LOW TOTAL TRACK LENGTH FOR LARGE SENSOR FORMAT

Description

FIELD

[0001] Embodiments disclosed herein relate to optical lenses, and more particularly, to miniature lens assemblies.BACKGROUND

[0002] Digital camera modules are now standard in a variety of host devices. Such host devices include cellular telephones (smartphones), personal data assistants (PDAs), computers, and so forth. Cameras in smartphones in particular require a compact imaging lens system for good quality imaging and with a small total track length (TTL) relative to the size of the image sensor in such cameras. The image sensor size can always be expressed by the sensor diagonal, SDL.

[0003] Documents US 2018 / 149835 A1, US 2016 / 241756 A1, CN 104 570 280 A, US 2016 / 033742 A1, US 2019 / 025549 A1 and TW I 664 468 B disclose conventional lens assemblies.SUMMARY

[0004] The invention is defined in the appended independent claim 1. Further embodiments are defined in the dependent claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein and should not be considered limiting in any way. In the drawings: FIG. 1 shows an exemplary embodiment of a lens assembly disclosed herein.DETAILED DESCRIPTION

[0006] FIG. 1 shows an embodiment of an optical lens system disclosed herein and numbered 100. Embodiment 100 comprises in order from an object side to an image side a plurality of lens elements (here exemplarily seven lens elements numbered L1-L7) with a common optical axis 102. The lens further comprises three aperture stops marked S1 and two blocking surfaces S8 and S9. Lens element surfaces are marked "Si", with S2 marking an object side surface of first lens element L1 and S18 marking an image side of lens element L7. Lens 100 further comprises an optional glass window 104 disposed between surface S18 and an image sensor 106 for image formation of an object. Image sensor 106 has a size characterized by an image sensor diagonal SDL.

[0007] The TTL is defined as the distance from the S 1 to the image sensor. FIG. 1 also shows a back focal length (BFL), defined as the distance from the last surface of the last lens element S 2N to the image sensor.

[0008] For convenience in some equations and relations presented below, lens element surfaces are also marked "LO i " on the object side surface of lens element number i and "LI i " on the image side surface of lens element number i.Surface types

[0009] Surface types are defined in Table 1 and the coefficients for the surfaces are in Table 2: a) Plano: flat surfaces, no curvature b) Q type 1 (QT1) surface sag formula: z r = cr 2 1 + 1 − 1 + k c 2 r 2 + D con u D con u = u 4 ∑ n = 0 N A n Q n con u 2 u = r r norm , x = u 2 Q 0 con x = 1 Q 1 con = − 5 − 6 x Q 2 con = 15 − 14 x 3 − 2 x Q 3 con = − 35 − 12 x 14 − x 21 − 10 x Q 4 con = 70 − 3 x 168 − 5 x 84 − 11 x 8 − 3 x Q 5 con = − 126 − x 1260 − 11 x 420 − x 720 − 13 x 45 − 14 x where {z, r} are the standard cylindrical polar coordinates, c is the paraxial curvature of the surface, k is the conic parameter, r norm is generally one half of the surface's clear aperture, and A n are the polynomial coefficients shown in lens data tables. z - axis is positive towards image.

[0010] In this specification, the term "RMO i " refers to the aperture radius of a surface LOi. The term "RMI i " refers to the aperture radius of a surface LI i .

[0011] In this specification, the term "normal thickness" (NT) is a function of r marked NT i (r), and refers to the distance between the two surfaces of a lens element at coordinate r along the normal vector of the surface closer to object. Several functions and constants are defined per normal thickness: For r=0, NT i (r=0) is defined as the central thickness (CT) of lens element i (CT i ) A "thickness average" (T_AVG i ) constant is given by: T _ AVG i = 1 N ∑ k = 0 N NT i k ⋅ RMO i N where k is a discrete variable that runs from 0 to N, where N is an integer >10 (for this and all other functions and constants below).

[0012] A normalized thickness standard deviation (T_STD i ) constant is given by: T _ STD i = 1 RMO i 1 N ∑ k = 0 N NT i k ⋅ RMO i N − T _ AVG i 2 where k is a discrete variable that runs from 0 to N, and where T_AVGi is defined as in (Eq.2).

