U.S. patent application number 15/600871 was filed with the patent office on 2018-06-28 for lens assembly.
The applicant listed for this patent is Asia Optical Co., Inc., Sintai Optical (Shenzhen) Co., Ltd.. Invention is credited to Tao Fu.
Application Number | 20180180844 15/600871 |
Document ID | / |
Family ID | 62234974 |
Filed Date | 2018-06-28 |
United States Patent
Application |
20180180844 |
Kind Code |
A1 |
Fu; Tao |
June 28, 2018 |
LENS ASSEMBLY
Abstract
A lens assembly includes sequentially from an object side to an
image side along an optical axis a first lens, a second lens, a
third lens, a fourth lens, a stop, a fifth lens, a sixth lens, a
seventh lens and an eighth lens. The first lens is a meniscus lens
with refractive power. The second lens is a meniscus lens with
refractive power. The third lens is a biconcave lens with negative
refractive power. The fourth lens is a biconvex lens with positive
refractive power. The fifth lens is a biconvex lens with positive
refractive power. The sixth lens is with positive refractive power.
The seventh lens is with negative refractive power. The eighth lens
is with positive refractive power. The sixth lens and the seventh
lens are cemented together.
Inventors: |
Fu; Tao; (ShenZhen City,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sintai Optical (Shenzhen) Co., Ltd.
Asia Optical Co., Inc. |
ShenZhen City
Taichung |
|
CN
TW |
|
|
Family ID: |
62234974 |
Appl. No.: |
15/600871 |
Filed: |
May 22, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 13/18 20130101;
G02B 1/041 20130101; G02B 13/06 20130101; G02B 13/006 20130101;
G02B 13/0045 20130101 |
International
Class: |
G02B 9/64 20060101
G02B009/64; G02B 1/04 20060101 G02B001/04; G02B 1/00 20060101
G02B001/00; G02B 13/00 20060101 G02B013/00; G02B 27/00 20060101
G02B027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2016 |
CN |
201611205833.7 |
Claims
1. A lens assembly, comprising a first lens, a second lens, a third
lens, a fourth lens, a stop, a fifth lens, a sixth lens, a seventh
lens and an eighth lens, all of which are arranged in order from an
object side to an image side along an optical axis, wherein: the
first lens is a meniscus lens with refractive power; the second
lens is a meniscus lens with refractive power; the third lens is a
biconcave lens with negative refractive power; the fourth lens is a
biconvex lens with positive refractive power; the fifth lens is a
biconvex lens with positive refractive power; the sixth lens is
with positive refractive power; the seventh lens is with negative
refractive power; the eighth lens is with positive refractive
power; and the sixth lens and the seventh lens are cemented
together.
2. The lens assembly as claimed in claim 1, wherein the first lens
is with negative refractive power, and the second lens is with
negative refractive power.
3. The lens assembly as claimed in claim 2, wherein the lens
assembly satisfies: -15<f.sub.1/f<-1.8, wherein f.sub.1 is an
effective focal length of the first lens and f is an effective
focal length of the lens assembly.
4. The lens assembly as claimed in claim 3, wherein the lens
assembly satisfies: -15<f.sub.2/f<-1.8, wherein f.sub.2 is an
effective focal length of the second lens and f is an effective
focal length of the lens assembly.
5. The lens assembly as claimed in claim 4, wherein the lens
assembly satisfies: -15<f.sub.3/f<-1.8, wherein f.sub.3 is an
effective focal length of the third lens and f is an effective
focal length of the lens assembly.
6. The lens assembly as claimed in claim 2, wherein the lens
assembly satisfies: -0.8<f.sub.123/f<-0.6, wherein f.sub.123
is an effective focal length of a combination of the first lens,
the second lens and the third lens, and f is an effective focal
length of the lens assembly.
7. The lens assembly as claimed in claim 6, wherein the lens
assembly satisfies: 2.4<f.sub.8/f<2.8, wherein f.sub.8 is an
effective focal length of the eighth lens and f is an effective
focal length of the lens assembly.
8. The lens assembly as claimed in claim 7, wherein the lens
assembly satisfies: 0.8<f.sub.1234/f.sub.5678<-0.6, wherein
f.sub.1234 is an effective focal length of a combination of the
first lens, the second lens, the third lens and the fourth lens,
and f.sub.5678 is an effective focal length of a combination of the
fifth lens, the sixth lens, the seventh lens and the eighth
lens.
