Lens system

1. Technical Field

The disclosure relates to a lens system.

2. Description of Related Art

Where a short overall length is demanded for use in lens module for image acquisition. The lens module is mounted in relatively thin equipment, such as simple digital cameras, webcams for personal computers, and portable imaging systems in general. In order to satisfy this demand of compact lens system, conventional lens systems reduce the number of lenses to shorten the overall length, but this will decrease the resolution. Increasing the number of lenses can increase resolution, but will also increase the overall length of the lens systems.

What is needed, therefore, is a lens system to overcome the above-described problem.

Many aspects of the present disclosure 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 disclosure.

FIG. 1 is a schematic view of a lens system of the present disclosure.

FIGS. 2-4 are graphs respectively showing spherical aberration, field curvature, distortion and lateral chromatic aberration occurring in the lens system of FIG. 1 .

Embodiments of the disclosure will now be described in detail below, with reference to the accompanying drawings.

Referring to FIG. 1 , a lens system 100 of the present disclosure is used for imaging an object to an image plane 40 . The lens system 100 includes, in this order from the object-side to the image-side, a first lens group 10 with negative refraction power, a second lens group 20 with positive refraction power, and a color filter 30 . In the embodiment, the lens system 100 has positive refraction power and a total length of the lens system 100 is 15 mm, and a focal length of the lens system 100 is 2.9 mm.

In the embodiment, the first lens group 10 includes, in order from the object-side to the image-side of the lens system 100 , a first lens 11 having negative refraction power, a second lens 12 having negative refraction power, and a third lens 13 with positive refraction power. In the embodiment, a focal length F 1 of the first lens group 10 is −6.1366 mm; a focal length F 11 of the first lens 11 is −3.685 mm; a focal length F 12 of the second lens 12 is −35.695 mm; a focal length F 13 of the third lens 13 is 8.17585 mm. The first lens 11 includes, in order from the object-side to the image-side of the lens system 100 , a first surface S 1 and a second surface S 2 . The second lens 12 includes, in this order from the object-side to the image-side of the lens system 100 , a third surface S 3 , and a fourth surface S 4 . The third lens 13 includes, in this order from the object-side to the image-side of the lens system 100 , a fifth surface S 5 and a sixth surface S 6 . The first lens 11 and the second lens 12 are spaced from each other, therefore, an opaque plate (not shown) can be sandwiched between the first lens 11 and the second lens 12 for blocking off-axis light rays entering the lens system 100 .

The second lens group 20 has a positive refractive power and includes, in the order from the object-side to the image-side of the lens system 100 , a fourth lens 21 having positive refraction power, a fifth lens 22 , and a sixth lens 23 . In the embodiment, the fifth lens 22 and the sixth lens 23 are attached together to form a single unit. The attached fifth lens 22 and the sixth lens 23 have a positive refraction power. In the embodiment, a focal length F 2 of the second lens group 20 is 3.9915 mm; a focal length F 21 of the fourth lens 21 is 5.84 mm; a focal length F 22 of the adhered fifth lens 22 and sixth lens 23 is 11.846 mm. The fourth lens 21 includes, in this order from the object-side to the image-side of the lens system 100 , a seventh surface S 7 , and an eighth surface S 8 . The fifth lens 22 includes, in this order from the object-side to the image-side of the lens system 100 , a ninth surface S 9 , and a tenth surface S 10 . The sixth lens 23 includes, in this order from the object-side to the image-side of the lens system 100 , the tenth surface S 10 and an eleventh surface S 11 .

The lens system 100 further includes an aperture stop 25 installed between the first lens group 10 and the second lens group 20 . In particular, the aperture stop 25 is installed between the third lens 13 and the fourth lens 21 . The aperture stop 25 adjusts light flux from the first lens group 10 to the second lens group 20 . In addition, the aperture stop 25 facilitates uniform light transmission when light passes through the second lens group 20 to correct coma aberrations of the lens system 100 . To minimize the manufacture cost and the total length of the lens system 100 , the aperture stop 25 can be a black adhesive positioned on a periphery of the seventh surface S 7 of the fourth lens 21 .

