Miniature telephoto lens assembly

Abstract

An optical lens assembly includes five lens elements and provides a TTL/EFL<1.0. In an embodiment, the focal length of the first lens element f1<TTL/2, an air gap between first and second lens elements is smaller than half the second lens element thickness, an air gap between the third and fourth lens elements is greater than TTL/5 and an air gap between the fourth and fifth lens elements is smaller than about 1.5 times the fifth lens element thickness. All lens elements may be aspheric.

Claims

1. A lens assembly mounted on an image sensor in a lens system, the lens assembly comprising: a plurality of refractive lens elements arranged along an optical axis and comprising, in order from an object side to an image side, a first lens element with a focal length f1 and positive refractive power, a second lens element with a focal length f2 and negative refractive power, a third lens element with a focal length f3, a fourth lens element and a fifth lens element, wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm, wherein the first lens element has an Abbe number greater than 50 and the second lens element has an Abbe number smaller than 30, wherein the lens system includes an optical window positioned between the plurality of lens elements and the image sensor and has a total track length (TTL) of 6.5 millimeters or less, wherein either f1, f2 and f3 fulfil the condition 1.2×|f3|>|f2|>1.5×f1 or f1<TTL/2, wherein the lens system has an effective focal length (EFL) of 7 mm or less, wherein at least one surface of at least one lens element is aspheric, wherein adjacent lens elements are separated by an air gap and wherein a maximal air gap between lens elements is greater than TTL/5, wherein the image sensor has a half diagonal of 3.0 mm or less, wherein the lens assembly provides a field of view (FOV) of 44 degrees or less on the image sensor, and wherein the lens assembly has an f number F# smaller than 2.9.

2. The lens assembly of claim 1, wherein a minimal air gap between lens elements is smaller than TTL/20.

3. The lens assembly of claim 1, wherein the third lens element has a negative refractive power.

4. The lens assembly claim 1, wherein the third, fourth and fifth lens element are made of plastic.

5. The lens assembly of claim 1, wherein all the lens elements are made of plastic.

6. The lens assembly of claim 1, wherein the first lens element has a convex object-side surface and a convex or concave image-side surface and wherein the second lens element is a meniscus lens having a convex object-side surface.

7. The lens assembly of claim 1, wherein one of the fourth and the fifth lens elements has a positive refractive power and the other of the fourth and fifth lens elements has a negative refractive power, wherein one of the fourth and fifth lens elements is characterized by an Abbe number smaller than 30 and wherein the other of the fourth and fifth lens elements is characterized by an Abbe number greater than 50.

8. The lens assembly of claim 1, wherein the maximal air gap is between the third and fourth lens elements.

9. The lens assembly of claim 2, wherein the minimal air gap is between the first and second lens elements.

10. A lens assembly mounted on an image sensor in a lens system, the lens assembly comprising: a plurality of refractive lens elements arranged along an optical axis and comprising, in order from an object side to an image side, a first lens element with a focal length f1 and positive refractive power, a second lens element with a focal length f2 and negative refractive power, and a third lens element with a focal length f3, wherein the first lens element has a convex object-side surface and a convex or concave image-side surface and wherein the second lens element is a meniscus lens having a convex object-side surface, wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm, wherein the first lens element has an Abbe number greater than 50 and the second lens element has an Abbe number smaller than 30, wherein the lens system includes an optical window positioned between the plurality of lens elements and the image sensor and has a total track length (TTL) of 6.5 millimeters or less, wherein either f1, f2 and f3 fulfil the condition 1.2×|f3|>|f2|>1.5×f1 or f1<TTL/2, wherein the lens system has an effective focal length (EFL) of 7 mm or less, wherein at least one surface of at least one lens element is aspheric, wherein the image sensor has a half diagonal of 3.0 mm or less, wherein the lens assembly provides a field of view (FOV) of 44 degrees or less on the image sensor, and wherein the lens assembly has an f number F# smaller than 2.9.