9. The lens assembly as claimed in claim 2, wherein the lens
assembly satisfies: 0.8<TTL/D.sub.1<1.6, wherein TTL is an
interval from an object surface of the first lens to an image plane
along the optical axis and D.sub.1 is an effective diameter of the
first lens.
10. The lens assembly as claimed in claim 2, wherein the lens
assembly satisfies: 200.degree.<FOV<240.degree., wherein FOV
is a maximum field of view in degree for the lens assembly.
11. The lens assembly as claimed in claim 2, wherein the first lens
further comprises a convex surface facing the object side and a
concave surface facing the image side.
12. The lens assembly as claimed in claim 2, wherein the second
lens further comprises a convex surface facing the object side and
a concave surface facing the image side.
13. The lens assembly as claimed in claim 2, wherein the third lens
is a spherical lens.
14. The lens assembly as claimed in claim 2, wherein the second
lens further comprises two surfaces, at least one of which is an
aspheric surface, the third lens further comprises two surfaces, at
least one of which is an aspheric surface, the fifth lens further
comprises two surfaces, at least one of which is an aspheric
surface, and the eighth lens further comprises two surfaces, at
least one of which is an aspheric surface.
15. The lens assembly as claimed in claim 14, wherein the first
lens, the second lens, the third lens, the fourth lens, the fifth
lens, the sixth lens, the seventh lens and the eighth lens are made
of glass material.
16. A lens assembly, comprising a first lens, a second lens, a
third lens, a fourth lens, a fifth lens, a sixth lens, a seventh
lens and an eighth lens, all of which are arranged in order from an
object side to an image side along an optical axis, wherein: the
first lens is with negative refractive power; the second lens is
with negative refractive power; the third lens is a biconcave lens
with negative refractive power; the fourth lens is a biconvex lens
with positive refractive power; the fifth lens is a biconvex lens
with positive refractive power; the sixth lens is with positive
refractive power; the seventh lens is with negative refractive
power; the eighth lens is with positive refractive power; and the
lens assembly satisfies:
-15<f.sub.1/f<f.sub.2/f<f.sub.3/f<-1.8, wherein f.sub.1
is an effective focal length of the first lens, f.sub.2 is an
effective focal length of the second lens, f.sub.3 is an effective
focal length of the third lens and f is an effective focal length
of the lens assembly.
17. The lens assembly as claimed in claim 16, wherein the first
lens further comprises a convex surface facing the object side and
a concave surface facing the image side.
18. The lens assembly as claimed in claim 16, wherein the second
lens further comprises a convex surface facing the object side and
a concave surface facing the image side.
19. The lens assembly as claimed in claim 16, further comprising a
stop disposed between the fourth lens and the fifth lens.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims priority of China Patent Application
No. 201611205833.7 filed on Dec. 23, 2016, the entirety of which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates to a lens assembly.
Description of the Related Art
[0003] Nowadays, the total lens length and diameter are large for a
lens assembly with field of view of more than 200 degrees. It is
difficult to meet the requirements of miniaturization. Therefore,
the lens assembly needs a new structure in order to meet the
requirements of wide field of view, small F-number and
miniaturization.
BRIEF SUMMARY OF THE INVENTION
[0004] The invention provides a lens assembly to solve the above
problems. The lens assembly of the invention is provided with
characteristics of a shortened total lens length, a wider field of
view, a decreased F-number, and still has a good optical
performance.
[0005] The lens assembly in accordance with an exemplary embodiment
of the invention includes a first lens, a second lens, a third
lens, a fourth lens, a stop, a fifth lens, a sixth lens, a seventh
lens and an eighth lens, all of which are arranged in order from an
object side to an image side along an optical axis. The first lens
is a meniscus lens with refractive power. The second lens is a
meniscus lens with refractive power. The third lens is a biconcave
lens with negative refractive power. The fourth lens is a biconvex
lens with positive refractive power. The fifth lens is a biconvex
lens with positive refractive power. The sixth lens is with
positive refractive power. The seventh lens is with negative
refractive power. The eighth lens is with positive refractive
power. The sixth lens and the seventh lens are cemented
together.
[0006] The first lens is with negative refractive power, and the
second lens is with negative refractive power.
[0007] The lens assembly satisfies: -15<f.sub.1/f<-1.8,
wherein f.sub.1 is an effective focal length of the first lens and
f is an effective focal length of the lens assembly.
[0008] The lens assembly satisfies: -15<f.sub.2/f<-1.8,
wherein f.sub.2 is an effective focal length of the second lens and
f is an effective focal length of the lens assembly.
[0009] The lens assembly satisfies: -15<f.sub.3/f<-1.8,
wherein f.sub.3 is an effective focal length of the third lens and
f is an effective focal length of the lens assembly.
