lens 201, the lens surfaces 202a and 202b
on both sides of the second lens 202, and the lens surfaces 203a
and 203b on both sides of the third lens 203 are aspherical. All
of the aspherical shapes employed in the present example are also
such that no inflection points appear in the effective lens surface
regions of the lens surfaces.
[0089] The lens data for the entire optical system of the imaging
lens 200 are as follows.
[0090] F-number: 2.8
[0091] Focal distance: f=3.65 mm
[0092] Back focus: BF=1.863 mm
[0093] Focal distance of first lens 201: f1=3.769 mm
[0094] The lens data for the lens surfaces of the imaging lens
200 are shown in Table 6A, and the aspherical coefficients for determining
the aspherical shape of the lens surfaces thereof are shown in Table
6B. TABLE-US-00011 TABLE 6A FNo.: 2.8; f = 3.65 mm i R d Nd .nu.d
1* 1.153 0.8 1.5247 56.2 2* 2.105 0.15 3 0.00 0.35 4* -1.066 0.7
1.5850 29.0 5* -1.546 0.1 6* 3.180 0.9 1.5247 56.2 7* 60.657 0.563
8 0.00 0.3 1.51633 64.2 9 0.00 1.0 (*indicates an aspherical shape)
[0095] TABLE-US-00012 TABLE 6B i k A B C D 1 4.577272 .times. 10.sup.-1
-3.645425 .times. 10.sup.-3 -2.554281 .times. 10.sup.-2 2.607501
.times. 10.sup.-2 2 -2.153226 5.788633 .times. 10.sup.-2 4.7621418
.times. 10.sup.-1 4 -2.641633 .times. 10.sup.-2 5 -6.245341 .times.
10.sup.-1 6 -1.167034 .times. 10 1.864785 .times. 10.sup.-2 -1.905218
.times. 10.sup.-3 -6.772919 .times. 10.sup.-4 2.049794 .times. 10.sup.-4
7 -1.749072 .times. 10.sup.5
[0096] In Tables 6A and 6B, i indicates the sequence of lens surfaces
counted from the object side; R indicates the curvature of each
lens surface on the optical axis L; d indicates the distance between
lens surfaces; Nd indicates the refractive index of each lens; and
.nu.d indicates the Abbe number of the lenses. An asterisk (*) by
the i of a lens surface indicates that the lens surface is aspherical.
The aspherical shapes employed in the lens surfaces can be indicated
by the equation shown in the description of Example 1.
[0097] The meanings of each symbol and the equation for indicating
the aspherical shape are also the same in Examples B and C below.
[0098] In the present example, the focal distance f1 of the first
lens 201 is a value within the range of 0.5 f (=1.825 mm) and 1.5
f (=5.475 mm), and satisfies conditional expression (A). The value
of BF/f is 0.5109 . . . , and satisfies conditional expression (B).
Furthermore, since the curvature Ra of the lens surface 203a on
the object side of the third lens 203 is 3.180, and the curvature
Rb of the lens surface 203b on the image side thereof is 60.657,
then Rb/Ra=19.074 . . . , and conditional expression (C) is satisfied.
The maximum exit angle of the principal ray is also 30 degrees or
less.
[0099] FIG. 11 is an aberration diagram showing aberrations in
the imaging lens of Example A. FIG. 11(a) is an aberration diagram
showing the spherical aberration SA; FIG. 11(b) is an aberration
diagram showing the astigmatic aberration AS; and FIG. 11(c) is
an aberration diagram showing the distortion DIST. The T in the
astigmatic aberration AS indicates a tangential image surface, and
the S indicates a sagittal image surface. FIG. 11(d) shows the lateral
aberration, and in the figure, DX indicates the laterally directed
X aberration relating to the X pupil coordinate; and DY indicates
the laterally directed Y aberration relating to the Y pupil coordinate.
The meanings of these symbols are also the same in Examples B and
C described hereinafter.
