Lens group
[technical field]
The present invention relates to a kind of lens group, refer in particular to a kind of microminiature lens group that is applicable on the digital image products such as mobile phone.
[background technology]
The lens design of early stage camera lens is to adopt the sphere design, that is to say that any one tangent plane all is the part of circular camber line.The reason that adopts sphere is because processing is than being easier to, and can reach higher yield.But sphere is not best suited for the lens shape of optical imagery, because spherical mirror can produce on many spherical aberrations, the axle optical defects such as chromatic dispersion, it is burnt to cause image fog to be lost.And for overcoming above-mentioned aberration, lens design person must use a lot of sheet lens to compensate in camera lens.Therefore, when image quality improves, all corresponding increase of the length of camera lens, external diameter, weight and cost, thus make camera lens become not only big but also heavy.But various in recent years digital image products all develop towards the direction of microminiaturization, but and the taking lens group that is complementary with it also just must be more and more littler, promptly the length overall of lens group will further shorten, therefore above-mentioned design concept can't be used again.
The appearance of aspheric mirror can address the above problem, be applied in the optical system of camera lens, image quality in the time of can increasing substantially camera use large aperture, reduce the barrel distortion of wide-angle lens, and a slice non-spherical lens can substitute several spherical lens aberration for compensation, can simplify the optical design of camera lens very significantly, reduce its volume and weight.
No matter be spherical mirror or aspheric mirror, it is made material and mainly contains glass and plastics, and wherein the light-transmission coefficient of glass lens is bigger, and imaging effect is good, but price is higher, is mainly used in the high-order product; The light-transmission coefficient of plastic lens is less, and is cheap, is mainly used in low end.But because of plastic material is light, and glass material is more thick and heavy, so can adopt plastic lens and the combined mode of glass lens when lens design, learns from other's strong points to offset one's weaknesses whereby, thereby designs needed lens group.
Mobile lens in the market adopts the all-plastic combination of lenses (for example: the pattern of 2P) or (for example: the pattern of 1G2P) the mixing of glass and plastic lens mostly, if adopt 2P (Plastic, plastics) pattern not only influences its optical property, and also relatively stricter to tolerance, so this pattern is difficult to promote the use of; And so-called 1G (Glass, glass) 2P (Plastic, plastics) design type can be with reference to United States Patent (USP) the 6th, 441, the content that is disclosed for No. 971, lens group 90 structures of this patent as shown in Figure 1, it mainly is made up of three lens, order is successively from the object side to the image side: aperture 91, first lens 92, second lens 93, the 3rd lens 94, glass plate 95 and imaging surface 96, wherein first lens 92 are made for crescent lens and by glass material, and its convex surface is towards object space, and its major function is taken imaging as the leading factor, stronger refracting power is provided, and makes not temperature influence of system; Second, third lens 93,94 are made by resin material, and two lens 93,94 all can be aspheric mirror, and its major function is to proofread and correct various aberrations, and escapable cost and dwindle total optical length of lens group 90 simultaneously.But, be used for second, third lens the 93, the 94th of aberration correction, be asymmetric pattern, the eyeglass of this asymmetric pattern can make that assembling position is difficult to proofread and correct, this structure can be joined United States Patent (USP) the 4th, 212, the content that is disclosed for No. 517.In addition,, will inevitably make that the curvature of this glass lens 92 is very big because the main refracting power of the optical system of this lens group 90 is to be provided by first lens 92, and under the very little situation in aperture, totally unfavorable to its processing, thus cause throughput rate to reduce.
Therefore, how to provide a kind of and can be applicable to the good in optical property on the digital image product, total length, easily processing and the loose microminiature lens group of tolerance are the problems that present urgent need will solve.
[summary of the invention]
The object of the present invention is to provide the total length of a kind of optics, easily processing, cost low, and have the microminiature lens group of high imaging quality.
According to above-mentioned purpose of the present invention, the invention provides a kind of lens group, it can be applicable on the digital image product, this lens group include successively from the object side to the image side first lens, with second lens of the first lens symmetry arrangement, and the 3rd lens that are adjacent to picture side, wherein the convex surface of first lens is towards object space, the convex surface of second lens is towards picture side, the concave surface of first, second lens is relatively and establishes, and the 3rd lens towards the radius-of-curvature on the surface of picture side greater than its radius-of-curvature towards the surface of object space.
First, second lens of above-mentioned lens group are to be made and all be crescent by plastic material, and the 3rd lens are to be made by glass material, and two surfaces of the 3rd lens can be to be the biconvex pattern, also can be to be the plano-convex pattern.
