U.S. patent application number 09/921248 was filed with the patent office on 2002-01-31 for compact lens with external aperture stop.
Invention is credited to Ning, Alex.
Application Number | 20020012176 09/921248 |
Document ID | / |
Family ID | 23602185 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012176 |
Kind Code |
A1 |
Ning, Alex |
January 31, 2002 |
Compact lens with external aperture stop
Abstract
A lens assembly particularly suited to use with high resolution
digital cameras suitable for incorporation in compact portable
electronic devices such as cellular telephones, portable digital
assistants and the like. The lens assembly includes a distal
meniscus lens element formed from glass, and first and second,
aberration correcting, aspheric lens elements formed from plastic,
such as an acrylic, and positioned proximal to said meniscus lens
element. An aperture stop plane is provided just in front of the
front group. A fixed aperture stop or a combined variable aperture
and shutter device may be positioned at the aperture stop
plane.
Inventors: |
Ning, Alex; (Carlsbad,
CA) |
Correspondence
Address: |
DONN K. HARMS
12792 Via Cortina, Suite 100
Del Mar
CA
92014
US
|
Family ID: |
23602185 |
Appl. No.: |
09/921248 |
Filed: |
August 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09921248 |
Aug 3, 2001 |
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09405076 |
Sep 27, 1999 |
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6282033 |
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Current U.S.
Class: |
359/728 ;
359/739; 359/740 |
Current CPC
Class: |
G02B 13/0035 20130101;
G02B 9/16 20130101 |
Class at
Publication: |
359/728 ;
359/739; 359/740 |
International
Class: |
G02B 017/00; G02B
009/00; G02B 009/08 |
Claims
I claim:
1. A compact lens assembly which comprises: a glass meniscus lens
element at a distal assembly end; a first aspherical plastic lens
element spaced proximally from said first lens element; a second
aspherical plastic lens element spaced proximally from said first
aspherical plastic lens element; and an aperture stop located at an
aperture stop plane adjacent to said distal end of said glass lens
element at a predetermined distance from said glass lens
element.
2. The compact lens assembly according to claim 1 wherein said lens
assembly has a focal length from about 4.1 to 4.3 mm and an overall
length from said aperture stop to an image plane of from about 5.2
to 5.4 mm.
3. The compact lens assembly according to claim 1 wherein said
meniscus lens element is formed from a glass selected from the
group consisting of C-ZLAF2, BK-7 and SK-16 glasses and said
aspherical lens elements are formed from an acrylic material.
4. The compact lens assembly according to claim 1 further including
a cover glass position proximal to said second lens element.
5. The compact lens assembly according to claim 1 wherein lens
assembly satisfies the following data:
5 Surface Description Radius Thickness Material Diameter Conic 22
Aperture location Infinity -3.289371e-005 1.674 0 26 Spherical
Surface 1.883689 0.8158032 SK16 2.009056 0 28 Spherical surface
3.045904 0.6753982 2.031429 0 30 Aspheric surface 3.566412
0.6999804 ACRYLIC 2.324429 0 32 Conic surface 2.083898 0.4980362
2.859842 -19.09159 34 Conic surface 1.590613 1.164754 ACRYLIC
4.248483 -4.613664 36 Aspheric surface 3.246891 0.3960773 4.485452
0 38 Cover glass Infinity 0.55 BK7 4.490254 0 40 Cover glass
Infinity 0.5 4.50803 0 42 Image plane Infinity 4.607606 0
wherein the conic and aspheric surfaces for said lens assembly are
defined by the equation, the surfaces indicated being those
