# Patent

## Title
Lens system

## Abstract

A lens system comprises a first lens negative in power, a second lens positive in power, a third lens negative in power, a fourth lens positive in power, a fifth lens negative in power, and a sixth lens positive in power. The lens system meets a criteria of TT/f≦1.68 and 0.3<f/f23<0.4, wherein TT denotes a distance between an object-side surface of the first lens and an image plane of the lens system; f23 denoting an effective focal length of a combination of the second lens and the third lens; f denoting an effective focal length of the entire lens system.

## Background
TECHNICAL FIELD
The present invention relates to a lens system, and particularly to a lens system for use in electronic devices.
DESCRIPTION OF RELATED ART
In recent years, camera modules using an image sensor like a charged coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) for capturing images have begun to be incorporated in portable electronic devices such as mobile phones and laptop computers. Downsizing the camera modules is a prerequisite for enhancing the portability of these electronic devices.
Recently, the image sensor having the size of approximately a few micrometers has become commercially feasible, and an image pickup device with high resolution and a compact size can now be mass manufactured and marketed. This accelerates the demand for downsizing of the image pickup lens systems so that they are usable with miniaturized image sensors. It is desired to provide a lens system with short length, compact size, excellent optical performance, and great image quality. Obtaining a short length requires very short distance between the first lens and the image plane of the lens system.
SUMMARY
In accordance with a present embodiment, a lens system comprising a first lens negative in power, a second lens positive in power, a third lens negative in power, a fourth lens positive in power, a fifth lens negative in power, and a sixth lens positive in power is disclosed. The lens system meets a criteria of TT/f≦1.68 and 0.3<f/f23<0.4, wherein TT denotes a distance between an object-side surface of the first lens and an image plane of the lens system; f23 denoting an effective focal length of a combination of the second lens and the third lens; f denoting an effective focal length of the entire lens system.
Other advantages and novel features will be drawn from the following detailed description of at least one preferred embodiment, when considered conjunction with the attached drawings.



BRIEF DESCRIPTION OF THE DRAWING
Many aspects of the present lens system can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present assembling method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a schematic drawing of a lens system according to a first present embodiment;
FIG. 2 is a spherical aberration diagram of the lens system in FIG. 1;
FIG. 3 is a field curvature diagram of the lens system in FIG. 1;
FIG. 4 is a distortion diagram of the lens system in FIG. 1;
FIG. 5 is a spherical aberration diagram of the lens system according to a second present embodiment;
FIG. 6 is a field curvature diagram of the lens system according to the second present embodiment; and
FIG. 7 is a distortion diagram of the lens system according to the second present embodiment.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Embodiments will now be described in detail below, with reference to the drawings.
Referring to FIG. 1, a lens system 100 according to a present embodiment is disclosed. The lens system includes, in order from an object-side to an image-side, a first lens negative in power, a second lens positive in power, a third lens negative in power, a fourth lens positive in power, a fifth lens negative in power, and a sixth lens positive in power.
Light coming from the object-side of the lens system 100 transits through the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, the sixth lens 60 and ultimately projects onto an image plane 90. A CCD or CMOS can be disposed in the image plane 90 for capturing an image in view of the lens system.
In order to provide the lens system 100 with a compact size and excellent optical performance, the lens system 100 meets the following conditions:

TT/f≦1.68   (1)

and

0.3<f/f23<0.4,  (2)

wherein TT denotes a distance between an object-side surface of the first lens and the image plane 90; f23 denotes an effective focal length of the combination of the second lens 20 and the third lens 30; and f denotes an effective focal length of the entire lens system 100. Condition (1) defines a compact total length of the lens system 100 and condition (2) provides balance between total length, spherical aberration and chromatic aberration of the lens system 100.

Preferably, the sixth lens 60 further meets the following condition:

1<f/f6<1.2,  (3)

wherein f denotes the effective focal length of the entire lens system 100, f6 denotes the focal length of the sixth lens. Condition (3) ensures the lens system 100 possesses a qualified dioptric strength and is nearly a telecentric optic system for providing uniform illumination of the image plane.