[0010] The lens assembly satisfies: -0.8<f.sub.123/f<-0.6,
wherein f.sub.123 is an effective focal length of a combination of
the first lens, the second lens and the third lens, and f is an
effective focal length of the lens assembly.
[0011] The lens assembly satisfies: 2.4<f.sub.8/f<2.8,
wherein f.sub.8 is an effective focal length of the eighth lens and
f is an effective focal length of the lens assembly.
[0012] The lens assembly satisfies:
-0.8<f.sub.1234/f.sub.5678<-0.6, wherein f.sub.1234 is an
effective focal length of a combination of the first lens, the
second lens, the third lens and the fourth lens, and f.sub.5678 is
an effective focal length of a combination of the fifth lens, the
sixth lens, the seventh lens and the eighth lens.
[0013] The lens assembly satisfies: 0.8<TTL/D.sub.1<1.6,
wherein TTL is an interval from an object surface of the first lens
to an image plane along the optical axis and D.sub.1 is an
effective diameter of the first lens.
[0014] The lens assembly satisfies:
200.degree.<FOV<240.degree., wherein FOV is a maximum field
of view in degree for the lens assembly.
[0015] The first lens further comprises a convex surface facing the
object side and a concave surface facing the image side.
[0016] The second lens further comprises a convex surface facing
the object side and a concave surface facing the image side.
[0017] The third lens is a spherical lens.
[0018] The second lens further includes two surfaces, at least one
of which is an aspheric surface, the third lens further includes
two surfaces, at least one of which is an aspheric surface, the
fifth lens further includes two surfaces, at least one of which is
an aspheric surface, and the eighth lens further includes two
surfaces, at least one of which is an aspheric surface.
[0019] The first lens, the second lens, the third lens, the fourth
lens, the fifth lens, the sixth lens, the seventh lens and the
eighth lens are made of glass material.
[0020] The lens assembly in accordance with an exemplary embodiment
of the invention includes a first lens, a second lens, a third
lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and
an eighth lens, all of which are arranged in order from an object
side to an image side along an optical axis. The first lens is with
negative refractive power. The second lens is with negative
refractive power. The third lens is a biconcave lens with negative
refractive power. The fourth lens is a biconvex lens with positive
refractive power. The fifth lens is a biconvex lens with positive
refractive power. The sixth lens is with positive refractive power.
The seventh lens is with negative refractive power. The eighth lens
is with positive refractive power. The lens assembly satisfies:
-15<f.sub.1/f<f.sub.2/f<f.sub.3/f<-1.8, wherein f.sub.1
is an effective focal length of the first lens, f.sub.2 is an
effective focal length of the second lens, f.sub.3 is an effective
focal length of the third lens and f is an effective focal length
of the lens assembly.
[0021] The lens assembly further comprises a stop disposed between
the fourth lens and the fifth lens.
[0022] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0024] FIG. 1 is a lens layout diagram of a lens assembly in
accordance with a first embodiment of the invention;
[0025] FIG. 2A depicts a longitudinal aberration diagram of the
lens assembly in accordance with the first embodiment of the
invention;
[0026] FIG. 2B is a field curvature diagram of the lens assembly in
accordance with the first embodiment of the invention;
[0027] FIG. 2C is a distortion diagram of the lens assembly in
accordance with the first embodiment of the invention;
[0028] FIG. 3 is a lens layout diagram of a lens assembly in
accordance with a second embodiment of the invention;
[0029] FIG. 4A depicts a longitudinal aberration diagram of the
lens assembly in accordance with the second embodiment of the
invention;
[0030] FIG. 4B is a field curvature diagram of the lens assembly in
accordance with the second embodiment of the invention; and
[0031] FIG. 4C is a distortion diagram of the lens assembly in
accordance with the second embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The following description is made for the purpose of
illustrating the general principles of the invention and should not
be taken in a limiting sense. The scope of the invention is best
determined by reference to the appended claims.
[0033] Referring to FIG. 1, FIG. 1 is a lens layout diagram of a
lens assembly in accordance with a first embodiment of the
invention. The lens assembly 1 includes a first lens L11, a second
lens L12, a third lens L13, a fourth lens L14, a stop ST1, a fifth
lens L15, a sixth lens L16, a seventh lens L17, an eighth lens L18
and an optical filter OF1, all of which are arranged in order from
an object side to an image side along an optical axis OA1. In
operation, an image of light rays from the object side is formed at
an image plane IMA1.