11. The lens assembly of claim 10, wherein a minimal air gap between lens elements is smaller than TTL/20.

12. The lens assembly of claim 10, wherein the third lens element has a negative refractive power.

13. The lens assembly claim 10, wherein the third, fourth and fifth lens element are made of plastic.

14. The lens assembly of claim 10, wherein all the lens elements are made of plastic.

15. The lens assembly of claim 10, wherein one of the fourth and the fifth lens elements has a positive refractive power and the other of the fourth and fifth lens elements has a negative refractive power, wherein one of the fourth and fifth lens elements is characterized by an Abbe number smaller than 30 and wherein the other of the fourth and fifth lens elements is characterized by an Abbe number greater than 50.

16. The lens assembly of claim 10, wherein adjacent lens elements are separated by an air gap and wherein a maximal air gap between lens elements is greater than TTL/5.

17. The lens assembly of claim 11, wherein the minimal air gap is between the first and second lens elements.

18. The lens assembly of claim 16, wherein the maximal air gap is between the third and fourth lens elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows a first embodiment of an optical lens system disclosed herein;

(2) FIG. 1B shows the modulus of the optical transfer function (MTF) vs. focus shift of the entire optical lens assembly for various fields in the first embodiment;

(3) FIG. 1C shows the distortion vs. field angle (+Y direction) in percent in the first embodiment;

(4) FIG. 2A shows a second embodiment of an optical lens system disclosed herein;

(5) FIG. 2B shows the MTF vs. focus shift of the entire optical lens assembly for various fields in the second embodiment;

(6) FIG. 2C shows the distortion +Y in percent in the second embodiment;

(7) FIG. 3A shows a third embodiment of an optical lens system disclosed herein;

(8) FIG. 3B shows the MTF vs. focus shift of the entire optical lens system for various fields in the third embodiment;

(9) FIG. 3C shows the distortion +Y in percent in the third embodiment.

DETAILED DESCRIPTION

(10) In the following description, the shape (convex or concave) of a lens element surface is defined as viewed from the respective side (i.e. from an object side or from an image side). FIG. 1A shows a first embodiment of an optical lens system disclosed herein and marked 100. FIG. 1B shows the MTF vs. focus shift of the entire optical lens system for various fields in embodiment 100. FIG. 1C shows the distortion +Y in percent vs. field. Embodiment 100 comprises in order from an object side to an image side: an optional stop 101; a first plastic lens element 102 with positive refractive power having a convex object-side surface 102a and a convex or concave image-side surface 102b; a second plastic lens element 104 with negative refractive power and having a meniscus convex object-side surface 104a, with an image side surface marked 104b; a third plastic lens element 106 with negative refractive power having a concave object-side surface 106a with an inflection point and a concave image-side surface 106b; a fourth plastic lens element 108 with positive refractive power having a positive meniscus, with a concave object-side surface marked 108a and an image-side surface marked 108b; and a fifth plastic lens element 110 with negative refractive power having a negative meniscus, with a concave object-side surface marked 110a and an image-side surface marked 110b. The optical lens system further comprises an optional glass window 112 disposed between the image-side surface 110b of fifth lens element 110 and an image plane 114 for image formation of an object. Moreover, an image sensor (not shown) is disposed at image plane 114 for the image formation.