EXAMPLE B
[0100] FIG. 12 is a structural diagram of an imaging lens according
to Example B in which the second invention of the present application
is applied. In an imaging lens 210, a first lens 211 whose meniscus
has a positive power and whose convex surface faces an object side,
an aperture 214, a second lens 212 whose meniscus has a positive
power and whose concave surface faces the object side, and a third
lens 213 having a positive power are arranged in sequence from the
object side towards an imaging surface 216. A cover glass 215 is
mounted between the third lens 213 and the imaging surface 216,
the same as in Example A. In the case of the present example, the
lens surfaces 211a and 211b on both sides of the first lens 211,
the lens surfaces 212a and 212b on both sides of the second lens
212, and the lens surface 213b on image side of the third lens 213
are aspherical. All of the aspherical shapes employed in the present
example are also such that no inflection points appear in the effective
lens surface regions of the lens surfaces.
[0101] The lens data for the entire optical system of the imaging
lens of the present example are as follows.
[0102] F-number: 3.5
[0103] Focal distance: f=3.5 mm
[0104] Back focus: BF=1.992 mm
[0105] Focal distance of first lens 211: f1=4.733 mm
[0106] The lens data for the lens surfaces of the imaging lens
210 are shown in Table 7A, and the aspherical coefficients for determining
the aspherical shape of the lens surfaces thereof are shown in Table
7B. TABLE-US-00013 TABLE 7A FNo.: 3.5; f = 3.50 mm i R d Nd .nu.d
1* 1.155 0.8 1.5850 29.0 2* 1.475 0.25 3 0.00 0.25 4* -1.234 0.8
1.5247 56.2 5* -1.31 0.15 6 5.87 0.75 1.6070 29.9 7* -27.245 0.3
8 0.00 0.6 1.51633 64.2 9 0.00 1.092 10 11 (*indicates an aspherical
shape)
[0107] TABLE-US-00014 TABLE 7B i k A B C D 1 6.288194 .times. 10.sup.-1
8.880798 .times. 10.sup.-3 -3.552012 .times. 10.sup.-2 5.541189
.times. 10.sup.-2 -2.595815 .times. 10.sup.-3 2 5.605423 -5.846783
.times. 10.sup.-2 3.132873 .times. 10.sup.-1 7.279427 -2.513030
.times. 10.sup. 4 2.369842 1.156048 .times. 10.sup.-1 1.324990 5
4.089558 .times. 10.sup.-1 5.253695 .times. 10.sup.-2 1.227547 .times.
10.sup.-1 -5.871821 .times. 10.sup.-2 9.212771 .times. 10.sup.-2
7 0.00 -1.935001 .times. 10.sup.-2 1.343275 .times. 10.sup.-3
[0108] In the present example, the focal distance f1 of the first
lens 211 is a value within the range of 0.5 f (=1.75 mm) and 1.5
f (=5.25 mm), and satisfies conditional expression (A). The value
of BF/f is 0.549 . . . , and satisfies conditional expression (B).
Furthermore, since the curvature Ra of the lens surface 213a on
the object side of the third lens 213 is 5.87, and the curvature
Rb of the lens surface 213b on the image side thereof is -27.245,
then |Rb/Ra|=4.641 . . . , and conditional expression (C) is satisfied.
The maximum exit angle of the principal ray is also 30 degrees or
less.
[0109] FIGS. 13(a) through 13(d) are aberration diagrams showing
the aberrations in the imaging lens 20 of the present example.
EXAMPLE C
[0110] The configuration of an imaging lens according to Example
C in which the second invention of the present application is applied
is the same as the configuration of the imaging lens 210 of Example
B, and a first lens 211 whose meniscus has a positive power and
whose convex surface faces an object side, an aperture 214, a second
lens 212 whose meniscus has a negative power and whose concave surface
faces the object side, and a third lens 213 having a positive power
are arranged in sequence from the object side toward an imaging
surface 216 therein. A cover glass 215 is mounted between the third
lens 213 and the imaging surface 216. Furthermore, in the present
example, the lens surfaces 211a and 211b on both sides of the first
lens 211, the lens surfaces 212a and 212b on both sides of the second
lens 212, and the lens surfaces 213a and 213b on both sides of the
third lens 213 are each aspherical. All of the aspherical shapes
are also such that no inflection points appear in the effective
lens surface regions of the lens surfaces.
[0111] The lens data for the entire optical system of the imaging
lens of the present example are as follows.