designated in FIG. 1: Where: Z is the surface sag C=1/R, R is the
radius of the surface k is the conic constant r is the distance
from optical axis .alpha. (1, 2, 3, 4, 5, etc) are the aspheric
coefficients wherein the listed elements and surfaces are numbered
from the distal end of said lens assembly. Surface data detail for
said aspheric lens elements:
6 Surface 30 Coef. on r 2 0 Coef. on r 4 -0.06370215 Coef. on r 6
-0.016150584 Coef. on r 8 0.039375843 Coef. on r 10 -0.026321689
Surface 36 Coef. on r 2 0 Coef. on r 4 -0.012203864 Coef. on r 6
-0.0026530826 Coef. on r 8 0.00030428755 Coef. on r 10
-4.7006906e-005
6. The compact lens assembly according to claim 1 wherein lens
assembly satisfies the following data:
7 Surface Description Radius Thickness Material Diameter Conic 60
Aperture Infinity -2.735838e-005 1.674 0 64 Spherical surface
2.058406 0.7793137 C-ZLAF2 1.96092 0 66 Spherical Surface 2.883771
0.7532283 1.956528 0 68 Aspheric surface 3.696814 0.6999906 ACRYLIC
2.359079 0 70 Conic surface 2.186806 0.4870961 2.906413 -22.34914
72 Conic surface 1.645422 1.198582 ACRYLIC 4.283354 -5.091541 74
Aspheric Surface 3.544696 0.3318456 4.545027 0 76 Cover glass
Infinity 0.55 BK7 4.544323 0 78 Cover glass Infinity 0.5 4.541721 0
62 Image plane Infinity 4.613017 0
Wherein the conic and aspheric surfaces for said lens assembly are
defined by the equation, the surfaces being those as indicated in
FIG. 2: Where: Z is the surface sag C=1/R, R is the radius of the
surface k is the conic constant r is the distance from optical axis
.alpha. (1, 2, 3, 4, 5, etc) are the aspheric coefficients Surface
data detail for said aspheric lens elements:
8 Surface 68 Coef. on r 2 0 Coef. on r 4 -0.055969229 Coef. on r 6
-0.016164047 Coef. on r 8 0.034963476 Coef. on r 10 -0.021598842
Surface 74 Coef. on r 2 0 Coef. on r 4 -0.011453885 Coef. on r 6
-0.0023845294 Coef. on r 8 0.00033512568 Coef. on r 10
-5.3608643e-005
7. The compact lens assembly according to claim 1 wherein said
aperture stop is selected from a fixed aperture and a variable
aperture means.
8. The compact lens assembly according to claim 7 further including
a shutter means also located substantially at said aperture stop
plane.
9. In a compact digital camera having a camera body, a sensor for
forming a digital image corresponding to varying light image
falling thereon, a lens assembly for forming said light image, and
an aperture stop for controlling light image intensity passing
through said lens assembly, the improvement comprising: said lens
assembly comprising a glass meniscus lens element at a distal end
of said lens assembly, a first aspherical plastic lens element
spaced proximally from said first lens element; and a second
aspherical plastic lens element spaced proximally from said first
bi-aspheric plastic lens element; said aperture stop located
adjacent to said distal end of said lens assembly at a
predetermined distance from said glass lens element; and a
shutter/variable aperture combined with said aperture stop for
shielding the sensor during digital image read-out from said
sensor.
10. The improvement according to claim 9 wherein said lens assembly
has a focal length of from about 4.0 to 4.3 mm and an overall
length from said aperture stop to an image plane of from about 5.2
to 5.4 mm.
11. The improvement according to claim 9 wherein said meniscus lens
element is formed from a glass selected from the group consisting
of C-ZLAF2, BK-7 and SK-16 glasses and said bi-aspheric lens
elements are formed from an acrylic material.
12. The improvement according to claim 9 further including a cover
glass position proximal to said second lens element.
