Zoom lens system with wide angle of view   

Abstract: A high zoom ratio wide-angle zoom lens system includes a first lens group comprising a first lens of biconcave, a second lens of positive meniscus, a third lens of biconvex, and a fourth lens of biconvex wherein the first lens and the second lens are lenses not cemented together by adhesive; a second lens group comprising a fifth lens of positive meniscus, a sixth lens of biconcave, a seventh lens of biconvex, and an eighth lens of plano-concave; a third lens group comprising a ninth lens of biconvex; and a fourth lens group comprising a tenth lens of biconvex, an eleventh lens of plano-concave, a twelfth lens of biconvex, and a thirteenth lens of biconcave. The zoom lens system has a wide angle of view of at least 70-degree, high zoom ratio, and other advantages.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to zoom lens systems for compact video cameras, electronic still cameras, digital cameras, etc. and more particularly to such a high zoom ratio wide-angle zoom lens system having a first lens group of positive diopter, a second lens group of negative diopter, a third lens group of positive diopter, and a fourth lens group of positive diopter so as to have a wide angle of view greater than 70 degrees and more than 10× zoom ratio.

2. Description of Related Art

Recently, compact zoom lens systems as the most important component for a compact video camera, an electronic still camera, digital camera, etc. are developed and commercially available. A compact zoom lens has the benefits of decreasing weight and greatly reducing cost. As a result, for example, the size, weight, and unit price of a compact video camera are decreased greatly.

To achieve the above objective, the focus mechanism is moved from the front element (or first element) to the least lens set. It has the benefits of greatly reducing the size of the first lens group so as to achieve the goal of minimizing the zoom lens system. This in turn can decrease power required for focusing. Therefore, a quick focusing can be achieved.

However, aberration of the rear focusing arrangement is not easy to control. This in turn can increase the difficulty of focusing and lower the image quality due to the increase of zooming range.

Moreover, there are a number of drawbacks associated with rear focusing arrangement systems such as lower resolution, limited angle of view (or angle in short), great distortion, somewhat bulky for carry, and inconvenience in use.

For a digital video camera (DVC) having the features of being lightweight and compact, its lens system cannot achieve the goal of having a wide angle (e.g., about 60-degree of angle) due to optical limitations. Further, there is no suggestion in prior art literatures about a high zoom ratio wide-angle zoom lens system having at least 64-degree angle. Thus, the need for improvement still exists.

SUMMARY

It is therefore one object of the invention to provide a high zoom ratio wide-angle zoom lens system comprising a first lens group comprising a first lens of biconcave, a second lens of positive meniscus, a third lens of biconvex, and a fourth lens of biconvex wherein the first lens and the second lens are lenses not cemented together by adhesive; a second lens group comprising a fifth lens of positive meniscus, a sixth lens of biconcave, a seventh lens of biconvex, and an eighth lens of plano-concave; a third lens group comprising a ninth lens of biconvex; and a fourth lens group comprising a tenth lens of biconvex, an eleventh lens of plano-concave, a twelfth lens of biconvex, and a thirteenth lens of aspheric; wherein the zoom lens system satisfies the following conditions (a)-(e): (a): −2 0.03<R1/R2<−1.89; (b): 0.13<fw/f1<0.14; (c): −0.6<fw/f2<−0.53; (d):0.11<fw/f3<0.14; and (e): 0.18<fw/f4<0.21 where R1 is a curvature of a first surface of the first lens, R2 is a curvature of a second surface of the first lens, fw is a focal length of the overall system at a wide angle, f1 is a focal length of the first lens group, f2 is a focal length of the second lens group, f3 is a focal length of the third lens group, and f4 is a focal length of the fourth lens group.

It is another object of the invention to provide a high zoom ratio wide-angle zoom lens system having a wide angle of view greater than 70 degrees and more than 10× zoom ratio. Moreover, the invention is a miniature system so as to greatly decrease size of the image fetching device. Further, the invention can be made of plastic aspheric lenses and conventional glass lenses so as to greatly reduce the manufacturing cost, have a simple construction, and be easy to assemble.

The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts in section of locations of all lenses of a zoom lens system according to the invention;

FIG. 2A schematically depicts in section of locations of the lenses of FIG. 1 at a wide angle according to a first preferred embodiment of the invention;

FIG. 2B plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the first preferred embodiment at the wide angle respectively;

FIG. 2C plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the first preferred embodiment at an intermediate focal length respectively;

FIG. 2D plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the first preferred embodiment at a narrow angle respectively;

FIG. 3A schematically depicts in section of locations of the lenses of FIG. 1 at the wide angle according to a second preferred embodiment of the invention;

FIG. 3B plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the second preferred embodiment at the wide angle respectively;

FIG. 3C plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the second preferred embodiment at the intermediate focal length respectively;

FIG. 3D plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the second preferred embodiment at the narrow angle respectively;

FIG. 4A schematically depicts in section of locations of the lenses of FIG. 1 at the wide angle according to a third preferred embodiment of the invention;

FIG. 4B plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the third preferred embodiment at the wide angle respectively;

FIG. 4C plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the third preferred embodiment at the intermediate focal length respectively;

FIG. 4D plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the third preferred embodiment at the narrow angle respectively;

FIG. 5A schematically depicts in section of locations of the lenses of FIG. 1 at the wide angle according to a fourth preferred embodiment of the invention;

FIG. 5B plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the fourth preferred embodiment at the wide angle respectively;

FIG. 5C plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the fourth preferred embodiment at the intermediate focal length respectively; and

FIG. 5D plots curves of longitudinal spherical aberration versus focal length, astigmatic field curves versus focal length, and a curve of distortion versus focal length according to the fourth preferred embodiment at the narrow angle respectively.