[0034] The first lens L11 is a meniscus lens with negative
refractive power and made of glass material, wherein the object
side surface S11 is a convex surface, the image side surface S12 is
a concave surface and both of the object side surface S11 and image
side surface S12 are spherical surfaces.
[0035] The second lens L12 is a meniscus lens with negative
refractive power and made of glass material, wherein the object
side surface S13 is a convex surface, the image side surface S14 is
a concave surface and both of the object side surface S13 and image
side surface S14 are aspheric surfaces.
[0036] The third lens L13 is a biconcave lens with negative
refractive power and made of glass material, wherein the object
side surface S15 is a concave surface, the image side surface S16
is a concave surface and both of the object side surface S15 and
image side surface S16 are aspheric surfaces.
[0037] The fourth lens L14 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S17 is a convex surface, the image side surface S18 is
a convex surface and both of the object side surface S17 and image
side surface S18 are spherical surfaces.
[0038] The fifth lens L15 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S110 is a convex surface, the image side surface S111
is a convex surface and both of the object side surface S110 and
image side surface S111 are aspheric surfaces.
[0039] The sixth lens L16 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S112 is a convex surface, the image side surface S113
is a convex surface and both of the object side surface S112 and
image side surface S113 are spherical surfaces.
[0040] The seventh lens L17 is a biconcave lens with negative
refractive power and made of glass material, wherein the object
side surface S113 is a concave surface, the image side surface S114
is a concave surface and both of the object side surface S113 and
image side surface S114 are spherical surfaces.
[0041] The sixth lens L16 and the seventh lens L17 are cemented
together. That is, the air gap is not provided between the sixth
lens L16 and the seventh lens L17.
[0042] The eighth lens L18 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S115 is a convex surface, the image side surface S116
is a convex surface and both of the object side surface S115 and
image side surface S116 are aspheric surfaces.
[0043] Both of the object side surface S117 and image side surface
S118 of the optical filter OF1 are plane surfaces.
[0044] In order to maintain excellent optical performance of the
lens assembly in accordance with the first embodiment of the
invention, the lens assembly 1 satisfies at least one of the
following conditions:
-15<f1.sub.123/f1<f1.sub.2/f1<f1.sub.3/f1<-1.8 (1)
-0.8<f1.sub.123/f1<-0.6 (2)
2.4<f1.sub.8/f1<2.8 (3)
-0.8<f1.sub.1234/f1.sub.5678<-0.6 (4)
0.8<TTL1/D1.sub.1<1.6 (5)
200.degree.<FOV1<240.degree. (6)
[0045] wherein f1.sub.1 is an effective focal length of the first
lens L11, f1.sub.2 is an effective focal length of the second lens
L12, f1.sub.3 is an effective focal length of the third lens L13,
f1 is an effective focal length of the lens assembly 1, f1.sub.123
is an effective focal length of a combination of the first lens
L11, the second lens L12 and the third lens L13, f1.sub.8 is an
effective focal length of the eighth lens L18, f1.sub.1234 is an
effective focal length of a combination of the first lens L11, the
second lens L12, the third lens L13 and the fourth lens L14,
f1.sub.5678 is an effective focal length of a combination of the
fifth lens L15, the sixth lens L16, the seventh lens L17 and the
eighth lens L18, TTL1 is an interval from the object surface S11 of
the first lens L11 to the image plane IMA1 along the optical axis
OA', D1.sub.1 is an effective diameter of the first lens L11 and
FOV1 is a maximum field of view in degree for the lens assembly
1.
[0046] Since f1 is a positive value, so that
f1.sub.3>f1.sub.2>f1.sub.1 can be deduced from condition (1).
The condition (1) can also be expressed as
-15<f1.sub.1/f1<-1.8, -15<f1.sub.2/f1<-1.8,
-15<f1.sub.3/f1<-1.8.
[0047] By the above design of the lenses and stop ST1, the lens
assembly 1 is provided with an increased field of view, a decreased
F-number, a shortened total lens length and an effective corrected
aberration.
[0048] In order to achieve the above purposes and effectively
enhance the optical performance, the lens assembly 1 in accordance
with the first embodiment of the invention is provided with the
optical specifications shown in Table 1, which include the
effective focal length, F-number, total lens length, radius of
curvature of each lens surface, thickness between adjacent surface,
refractive index of each lens and Abbe number of each lens. Table 1
shows that the effective focal length is equal to 1.26 mm, F-number
is equal to 2.4, total lens length is equal to 19.5 mm and maximum
field of view is equal to 235 degrees for the lens assembly 1 of
the first embodiment of the invention.