13. The improvement according to claim 9 wherein the lens assembly
satisfies the following data:
9 Surface Description Radius Thickness Material Diameter Conic 22
Aperture location Infinity -3.289371e-005 1.674 0 26 Spherical
Surface 1.883689 0.8156032 SK16 2.009056 0 28 Spherical surface
3.045904 0.6753982 2.031429 0 30 Aspheric surface 3.566412
0.6999804 ACRYLIC 2.324429 0 32 Conic surface 2.083898 0.4980362
2.859842 -19.09159 34 Conic surface 1.590613 1.164754 ACRYLIC
4.248483 -4.613664 36 Aspheric surface 3.246891 0.3960773 4.485452
0 38 Cover glass Infinity 0.55 BK7 4.490254 0 40 Cover glass
Infinity 0.5 4.50803 0 42 Image plane Infinity 4.607606 0
Wherein the conic and aspheric surfaces for said lens assembly are
defined by the equation, the designated surfaces being as indicated
in FIG. 1: Where: Z is the surface sag C=1/R, R is the radius of
the surface k is the conic constant r is the distance from optical
axis .alpha. (1, 2, 3, 4, 5, etc) are the aspheric coefficients
wherein the listed elements and surfaces are numbered from the
distal end of said lens assembly. Surface data detail for said
aspheric lens elements:
10 Surface 30 Coef. on r 2 0 Coef. on r 4 -0.06370215 Coef. on r 6
-0.016150584 Coef. on r 8 0.039375843 Coef. on r 10 -0.026321689
Surface 36 Coef. on r 2 0 Coef. on r 4 -0.012203864 Coef. on r 6
-0.0026530826 Coef. on r 8 0.00030428755 Coef. on r 10
-4.7006906e-005
wherein the listed elements and surfaces are numbered from the
distal end of said lens assembly.
14. The improvement according to claim 9 wherein the lens assembly
satisfies the following data, wherein the surfaces are as
designated in FIG. 2:
11 Surface Description Radius Thickness Material Diameter Conic 60
Aperture Infinity -2.735838e-005 1.674 0 64 Spherical surface
2.058406 0.7793137 C-ZLAF2 1.96092 0 66 Spherical Surface 2.883771
0.7532283 1.956529 0 68 Aspheric surface 3.696814 0.6999906 ACRYLIC
2.359079 0 70 Conic surface 2.186806 0.4870961 2.906413 -22.34914
72 Conic surface 1.645422 1.198582 ACRYLIC 4.283354 -5.091541 74
Aspheric Surface 3.544696 0.3318456 4.545027 0 76 Cover glass
Infinity 0.55 BK7 4.544323 0 78 Cover glass Infinity 0.5 4.541721 0
62 Image plane Infinity 4.613017 0
Wherein the conic and aspheric surfaces for said lens assembly are
defined by the equation: e: Z is the surface sag C=1/R, R is the
radius of the surface k is the conic constant r is the distance
from optical axis .alpha. (1, 2, 3, 4, 5, etc) are the aspheric
coefficients Surface data detail for said aspheric lens
elements:
12 Surface 68 Coef. on r 2 0 Coef. on r 4 -0.055969229 Coef. on r 6
-0.016164047 Coef. on r 8 0.034963476 Coef. on r 10 -0.021598842
Surface 74 Coef. on r 2 0 Coef. on r 4 -0.011453885 Coef. on r 6
-0.0023845294 Coef. on r 8 0.00033512568 Coef. on r 10
-5.3608643e-005
Description
[0001] This Application is a Continuation-in-part of copending U.S.
patent application Ser. No. 09/405,076, filed Sep. 23, 1999.
FIELD OF THE INVENTION
[0002] This invention relates to compact lenses for digital camera
applications; in particular, for very compact digital cameras such
as could be incorporated into a cellular telephone, personal
digital assistant, or other very small electronic device.
BACKGROUND OF THE INVENTION
[0003] Digital cameras utilizing high-resolution electronic imaging
sensors require high resolution optics. For the consumer market, it
is important that the lenses can be produced in high volume
inexpensively. For use in very compact digital cameras, and cameras
that might be incorporated into devices such as palm-sized
computers, cellular telephones and the like, the lens must be very
compact. In particular, it must have a very short length from the
lens front surface to the image plane.