(11) In embodiment 100, all lens element surfaces are aspheric. Detailed optical data is given in Table 1, and the aspheric surface data is given in Table 2, wherein the units of the radius of curvature (R), lens element thickness and/or distances between elements along the optical axis and diameter are expressed in mm. “Nd” is the refraction index. The equation of the aspheric surface profiles is expressed by:

(12) $z=\frac{{\mathrm{cr}}^2}{1+\sqrt{1-\left(1+k\right)c^2{r}^2}}+{\alpha }_1{r}^2+{\alpha }_2{r}^4+{\alpha }_3{r}^6+{\alpha }_4{r}^8+{\alpha }_5{r}^{10}+{\alpha }_6{r}^{12}+{\alpha }_7{r}^{14}$
where r is distance from (and perpendicular to) the optical axis, k is the conic coefficient, c=1/R where R is the radius of curvature, and a are coefficients given in Table 2. In the equation above as applied to embodiments of a lens assembly disclosed herein, coefficients α.sub.1 and α.sub.7 are zero. Note that the maximum value of r “max r”=Diameter/2. Also note that Table 1 (and in Tables 3 and 5 below), the distances between various elements (and/or surfaces) are marked “Lmn” (where m refers to the lens element number, n=1 refers to the element thickness and n =2 refers to the air gap to the next element) and are measured on the optical axis z, wherein the stop is at z=0. Each number is measured from the previous surface. Thus, the first distance −0.466 mm is measured from the stop to surface 102a, the distance L11 from surface 102a to surface 102b (i.e. the thickness of first lens element 102) is 0.894 mm, the gap L12 between surfaces 102b and 104a is 0.020 mm, the distance L21 between surfaces 104a and 104b (i.e. thickness d.sub.2 of second lens element 104) is 0.246 mm, etc. Also, L21=d.sub.2 and L51=d.sub.5. L11 for lens element 102 is indicated in FIG. 1A. Also indicated in FIG. 1A is a width L1e of a flat circumferential edge (or surface) of lens element 102. L11 and L1e are also indicated for each of first lens elements 202 and 302 in, respectively, embodiments 200 (FIG. 2A) and 300 (FIG. 3A).

(13) TABLE-US-00001 TABLE 1 Radius R Distances Diameter # Comment [mm] [mm] Nd/Vd [mm] 1 Stop Infinite −0.466 2.4 2 L11 1.5800 0.894 1.5345/57.095 2.5 3 L12 −11.2003 0.020 2.4 4 L21 33.8670 0.246 1.63549/23.91  2.2 5 L22 3.2281 0.449 1.9 6 L31 −12.2843 0.290 1.5345/57.095 1.9 7 L32 7.7138 2.020 1.8 8 L41 −2.3755 0.597 1.63549/23.91  3.3 9 L42 −1.8801 0.068 3.6 10 L51 −1.8100 0.293 1.5345/57.095 3.9 11 L52 −5.2768 0.617 4.3 12 Window Infinite 0.210 1.5168/64.17  3.0 13 Infinite 0.200 3.0

(14) TABLE-US-00002 TABLE 2 Conic coefficient # k α.sub.2 α.sub.3 α.sub.4 α.sub.5 α.sub.6 2 −0.4668   7.9218E−03   2.3146E−02 −3.3436E−02   2.3650E−02 −9.2437E−03 3 −9.8525   2.0102E−02   2.0647E−04   7.4394E−03 −1.7529E−02   4.5206E−03 4 10.7569 −1.9248E−03   8.6003E−02   1.1676E−02 −4.0607E−02   1.3545E−02 5 1.4395   5.1029E−03   2.4578E−01 −1.7734E−01   2.9848E−01 −1.3320E−01 6 0.0000   2.1629E−01   4.0134E−02   1.3615E−02   2.5914E−03 −1.2292E−02 7 −9.8953   2.3297E−01   8.2917E−02 −1.2725E−01   1.5691E−01 −5.9624E−02 8 0.9938 −1.3522E−02 −7.0395E−03   1.4569E−02 −1.5336E−02   4.3707E−03 9 −6.8097 −1.0654E−01   1.2933E−02   2.9548E−04 −1.8317E−03   5.0111E−04 10 −7.3161 −1.8636E−01   8.3105E−02 −1.8632E−02   2.4012E−03 −1.2816E−04 11 0.0000 −1.1927E−01   7.0245E−02 −2.0735E−02   2.6418E−03 −1.1576E−04