TABLE-US-00001 TABLE 1 Effective Focal Length = 1.26 mm F-number =
2.4 Total Lens Length = 19.5 mm Maximum Field of View = 235 Degrees
Radius of Surface Curvature Thickness Number (mm) (mm) Nd Vd Remark
S11 14.840 2.270 1.95 18.0 The First Lens L11 S12 6.610 3.400 S13
40.018 0.550 1.59 61.2 The Second Lens L12 S14 2.366 1.790 S15
-3.910 0.500 1.62 63.7 The Third Lens L13 S16 3.265 0.390 S17 5.100
3.150 1.85 23.8 The Fourth Lens L14 S18 -11.870 0.080 S19 .infin.
0.020 1.866 Stop ST1 S110 3.165 1.310 1.50 81.1 The Fifth Lens L15
S111 -4.954 0.100 S112 3.720 1.760 1.50 81.6 The Sixth Lens L16
S113 -2.050 0.500 1.85 23.8 The Seventh Lens L17 S114 4.620 0.280
S115 3.667 1.430 1.80 40.9 The Eighth Lens L18 S116 -7.154 0.100
S117 .infin. 0.500 1.52 64.2 Optical Filter OF1 S118 .infin.
1.377
[0049] The aspheric surface sag z of each lens in table 1 can be
calculated by the following formula:
z=ch.sup.2/{1+[1-(k+1)c.sup.2h.sup.2].sup.1/2}+Ah.sup.4+Bh.sup.6+Ch.sup.-
8+Dh.sup.10+Eh.sup.12+Fh.sup.14+Gh.sup.16
where c is curvature, h is the vertical distance from the lens
surface to the optical axis, k is conic constant and A, B, C, D, E,
F and G are aspheric coefficients.
[0050] In the first embodiment, the conic constant k and the
aspheric coefficients A, B, C, D, E, F, G of each surface are shown
in Table 2.
TABLE-US-00002 TABLE 2 Surface Number k A B C D E F G S13 -78.023
3.72E-04 7.56E-05 -8.14E-07 -2.17E-07 6.60E-09 1.53E-10 -5.31E-12
S14 -0.262 -3.53E-03 9.32E-04 -7.58E-05 -8.15E-05 2.18E-05 1.68E-06
-4.53E-07 S15 -0.700 1.11E-03 4.46E-04 5.64E-05 7.57E-07 -2.30E-06
-3.35E-07 0.00E+00 S16 0.864 1.38E-02 -4.55E-04 1.13E-03 -3.41E-04
3.12E-05 -3.49E-06 0.00E+00 S110 0.665 2.50E-03 -1.30E-03 3.22E-03
-1.79E-03 4.83E-04 -7.32E-05 0.00E+00 S111 -11.248 -3.32E-03
1.04E-03 1.33E-03 -3.34E-04 6.45E-04 -2.58E-04 0.00E+00 S115 0.246
-9.70E-03 1.87E-03 -1.83E-04 2.87E-05 -9.54E-06 1.26E-06 -5.63E-08
S116 -3.296 2.32E-03 8.48E-04 1.19E-04 3.19E-05 -1.27E-05 3.16E-07
5.62E-08
[0051] For the lens assembly 1 of the first embodiment, the
effective focal length f1 is equal to 1.26 mm, the effective focal
length f1.sub.1 of the first lens L11 is equal to -14.38 mm, the
effective focal length f1.sub.2 of the second lens L12 is equal to
-4.27 mm, the effective focal length f1.sub.3 of the third lens L13
is equal to -2.79 mm, the effective focal length f1.sub.8 of the
eighth lens L18 is equal to 3.19 mm, the effective focal length
f1.sub.123 of the combination of the first lens L11, the second
lens L12 and the third lens L13 is equal to -0.98 mm, the effective
focal length f1.sub.1234 of the combination of the first lens L11,
the second lens L12, the third lens L13 and the fourth lens L14 is
equal to -2.74 mm, the effective focal length f1.sub.5678 of the
combination of the fifth lens L15, the sixth lens L16, the seventh
lens L17 and the eighth lens L18 is equal to 3.47 mm, the interval
TTL1 from the object side surface S11 of the first lens L11 to the
image plane IMA1 along the optical axis OA' is equal to 19.5 mm,
the effective diameter D1.sub.1 of the first lens L11 is equal to
22.6 mm and the maximum field of view FOV1 for the lens assembly 1
is equal to 235 degrees. According to the above data, the following
values can be obtained:
f1.sub.1/f1=-11.41,
f1.sub.2/f1=-3 0.39,
f1.sub.3/f1=-2.21,
f1.sub.123/f1=-0.78,
f1.sub.8/f1=2.53,
f1.sub.1234/f1.sub.5678=-0.789,
TTL1/D1.sub.1=0.86,
FOV1=235 Degrees
[0052] which respectively satisfy the above conditions (1)-(6).