[0004] In the prior art, high resolution lenses have generally been
made up of several individual lens elements in order to balance the
inherent optical aberrations. These lenses that require a large
number of elements tend to be relatively large, heavy, and
expensive to manufacture. (The cost of these lenses increases with
the number of elements, also resulting in increased costs in
assembling and mounting them in a lens cell.) Prior lenses are
generally designed using all spherical surfaces or using at least
some aspheric elements in which one or both surfaces are
non-spherical. Where all elements have spherical surfaces,
generally a high number of lens elements is required, making the
lens long and expensive to produce.
[0005] Aspheric lenses have some optical advantages, but cannot be
easily produced by traditional glass grinding and polishing
techniques. Aspheric elements are typically produced by molding
plastics or low melt temperature glasses. While molded plastic
elements are inexpensive to produce, the level of precision of the
lenses is not always sufficient for high-resolution cameras,
especially if a plastic element is used primarily as a focusing
element. In addition, the optical properties of most plastic
materials change with changes in temperature and humidity. The
index of refraction of the plastic lens materials changes with
changes in temperature, such as going in and out of doors on very
hot or very cold days. This change is a significant problem with
the focusing element(s), but is of much less consequence with other
elements which primarily correct for aberrations. Lenses with all
glass elements can overcome this problem, but tend to be large and
excessively expensive for use in compact digital cameras used in
other devices, such as an accessory built into a cellular
phone.
[0006] Chemical film, as used in conventional film cameras, can be
exposed with light coming from any direction, even at a low angle
to the film surface. For digital cameras using inexpensive
electronic imagers, to achieve optimum performance the light should
contact the imaging media at angles of less than about 15.degree.
to a line normal to the imaging media surface.
[0007] Prior lens designs generally have separate variable
apertures and shutters, increasing the length of the lens assembly.
Even where both these functions are combined in one device, that
device must be positioned between lens elements because the
aperture stops of conventional designs are located between lens
elements.
[0008] Having the aperture stop between lens elements, as in the
Double Gaussian designs, is believed to make correction of
aberrations easier. Typical of such lens designs is that described
by Fugii in U.S. Pat. No. 4,212,517, where the aperture stop is
located between the third and fourth elements. This provides a
degree of lens symmetry about the apertures stop, resulting in
reduction in off-axis aberrations such as coma and distortion. It
is generally believed that achieving good aberration correction
without this symmetrical arrangement of lens elements would be
difficult. However, it is difficult and expensive to integrate a
variable aperture/shutter device with this type of optical design
since it is difficult to keep the lens elements positioned
precisely with the aperture device located between the
elements.
[0009] Defuans, in U.S. Pat. No. 4,505,039, describes a lens design
with the aperture stop in front of the first element.
[0010] That design requires that the first element be plano-convex,
with the plano surface facing the aperture. However, that design
has a maximum relative aperture of f/4, too slow for use with
cameras to be used at relatively low light levels. That design
further requires seven elements, making it excessively long, heavy
and expensive to produce for use in compact digital cameras.
[0011] Therefore, there is a continuing need for improved lenses
that are not temperature sensitive, have excellent low-light
performance and are compact, short, light weight and inexpensive to
produce while using conventional, well-proven manufacturing
methods.
SUMMARY OF THE INVENTION
[0012] The above-noted problems, and others, are overcome in
accordance with this invention by a lens for digital cameras; in
particular, such cameras that are incorporated into another device
such as a cell phone, personal digital assistant and the like, that
is extremely compact and has a short length from the front element
surface to the imaging plane, have three lens elements with the
front element formed from glass and the others from plastic and
have excellent optical characteristics. For optimum results the
lens has an aperture stop in front of the lens, external to the
lens. If desired, an optional variable aperture/shutter can be
positioned at the aperture stop position with precision.
