Wide-angle zoom lens system

[0001] 1. Technical Field

[0002] The present disclosure relates to wide-angle zoom lens systems and, particularly, to a wide-angle zoom lens system with a high image quality.

[0003] 2. Description of Related Art

[0004] Wide-angle zoom lens systems with a large F number are widely used. However, there are certain challenges in designing such lenses. For example, the amount of light rays entering into the wide-angle zoom increases as the F number of the wide-angle zoom lens system increases, and, as a result, the field curvature, distortion and aberration occurring in the wide-angle zoom lens system will increase, degrading the image quality. Therefore, it is hard to design a wide-angle zoom lens system with a large F number while remaining the image quality at a high level.

[0005] Therefore, it is desirable to provide a wide-angle zoom lens system which can overcome the limitations described above.

[0012] Embodiments of the disclosure will now be described in detail with reference to the accompanying drawings.

[0013] Referring to FIG. 1, a wide-angle zoom lens system 100, according to a first exemplary embodiment, optically captures an image of an object at an object side and forms a corresponding image at an image side. The wide-angle zoom lens system 100 includes, in the 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 third lens group 30 with positive refraction power. During the focusing process, the first lens group 10, the second lens group 20, and the third lens group 30 move along an optical axis of the wide-angle zoom lens system 100. The wide-angle zoom lens system 100 can be set among a wide-angle state and a telephoto state.

[0014] The wide-angle zoom lens system 100 further includes two apertures 40 and a filter glass 50. One of the two apertures 40 is positioned between the first lens group 10 and the second lens group 20, and the other aperture 40 is positioned between the second lens group 20 and the third lens group 30. The filter glass 50 is positioned at the image side of the third lens group 30. Light rays enter the wide-angle zoom 100, passing through the first lens group 10, the first aperture 40, the second lens group 20, the second aperture 40, the third lens group 30, and the filter glass 60, and finally forming optical images on an image surface 60. In this embodiment, the two apertures 40 are fixed together with the second lens group 20. During the focusing process from the wide-angle state to the telephoto state, the distance between the first lens group 10 and the second lens group 20 is decreased, and the distance between the second lens group 20 and the third lens group 30 is increased.

[0015] The first lens group 10 includes, in the order from the object side to the image side of the wide-angle zoom lens system 100, a first lens 11 with negative refraction power and a second lens 12 with negative refraction power. The first lens 11 is aspherical lens, and the second lens 12 is spherical lens. The first lens 11 is meniscus shaped and includes a convex first surface S1 facing the object side, and a concave second surface S2 facing the image side. The second lens 12 is meniscus shaped and includes a convex third surface S3 facing the object side, and a concave fourth surface S4 facing the image side.

[0016] The second lens group 20 includes, in the order from the object side to the image side of the wide-angle zoom lens system 100, a third lens 21 with positive refraction power, a fourth lens 22 with positive refraction power, a fifth lens 23 with negative refraction power, and a sixth lens 24 with positive refraction power. The third lens 21 and the sixth lens 24 are aspherical lenses. The fourth lens 22 and the fifth lens 23 are adhered to a compound spherical lens. The third lens 21 is meniscus shaped and includes a convex fifth surface S5 facing the object side, and a concave sixth surface S6 facing the image side. The fourth lens 22 is meniscus shaped and includes a convex seventh surface S7 facing the object side, and a concave eighth surface S8 facing the image side. The fifth lens 23 is meniscus shaped and includes a convex ninth surface S9 facing the object side, and a concave tenth surface S10 facing the image side. The sixth lens 24 is biconvex shaped and includes a convex eleventh surface S11 facing the object surface, and a convex twelfth surface S12 facing the image surface. In this embodiment, the third lens 21 and the sixth lens 24 are made of plastic material.

[0017] The third lens group 30 includes a seventh lens 31 with positive refraction power. The seventh lens 31 is aspherical lens. The seventh lens 31 is meniscus shaped and includes a convex thirteenth surface S13 facing the object side, and a fourteenth surface S14 facing the image side.

[0018] The filter glass 50 is flat plate shaped, and filters infrared light rays. The filter glass 50 includes a fifteenth surface S15 facing the object side and a sixteenth surface S16 facing the image side.

