A wide-conversion lens, in order from the object-side to the image-side, includes a first lens with negative refraction power, a second lens with negative refraction power, a third lens with positive refraction power, a fourth lens with positive refraction power, and a fifth lens with negative refraction power. The first lens includes a surface facing the object side. The wide-conversion lens satisfies the following conditions: R1<0; Vd−Vd1≧19; Vd2−Vd3≧35. Wherein, R1 is the curvature radius of the surface of the first lens; Vd1 is the Abbe number of the first lens; Vd2 is the Abbe number of the second lens; Vd3 is the Abbe number of the third lens.

BACKGROUND

1. Technical Field

The disclosure relates to a lens system and, particularly, to a wide-conversion lens having a small number of lens components and a short overall length.

2. Description of Related Art

A short overall length is demanded for use in wide-conversion lens for image acquisition. The wide-conversion lens 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 wide-conversion lens, conventional wide-conversion lens 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 wide-conversion lens.

What is needed, therefore, is a wide-conversion lens to overcome the limitations described above.

DETAILED DESCRIPTION

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

FIG. 1, is a wide-conversion lens100including, in order from the object-side to the image-side, a first lens L1with negative refraction power, a second lens L2with negative refraction power, a third lens L3with positive refraction power, a fourth lens L4with positive refraction power, and a fifth lens L5with negative refraction power. In the embodiment, a total length of the wide-conversion lens100is 43.7 mm, and a zoom magnification is 0.66.

The first lens L1is glass lens having biconcave shape. The first lens L1includes, in order from the object-side to the image-side of the wide-conversion lens100, a first surface S1facing the object side and a second surface S2facing the image side.

The second lens L2is glass lens having biconcave shape. The second lens L2includes, in order from the object-side to the image-side of the wide-conversion lens100, a third surface S3facing the object side and a fourth surface S4facing the image side.

The third lens L3and the second lens L2are attached together to form a single unit. The third lens L3is glass lens having biconvex shape. The third lens L3includes, in order from the object-side to the image-side of the wide-conversion lens100, the fourth surface S4and a fifth surface S5facing the image side.

The fourth lens L4is glass lens having biconvex shape. The fourth lens L4includes, in order from the object-side to the image-side of the wide-conversion lens100, a sixth surface S6and a seventh surface S7facing the image side.

The fifth lens L5and the fourth lens L4are attached together to form a single unit. The fifth lens L5is glass lens having meniscus shape. The fifth lens L5includes, in order from the object-side to the image-side of the wide-conversion lens100, the seventh surface S7and a convex eighth surface S8facing the image side.

In order to obtain low distortion, good imaging quality, a compact configuration, and wide angle view, the wide-conversion lens100satisfies the following conditions:
R1<0;  (1)
Vd2−Vd1≧19;  (2)
Vd2−Vd3≧35;  (3)

wherein, R1 is the curvature radius of the first surface S1of the first lens L1; Vd1is the Abbe number of the first lens L1; Vd2is the Abbe number of the second lens L2; Vd3is the Abbe number of the third lens L3.

The conditions (1)-(3) can favorably limit the relation between the focal length of every lens group and the focal length of the lens system100to obtain a high resolution. When the conditions Vd2−Vd1≧19 and Vd2−Vd3≧35 are met, chromatic aberrations are effectively reduced and imaging performance is improved.

In one embodiment, the wide-conversion lens100further satisfies the following condition:
0.5≦f1/f2≦1;  (4)

wherein, f1is a focal length of the first lens L1; f2is a focal length of the second lens L2. The condition (4) can reduce the aberration of the field curvature and spherical aberration in the wide-conversion lens100.

Example diagrams of the wide-conversion lens100will be described below with reference toFIGS. 2-5. The disclosure is not limited to these examples. The following are symbols used in each exemplary embodiment.

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

Table 1 shows the specifications of a first embodiment of the wide-conversion lens100.

In the embodiment, the focal length f1of the first lens L1is −58.6 mm, the focal length f2of the second lens L2is −75.78 mm.

FIGS. 2-3, are graphs of aberration (spherical aberration) of the wide-conversion lens100. InFIG. 2, curves are spherical aberration characteristic curves of a1 light (wavelength: 436 nm), a2 light (wavelength: 486 nm), a3 light (wavelength: 546 nm), a4 light (wavelength: 588 nm), and a5 light (wavelength: 588 nm) of the lens system100. The axes spherical aberration of wide-conversion lens100of the first exemplary embodiment is from −0.002 mm to 0.002 mm. As illustrated inFIG. 3, the vertical axes spherical aberration of wide-conversion lens100of the first exemplary embodiment is from −0.005 mm to 0.005 mm.

Aberrations occurring in the wide-conversion lens100are controlled/corrected to an acceptable level, and changes in aberrations are reduced to acceptable levels as well, accordingly, a high resolution of the wide-conversion lens100is obtained, and wide angle view of the wide-conversion lens100is also obtained.

Table 2 shows the specifications of a second embodiment of the wide-conversion lens100.

In the embodiment, the focal length f1of the first lens L1is −66.52 mm, the focal length f2of the second lens L2is −87.05 mm.

FIGS. 4-5, are graphs of aberration (spherical aberration) of the wide-conversion lens100. InFIG. 4, curves are spherical aberration characteristic curves of a1 light (wavelength: 436 nm), a2 light (wavelength: 486 nm), a3 light (wavelength: 546 nm), a4 light (wavelength: 588 nm), and a5 light (wavelength: 588 nm) of the lens system100. The axes spherical aberration of wide-conversion lens100of the second exemplary embodiment is from −0.002 mm to 0.002 mm. As illustrated inFIG. 5, the vertical axes spherical aberration of wide-conversion lens100of the second exemplary embodiment is from −0.005 mm to 0.005 mm.

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.