(15) Embodiment 100 provides a field of view (FOV) of 44 degrees, with EFL=6.90 mm, F#=2.80 and TTL of 5.904 mm. Thus and advantageously, the ratio TTL/EFL=0.855. Advantageously, the Abbe number of the first, third and fifth lens element is 57.095. Advantageously, the first air gap between lens elements 102 and 104 (the gap between surfaces 102b and 104a) has a thickness (0.020 mm) which is less than a tenth of thickness d.sub.2 (0.246 mm). Advantageously, the Abbe number of the second and fourth lens elements is 23.91. Advantageously, the third air gap between lens elements 106 and 108 has a thickness (2.020 mm) greater than TTL/5 (5.904/5 mm). Advantageously, the fourth air gap between lens elements 108 and 110 has a thickness (0.068 mm) which is smaller than 1.5d.sub.5 (0.4395 mm).

(16) The focal length (in mm) of each lens element in embodiment 100 is as follows: f1=2.645, f2=−5.578, f3=−8.784, f4=9.550 and f5=−5.290. The condition 1.2×|f3|>|f2|<1.5×f1 is clearly satisfied, as 1.2×8.787>5.578>1.5×2.645. f1 also fulfills the condition f1<TTL/2, as 2.645<2.952.

(17) Using the data from row #2 in Tables 1 and 2, L1e in lens element 102 equals 0.297 mm, yielding a center-to-edge thickness ratio L11/L1e of 3.01.

(18) FIG. 2A shows a second embodiment of an optical lens system disclosed herein and marked 200. FIG. 2B shows the MTF vs. focus shift of the entire optical lens system for various fields in embodiment 200. FIG. 2C shows the distortion +Y in percent vs. field. Embodiment 200 comprises in order from an object side to an image side: an optional stop 201; a first plastic lens element 202 with positive refractive power having a convex object-side surface 202a and a convex or concave image-side surface 202b; a second glass lens element 204 with negative refractive power, having a meniscus convex object-side surface 204a, with an image side surface marked 204b; a third plastic lens element 206 with negative refractive power having a concave object-side surface 206a with an inflection point and a concave image-side surface 206b; a fourth plastic lens element 208 with positive refractive power having a positive meniscus, with a concave object-side surface marked 208a and an image-side surface marked 208b; and a fifth plastic lens element 210 with negative refractive power having a negative meniscus, with a concave object-side surface marked 110a and an image-side surface marked 210b. The optical lens system further comprises an optional glass window 212 disposed between the image-side surface 210b of fifth lens element 210 and an image plane 214 for image formation of an object.

(19) In embodiment 200, all lens element surfaces are aspheric. Detailed optical data is given in Table 3, and the aspheric surface data is given in Table 4, wherein the markings and units are the same as in, respectively, Tables 1 and 2. The equation of the aspheric surface profiles is the same as for embodiment 100.

(20) TABLE-US-00003 TABLE 3 Radius R Distances Diameter # Comment [mm] [mm] Nd/Vd [mm] 1 Stop Infinite −0.592 2.5 2 L11 1.5457 0.898  1.53463/56.18 2.6 3 L12 −127.7249 0.129 2.6 4 L21 6.6065 0.251  1.91266/20.65 2.1 5 L22 2.8090 0.443 1.8 6 L31 9.6183 0.293  1.53463/56.18 1.8 7 L32 3.4694 1.766 1.7 8 L41 −2.6432 0.696 1.632445/23.35 3.2 9 L42 −1.8663 0.106 3.6 10 L51 −1.4933 0.330  1.53463/56.18 3.9 11 L52 −4.1588 0.649 4.3 12 Window Infinite 0.210  1.5168/64.17 5.4 13 Infinite 0.130 5.5

