Lens assembly

A lens assembly includes a front lens group and a rear lens group. The front lens group includes a first lens having positive refractive power and a second lens having negative refractive power. The rear lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, wherein the third lens includes a convex surface facing an object side and another convex surface facing an image side and the fourth lens includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: 13.5 mm<f+f1<20 mm; wherein f is an effective focal length of the lens assembly and f1 is an effective focal length of the first lens.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of China Patent Application No. 201910217203.9, filed on Mar. 21, 2019, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a lens assembly.

Description of the Related Art

The current development trend of a lens assembly is toward miniaturization. Additionally, the lens assembly is developed to have light weight and high resolution in accordance with different application requirements. However, the known lens assembly can't satisfy such requirements. Therefore, the lens assembly needs a new structure in order to meet the requirements of miniaturization, light weight, and high resolution at the same time.

BRIEF SUMMARY OF THE INVENTION

The invention provides a lens assembly to solve the above problems. The lens assembly of the invention is provided with characteristics of a shortened total lens length, a reduced weight, an increased resolution, and still has a good optical performance.

The lens assembly in accordance with an exemplary embodiment of the invention includes a front lens group and a rear lens group. The front lens group includes a first lens having positive refractive power and a second lens having negative refractive power. The rear lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, wherein the third lens includes a convex surface facing an object side and another convex surface facing an image side and the fourth lens includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: 13.5 mm<f+f1<20 mm; wherein f is an effective focal length of the lens assembly and f1is an effective focal length of the first lens.

The lens assembly in accordance with another exemplary embodiment of the invention includes a front lens group and a rear lens group. The front lens group includes a first lens having positive refractive power and a second lens having negative refractive power. The rear lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, wherein the third lens includes a convex surface facing an object side and another convex surface facing an image side and the fourth lens includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: 60<Vd3+Vd4<80; wherein Vd3is an Abbe number of the third lens and Vd4is an Abbe number of the fourth lens.

In another exemplary embodiment, the lens assembly satisfies: 9.5 mm<f+f3<13 mm; 2 mm<f+f4<4 mm; wherein f is an effective focal length of the lens assembly, f3is an effective focal length of the third lens, and f4is an effective focal length of the fourth lens.

In yet another exemplary embodiment, the lens assembly satisfies: 60<Vd3+Vd4<80; 0.5<f/TTL<0.8; wherein Vd3is an Abbe number of the third lens, Vd4is an Abbe number of the fourth lens, f is an effective focal length of the lens assembly, and TTL is an interval from an object side surface of the first lens to an image plane along the optical axis.

In another exemplary embodiment, the lens assembly satisfies: 0.1<|f/fF|<0.6; 0.2<|(fR−f)/f|<1.5; wherein f is an effective focal length of the lens assembly, fFis an effective focal length of the front lens group, and fRis an effective focal length of the rear lens group.

In yet another exemplary embodiment, the lens assembly satisfies: 0.1<|fR/fF|<1.5; wherein fFis an effective focal length of the front lens group and fRis an effective focal length of the rear lens group.

In another exemplary embodiment, the lens assembly further includes a stop disposed between the front lens group and the rear lens group, and the lens assembly is a fixed-focus lens assembly.

In yet another exemplary embodiment, the second lens includes a concave surface facing the object side and another concave surface facing the image side and the fourth lens further includes a concave surface facing the object side.

In another exemplary embodiment, the first lens includes a convex surface facing the object side and another convex surface facing the image side.

In yet another exemplary embodiment, the first lens includes a convex surface facing the object side and a concave surface facing the image side.

In another exemplary embodiment, the front lens group includes an aspheric lens and the rear lens group includes an aspheric lens.

In yet another exemplary embodiment, the lens assembly satisfies: 0.5<f/TTL<0.8; 0.1<|f/fF|<0.6; 0.2<|(fR−f)/f|<1.5; 0.1<|fR/fF|<1.5; wherein f is an effective focal length of the lens assembly, fFis an effective focal length of the front lens group, fRis an effective focal length of the rear lens group, and TTL is an interval from the convex surface of the first lens to an image plane along the optical axis.

In another exemplary embodiment, the first lens includes a convex surface facing the object side and a concave surface facing the image side, the second lens includes a concave surface facing the object side and another concave surface facing the image side, and the fourth lens further includes a concave surface facing the object side.