DETAILED DESCRIPTION

Referring to FIG. 1, a high zoom ratio wide-angle zoom lens system in accordance with the invention is shown. The zoom lens system comprises 13 lenses divided into a front first lens group G1, a front second lens group G2 adjacent to the first lens group G1, an intermediate third lens group G3, and a rear fourth lens group G4. The first lens group G1 is of positive diopter, the second lens group G2 is of negative diopter, the third lens group G3 is of positive diopter, and the fourth lens group G4 is of positive diopter. Position of the first lens group G1 is fixed during zooming and focusing. The second lens group G2 that is moved for zooming along the optical axis. Position of the third lens group G3 is fixed during zooming and focusing. The fourth lens group G4 that is moved along the optical axis to correct any shift in the focal position due to zooming.

The first lens group G1 comprises a first lens L1 of biconcave, a second lens L2 of positive meniscus, a third lens L3 of biconvex, and a fourth lens L4 of biconvex. The second lens group G2 comprises a fifth lens L5 of positive meniscus, a sixth lens L6 of biconcave, a seventh lens L7 of biconvex, and an eighth lens L8 of plano-concave. The third lens group G3 comprises a ninth lens L9 of biconvex. Aperture is designated by reference numeral “S” in front of the ninth lens L9. The fourth lens group G4 comprises a tenth lens L10 of biconvex, an eleventh lens L11 of plano-concave, a twelfth lens L12 of biconvex, and a thirteenth lens L13 of biconcave. Preferably, the first lens L1 and the second lens L2 are lenses not cemented together by adhesive.

For achieving the goals of having a wide angle of at least 70-degree and “10×” zoom (“10×” zoom means a zoom lens with focal lengths ranging from 100 mm to 1,000 mm), the zoom lens system of the invention is required to satisfy the following conditions:

−20.03<R1/R2<−1.89;   (a)

0.13<fw/f1<0.14;   (b)

−0.60<fw/f2<−0.53;   (c)

0.11<fw/f3<0.14; and   (d)

0.18<fw/f4<0.21;   (e)

where R1 is a curvature of a first surface of the first lens L1, R2 is a curvature of a second surface of the first lens L2, fw is a focal length of the overall system at a wide angle, f1 is a focal length of the first lens group G1, f2 is a focal length of the second lens group G2, f3 is a focal length of the third lens group G3, and f4 is a focal length of the fourth lens group G4.

Preferably, the seventh and the thirteenth lenses L7, L13 are aspheric lenses. The remaining lenses are conventional glass lenses so as to reduce the production cost. The invention can have a wide angle and an increased ratio of its longest to shortest focal lengths, and can be made compact and has improved image quality because the aspheric lenses can greatly decrease aberration beyond the optical axis. Preferably, the second and third lenses L2, L3 are formed as single lenses and are cemented together by applying adhesive therebetween. Hence, there is no distance between the second and third lenses L2 and L3 so as to facilitate assembly.

Referring to FIGS. 2A to 2D, a high zoom ratio wide-angle zoom lens system in accordance with a first preferred embodiment of the invention is shown. FIG. 2A is similar to FIG. 1 except minor changes in the shapes. Further, distances of some lenses with respect to a reference point along an optical axis are designated by reference numerals d8, d16, d19, and 26. Above is also applied to second to fourth preferred embodiments of the invention as detailed later.

Initial optical data of the first embodiment is Fno=1:4.15-5.33, f=3.85-40.40, and w=36.98°−4.00°

where Fno is the diameter of aperture at a wide angle or at a narrow angle, f is the focal length of the overall system at the wide angle or at the narrow angle, and w is half view angle at the wide angle or at the narrow angle. Specific numerical examples are shown in the following Table 1 in which r is the radius of curvature, d is an axial distance between any two lenses, n is the refractive index, and v is Abbe number which represents a value of chromatic aberration of a material, and v is inversely proportional to the value of chromatic aberration.

TABLE 1 r d n v Surface INFINITY 8000.000000 AIR  1: −65.09 1.00 1.836108 26.3  2: 28.37 2.58  3: −225.87 2.48 1.640601 58.3  4: −50.86 0.10  5: 76.59 2.82 1.731556 54.1  6: −87.75 0.10  7: 27.21 4.22 1.750631 49.7  8: −80.30 d8  9: 29.60 1.00 1.806098 40.9 10: 4.56 2.55 AIR 11: −15.67 1.00 1.799227 41.8 12: 21.96 0.10 13: 10.67 2.98 1.744132 26.6 14: −9.51 0.10 15: −14.49 1.00 1.795994 42.2 16: 47.34 d16 Aperture INFINITY 0.10 18: 24.43 1.39 1.588071 49.0

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