First lens and second lens of above-mentioned lens group are non-spherical lens, and it satisfies following aspheric surface formula:
Wherein z be along optical axis direction highly for the position of h with the surface vertices shift value apart from optical axis for referencial use, k is the tapering constant, c represents the inverse of radius-of-curvature, h represents the eyeglass height, A, B, C, D, E are asphericity coefficient.
First, second and third lens of above-mentioned lens group need meet the following conditions:
1.5<-f2/f1<3.5
1.2<f3/f1<1.8
1.73<nd<1.84
42<vd<55
Wherein: f1 is the focal length of first lens, and f2 is the focal length of second lens, and f3 is the focal length of the 3rd lens, and nd is the refractive index of the 3rd lens, and vd is the Abbe number of the 3rd lens.
Compared to prior art, lens group of the present invention is by also all having adopted aspheric design with first, second lens symmetry arrangement in the top of lens group, be easy to aberration correction whereby, shorten the optics length overall of lens group and improve yield, the 3rd glass lens then is positioned over after second lens, it can have larger aperture, be fit to a large amount of production, can avoid the defective of prior art in this way.
[description of drawings]
Fig. 1 is the structural representation of existing lens group.
Fig. 2 is the structural representation of lens group of the present invention.
Fig. 3 A is that lens group of the present invention is according to the formed longitudinal spherical aberration of the first numerical value embodiment.
Fig. 3 B is that lens group of the present invention is according to the formed filed curvature of the first numerical value embodiment.
Fig. 3 C is that lens group of the present invention is according to the formed image field distortion of the first numerical value embodiment.
Fig. 3 D is that lens group of the present invention is according to the formed lateral chromatic aberration of the first numerical value embodiment.
Fig. 4 A is that lens group of the present invention is according to the formed longitudinal spherical aberration of second value embodiment.
Fig. 4 B is that lens group of the present invention is according to the formed filed curvature of second value embodiment.
Fig. 4 C is that lens group of the present invention is according to the formed image field distortion of second value embodiment.
Fig. 4 D is that lens group of the present invention is according to the formed lateral chromatic aberration of second value embodiment.
Fig. 5 A is that lens group of the present invention is according to the formed longitudinal spherical aberration of third value embodiment.
Fig. 5 B is that lens group of the present invention is according to the formed filed curvature of third value embodiment.
Fig. 5 C is that lens group of the present invention is according to the formed image field distortion of third value embodiment.
Fig. 5 D is that lens group of the present invention is according to the formed lateral chromatic aberration of third value embodiment.
[embodiment]
Please refer to the composition structure of lens group of the present invention shown in Figure 2, it includes an aperture 4 and an optical group, wherein optical group mainly is made up of three lens, order is successively from the object side to the image side: first lens 1 are positive lenss, it is crescent plastic lens and the top that is positioned at camera lens, and its convex surface 10 is towards object space; Second lens 2 are negative lenses, and it is also for crescent plastic lens and be symmetry arrangement with first lens 1, and promptly the convex surface 20 of these second lens 2 is towards picture side (imaging surface 6), and its concave surface 21 is then relative with the concave surface 11 of first lens 1 and establish; The 3rd lens 3 are positive lenss, and it is the glass lens of biconvex pattern, and the radius-of-curvature on the surface 30 of the close picture side of the 3rd lens 3 is greater than its radius-of-curvature near the surface 31 of object space; Aperture 4 is with control light amount of incident between first lens 1 and second lens 2.
For obtaining imaging effect preferably, be provided with glass plate 5 being adjacent to imaging surface 6 places, and on glass plate 5, can plate the have certain effect film of (for example: antireflection or infrared ray filter).
Above-mentioned first, second lens the 1, the 2nd are symmetrical in aperture 4, it is similar to Gauss's pattern, is easy to proofread and correct lateral aberration whereby, and utilizes both recoverable aberrations of its aspheric characteristic, can shorten the optics length overall of whole lens group again, thereby obtain the microminiature lens group of a tool high imaging quality.In addition, two symmetric lenses compensate each other, can significantly alleviate the requirement to relative tolerance, help to improve yield, and are applicable to a large amount of productions.
The material of above-mentioned the 3rd lens 3 is a glass, and therefore the requirement to tolerance also is comparatively loose; More can promote the production yield of whole lens group.In addition, because the radius-of-curvature on the surface 30 of the 3rd lens 3 close picture sides is suitable for its coating surface IR film greater than its radius-of-curvature near the surface 31 of object space, and reduce colour cast (color shift) problem.