In yet another exemplary embodiment, the first lens includes a convex surface facing the object side and another convex surface facing the image side, the second lens includes a concave surface facing the object side and another concave surface facing the image side, and the fourth lens further includes a concave surface facing the object side.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a lens assembly including a front lens group and a rear lens group. The front lens group includes a first lens having positive refractive power and a second lens having negative refractive power. The rear lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, wherein the third lens includes a convex surface facing an object side and another convex surface facing an image side and the fourth lens includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: 13.5 mm<f+f1<20 mm; wherein f is an effective focal length of the lens assembly and f1is an effective focal length of the first lens.

The present invention provides another lens assembly including a front lens group and a rear lens group. The front lens group includes a first lens having positive refractive power and a second lens having negative refractive power. The rear lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, wherein the third lens includes a convex surface facing an object side and another convex surface facing an image side and the fourth lens includes a concave surface facing the image side. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side along an optical axis. The lens assembly satisfies: 60<Vd3+Vd4<80; wherein Vd3is an Abbe number of the third lens and Vd is an Abbe number of the fourth lens.

Referring to Table 1, Table 2, Table 4, Table 5, Table 7, and Table 8, wherein Table 1, Table 4, and Table 7 show optical specifications in accordance with a first, second, and third embodiments of the invention respectively and Table 2, Table 5, and Table 8 show aspheric coefficients of each aspheric lens in Table 1, Table 4, and Table 7 respectively.

FIG.1,FIG.3, andFIG.5are lens layout diagrams of the lens assemblies in accordance with the first, second, and third embodiments of the invention respectively. The front lens groups LG1F, LG2F, LG3Finclude the first lenses L11, L21, L31and the second lenses L12, L22, L32respectively. The rear lens groups LG1R, LG2R, LG3Rinclude the third lenses L13, L23, L33and the fourth lenses L14, L24, L34respectively.

The first lenses L11, L21, L31are with positive refractive power and made of plastic material, wherein the object side surfaces S11, S21, S31and the image side surfaces S12, S22, S32are aspheric surfaces.

The second lenses L12, L22, L32are with negative refractive power and made of plastic material, wherein the object side surfaces S13, S23, S33and the image side surfaces S14, S24, S34are aspheric surfaces.

The third lenses L13, L23, L33are with positive refractive power and made of plastic material, wherein the object side surfaces S16, S26, S36are convex surfaces and the image side surfaces S17, S27, S37are convex surfaces.

The fourth lenses L14, L24, L34are with negative refractive power and made of plastic material, wherein the image side surfaces S19, S29, S39are concave surfaces and the object side surfaces S18, S28, S38and the image side surfaces S19, S29, S39are aspheric surfaces.

wherein f is an effective focal length of the lens assemblies1,2,3for the first to third embodiments, f1is an effective focal length of the first lenses L11, L21, L31for the first to third embodiments, f3is an effective focal length of the third lenses L3, L23, L33for the first to third embodiments, f4is an effective focal length of the fourth lenses L14, L24, L34for the first to third embodiments, Vd3is an Abbe number of the third lenses L13, L23, L33for the first to third embodiments, Vd4is an Abbe number of the fourth lenses L14, L24, L34for the first to third embodiments, TTL is an interval from the object side surfaces S11, S21, S31of the first lenses L11, L21, L31to the image planes IMA1, IMA2, IMA3along the optical axises OA1, OA2, OA3for the first to third embodiments, fFis an effective focal length of the front lens groups LG1F, LG2F, LG3Ffor the first to third embodiments, and fRis an effective focal length of the rear lens groups LG1R, LG2R, LG3Rfor the first to third embodiments. With the lens assemblies1,2,3satisfying at least one of the above conditions (1)-(8), the total lens length can be effectively shortened, the weight can be effectively reduced, the resolution can be effectively increased, the chromatic aberration can be effectively corrected, and the aberration can be effectively corrected.