(21) TABLE-US-00004 TABLE 4 Conic coefficient # k α.sub.2 α.sub.3 α.sub.4 α.sub.5 α.sub.6 2 0.0000 −2.7367E−03   2.8779E−04 −4.3661E−03   3.0069E−03 −1.2282E−03 3 −10.0119   4.0790E−02 −1.8379E−02   2.2562E−02 −1.7706E−02   4.9640E−03 4 10.0220   4.6151E−02   5.8320E−02 −2.0919E−02 −1.2846E−02   8.8283E−03 5 7.2902   3.6028E−02   1.1436E−01 −1.9022E−02   4.7992E−03 −3.4079E−03 6 0.0000   1.6639E−01   5.6754E−02 −1.2238E−02 −1.8648E−02   1.9292E−02 7 8.1261   1.5353E−01   8.1427E−02 −1.5773E−01   1.5303E−01 −4.6064E−02 8 0.0000 −3.2628E−02   1.9535E−02 −1.6716E−02 −2.0132E−03   2.0112E−03 9 0.0000   1.5173E−02 −1.2252E−02   3.3611E−03 −2.5303E−03   8.4038E−04 10 −4.7688 −1.4736E−01   7.6335E−02 −2.5539E−02   5.5897E−03 −5.0290E−04 11 0.00E+00 −8.3741E−02   4.2660E−02 −8.4866E−03   1.2183E−04   7.2785E−05

(22) Embodiment 200 provides a FOV of 43.48 degrees, with EFL=7 mm, F#=2.86 and TTL=5.90 mm. Thus and advantageously, the ratio TTL/EFL=0.843. Advantageously, the Abbe number of the first, third and fifth lens elements is 56.18. The first air gap between lens elements 202 and 204 has a thickness (0.129 mm) which is about half the thickness d.sub.2 (0.251 mm). Advantageously, the Abbe number of the second lens element is 20.65 and of the fourth lens element is 23.35. Advantageously, the third air gap between lens elements 206 and 208 has a thickness (1.766 mm) greater than TTL/5 (5.904/5 mm). Advantageously, the fourth air gap between lens elements 208 and 210 has a thickness (0.106 mm) which is less than 1.5×d.sub.5 (0.495 mm).

(23) The focal length (in mm) of each lens element in embodiment 200 is as follows: f1=2.851, f2=−5.468, f3=−10.279, f4=7.368 and f5=−4.536. The condition 1.2×|f3|>|f2|<1.5×f1 is clearly satisfied, as 1.2×10.279>5.468>1.5×2.851. f1 also fulfills the condition f1<TTL/2, as 2.851<2.950.

(24) Using the data from row #2 in Tables 3 and 4, L1e in lens element 202 equals 0.308 mm, yielding a center-to-edge thickness ratio L11/L1e of 2.916.

(25) FIG. 3A shows a third embodiment of an optical lens system disclosed herein and marked 300. FIG. 3B shows the MTF vs. focus shift of the entire optical lens system for various fields in embodiment 300. FIG. 3C shows the distortion +Y in percent vs. field. Embodiment 300 comprises in order from an object side to an image side: an optional stop 301; a first glass lens element 302 with positive refractive power having a convex object-side surface 302a and a convex or concave image-side surface 302b; a second plastic lens element 204 with negative refractive power, having a meniscus convex object-side surface 304a, with an image side surface marked 304b; a third plastic lens element 306 with negative refractive power having a concave object-side surface 306a with an inflection point and a concave image-side surface 306b; a fourth plastic lens element 308 with positive refractive power having a positive meniscus, with a concave object-side surface marked 308a and an image-side surface marked 308b; and a fifth plastic lens element 310 with negative refractive power having a negative meniscus, with a concave object-side surface marked 310a and an image-side surface marked 310b. The optical lens system further comprises an optional glass window 312 disposed between the image-side surface 310b of fifth lens element 310 and an image plane 314 for image formation of an object.