[0053] By the above arrangements of the lenses and stop ST1, the
lens assembly 1 of the first embodiment can meet the requirements
of optical performance as seen in FIGS. 2A-2C, wherein FIG. 2A
shows a longitudinal aberration diagram of the lens assembly 1 in
accordance with the first embodiment of the invention, FIG. 2B
shows a field curvature diagram of the lens assembly 1 in
accordance with the first embodiment of the invention and FIG. 2C
shows a distortion diagram of the lens assembly 1 in accordance
with the first embodiment of the invention.
[0054] It can be seen from FIG. 2A that the longitudinal aberration
in the lens assembly 1 of the first embodiment ranges from -0.0012
mm to 0.016 mm for the wavelength of 0.436 .mu.m, 0.486 .mu.m,
0.546 .mu.m, 0.588 .mu.m and 0.656 .mu.m.
[0055] It can be seen from FIG. 2B that the field curvature of
tangential direction and sagittal direction in the lens assembly 1
of the first embodiment ranges from -0.005 mm to 0.05 mm for the
wavelength of 0.436 .mu.m, 0.486 .mu.m, 0.546 .mu.m, 0.588 .mu.m
and 0.656 .mu.m.
[0056] It can be seen from FIG. 2C (in which the five lines in the
figure almost coincide to appear as if a signal line) that the
distortion in the lens assembly 1 of the first embodiment ranges
from -16% to 0% for the wavelength of 0.436 .mu.m, 0.486 .mu.m,
0.546 .mu.m, 0.588 .mu.m and 0.656 .mu.m.
[0057] It is obvious that the longitudinal aberration, the field
curvature and the distortion of the lens assembly 1 of the first
embodiment can be corrected effectively. Therefore, the lens
assembly 1 of the first embodiment is capable of good optical
performance.
[0058] Referring to FIG. 3, FIG. 3 is a lens layout diagram of a
lens assembly in accordance with a second embodiment of the
invention. The lens assembly 2 includes a first lens L21, a second
lens L22, a third lens L23, a fourth lens L24, a stop ST2, a fifth
lens L25, a sixth lens L26, a seventh lens L27, an eighth lens L28
and an optical filter OF2, all of which are arranged in order from
an object side to an image side along an optical axis OA2. In
operation, an image of light rays from the object side is formed at
an image plane IMA2.
[0059] The first lens L21 is a meniscus lens with negative
refractive power and made of glass material, wherein the object
side surface S21 is a convex surface, the image side surface S22 is
a concave surface and both of the object side surface S21 and image
side surface S22 are spherical surfaces.
[0060] The second lens L22 is a meniscus lens with negative
refractive power and made of glass material, wherein the object
side surface S23 is a convex surface, the image side surface S24 is
a concave surface and both of the object side surface S23 and image
side surface S24 are aspheric surfaces.
[0061] The third lens L23 is a biconcave lens with negative
refractive power and made of glass material, wherein the object
side surface S25 is a concave surface, the image side surface S26
is a concave surface and both of the object side surface S25 and
image side surface S26 are aspheric surfaces.
[0062] The fourth lens L24 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S27 is a convex surface, the image side surface S28 is
a convex surface and both of the object side surface S27 and image
side surface S28 are spherical surfaces.
[0063] The fifth lens L25 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S210 is a convex surface, the image side surface S211
is a convex surface and both of the object side surface S210 and
image side surface S211 are aspheric surfaces.
[0064] The sixth lens L26 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S212 is a convex surface, the image side surface S213
is a convex surface and both of the object side surface S212 and
image side surface S213 are spherical surfaces.
[0065] The seventh lens L27 is a biconcave lens with negative
refractive power and made of glass material, wherein the object
side surface S213 is a concave surface, the image side surface S214
is a concave surface and both of the object side surface S213 and
image side surface S214 are spherical surfaces.
[0066] The sixth lens L26 and the seventh lens L27 are cemented
together. That is, the air gap is not provided between the sixth
lens L26 and the seventh lens L27.
[0067] The eighth lens L28 is a biconvex lens with positive
refractive power and made of glass material, wherein the object
side surface S215 is a convex surface, the image side surface S216
is a convex surface and both of the object side surface S215 and
image side surface S216 are aspheric surfaces.