In order to correct chromatic aberrations of the lens system 100, especially the chromatic difference of magnification, the second lens 20, the third lens 30, and the fourth lens 40 further meet the following conditions:

Vd2>Vd3,  (4)

and

Vd4>Vd5  (5)

wherein Vd2 denotes the Abbe number of the second lens 20; Vd3 denotes the Abbe number of the third lens 30; Vd4 denotes the Abbe number of the fourth lens 40; Vd5 denotes the Abbe number of the fifth lens 50. Conditions (4) and (5) collectively keep the lens system 100 a compact size and guarantee a balance between obtaining a reduction in the total length of the lens system 100 and keeping the chromatic difference at a minimum.

In order to install an aperture between the first lens 10 and the second lens 20, the first lens 10 and the second lens 20 further meet the following condition:

0.2<DA1-2/f<0.3  (6)

wherein DA1-2 denotes a distance between the image-side surface of the first lens 10 and the object-side surface of the second lens 20; f denotes the focal length of the entire lens system 100.

The lens system 100 can further include an aperture stop 70 and a filter 80. The aperture stop 70 is installed between the first lens 10 and the second lens 20 and is configured for adjusting the light flux transmitted through the first lens 10 to the second lens 20. The aperture 70 ensures uniform light transmission through the first lens 10 to correct chromatic aberration of the lens system 100. To save on production cost and downsize the lens system 100, the aperture 70 can be formed by applying an opaque material on an outer rim of the object-side surface of the second lens 20. The filter 80 is installed between the sixth lens 60 and the image plane 90 and is configured for filtering out IR light that enters the lens system 100.
Preferably, the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, and the sixth lens 60 in the lens system 100 can be made of glass to achieve better image quality but lower production cost.
Referring to FIGS. 2 ̃7, embodiments of the lens system 100 are disclosed in the following. The first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, and the sixth lens 60 as disclosed in the following embodiments are all spherical lenses. In these embodiments, “f” represents a focal length of the lens system 100; “FNo” represents the aperture F-number; “2ω” represents a field angle.
Embodiment 1: The following table 1 shows specifications of a first embodiment of the lens system 100, wherein TT=11.64 mm; f=6.91 mm; f23=19.2939 mm; FNo=3.19; 2ω=56°.











TABLE 1






Radius of

Reflective
Abbe


Lens system 100
curvature (mm)
Thickness (mm)
index
number



















Object
∞
1000
—
—


Object-side surface of the first lens 10
55.82214
0.52
1.58913 
61.135


Image-side surface of the first lens 10
27.47293
1.3
—
—


Aperture stop70
∞
0.22
—
—


Object-side surface of the second lens 20
3.571711
0.9761735
1.882997
40.7651


Image-side surface of the second lens 20
−10.97649
0.1
—
—


Object-side surface of the third lens 30
−5.59937
0.52
1.698947
30.1279


Image-side surface of the third lens 30
3.373019
0.552519
—
—


Object-side surface of the fourth lens 40
10.15544
1.23667
1.788001
47.3685


Image-side surface of the fourth lens 40
−3.815141
0.7072471
—
—


Object-side surface of the fifth lens 50
−2.661624
0.52
1.592701
35.3101


Image-side surface of the fifth lens 50
8.585195
0.9975566
—
—


Object-side surface of the sixth lens 60
9.9103
1.880943
1.816  
46.62 


Image-side surface of the sixth lens 60
−11.4479
0.4134666
—
—


Object-side surface of the filter 80
∞
0.8
1.5168 
64.16 


Image-side surface of the filter 80
∞
0.9
—
—









The spherical aberration diagram, the field curvature diagram, and the distortion diagram of the lens system 100 are respectively shown in FIGS. 2 ̃4. Spherical aberrations of line g (λ=435.8 nm) and line d (λ=587.6 nm) and line c (λ=656.3 nm) are shown in FIG. 2. Generally, spherical aberration of visible light (with a wavelength between 400 ̃700 nm) of the lens system 100 in the first embodiment is within a range of −0.1 mm to 0.1 mm. The sagittal field curvature and tangential field curvature shown in FIG. 3 are kept within a range of −0.1 mm to 0.1 mm. The distortion in FIG. 4 falls within a range of −2% to 2%. Obviously, spherical aberration, field curvature, and distortion are well controlled in the first embodiment of the lens system 100.
Embodiment 2: The following table 2 shows specifications of a second embodiment of the lens system 100, wherein f=7.098 mm; f23=18.8125 mm; FNo=3.19; 2ω=53.38°.











