Imaging lens system and imaging module having same

1. Technical Field

The disclosure relates to imaging lenses and, particularly, to an imaging lens system providing a high resolution and a reduced overall length and an imaging module having the same.

2. Description of Related Art

To optimize resolution and reduce size, imaging modules for use in thin devices, such as mobile phones or personal digital assistant (PDA), must employ an imaging lens system with a high resolution and a small overall length (the distance between the object-side surface of the imaging lens system and the image plane of the imaging module). However, in optical design of an imaging lens system, increasing resolution thereof commonly increases overall lens thereof.

Therefore, it is desirable to provide an imaging lens system and an imaging module using the system which can overcome the described limitations.

FIG. 1 is a schematic view of an imaging module in accordance with an exemplary embodiment.

FIG. 2 is a spherical aberration graph of the imaging module of FIG. 1 , according to a first exemplary embodiment.

FIG. 3 is a field curvature graph of the imaging module of FIG. 1 , according to the first exemplary embodiment.

FIG. 4 is a distortion graph of the imaging module of FIG. 1 , according to the first exemplary embodiment.

FIG. 5 is a spherical aberration graph of the imaging module of FIG. 1 , according to a second exemplary embodiment.

FIG. 6 is a field curvature graph of the imaging module of FIG. 1 , according to the second exemplary embodiment.

FIG. 7 is a distortion graph of the imaging module of FIG. 1 , according to the second exemplary embodiment.

Embodiments of the present imaging module and imaging lens system will now be described in detail with reference to the drawings.

Referring to FIG. 1 , the imaging module 100 , according to an exemplary embodiment, is shown. The imaging module 100 includes an imaging lens system 10 and an image sensor 20 . The imaging lens system 10 includes, in the order from the object side to the image side thereof, a first lens 101 , a second lens 102 , a third lens 103 , and a fourth lens 104 . The first lens 101 and the third lens 103 provide positive refraction power. The image sensor 20 is aligned with the imaging lens system 10 and placed at the image side of the imaging lens system 10 . The second lens 102 and the fourth lens 104 provide negative refraction power. The image sensor 20 includes a sensing surface S 11 facing the imaging lens system 10 .

The first lens 101 includes a convex first surface S 1 facing the object side of the image lens system 10 , and a convex second surface S 2 facing the image side of the image lens system 10 . The first and second surfaces S 1 , S 2 are spherical.

The second lens 102 includes a convex third surface S 3 facing the object side of the image lens system 10 , and a concave fourth surface S 4 facing the image side of the image lens system 10 , thereby defining a meniscus shape of the second lens 102 . The third and fourth surfaces S 3 , S 4 are aspherical.

The third lens 103 includes a concave fifth surface S 5 facing the object side of the image lens system 10 , and a convex sixth surface S 6 facing the image side of the image lens system 10 , thereby defining a meniscus shape of the third lens 103 . The fifth and sixth surfaces S 5 , S 6 are aspherical.

The fourth lens 104 includes a convex seventh surface S 7 facing the object side of the image lens system 10 , and a concave eighth surface S 8 facing the image side of the image lens system 10 , thereby defining a meniscus shape of the fourth lens 104 . The seventh and eighth surfaces S 7 , S 8 are aspherical.

In order to obtain an imaging module 100 that has a high resolution and a reduced overall length, the imaging module 100 satisfies the formulas:

2.4 <F 1/ TTL< 3.0,  (1)

−7.0 <F 2/ TTL<− 5.5,  (2)

0.95 <F 3/ TTL< 2.0, and  (3)

−3.5 <F 4/ TTL<− 2.5,  (4)

where TTL is the distance from the first surface S 1 to the sensing surface S 11 on the optical axis of the imaging lens system 10 , F 1 is the focal length of the first lens 101 , F 2 is the focal length of the second lens 102 , F 3 is the focal length of the third lens 103 , and the F 4 is the focal length of the fourth lens 104 .

Formulas (1)-(4) are for reducing overall length of the imaging module 100 .

The imaging module 100 further satisfies the formula: (5) −0.5<R 2 /R 1 <0.5, where R 1 is the radius of curvature of the first surface S 1 , R 2 is the radius of curvature of the second surface S 2 . Formula (5) is for correcting the distortion of the imaging module 100 , and increasing the refractive power of the first lens 101 .

The imaging module 100 further satisfies the formulas: (6) 1.7<EFL/F 1 <2.0, (7) −1.85<EFL/F 2 <−1.5, (8) 1.7<EFL/F 3 <2.0, and (9) −0.4<EFL/F 4 <−0.2, where EFL is the effective focal length of the imaging lens system 10 . Formulas (6)-(9) are for correcting the aberration (i.e., spherical aberration, field curvature, and distortion) of the imaging module 100 .