[0068] Both of the object side surface S217 and image side surface
S218 of the optical filter OF2 are plane surfaces.
[0069] In order to maintain excellent optical performance of the
lens assembly in accordance with the second embodiment of the
invention, the lens assembly 2 satisfies at least one of the
following conditions:
-15<f2.sub.1/f2<f2.sub.2/f2<f2.sub.3/f2<-1.8 (7)
-0.8<f2.sub.123/f2<-0.6 (8)
2.4<f2.sub.8/f2<2.8 (9)
-0.8<f2.sub.1234/f2.sub.5678<-0.6 (10)
0.8<TTL2/D2.sub.1<1.6 (11)
200.degree.<FOV2<240.degree. (12)
[0070] The definition of f2, f2.sub.1, f2.sub.2, f2.sub.3,
f2.sub.8, f2.sub.123, f2.sub.1234, f.sup.2.sub.5678, TTL2, D2.sub.1
and FOV2 are the same as that of f1, f1.sub.1, f1.sub.2, f1.sub.3,
f1.sub.8, f1.sub.123, f1.sub.1234, f1.sub.5678, TTL1, D1.sub.1 and
FOV1 in the first embodiment, and is not described here again.
[0071] Since f2 is a positive value, so that
f2.sub.3>f2.sub.2>f2.sub.1 can be deduced from condition (7).
The condition (7) can also be expressed as
-15<f2.sub.1/f2<-1.8, -15<f2.sub.2/f2<-1.8,
-15<f2.sub.3/f2<-1.8.
[0072] By the above design of the lenses and stop ST2, the lens
assembly 2 is provided with an increased field of view, a decreased
F-number, a shortened total lens length and an effective corrected
aberration.
[0073] In order to achieve the above purposes and effectively
enhance the optical performance, the lens assembly 2 in accordance
with the second embodiment of the invention is provided with the
optical specifications shown in Table 3, which include the
effective focal length, F-number, total lens length, radius of
curvature of each lens surface, thickness between adjacent surface,
refractive index of each lens and Abbe number of each lens. Table 3
shows that the effective focal length is equal to 1.63 mm, F-number
is equal to 2.4, total lens length is equal to 19.0 mm and maximum
field of view is equal to 207 degrees for the lens assembly 2 of
the second embodiment of the invention.
TABLE-US-00003 TABLE 3 Effective Focal Length = 1.63 mm F-number =
2.4 Total Lens Length = 19.0 mm Maximum Field of View = 207 Degrees
Radius of Surface Curvature Thickness Number (mm) (mm) Nd Vd Remark
S21 11.240 0.690 1.95 18.0 The First Lens L21 S22 4.390 2.030 S23
8.269 0.500 1.59 61.2 The Second Lens L22 S24 2.708 1.880 S25
-4.830 0.500 1.62 63.7 The Third Lens L23 S26 3.440 0.370 S27 4.890
4.290 1.85 23.8 The Fourth Lens L24 S28 -28.190 0.260 S29 .infin.
-0.180 2.743 Stop ST2 S210 2.782 1.500 1.50 81.1 The Fifth Lens L25
S211 -7.336 0.600 S212 3.950 2.030 1.49 70.4 The Sixth Lens L26
S213 -2.000 0.500 1.85 23.8 The Seventh Lens L27 S214 6.200 0.450
S215 4.515 1.480 1.81 40.9 The Eighth Lens L28 S216 -12.695 0.100
S217 .infin. 0.500 1.52 64.2 Optical Filter OF2 S218 .infin.
1.504
[0074] The aspheric surface sag z of each lens in table 3 can be
calculated by the following formula:
z=ch.sup.2/{1+[1-(k+1)c.sup.2h.sup.2].sup.1/2}+Ah.sup.4+Bh.sup.6+Ch.sup.-
8+Dh.sup.10+Eh.sup.12.+-.Fh.sup.14.+-.Gh.sup.16
where c is curvature, h is the vertical distance from the lens
surface to the optical axis, k is conic constant and A, B, C, D, E,
F and G are aspheric coefficients.
[0075] In the second embodiment, the conic constant k and the
aspheric coefficients A, B, C, D, E, F, G of each surface are shown
in Table 4.