TABLE 2






Radius of

Reflective
Abbe


Lens system 100
curvature (mm)
Thickness (mm)
index
number



















Object
∞
1000
—
—


Object-side surface of the first lens 10
138
0.515
1.48749 
70.4058


Image-side surface of the first lens 10
38.5071
1.2933
—
—


Aperture stop70
∞
0.2166
—
—


Object-side surface of the second lens 20
3.434642
0.9954933
1.90217 
40.7651


Image-side surface of the second lens 20
−12.82318
0.1
—
—


Object-side surface of the third lens 30
−6.115171
0.515
1.729672
28.6914


Image-side surface of the third lens 30
3.257676
0.553578
—
—


Object-side surface of the fourth lens 40
8.529067
1.220021
1.743972
44.8504


Image-side surface of the fourth lens 40
−3.63408
0.681474
—
—


Object-side surface of the fifth lens 50
−2.509925
0.515
1.642602
34.2214


Image-side surface of the fifth lens 50
10.56706
0.901031
—
—


Object-side surface of the sixth lens 60
10.2255
1.944665
1.8068 
45.6199


Image-side surface of the sixth lens 60
−10.11677
0.464267
—
—


Object-side surface of the filter 80
∞
0.8
1.5168 
64.16 


Image-side surface of the filter 80
∞
0.9
—
—









The spherical aberration diagram, the field curvature diagram, and the distortion diagram of the second embodiment in the lens system 100 are respectively shown in FIGS. 5 ̃7. Spherical aberrations of line g (λ=435.8 nm) and line d (λ=587.6 nm) and line c (λ=656.3 nm) are shown in FIG. 5. Generally, the spherical aberration of visible light (with a wavelength between 400 ̃700 nm) of the lens system 100 in the second embodiment is kept within a range of −0.1 mm to 0.1 mm. The sagittal field curvature and tangential field curvature shown in FIG. 6 are kept within a range of −0.1 mm to 0.1 mm. The distortion shown in FIG. 7 falls within a range of −2% to 2%. Obviously, spherical aberration, field curvature, and distortion are well controlled in the second embodiment of the lens system 100.
The aforementioned lens system 100 has a compact size and excellent optical performance to meet the trend toward miniature lens systems. The lens system 100 works to keep chromatic aberrations at a minimum while reducing the total length of the lens system.
While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.

## Claims

1. A lens system, from an object-side to an image-side of the lens system, comprising:
a first lens negative in power,
a second lens positive in power,
a third lens negative in power,
a fourth lens positive in power,
a fifth lens negative in power, and
a sixth lens positive in power; the lens system meeting a criteria of TT/f≦1.68 and 0.3<f/f23<0.4; wherein TT denotes a distance between an object-side surface of the first lens and an image plane of the lens system; f23 denoting an effective focal length of a combination of the second lens and the third lens; f denoting an effective focal length of the entire lens system.

2. The lens system as claimed in claim 1, wherein the sixth lens meets a criteria of 1<f/f6<1.2 and f6 denotes a focal length of the sixth lens.

3. The lens system as claimed in claim 1, wherein the lens system meets a criteria of Vd2>Vd3 and Vd4>Vd5; Vd2 denoting an Abbe number of the second lens 20; Vd3 denoting an Abbe number of the third lens 30; Vd4 denoting an Abbe number of the fourth lens 40; and Vd5 denoting an Abbe number of the fifth lens.

4. The lens system as claimed in claim 1, wherein the sixth lens meets a criteria of 0.2<DA1-2/f<0.3 and DA1-2 denotes a distance between an image-side surface of the first lens and an object-side surface of the second lens.

5. The lens system as claimed in claim 1, wherein the lens system further comprises an aperture stop installed between the first lens and the second lens.

6. The lens system as claimed in claim 5, wherein the aperture stop is formed by applying an opaque material on an outer rim of the object-side surface of the second lens.

7. The lens system as claimed in claim 1, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are spherical lenses.

8. The lens system as claimed in claim 1, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are made of glass.

9. The lens system as claimed in claim 1, further comprising a filter installed in an image-side of the sixth lens configured for filtering IR light.