(26) In embodiment 300, all lens element surfaces are aspheric. Detailed optical data is given in Table 5, and the aspheric surface data is given in Table 6, wherein the markings and units are the same as in, respectively, Tables 1 and 2. The equation of the aspheric surface profiles is the same as for embodiments 100 and 200.

(27) TABLE-US-00005 TABLE 5 Radius R Distances Diameter # Comment [mm] [mm] Nd/Vd [mm] 1 Stop Infinite −0.38 2.4 2 L11 1.5127 0.919 1.5148/63.1  2.5 3 L12 −13.3831 0.029 2.3 4 L21 8.4411 0.254 1.63549/23.91  2.1 5 L22 2.6181 0.426 1.8 6 L31 −17.9618 0.265 1.5345/57.09  1.8 7 L32 4.5841 1.998 1.7 8 L41 −2.8827 0.514 1.63549/23.91  3.4 9 L42 −1.9771 0.121 3.7 10 L51 −1.8665 0.431 1.5345/57.09  4.0 11 L52 −6.3670 0.538 4.4 12 Window Infinite 0.210 1.5168/64.17  3.0 13 Infinite 0.200 3.0

(28) TABLE-US-00006 TABLE 6 Conic coefficient # k α.sub.2 α.sub.3 α.sub.4 α.sub.5 α.sub.6 2 −0.534   1.3253E−02   2.3699E−02 −2.8501E−02   1.7853E−02 −4.0314E−03 3 −13.473   3.0077E−02   4.7972E−03   1.4475E−02 −1.8490E−02   4.3565E−03 4 −10.132   7.0372E−04   1.1328E−01   1.2346E−03 −4.2655E−02   8.8625E−03 5 5.180 −1.9210E−03   2.3799E−01 −8.8055E−02   2.1447E−01 −1.2702E−01 6 0.000   2.6780E−01   1.8129E−02 −1.7323E−02   3.7372E−02 −2.1356E−02 7 10.037   2.7660E−01 −1.0291E−02 −6.0955E−02   7.5235E−02 −1.6521E−02 8 1.703   2.6462E−02 −1.2633E−02 −4.7724E−04 −3.2762E−03   1.6551E−03 9 −1.456   5.7704E−03 −1.8826E−02   5.1593E−03 −2.9999E−03   8.0685E−04 10 −6.511 −2.1699E−01   1.3692E−01 −4.2629E−02   6.8371E−03 −4.1415E−04 11 0.000 −1.5120E−01   8.6614E−02 −2.3324E−02   2.7361E−03 −1.1236E−04

(29) Embodiment 300 provides a FOV of 44 degrees, EFL=6.84 mm, F#=2.80 and TTL=5.904 mm. Thus and advantageously, the ratio TTL/EFL=0.863. Advantageously, the Abbe number of the first lens element is 63.1, and of the third and fifth lens elements is 57.09. The first air gap between lens elements 302 and 304 has a thickness (0.029 mm) which is about 1/10.sup.th the thickness d.sub.2 (0.254 mm). Advantageously, the Abbe number of the second and fourth lens elements is 23.91. Advantageously, the third air gap between lens elements 306 and 308 has a thickness (1.998 mm) greater than TTL/5 (5.904/5 mm). Advantageously, the fourth air gap between lens elements 208 and 210 has a thickness (0.121 mm) which is less than 1.5d.sub.5 (0.6465 mm).

(30) The focal length (in mm) of each lens element in embodiment 300 is as follows: f1=2.687, f2=−6.016, f3=−6.777, f4=8.026 and f5=−5.090. The condition 1.2×|f3|>|f2|<1.5×f1 is clearly satisfied, as 1.2×6.777>6.016>1.5×2.687. f1 also fulfills the condition f1<TTL/2, as 2.687<2.952.

(31) Using the data from row #2 in Tables 5 and 6, L1e in lens element 302 equals 0.298 mm, yielding a center-to-edge thickness ratio L11/L1e of 3.08.

(32) While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.