In a specific embodiment, the focal length ratio of second lens 2 of lens group of the present invention and first lens 1 meets the following conditions:
1.5<-f2/f1<3.5 (1)
Wherein: f1 is the focal length of first lens 1, and f2 is the focal length of second lens 2.
The 3rd lens 3 of lens group of the present invention can be the glass lenss of biconvex pattern, it also can be the glass lens of plano-convex pattern, it has larger aperture, can be fit to adopt many eyeglasses lapping mode to produce in a large number, and the refractive index of the 3rd lens (nd) meets the following conditions:
1.73<nd<1.84 (2)
The Abbe number (vd) of the 3rd lens 3 of lens group of the present invention should meet the following conditions:
42<vd<55 (3)
The 3rd lens 3 of lens group of the present invention and the focal length ratio of first lens 1 meet the following conditions:
1.2<f3/f1<1.8 (4)
Wherein: f3 is the focal length of the 3rd lens 3.
First, second lens 1,2 of the present invention are all along symmetrical, and its convex surface 10,20 and concave surface 11,21 have all adopted aspheric design, in this way aberration correction, shorten the optics length overall of lens group and reduce cost.
The aspheric surface formulate of said lens 1,2 is as follows:
Wherein: z be along optical axis direction highly for the position of h with the surface vertices shift value apart from optical axis for referencial use, and non-spherical lens rotates around optical axis direction by the curved surface by this formula (5) gained and forms; K is the tapering constant; C=1/r, r represents radius-of-curvature; H represents the eyeglass height; A represents four times asphericity coefficient (4th Order Aspherical Coefficient); B represents six times asphericity coefficient (6th OrderAspherical Coefficient); C represents eight times asphericity coefficient (8th Order AsphericalCoefficient); D represents ten times asphericity coefficient (10th Order Aspherical Coefficient); E represents the asphericity coefficient (12th Order Aspherical Coefficient) of ten secondaries.
To illustrate the numerical value embodiment of lens group of the present invention in specific implementation process below, wherein related surperficial sequence number 1,2,3,4,5,6 will be represented the concave surface 11 of the convex surface 10 of first lens 1, first lens 1, the concave surface 21 of second lens 2, the convex surface 20 of second lens 2, wherein another surface 30 of a surface 31, the 3rd lens 3 of the 3rd lens 3 respectively.
The first numerical value embodiment in specific implementation process is as shown in the table for lens group of the present invention:
The surface sequence number |
Radius-of-curvature (mm) (Radius) |
Thickness (mm) (Thickness) |
Refractive index (Nd) |
Abbe coefficient (Vd) |
Conicity (Conic) |
1 |
1.254371 |
1.0 |
1.5435 |
56.8 |
-1 |
2 |
2.891737 |
0.7 |
|
|
-25.70336 |
3 |
-0.8398514 |
0.6 |
1.5854 |
30.0 |
0.4515092 |
4 |
-1.422601 |
0.1 |
|
|
-0.531608 |
5 |
4.534197 |
1.65 |
1.8160 |
46.6 |
0 |
6 |
-67.19731 |
|
|
|
0 |
It is listed that wherein the concrete numerical value of asphericity coefficient can be joined following table:
In the above-mentioned first numerical value embodiment, the focal length ratio that is limited to (4) by relational expression (1) (f2/f1) be 1.657, refractive index (nd) is 1.8160, Abbe number (vd) is 46.6, focal length ratio (f3/f1) is 1.568.Focal length according to the lens group of this first numerical value embodiment gained is 3.88mm, and maximum image height is 2.3mm, and F# equals 3.3, and wherein F# refers to light by the formed effective focal length of infinity incident and the effective ratio of pupil diameter.
In this first numerical value embodiment, the aberration of lens group of the present invention can effectively be proofreaied and correct, shown in Fig. 3 A to Fig. 3 D, wherein the longitudinal spherical aberration shown in Fig. 3 A (Longitudinal Aberration) is to be measured under the situation of 0.6080mm at the pupil radius, and three curves shown in from left to right are respectively to be by wavelength among the figure: 0.486 μ m, 0.588 μ m, 0.656 μ m incident light produced, and in the filed curvature (Field Curvature) shown in Fig. 3 B to Fig. 3 D, image field distortion (Field Distortion) and lateral chromatic aberration curve (Transverse Ray Fan Plot) all are to be that the incident light of 0.588 μ m is produced by wavelength, and are 0.0000mm with gained image height (IMA) also in Fig. 3 D, 1.1500mm, 1.6100mm, 2.3000mm the time the lateral chromatic aberration curve-equipartition do not present.