[0013] In this specification, a "gap" or an "air gap" refers to the space between consecutive lens elements. Several functions and constants per gap are defined: A "Gapi(r)" function (for r = 0, an "on-axis gap" OA_Gap i ) is defined as the thickness LI i Gapi(r) = OA_Gapi + z(r) of LI i - z(r) of LO i+1 , where z(r) is it standard polar coordinate z. OA_Gapi(r=0) of LI i is the air thickness which is the air gap for r=0. A "gap average" (G_AVGi) constant is given by: G _ AVG i = 1 N ∑ k = 0 N Gap i k ⋅ Rmin i N where k is a discrete variable that runs from 0 to N, where N is an integer >10, and where Rmin i is the minimum aperture radius value of surfaces {RMI i , RMO i+1 };

[0014] A normalized gap standard deviation (G_STD i ) constant is given by: G _ STD i = 1 Rmin i 1 N ∑ k = 0 N Gap i k ⋅ Rmin i N − G _ AVG i 2 and G_AVG i is defined as in (Eq.4). Table 1EFL=6.75 mm, F# = 1.80, HFOV = 41.0 deg.Surface #CommentTypeCurvature RadiusCentral ThicknessAperture Radius (D / 2)MaterialIndexAbbe #Focal Length f1A.SPlanoInfinity-0.9081.8802L 1 QT12.3310.9651.910Plastic1.5455.96.5535.7440.0321.8004L 2 QT14.8280.2081.790Plastic1.6719.4-13.8853.1220.2891.6306L 3 QT15.1310.4521.620Plastic1.5455.917.40710.8340.1101.5308StopPlanoInfinity0.0801.4709StopPlanoInfinity0.3831.48010L 4 QT1-725.0520.3581.620Plastic1.6719.4-55.341139.028-0.2901.90012StopPlanoInfinity0.7601.90513L 5 QT116.2470.2812.150Plastic1.5737.4308.741417.80.6312.36015L 6 QT13.6280.5033.180Plastic1.6028.311.50167.2051.2953.42017L 7 QT1-4.6840.3694.500Plastic1.5455.9-4.97186.6120.3664.74019FilterPlanoInfinity0.21006.600Glass1.5264.220Infinity0.30006.60021ImagePlanoInfinity-6.200* Units are in mm except for index and Abbe #. HFOV indicates half field of view *Reference wavelength is 587.6 mm (d-line) Table 2 Aspheric CoefficientsSurface #R norm A4A6A8A1021.9329.9940E-03-4.7500E-03-2.9987E-03-9.0698E-0431.9328.7490E-026.5977E-022.4979E-021.6077E-0241.8471.1859E-026.3506E-029.9150E-046.1490E-0351.6775.3358E-025.0530E-02-3.1217E-03-1.4993E-0361.6664.9696E-025.5310E-021.6953E-025.2611E-0371.610-1.3866E-022.8507E-021.4152E-026.3734E-03101.717-4.2084E-01-4.7698E-02-1.6836E-02-9.1824E-03111.972-4.8789E-012.9587E-022.9227E-029.8845E-03132.107-8.3702E-01-4.1159E-022.3372E-022.7289E-02142.399-1.0545E+001.1548E-018.9981E-034.5560E-03153.049-2.8037E+002.8375E-015.5647E-02-2.1641E-02163.398-2.3573E+003.7757E-013.7804E-02-4.3086E-02174.3166.5309E-018.4437E-01-4.0343E-011.9637E-01184.670-4.2765E+009.9979E-01-3.6429E-012.0098E-01 Table 2 (continued) Aspheric CoefficientsSurface #A12A14A16A18A202-3.3763E-04-8.8742E-05-5.9283E-050.0000E+000.0000E+0035.9956E-035.5077E-031.2558E-030.0000E+000.0000E+004-4.1612E-042.6196E-035.9748E-040.0000E+000.0000E+005-2.6943E-03-4.6173E-04-1.5513E-040.0000E+000.0000E+0061.1659E-032.5551E-045.3420E-050.0000E+000.0000E+0072.6374E-038.6554E-042.1797E-040.0000E+000.0000E+0010-4.7317E-03-1.8472E-03-4.5679E-040.0000E+000.0000E+00111.3992E-03-2.7093E-04-2.0424E-040.0000E+000.0000E+00135.2402E-039.4540E-042.0861E-041.8088E-040.0000E+0014-1.0297E-023.1228E-034.0339E-031.4174E-030.0000E+0015-1.1934E-022.9700E-034.8437E-03-6.6223E-04-6.9121E-04168.4277E-037.9687E-033.9145E-03-3.9617E-03-8.7507E-0417-6.6969E-022.4300E-02-6.4810E-031.6529E-03-1.0244E-0418-1.0479E-013.6269E-02-1.0994E-024.8537E-03-4.6735E-04