[0112] F-number: 2.8
[0113] Focal distance: f=3.60 mm
[0114] Back focus: BF=1.967 mm
[0115] Focal distance of first lens 211: f1=3.844 mm
[0116] The lens data for the lens surfaces in the imaging lens
of the present example are shown in Table 8A, and the aspherical
coefficients for determining the aspherical shape of the lens surfaces
thereof are shown in Table 8B. TABLE-US-00015 TABLE 8A FNo.: 2.8;
f = 3.60 mm i R d Nd .nu.d 1* 1.109 0.85 1.5247 56.2 2* 1.814 0.25
3 0.00 0.25 4* -0.908 0.7 1.585 29.0 5* -1.638 0.1 6* 3.115 0.95
1.5247 56.2 7* -4.464 0.4 8 0.00 0.3 1.51633 64.2 9 0.00 1.267 10
11 (*indicates an aspherical shape)
[0117] TABLE-US-00016 TABLE 8B i k A B C D 1 3.430395 .times. 10.sup.-1
5.175761 .times. 10.sup.-3 1.822436 .times. 10.sup.-3 -3.968977
.times. 10.sup.-2 4.390863 .times. 10.sup.-2 2 -1.192756 .times.
10 2.602025 .times. 10.sup.-1 2.316038 .times. 10.sup.-1 4 4.565904
.times. 10.sup.-1 5 -7.957068 .times. 10.sup.-1 -1.046904 .times.
10.sup.-1 7.812309 .times. 10.sup.-3 6 -2.865732 .times. 10 -1.057338
.times. 10.sup.-2 1.542895 .times. 10.sup.-2 -6.212535 .times. 10.sup.-3
8.950190 .times. 10.sup.-4 7 -2.000000 -7.488042 .times. 10.sup.-3
[0118] In the present example, the focal distance f1 of the first
lens 211 is a value within the range of 0.5 f (=1.80 mm) and 1.5
f (=5.40 mm), and satisfies conditional expression (A). The value
of BF/f is 0.546 . . . , and satisfies conditional expression (B).
Furthermore, since the curvature Ra of the lens surface 213a on
the object side of the third lens 213 is 3.115, and the curvature
Rb of the lens surface 213b on the image side thereof is -4.464,
then |Rb/Ra| =1.433 . . . , and conditional expression (C) is satisfied.
The maximum exit angle of the principal ray is also 30 degrees or
less.
[0119] FIGS. 14(a) through 14(d) are aberration diagrams showing
the aberrations in the imaging lens of the present example.
OTHER EMBODIMENTS OF THE SECOND INVENTION
[0120] The lens surfaces on both sides of the first through third
lenses are all aspherical in Examples A and C, and the lens surfaces
on both sides of the first lens, on both sides of the second lens,
and on the lens surface of the third lens facing the image side
are aspherical in Example B. It is apparent that at least one lens
surface among these lens surfaces may be aspherical, and that the
other lens surfaces may be spherical.
INDUSTRIAL APPLICABILITY
[0121] As described above, the imaging lens according to the first
invention of the present application is a lens composed of three
elements in three groups, the second lens and third lens are correction
lenses, the first lens positioned on the object side is configured
as a positive meniscus, and the convex surface thereof faces the
object side. As a result, the total length of the lens system can
be reduced. Since the lens surface of the third lens is configured
as an aspherical surface provided with one or a plurality of aspherical
inflection points, various types of aberration can be satisfactorily
corrected, while at the same time, the maximum exit angle of the
principal ray can be reduced and shading prevented. Furthermore,
aberration can be adequately corrected by the two correction lenses
that include the second lens and the third lens. Therefore, according
to the present invention, a small, compact imaging lens can be obtained
that is adapted to high resolution on the order of millions of pixels.
[0122] Since the imaging lens according to the second invention
of the present application is a lens system composed of three elements
in three groups, and the first lens positioned on the object side
is configured as a lens with a positive meniscus whose convex surface
faces the object side, the total length of the lens system can be
reduced. By also making the lens surface of the second lens facing
the object side concave, the position of the exit pupil can be lengthened,
whereby shading can be prevented. Furthermore, since an aspherical
shape having no inflection points is employed in the lens surface,
loss of resolution due to lens machining error or assembly error
can be minimized, and production is facilitated. Thus, by the present
invention, a small-size, compact imaging lens having a small number
of constituent lens elements can be obtained that is suited for
production and adapted to high resolution on the order of millions
of pixels. |