A detailed description of a lens assembly in accordance with a first embodiment of the invention is as follows. Referring toFIG.1, the lens assembly1includes a front lens group LG1F, a stop ST1, and a rear lens group LG1R, all of which are arranged in order from an object side to an image side along an optical axis OA1. The front lens group LG1Fincludes a first lens L11and a second lens L12. The rear lens group LG1Rincludes a third lens L13and a fourth lens L14. In operation, an image of light rays from the object side is formed at an image plane IMA1. The lens assembly1is a fixed-focus lens assembly, wherein the front lens group LG1F, the stop ST1, and the rear lens group LG1Rcan be moved along the optical axis OA1for focusing.

As described above, wherein: the first lens L11is a meniscus lens, wherein the object side surface S11is a convex surface and the image side surface S12is a concave surface; the second lens L12is a biconcave lens, wherein the object side surface S13is a concave surface and the image side surface S14is a concave surface; the third lens L13is a biconvex lens, wherein the object side surface S16and the image side surface S17are spherical surfaces; and the fourth lens L14is a biconcave lens, wherein the object side surface S18is a concave surface.

With the above design of the lenses and stop ST1and at least any one of the conditions (1)-(8) satisfied, the lens assembly1can have an effective shortened total lens length, an effective reduced weight, an effective increased resolution, an effective corrected chromatic aberration, and is capable of an effective corrected aberration.

Table 1 shows the optical specification of the lens assembly1inFIG.1.

The aspheric surface sag z of each aspheric lens in table 1 can be calculated by the following formula:
z=ch2/{1+[1−(k+1)c2h2]1/2}+Ah4+Bh6+Ch8+Dh10+Eh12
where c is curvature, h is the vertical distance from the lens surface to the optical axis, k is conic constant and A, B, C, D and E are aspheric coefficients.

In the first embodiment, the conic constant k and the aspheric coefficients A, B, C, D, E of each aspheric lens are shown in Table 2.

Table 3 shows the parameters and condition values for conditions (1)-(8) in accordance with the first embodiment of the invention. It can be seen from Table 3 that the lens assembly1of the first embodiment satisfies the conditions (1)-(8).

By the above arrangements of the lenses and stop ST1, the lens assembly1of the first embodiment can meet the requirements of optical performance as seen inFIGS.2A-2C.

It can be seen fromFIG.2Athat the longitudinal aberration in the lens assembly1of the first embodiment ranges from −0.002 mm to 0.002 mm.

It can be seen fromFIG.2Bthat the field curvature of tangential direction and sagittal direction in the lens assembly1of the first embodiment ranges from −0.015 mm to 0.005 mm.

It can be seen fromFIG.2Cthat the distortion in the lens assembly1of the first embodiment ranges from 0% to 2.1%.

It is obvious that the longitudinal aberration, the field curvature, and the distortion of the lens assembly1of the first embodiment can be corrected effectively. Therefore, the lens assembly1of the first embodiment is capable of good optical performance.

Referring toFIG.3,FIG.3is a lens layout diagram of a lens assembly in accordance with a second embodiment of the invention. The lens assembly2includes a front lens group LG2F, a stop ST2, and a rear lens group LG2R, all of which are arranged in order from an object side to an image side along an optical axis OA2. The front lens group LG2Fincludes a first lens L21and a second lens L22. The rear lens group LG2Rincludes a third lens L23and a fourth lens L24. In operation, an image of light rays from the object side is formed at an image plane IMA2. The lens assembly2is a fixed-focus lens assembly, wherein the front lens group LG2F, the stop ST2, and the rear lens group LG2Rcan be moved along the optical axis OA2for focusing.

As described above, wherein: the first lens L21is a biconvex lens, wherein the object side surface S21is a convex surface and the image side surface S22is a convex surface; the second lens L22is a biconcave lens, wherein the surface profiles of the second lens L22approximate to that of the second lens L12of the lens assembly1of the first embodiment, and is not described here again; the third lens L23is a biconvex lens, wherein the object side surface S26and the image side surface S27are aspheric surfaces; and the fourth lens L24is a biconcave lens, wherein the surface profiles of the fourth lens L24approximate to that of the fourth lens L14of the lens assembly1of the first embodiment, and is not described here again.

With the above design of the lenses and stop ST2and at least any one of the conditions (1)-(8) satisfied, the lens assembly2can have an effective shortened total lens length, an effective reduced weight, an effective increased resolution, an effective corrected chromatic aberration, and is capable of an effective corrected aberration.