The color filter 30 includes, in the order from the object-side to the image-side of the lens system 100 , a twelfth surface S 12 and a thirteenth surface S 13 . The color filter 30 is installed between the sixth lens 23 and the image plane 40 .

In order to obtain low distortion, good imaging quality and a compact configuration, the lens system 100 satisfies the following conditions:

5 <D/F< 5.3;  (1)

wherein, D is a total length of the lens system 100 ; F is a focal length of the lens system 100 . The conditions (1) can favorably limit the relation between the focal length of every lens group and the focal length of the lens system 100 to obtain a high resolution. If the ratio D/F of condition (1) is smaller than 5, the first lens 10 and the second lens 20 are too close to each other. On the other hand, if the ratio D/F of condition (1) is larger than 5.3, the total length D of the lens system 100 tends to be too long. This in turn tends to make the distance from the first surface 11 of the first lens 10 to the image plane too long, which also tends to increase the overall length of the lens system 100 .

In one embodiment, the lens system 100 further satisfies the following condition:

−0.48 <F/F 1<−0.45;  (2)

wherein, F is a focal length of the lens system 100 ; F 1 is a focal length of the first lens group 10 . The conditions (2) can favorably limit the focal length of the first lens group 10 .

In one embodiment, the lens system 100 further satisfies the following condition:

12.1 <|F 12 /F|< 12.6  (3)

wherein, F is a focal length of the lens system 100 ; F 12 is a focal length of the second lens 12 . The conditions (3) can reduce the aberration of the field curvature and spherical aberration in the lens system 100 .

The first lens 11 , the second lens 12 , the third lens 13 , the fourth lens 21 , the fifth lens 22 , and the sixth lens 23 are spherical lenses.

Example diagrams of the lens system 100 will be described below with reference to FIGS. 2-4 . The disclosure is not limited to these examples. The following are symbols used in each exemplary embodiment.

F No : F number;

2ω: field angle;

ri: radius of curvature of the surface Si;

Di: distance between surfaces on the optical axis of the surface Si and the surface Si+1;

Ni: refractive index of the surface Si;

Vi: Abbe constant of the surface Si; and

F: the focal length of the lens system 100 .

Tables 1-2 show the specifications of an embodiment of the lens system 100 .

FIGS. 2-4 , are graphs of aberrations (spherical aberration, field curvature, distortion, and lateral chromatic aberration) of the lens system 100 . In FIG. 2 , curves are spherical aberration characteristic curves of a 1 light (wavelength: 436 nm), a 2 light (wavelength: 486 nm), a 3 light (wavelength: 546 nm), a 4 light (wavelength: 588 nm), and a 5 light (wavelength: 588 nm) of the lens system 100 . The spherical aberration of the lens system 100 of the first exemplary embodiment is from −0.1 mm to 0.1 mm. As illustrated in FIG. 3 , the curves t 1 ˜t 5 and s 1 ˜s 5 are respectively the tangential field curvature curve and the sagittal field curvature curve. The field curvature of the lens system 100 is from −0.5 mm to 0.5 mm. In FIG. 4 , the distortion of the lens system 100 is from −50% to 0%.

In the exemplary embodiment, though the overall length of the lens system 100 is reduced, aberrations of the lens system 100 are maintained within an acceptable range. That is, the lens system 100 keeps chromatic aberrations at a minimum while reducing the total length of the lens system 100 .

Aberrations occurring in the lens system 100 are controlled/corrected to an acceptable level, and changes in aberrations are reduced to acceptable levels as well, accordingly, a high resolution of the lens system 100 is obtained, and maintained over the entire zooming range of the lens system 100 .

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 disclosure is not limited to the particular embodiments described and exemplified, and the embodiments are capable of considerable variation and modification without departure from the scope of the appended claims.