Second value embodiment in specific implementation process is as shown in the table for lens group of the present invention:
The surface sequence number |
Radius-of-curvature (mm) (Radius) |
Thickness (mm) (Thickness) |
Refractive index (Nd) |
Abbe coefficient (Vd) |
Conicity (Conic) |
1 |
1.302729 |
1 |
1.5435 |
56.8 |
-1 |
2 |
2.455596 |
0.7 |
|
|
-2.688061 |
3 |
-0.9016507 |
0.6 |
1.5854 |
30.0 |
0.462812 |
4 |
-1.292029 |
0.15 |
|
|
0.1123836 |
5 |
4.69296 |
1.087694 |
1.7725 |
49.6 |
0 |
6 |
Infinitely great |
|
|
|
0 |
It is listed that wherein the concrete numerical value of asphericity coefficient can be joined following table:
In above-mentioned second value embodiment, the focal length ratio that is limited to (4) by relational expression (1) (f2/f1) be 3.014, refractive index (nd) is 1.7725, Abbe number (vd) is 49.6, focal length ratio (f3/f1) is 1.553.Focal length according to the lens group of this second value embodiment gained is 3.88mm, and maximum image height is 2.3mm, and F# equals 2.84, and wherein F# refers to light by the formed effective focal length of infinity incident and the effective ratio of pupil diameter.
In this second value embodiment, the aberration of lens group of the present invention can effectively be proofreaied and correct, shown in Fig. 4 A to Fig. 4 D, wherein the longitudinal spherical aberration shown in Fig. 4 A (Longitudinal Aberration) is to be measured under the situation of 0.6937mm at the pupil radius, and three curves shown in from left to right are respectively to be by wavelength among the figure: 0.486 μ m, 0.588 μ m, 0.656 μ m incident light produced, and in the filed curvature (Field Curvature) shown in Fig. 4 B to Fig. 4 D, image field distortion (Field Distortion) and lateral chromatic aberration curve (Transverse Ray Fan Plot) all are to be that the incident light of 0.588 μ m is produced by wavelength, and are 0.0000mm with gained image height (IMA) also in Fig. 4 D, 1.1500mm, 1.6100mm, 2.3000mm the time the lateral chromatic aberration curve map present respectively.
Third value embodiment in specific implementation process is as shown in the table for lens group of the present invention:
The surface sequence number |
Radius-of-curvature (mm) (Radius) |
Thickness (mm) (Thickness) |
Refractive index (Nd) |
Abbe coefficient (Vd) |
Conicity (Conic) |
1 |
1.288 |
1 |
1.5435 |
56.8 |
-1 |
2 |
2.78 |
0.6 |
|
|
-3.790165 |
3 |
-0.846 |
0.6 |
1.5854 |
30.0 |
0.3034489 |
4 |
-1.345 |
0.1 |
|
|
-0.7088952 |
5 |
4.7 |
1.65 |
1.7725 |
49.6 |
0 |
6 |
-18.262 |
|
|
|
0 |
It is listed that wherein the concrete numerical value of asphericity coefficient can be joined following table:
In above-mentioned third value embodiment, the focal length ratio that is limited to (4) by relational expression (1) (f2/f1) be 1.96, refractive index (nd) is 1.7725, Abbe number (vd) is 49.6, focal length ratio (f3/f1) is 1.398.Focal length according to the lens group of this third value embodiment gained is 3.78mm, and maximum image height is 2.3mm, and F# equals 2.86, and wherein F# refers to light by the formed effective focal length of infinity incident and the effective ratio of pupil diameter.
In this third value embodiment, the aberration of lens group of the present invention can effectively be proofreaied and correct, shown in Fig. 5 A to Fig. 5 D, wherein the longitudinal spherical aberration shown in Fig. 5 A (Longitudinal Aberration) is to be measured under the situation of 0.6759mm at the pupil radius, and three curves shown in from left to right are respectively to be by wavelength among the figure: 0.486 μ m, 0.588 μ m, 0.656 μ m incident light produced, and at the filed curvature shown in Fig. 5 B to 5D (Field Curvature), image field distortion (Field Distortion) and lateral chromatic aberration curve (Transverse Ray Fan Plot) all are to be that the incident light of 0.588 μ m is produced by wavelength, and are 0.0000mm with gained image height (IMA) also in Fig. 5 D, 1.1500mm, 1.6100mm, 2.3000mm the time the lateral chromatic aberration curve map present respectively.
Lens group of the present invention designs all according to first, second and third numerical value embodiment can obtain preferable image quality.