[0013] The lens comprises three lens elements. The first, or front,
lens element is a meniscus lens and is formed from a suitable glass
by conventional lens grinding and polishing methods. Both surfaces
of this lenses are spherical. The second and third elements are
aspherical, formed from a suitable plastic by molding. Aspherical
elements have at least one surface being a non-spherical surface.
For optimum results, both surfaces of the aspheric elements are
aspherical. An electronic imaging sensor is spaced a suitable
distance from the rear element. Preferably, a cover glass is
provided over the sensor surface. The use of a glass front element
greatly reduces lens temperature sensitivity when the lens is taken
from areas at great temperature differences, such as when bringing
a camera into a building on a hot summer day or cold winter
day.
[0014] Preferably, the aperture/shutter device is external to the
optical elements so the optical elements can be assembled into a
precision lens barrel independent of the aperture/shutter device.
The performance of such a lens can be tested and verified before
integration with an optional aperture/shutter device. Integration
of such pre-assembled lenses with the aperture/shutter device can
be performed with high reliability and repeatability, resulting in
high yields in volume manufacturing.
[0015] It is, therefore, an object of this invention to provide a
compact lens assembly particularly suitable for use in compact
digital cameras, especially those incorporated into other compact
electronic devices such as cellular phones, personal digital
assistants and the like.
[0016] Another object of this invention is to provide a lens
assembly for digital cameras that has very low sensitivity to
changes in temperature.
[0017] A further object is to provide a digital camera lens having
an extremely short length from the aperture/shutter device to the
sensor imaging plane.
[0018] Yet another object is to provide a digital camera lens
having a glass front element and two plastic elements to provide an
optimum combination of imaging quality, small F-stop, and low
manufacturing cost.
BRIEF DESCRIPTION OF THE DRAWING
[0019] Details of the invention, and of preferred embodiments
thereof, will be further understood upon reference to the drawing,
wherein:
[0020] FIG. 1 is a schematic axial section view of a first
embodiment of the lens of this invention; and
[0021] FIG. 2 is a schematic axial section view of a second
embodiment of the lens of this invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Referring to FIG. 1, there is seen a schematic axial section
view of a lens assembly 10 for forming an image at a image plane on
imaging sensor 12, which in a digital camera is the sensor plane
and in a film type camera is the film plane. The front or distal
end of the lens is to the left in FIG. 1. Line 14 represents the
lens optical axis.
[0023] The lens assembly 10 includes a distal meniscus lens element
16, a central aspherical lens element 18 and a proximal aspherical
lens element 20. While lens element 18 may have one spherical
surface and one aspheric surface, if desired, having both surfaces
aspheric is preferred for optimum results. The aperture stop plane
is schematically indicated by line 22, closely adjacent to distal
lens element 16. At aperture stop plane, a conventional fixed
aperture stop, or a variable aperture stop and a shutter may be
provided as desired. In the absence of a shutter, the imaging
material is electronically operated to provide the desired exposure
length. Distal element 16 provides most of the focusing power while
elements 18 and 20 provide aberration compensation to correct for
any optical aberrations present in element 14. All light rays
passing through lens assembly 10 encounter the sensor 12 at angles
within 15 degrees on either side of a line normal to the sensor,
providing optimum efficiency.
[0024] The lens design shown in FIG. 1, and detailed in the lens
data table below, preferably uses Schott SK 16 glass for element 16
and an optical grade acrylic for aspherical elements 18 and 20. The
glass distal lens element 16 is very temperature insensitive,
avoiding any problems resulting from taking the lens between areas
at greatly differing temperatures, such as taking the device using
the lens into a building on a very hot summer day or a very cold
winter day.
[0025] The vertex spacings between lens elements are also listed in
Table 1. For best results, a cover glass 24 is placed over sensor
12. Aperture stop 22 is preferably as close to distal element 16 as
is practical. Overall length from aperture stop 22 to image plane
12 for the lens of this embodiment which has an effective focal
length of 4.8 mm and is suitable for 1/4" format images, is about
5.3 mm. While this overall length is optimum for a 1/4"-format
imager, the lens assembly may be scaled to provide other
configurations according to the format size of the imager.