Table 4 shows the optical specification of the lens assembly2inFIG.3.

The definition of aspheric surface sag z of each aspheric lens in table 4 is the same as that of in Table 1, and is not described here again.

In the second embodiment, the conic constant k and the aspheric coefficients A, B, C, D, E of each aspheric lens are shown in Table 5.

Table 6 shows the parameters and condition values for conditions (1)-(8) in accordance with the second embodiment of the invention. It can be seen from Table 6 that the lens assembly2of the second embodiment satisfies the conditions (1)-(8).

By the above arrangements of the lenses and stop ST2, the lens assembly2of the second embodiment can meet the requirements of optical performance as seen inFIGS.4A-4C.

It can be seen fromFIG.4Athat the longitudinal aberration in the lens assembly2of the second embodiment ranges from −0.005 mm to 0.02 mm.

It can be seen fromFIG.4Bthat the field curvature of tangential direction and sagittal direction in the lens assembly2of the second embodiment ranges from −0.015 mm to 0.00 mm.

It can be seen fromFIG.4Cthat the distortion in the lens assembly2of the second embodiment ranges from 0% to 2.8%.

It is obvious that the longitudinal aberration, the field curvature, and the distortion of the lens assembly2of the second embodiment can be corrected effectively. Therefore, the lens assembly2of the second embodiment is capable of good optical performance.

Referring toFIG.5,FIG.5is a lens layout diagram of a lens assembly in accordance with a third embodiment of the invention. The lens assembly3includes a front lens group LG3F, a stop ST3, and a rear lens group LG3R, all of which are arranged in order from an object side to an image side along an optical axis OA3. The front lens group LG3Fincludes a first lens L31and a second lens L32. The rear lens group LG3Rincludes a third lens L33and a fourth lens L34. In operation, an image of light rays from the object side is formed at an image plane IMA3. The lens assembly3is a fixed-focus lens assembly, wherein the front lens group LG3F, the stop ST3, and the rear lens group LG3Rcan be moved along the optical axis OA3for focusing.

As described above, wherein: the first lens L31is a biconvex lens, wherein the object side surface S31is a convex surface and the image side surface S32is a convex surface; the second lens L32is a biconcave lens, wherein the surface profiles of the second lens L32approximate to that of the second lens L12of the lens assembly1of the first embodiment, and is not described here again; the third lens L33is a biconvex lens, wherein the object side surface S36and the image side surface S37are aspheric surfaces; and the fourth lens L34is a biconcave lens, wherein the surface profiles of the fourth lens L34approximate to that of the fourth lens L14of the lens assembly1of the first embodiment, and is not described here again.

With the above design of the lenses and stop ST3and at least any one of the conditions (1)-(8) satisfied, the lens assembly3can have an effective shortened total lens length, an effective reduced weight, an effective increased resolution, an effective corrected chromatic aberration, and is capable of an effective corrected aberration.

Table 7 shows the optical specification of the lens assembly3inFIG.5.

The definition of aspheric surface sag z of each aspheric lens in table 7 is the same as that of in Table 1, and is not described here again.

In the third embodiment, the conic constant k and the aspheric coefficients A, B, C, D, E of each aspheric lens are shown in Table 8.

Table 9 shows the parameters and condition values for conditions (1)-(8) in accordance with the third embodiment of the invention. It can be seen from Table 9 that the lens assembly3of the third embodiment satisfies the conditions (1)-(8).

By the above arrangements of the lenses and stop ST3, the lens assembly3of the third embodiment can meet the requirements of optical performance as seen inFIGS.6A-6C.

It can be seen fromFIG.6Athat the longitudinal aberration in the lens assembly3of the third embodiment ranges from −0.006 mm to 0.010 mm.

It can be seen fromFIG.6Bthat the field curvature of tangential direction and sagittal direction in the lens assembly3of the third embodiment ranges from −0.03 mm to 0.005 mm.

It can be seen fromFIG.6Cthat the distortion in the lens assembly3of the third embodiment ranges from 0% to 3.5%.

It is obvious that the longitudinal aberration, the field curvature, and the distortion of the lens assembly3of the third embodiment can be corrected effectively. Therefore, the lens assembly3of the third embodiment is capable of good optical performance.