[0019] The wide-angle zoom lens system 100 satisfies the formulas:
0.77<|f2/f1|<1.1;and  (1)
0.7<L₂/f_T<1.08;  (2)
wherein f1 is the effective focal length of the first lens group 10, f2 is the effective focal length of the second lens group 20, L₂ is a distance of the second lens group 20 moving from the wide-angle state to the telephoto state, and f_T is the effective focal length of the wide-angle zoom lens system 100 in the telephoto state. Formulas (1) and (2) are for correcting the aberrations of the wide-angle zoom lens system 100 with a large F number. If f2 is too short, the spherical aberration and the chromatic aberration of the wide-angle zoom lens system 100 will be very serious, and it is difficult to correct the aberrations using fourth lenses of second lens group 20; if f1 is too short, the distortion of the wide-angle zoom lens system 100 in the wide-angle state will be very serious. If f2 and f1 are too long, the total length of the wide-angle zoom lens system 100 will be increased, the thickness and cost of the wide-angle zoom lens system 100 also will be increased. If the moving distance of the second lens group 200 is too long, the thickness of the wide-angle zoom lens system 100 will be increased; if the moving distance is too short, f2 will be decreased and the spherical aberration and the chromatic aberration of the wide-angle zoom lens system 100 will be increased.

[0020] The wide-angle zoom lens system 100 further satisfies the formula:
1.2<f3/f2<2.85;  (3)
wherein f3 is the effective focal length of the third lens group 30. Formula (3) is for ensuring the success rate during focusing of the wide-angle zoom lens system 100. If f3 is too long, the wide-angle zoom lens system 100 will need a longer time to focus; if f3 is too short, the focus accuracy of the wide-angle zoom lens system 100 will be decreased.

[0021] The wide-angle zoom lens system 100 further satisfies the formula:
1.02<N2/N1<1.15;  (4)
Wherein N1 is the refractive index for the Helium d-line (587.56 nm) of the first lens 11 and N2 is the refractive index for the Helium d-line (587.56 nm) of the second lens 12. Formula (4) is for decreasing the field curvature of the wide-angle zoom lens system 100, and ensuring resolution of the edge and center of images during focusing.

[0022] The wide-angle zoom lens system 100 further satisfies the formulas:
2<V1/V2<2.7;and  (5)
1.5<V4/V5<3.8;  (6)
Wherein V1 is the Abbe number of the first lens 11, V2 is the Abbe number of the second lens 12, V4 is the Abbe number of the fourth lens 22, and V5 is the Abbe number of the fifth lens 23. Formulas (5) and (6) are for correcting the lateral chromatic aberration in the wide-angle state and the axial chromatic aberration in the telephoto state.

[0023] The wide-angle zoom lens system 100 further satisfies the formula:
0.7<T2/IH<1.1;  (7)
wherein T2 is the thickness of the second lens group 20 (the distance between the fifth surface S5 to the twelfth surface S12 along the optical axis of the wide-angle zoom lens system 100), IH is the diagonal distance of the image surface 60. Formula (7) is for decreasing the total length of the wide-angle zoom lens system 100.

[0024] The above aspherical surfaces are shaped according to the formula:

[0025] $x=\frac{{\mathrm{ch}}^2}{1+\sqrt{1-\left(k+1\right)c^2{h}^2}}+\sum {\mathrm{Aih}}^i$
wherein h is a height from the optical axis of the wide-angle zoom lens system 100 to a point of 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.

[0026] The following symbols are used:

[0027] R: radius of curvature,

[0028] D: distance between surfaces on the optical axis,

[0029] Nd: refractive index for the Helium d-line (587.56 nm) of lens,

[0030] Vd: Abbe number,

[0031] F: effective focal length of the wide-angle zoom lens system 100,

[0032] F_No: F number of the wide-angle zoom lens system 100,

[0033] FOV: filed angle of the wide-angle zoom lens system 100,

[0034] D4: distance between the fourth surface S4 to the adjacent aperture 40,

[0035] D13: distance between the adjacent aperture 40 to the thirteenth surface S13, and

[0036] D15: distance between the fourteenth surface S14 to the fifteenth surface S15.

[0037] The wide-angle zoom lens system 100 of the first exemplary embodiment satisfies the parameters of Tables 1-3.