[0026] Lens element 16 has spherical surfaces and is formed from a
suitable glass, such as SK 16, a low-index, low-cost glass from
Schott Optical Glasses in Germany or Zlaf2, a high index
(Nd=1.80279, Vd=46.76), which is more expensive, available from
GuangMing Optical Glasses in China. Aspherical elements 18 and 20
are formed from an acrylic material, also known as PMMA, from
Imperial Chemical in the United Kingdom. Cover glass 24, when used,
is typically formed from B270 glass from Schott. Any suitable
anti-reflection or other coatings may be applied to the lens
elements and cover glass.
[0027] Lens 10 of FIG. 1 is completely asymmetrical. This lens will
provide excellent image quality over a field of view of +/-30
degrees at a relative aperture as large as f/2.5. This lens is well
suited for use with state of the art digital sensors having a
resolution about 640.times.480 pixels. The maximum geometric
distortion of this lens is typically under about 5%.
[0028] Details of the structure of an optimum version of the FIG. 1
general embodiment is provided in Table I. All radii and distances
are in millimeters. Each lens is identified by the corresponding
drawing reference number, with surfaces defined by serial radius
numbers from the distal to proximal end. The overall length from
the aperture stop to the image plane is 5.3 mm. The effective focal
length is 4.2 mm in air. The maximum aperture is f/2.5.
1TABLE I Surface Description Radius Thickness Material Diameter
Conic 25 Aperture location Infinity -3.289371e-005 1.674 0 26
Spherical Surface 1.883689 0.8158032 SK16 2.009056 D 28 Spherical
surface 3.045904 0.6753982 2.031429 D 30 Aspheric surface 3.566412
0.6999804 ACRYLIC 2.324429 0 32 Conic surface 2.083898 0.4980362
2.859842 -19.09159 34 Conic surface 1.590613 1.164754 ACRYLIC
4.248483 -4.613664 36 Aspheric surface 3.246891 0.3960773 4.485452
0 38 Cover glass Infinity 0.55 B270 4.490254 0 40 Cover glass
Infinity 0.5 4.50803 0 42 Image plane Infinity 4.607606 0
[0029] Surface 30, 32, 34 and 36 are all aspherical and described
the the following equation: 1 z ( r ) = cr 2 1 + 1 - ( 1 + k ) c 2
r 2 + 1 r 2 + 2 r 4 + 3 r 6 + 4 r 8 + 5 r 10
[0030] Where:
[0031] Z is the surface sag
[0032] C =1/R, R is the radius of the surface
[0033] k is the conic constant
[0034] r is the distance from optical axis
[0035] .alpha. (1, 2, 3, 4, 5, etc.) are the aspheric
coefficients
[0036] For surface 32 and 34 (both are conic surfaces), the .alpha.
(1, 2, 3, 4, 5, etc.) are all zero.
[0037] For surface 30 and 36, the conic constants are zero. The
.alpha. (1, 2, 3, 4, 5, etc.) are given as follows:
2 Surface 30 EVENASPH Coeff on r 2 0 Coeff on r 4 -0.06370215 Coeff
on r 6 -0.016150584 Coeff on r 8 -0.039375843 Coeff on r 10
-0.026321689 Surface 36 EVENASPH Coeff on r 2 0 Coeff on r 4
-0.012203864 Coeff on r 6 -0.0026530826 Coeff on r 8 0.00030428755
Coeff on r 10 -4.7006906e-005 Index of refraction of material: For
SK16 glass: Nd = 1.62041 Vd = 60.32 For Acrylic (PMMA) plastic: Nd
= 1.4917 Vd = 55.31
[0038] FIG. 2 is a schematic axial section view through a lens 50.