TABLE-US-00004 TABLE 4 Surface Number k A B C D E F G S23 0.763
-2.85E-03 6.60E-05 1.67E-05 -1.15E-06 5.80E-09 8.53E-10 0.00E+00
S24 -0.401 -1.74E-03 -1.58E-04 4.93E-04 -1.45E-04 7.95E-06 4.13E-06
-4.97E-07 S210 0.130 -3.31E-03 6.30E-04 -4.04E-04 2.03E-04
-3.68E-05 -1.89E-06 0.00E+00 S211 -18.852 -1.15E-03 2.14E-03
-8.72E-04 4.48E-04 -9.17E-05 5.75E-06 0.00E+00 S215 0.483 -4.39E-03
6.75E-04 -2.18E-04 5.59E-05 -9.16E-06 6.79E-07 -1.81E-08 S216
-8.085 3.59E-03 -2.25E-04 2.53E-05 2.09E-05 -5.92E-06 3.94E-07
-2.76E-09
[0076] For the lens assembly 2 of the second embodiment, the
effective focal length f2 is equal to 1.63 mm, the effective focal
length f2.sub.1 of the first lens L21 is equal to -7.91 mm, the
effective focal length f2.sub.2 of the second lens L22 is equal to
-7.04 mm, the effective focal length f2.sub.3 of the third lens L23
is equal to -3.17 mm, the effective focal length f2.sub.8 of the
eighth lens L28 is equal to 4.27 mm, the effective focal length
f2.sub.123 of the combination of the first lens L21, the second
lens L22 and the third lens L23 is equal to -1.11 mm, the effective
focal length f2.sub.1234 of the combination of the first lens L21,
the second lens L22, the third lens L23 and the fourth lens L24 is
equal to -2.56 mm, the effective focal length f2.sub.5678 of the
combination of the fifth lens L25, the sixth lens L26, the seventh
lens L27 and the eighth lens L28 is equal to 3.99 mm, the interval
TTL2 from the object side surface S21 of the first lens L21 to the
image plane IMA2 along the optical axis OA2 is equal to 19.0 mm,
the effective diameter D2.sub.1 of the first lens L21 is equal to
12.5 mm and the maximum field of view FOV2 for the lens assembly 2
is equal to 207 degrees. According to the above data, the following
values can be obtained:
f2.sub.1/f2=-4.84,
f2.sub.2/f2=-4.31,
f2.sub.3/f2=-1.94,
f2.sub.123/f2=-0.68,
f2.sub.8/f2=2.62,
f2.sub.1234/f2.sub.5678=-0.64,
TTL2/D2.sub.1=1.52,
FOV1=207 Degrees
[0077] which respectively satisfy the above conditions
(7)-(12).
[0078] By the above arrangements of the lenses and stop ST2, the
lens assembly 2 of the second embodiment can meet the requirements
of optical performance as seen in FIGS. 4A-4C, wherein FIG. 4A
shows a longitudinal aberration diagram of the lens assembly 2 in
accordance with the second embodiment of the invention, FIG. 4B
shows a field curvature diagram of the lens assembly 2 in
accordance with the second embodiment of the invention and FIG. 4C
shows a distortion diagram of the lens assembly 2 in accordance
with the second embodiment of the invention.
[0079] It can be seen from FIG. 4A that the longitudinal aberration
in the lens assembly 2 of the second embodiment ranges from -0.016
mm to 0.013 mm for the wavelength of 0.436 .mu.m, 0.486 .mu.m,
0.546 .mu.m, 0.587 .mu.m and 0.656 .mu.m.
[0080] It can be seen from FIG. 4B that the field curvature of
tangential direction and sagittal direction in the lens assembly 2
of the second embodiment ranges from -0.03 mm to 0.025 mm for the
wavelength of 0.436 .mu.m, 0.486 .mu.m, 0.546 .mu.m, 0.587 .mu.m
and 0.656 .mu.m.
[0081] It can be seen from FIG. 4C (in which the five lines in the
figure almost coincide to appear as if a signal line) that the
distortion in the lens assembly 2 of the second embodiment ranges
from -11% to 0% for the wavelength of 0.436 .mu.m, 0.486 .mu.m,
0.546 .mu.m, 0.587 .mu.m and 0.656 .mu.m.
[0082] It is obvious that the longitudinal aberration, the field
curvature and the distortion of the lens assembly 2 of the second
embodiment can be corrected effectively. Therefore, the lens
assembly 2 of the second embodiment is capable of good optical
performance.
[0083] While the invention has been described by way of example and
in terms of the preferred embodiment(s), it is to be understood
that the invention is not limited thereto. On the contrary, it is
intended to cover various modifications and similar arrangements
and procedures, and the scope of the appended claims therefore
should be accorded the broadest interpretation so as to encompass
all such modifications and similar arrangements and procedures.
* * * * *