The imaging module 100 further satisfies the formulas: (10) 1.6<Nd 2 <1.8, and (11) Vd 2 <30, where Nd 2 is the index of refraction of the second lens 102 , Vd 2 is the Abbe number of the second lens 102 . Formulas (10)-(11) are for correcting the chromatic aberration of the imaging module 100 .

The imaging module 100 further satisfies the formula: (12) T 2 <2.5 mm, where T 2 is the distance from the fourth surface S 4 to the fifth surface S 5 on the optical axis of the imaging lens system 10 . Formula (12) is for reducing overall length of the imaging module 100 .

The imaging module 100 further includes an aperture stop 30 . The aperture stop 30 is positioned at the object side of the first lens 101 and is configured to prevent too much off-axis light rays entering the first lens 101 . Also, positioning the aperture stop 30 at the object side of the first lens 101 is beneficial for reducing the overall length of the imaging module 100 .

The imaging module 100 also includes a cover glass 40 , which is positioned between the image lens system 10 and the image sensor 20 for protecting the sensing area (not labeled) of the image sensor 20 . The cover glass 40 includes an object side surface S 9 and an image surface S 10 .

The first lens 101 is made of glass, convenient for correcting the imaging aberration and increasing the resolution of the imaging module 100 . The second lens 102 , the third lens 103 , and fourth lenses 104 can be made of plasticm to reduce cost, and all have two aspherical surfaces (i.e., the aspherical object-side surface and the aspherical image-side surface) to efficiently correct aberrations. The aspherical surface is shaped according to the formula:

x = ch 2 1 + 1 - ( k + 1 ) ⁢ c 2 ⁢ h 2 + ∑ A ⁢ ⁢ i ⁢ ⁢ h i , ⁢

where h is a height from the optical axis of the imaging module 100 to the aspherical surface, c is a vertex curvature, k is a conic constant, and Ai are i-th order correction coefficients of the aspherical surfaces.

Detailed examples of the imaging module 100 are given below in company with FIGS. 2-7 , but it should be noted that the imaging module 100 is not limited by these examples. Listed below are the symbols used in these detailed examples:

TTL: distance from the first surface to the sensing surface on the optical axis of the imaging module;

EFL: effective focal length of the imaging module;

R: radius of curvature;

D: distance between surfaces on the optical axis of the lens;

Nd: refractive index of lens; and

Vd: Abbe constant.

When capturing an image, incident light enters the imaging lens system 10 , sequentially transmits through four lenses 101 , 102 , 103 , 104 , the cover glass 40 , and is finally focused onto the image sensor 20 .

Tables 1, 2 show the lens data of Example 1, wherein TTL=10.1 mm, EFL=7.8 mm.

The spherical aberration graph, the field curvature graph, and the distortion graph of the image module 100 of Example 1 are respectively shown in FIGS. 2˜4 . Spherical aberrations of line f (λ=486 nm) and line d (λ=587 nm) and line c (λ=656 nm) are shown in FIG. 2 . Generally, spherical aberration of visible light (with a wavelength between 400˜700 nm) of the image module 100 in the Example 1 is within a range of −0.05 mm to 0.05 mm. The sagittal field curvature and tangential field curvature shown in FIG. 3 are kept within a range of −0.20 mm to 0.20 mm. The distortion in FIG. 4 falls within a range of −2% to 2%. Obviously, the spherical aberration, field curvature, and distortion are well controlled in the Example 1 of the image module 100 .

Tables 3, 4 show the lens data of EXAMPLE 2, wherein TTL=10.4 mm, EFL=7.7 mm.

The spherical aberration graph, the field curvature graph, and the distortion graph of the image module 100 of Example 2 are respectively shown in FIGS. 5˜7 . Spherical aberrations of line f (λ=486 nm) and line d (λ=587 nm) and line c (λ=656 nm) are shown in FIG. 5 . Generally, spherical aberration of visible light (with a wavelength between 400˜700 nm) of the image module 100 in the Example 1 is within a range of −0.05 mm to 0.05 mm. The sagittal field curvature and tangential field curvature shown in FIG. 6 are kept within a range of −0.10 mm to 0.10 mm. The distortion in FIG. 7 falls within a range of −2% to 2%. Obviously, the spherical aberration, field curvature, and distortion are well controlled in the Example 2 of the image module 100 .

In summary, according to examples 1-2, though the overall length of the imaging module 100 is reduced, aberrations are controlled/corrected within an acceptable range.

It will be understood that the above particular embodiments and methods are shown and described by way of illustration only. The principles and the features of the disclosure may be employed in various and numerous embodiment thereof without departing from the scope of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.