Lens 50 is generally similar to lens 10, with changes to
accommodate a different glass in the distal element and the
corresponding changes in the other elements to accommodate the
effects of the different glass. Other glasses may be used, with
similar variations in lens element characteristics. As with the
lens of FIG. 1, the FIG. 2 lens is asymmetrical. Because of
excellent correction of aberrations, lens 30 will provide excellent
image quality over a field of view of +/-30 degrees. Lens 30 has an
effective focal length of 4.2, a length of 5.3 and a maximum
aperture of f/2.5.
[0039] Lens assembly 50 consists of one spherical glass element and
two aspheric plastic elements along an axis 52. Lens 50 includes a
distal glass meniscus lens element 54 and two proximal plastic
aspherical lens elements 56 and 58. The aperture stop plane is
schematically indicated by line 60, closely adjacent to element 54.
The image sensor plane is indicated at 62. A cover glass 64 is
preferably placed over the sensor. Distal element 54 provides most
of the focusing power while proximal elements 56 and 58 provides
aberration compensation. The spacings between the elements is given
in Table II. Aperture stop 42 is preferably as close to distal
element 32 as practical. Lens 50 may be mounted in a lens barrel in
any suitable manner, such as by threaded retaining rings.
[0040] Detailed structural parameters of an optimum lens of the
sort shown in FIG. 2 are provided in Table II, wherein surface
radius and axial distances are shown in millimeters and the
surfaces are identified by reference numbers from the distal to the
proximal end as shown.
3TABLE II Surface Description Radius Thickness Material Diameter
Conic 60 Aperture Infinity -2.735838e-005 1.674 0 64 Spherical
surface 2.058406 0.7793137 C-ZLAF2 1.96092 0 66 Spherical Surface
2.883771 0.7532283 1.956528 0 68 Aspheric surface 3.696814
0.6999906 ACRYLIC 2.359079 0 70 Conic surface 2.186806 0.4870961
2.906413 -22.34914 72 Conic surface 1.645422 1.198582 ACRYLIC
4.283354 -5.091541 74 Aspheric Surface 3.544696 0.3318456 4.545027
0 76 Cover glass Infinity 0.55 BK7 4.544323 0 78 Cover glass
Infinity 0.5 4.541721 0 62 Image plane Infinity 4.613017 0
[0041] Aspherical surfaces are surface 66, 68, 70 and 72. The
equations for those surfaces are given as follows:
[0042] Where:
[0043] Z is the surface sag
[0044] C=1/R, R is the radius of the surface
[0045] k is the conic constant
[0046] r is the distance from optical axis
[0047] .alpha. (1, 2, 3, 4, 5, etc.) are the aspheric
coefficients
[0048] For surface 68 and 70 (both are conic surfaces), the .alpha.
(1, 2, 3, 4, 5, etc.) are all zero.
[0049] For surface 66 and 72, the conic constants are zero. The
.alpha. (1, 4, 5, etc.) are given as follows:
4 Surface 66 EVENASPH Coeff on r 2 0 Coeff on r 4 -0.055969229
Coeff on r 6 -0.016164047 Coeff on r 8 0.034963476 Coeff on r 10
-0.021598842 Surface 72 EVENASPH Coeff on r 2 0 Coeff on r 4
-0.011453885 Coeff on r 6 -0.0023845294 Coeff on r 8 0.00033512568
Coeff on r 10 -5.3608643e-005 Index of refraction of material: For
Zlaf2 glass: Nd = 1.80279 Vd = 46.76 For Acrylic (PMMA) plastic: Nd
= 1.4917 Vd = 55.31
[0050] Lens 50 is a very compact lens for one having these
specifications, allowing the camera or other portable electronic
device to be very low-profile.
[0051] While certain specific relationships, materials and other
parameters have been detailed in the above description of preferred
embodiments, those can be varied, where suitable, with similar
results. Other applications, variation and ramifications of the
present invention will occur to those skilled in the art upon
reading the present disclosure. Those are intended to be included
within the scope of this invention as defined in the appended
claims.
* * * * *