[0038]

TABLE 1
surface	type	R(mm)	D(mm)	Nd	Vd	Conic
S1	aspherical	33.23615	1.1	1.85	40.1	−155.4779
S2	aspherical	5.858257	2.996	—	—	−3.66469
S3	spherical	11.054	1.61	1.92	18.9	—
S4	spherical	17.765	D4	—	—	—
40	flat	infinity	0	—	—	—
S5	aspherical	7.879887	1.533	1.85	40.1	−1.165794
S6	aspherical	33.57481	0.15	—	—	−62.16694
S7	spherical	5.428	1.747	1.5	81.6	—
S8/S9	spherical	11.759	0.5	1.85	23.8	—
S10	spherical	4.097	1.291	—	—	—
S11	aspherical	13.49798	1.016	1.55	71.7	11.76189
S12	aspherical	−21.00109	0.35	—	—	7.540376
40	flat	infinity	D13	—	—	—
S13	aspherical	8.331137	1.046	1.59	67	0
S14	spherical	14.54401	D15	—	—	0
S15	flat	infinity	0.8	1.52	64.2	—
S16	flat	infinity	0.7	—	—	—
60	flat	infinity	—	—	—	—

[0039]

TABLE 2
state	F	FNo	FOV	D4	D13	D15
wide-angle state	4.43	1.85	82.7	21.586	5.178	1.925
middle state	11.85	3.4	37.3	4.2	12.422	1.918
telephoto state	19.38	4.9	22.7	0.3	20.137	1.384

[0040]

TABLE 3
aspherical
coefficient	S1	S2	S5	S6	S11	S12	S13
A4	3.4259447e−005	0.0013388716	−3.7050473e−005	−5.4781716e−005	−0.0005581762	9.7424366e−005	−0.00031134224
A6	8.1020403e−007	−2.6978714e−005	−2.9912444e−006	−3.3588524e−006	−2.0165384e−005	−1.8559437e−005	8.0553982e−005
A8	−6.2352271e−008	6.6781619e−007	−3.895784e−007	−1.1463657e−006	1.6104361e−005	1.7242832e−005	−9.8779272e−006
A10	1.5589202e−009	−1.451814e−008	−5.5037686e−008	−4.6574324e−008	−3.4456356e−006	−3.1078458e−006	5.9552217e−007
A12	−1.7699116e−011	2.2366997e−010	−2.5910532e−009	−9.5078298e−010	0	0	−6.097194e−009
A14	7.4736094e−014	−3.1811676e−013	1.89106e−010	−2.9803345e−010	0	0	−8.1241883e−010
A16	−6.0668527e−017	−3.4140808e−014	−1.7254343e−011	1.0850019e−011	0	0	2.4487334e−011

[0041] In the first embodiment, f2/f1=0.828; L2/fT=0.744; f3/f2=2.83; N2/N1=1.038; V1/V2=2.21; V4/V5=3.43; T2/IH=0.8.

[0042] The aberration graph, the field curvature graph, and the distortion graph of the wide-angle zoom lens system 100 in the wide angle state are respectively shown in FIGS. 2-4. The curves presented in the FIGS. 2-4 are F light rays (wavelength: 486 nm), d light rays (wavelength: 588 nm), c light rays (wavelength: 655 nm). The aberration of visible light in FIG. 2 is within a range of −0.30 mm to 0.30 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 −20% to 0%. Obviously, the aberration, field curvature, and distortion are well controlled in the wide-angle zoom lens system 100.

[0043] The aberration graph, the field curvature graph, and the distortion graph of the wide-angle zoom lens system 100 in the telephoto state are respectively shown in FIGS. 5-7. The curves presented in the FIGS. 5-7 are F light rays (wavelength: 486 nm), d light rays (wavelength: 588 nm), c light rays (wavelength: 655 nm). The aberration of visible light in FIG. 5 is within a range of −0.30 mm to 0.30 mm. The sagittal field curvature and tangential field curvature shown in FIG. 6 are kept within a range of −0.20 mm to 0.20 mm. The distortion in FIG. 7 falls within a range of 0% to 3%. Obviously, the aberration, field curvature, and distortion are well controlled in the wide-angle zoom lens system 100.

[0044] Referring to FIG. 8, a wide-angle zoom lens system 100a according to a second exemplary embodiment is shown. The wide-angle zoom lens system 100a is essentially similar to the wide-angle zoom lens system 100, except that: the first surface S1, the sixth surface S6, the eleventh surface S11, and the thirteenth surface S13 are spherical surface, the fourteenth surface S14 are aspherical surfaces. The wide-angle zoom lens system 100a of the second exemplary embodiment satisfies the parameters of Tables 4-6.

[0045]

TABLE 4
surface	type	R(mm)	D(mm)	Nd	Vd	Conic
S1	spherical	−92.56602	1.1	1.77	49.2	0
S2	aspherical	6.489363	2.803	—	—	−0.4054246
S3	spherical	13.35	1.947	2	19.3	—
S4	spherical	28.134	D4	—	—	—
40	flat	infinity	0	—	—	—
S5	aspherical	8.718527	2.001	1.53	55.8	−0.4527443
S6	spherical	151.2296	0.15	—	—	0
S7	spherical	7.501	2.092	1.9	31.3	—
S8/S9	spherical	16.719	0.5	1.95	18	—
S10	spherical	5.727	1.801	—	—	—
S11	spherical	22.9114	1.017	1.53	55.8	0
S12	aspherical	−289.0291	0.35	—	—	0
40	flat	infinity	D13	—	—	—
S13	spherical	13.74286	1.476	1.61	26.6	0
S14	aspherical	−47.32361	D15	—	—	0
S15	flat	infinity	0.8	1.52	64.2	—
S16	flat	infinity	0.7	—	—	—
60	flat	infinity	—	—	—	—

[0046]

TABLE 5
state	F	FNo	FOV	D4	D13	D15
wide-angle state	4.43	1.85	82.7	28.62	6.895	2.748
middle state	11.85	3.4	36.2	9.322	17.726	2.415
telephoto state	19.37	4.9	22.2	5.005	28.042	1.723

[0047]

TABLE 6
aspherical
coefficient	S2	S5	S12	S14
A4	−0.00018812206	3.3838022e−005	0.00044422499	0.00040448117
A6	−6.4928506e−006	−1.4398007e−005	3.6452778e−006	−5.210592e−005
A8	3.0675209e−007	2.9750016e−006	9.8725587e−007	4.5693916e−006
A10	−8.615231e−009	−3.3123912e−007	−3.1513374e−008	−1.0144265e−007
A12	6.7778718e−012	2.0728688e−008	0	−1.173982e−008
A14	2.8869676e−012	−6.7791745e−010	0	8.1030444e−010
A16	−3.3347841e−014	9.0152281e−012	0	−1.4821344e−011

[0048] In the second exemplary embodiment, f2/f1=1.05; L2/fT=1.039; f3/f2=1.254; N2/N1=1.13; V1/V2=2.55; V4/V5=1.739; T2/IH=0.97.

[0049] The aberration graph, the field curvature graph, and the distortion graph of the wide-angle zoom lens system 100a in the wide angle state are respectively shown in FIGS. 9-11. The curves presented in the FIGS. 9-11 are F light rays (wavelength: 486 nm), d light rays (wavelength: 588 nm), c light rays (wavelength: 655 nm). The aberration of visible light in FIG. 9 is within a range of 0 mm to 0.30 mm. The sagittal field curvature and tangential field curvature shown in FIG. 10 are kept within a range of 0 mm to 0.20 mm. The distortion in FIG. 11 falls within a range of −20% to 0%. Obviously, the aberration, field curvature, and distortion are well controlled in the wide-angle zoom lens system 100a.

[0050] The aberration graph, the field curvature graph, and the distortion graph of the wide-angle zoom lens system 100a in the telephoto state are respectively shown in FIGS. 12-14. The curves presented in the FIGS. 12-14 are F light rays (wavelength: 486 nm), d light rays (wavelength: 588 nm), c light rays (wavelength: 655 nm). The aberration of visible light in FIG. 12 is within a range of −0.30 mm to 0.30 mm. The sagittal field curvature and tangential field curvature shown in FIG. 13 are kept within a range of −0.20 mm to 0.20 mm. The distortion in FIG. 14 falls within a range of 0% to 3%. Obviously, the aberration, field curvature, and distortion are well controlled in the wide-angle zoom lens system 100a.

[0051] Particular embodiments are shown and described by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiments thereof without departing from the scope of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.