[0015] Table 3 below summarizes the design characteristics and parameters as they appear in the example listed above. These characteristics help to achieve the goal of a compact lens (i.e. small TTL) with a large image height (i.e. large SDL) and small F number (F#): Table 3"AA":AA 1 ≡ TTL / EFL < 1.100, AA 2 ≡ TTL / EFL < 1.090, AA 3 ≡ TTL / EFL < 1.083;"BB":BB 1 ≡ TTL / SDL < 0.64, BB 2 ≡ TTL / SDL < 0.63, BB 3 ≡ TTL / SDL < 0.61;"CC":Lens 1 is convex on object side;"DD":the CA of Lens 3 or Lens 4 is the smallest of all element CAs;"EE":power sign sequence: +-+-++-;"FF":The central thickness (CT) of at least 6 of the 7 lens elements complies with: FF 1 = CT / TTL<0.07;"GG":The T_STD of at least 5 of the 7 lens elements complies with: GGi ≡ T_STD / CT<0.11, GG 2 ≡ T_STD / CT<0.1;"HH":The T_STD of at least 3 of the 7 lens elements complies with: HH 1 ≡ T_STD / CT<0.065, HH 2 ≡ T_STD / CT<0.05;"II"Sign of z(r) from z(0.85*D / 2) to z(D / 2) is positive for surfaces LO 1 , LI 1 , LO 2 , LI 2 , and negative for surfaces LO 4 , LI 4 , LO 5 , LI 5 , LO 6 , LI 6 , LO 7 , LI 7 ;"JJ":JJi ≡ f 1 / EFL<0.95, JJ 2 ≡ f 1 / EFL<0.9, JJ 3 ≡ f 1 / EFL <0.85;"KK":KK 1 = |f 5 / EFL|>4.0, KK 2 ≡|f 5 / EFL|>6.0, KK 3 ≡|f 5 / EFL|>8.0;"LL":LL 1 ≡ |f 6 / EFL|>15.0, LL 2 ≡|f 6 / EFL|>30.0, LL 2 ≡|f 6 / EFL|>45.0;"MM":Gap between Lens 1 and Lens 2 that complies with: MM 1 ≡ G_STD < 0.015, MM 2 ≡ G_STD < 0.01 and MM 3 ≡ G_STD < 0.007;"NN":for the given SDL (12mm), 0 ≤ FOV < 82.1 degrees.

[0016] In summary, various lens assembly embodiments disclosed herein have or fulfill different design characteristics and parameters listed in the Tables above.

[0017] While this disclosure describes a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of such embodiments may be made. In general, the disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.

Claims

1. A lens assembly (100) comprising, in order from an object side to an image side, a first lens element L1, a second lens element L2, a third lens element L3, a fourth lens element L4, a fifth lens element L5, a sixth lens element L6, and a seventh lens element L7 with a common optical axis (102), wherein the lens assembly comprises not more than seven lens elements and wherein the lens elements have, starting with the first lens element L1, a power sign sequence of positive-negative-positive-negative-positive-positive-negative; an optical window (104); and an image sensor (106) having a sensor diagonal length SDL, characterized in that the lens assembly has a total track length TTL that includes the optical window, an effective focal length EFL and a field of view (FOV) less than 90 degrees, wherein TTL / EFL < 1.100, wherein TTL / SDL < 0.64, wherein a normalized thickness standard deviation constant T_STD and a central thickness CT of at least three of the seven lens elements complies with T_STD / CT <0.065 mm-1, wherein a focal length f1 of the first lens element L1 fulfills f1 / EFL<0.95, wherein T_STDi for the ith lens element (Li) is equal to 1 RMO i 1 N ∑ k = 0 N NT i k ⋅ RMO i N − T _ AVG i 2 wherein T_AVGi is defined as 1 N ∑ k = 0 N NT i k ⋅ RMO i N wherein RMOi is an aperture radius of an object side surface LOi of the ith lens element (Li), wherein a normal thickness NTi (r) is a function of cylindrical polar coordinate r referring to the distance between the two surfaces of the ith lens element at coordinate r along the normal vector of the surface closer to an object, wherein k is a discrete variable that runs from 0 to N, 10. wherein N is an integer greater than2. The lens assembly (100) of claim 1, wherein D / 2 is an aperture radius and wherein a sign of surface sag z(r) from z(0.85*D / 2) to z(D / 2) is positive for surfaces LO1, LI1 of L1 and surfaces LO2, LI2 of L2, and negative for surfaces LO4, LI4 of L4, LO5, LI5 of L5, LO6, LI6 of L6 and LO7, LI7 of L7, wherein Li is the ith lens element, LOi is the object side surface of the ith lens element Li, and Lli is the image side surface of the ith lens element Li.

3. The lens assembly (100) of claim 1, wherein each element has a clear aperture CA and wherein a CA of lens elements L3 or L4 is the smallest of all CAs in the lens assembly.

4. The lens assembly (100) of claim 1, wherein TTL / EFL < 1.090 or <1.083.

5. The lens assembly (100) of claim 1, wherein lens element L1 is convex on the object side.

6. The lens assembly (100) of claim 1, wherein the CT of at least 6 of the 7 lens elements complies CT / TTL<0.07.

7. The lens assembly (100) of claim 1, wherein the T_STD of at least 5 of the 7 lens elements comply with T_STD / CT < 0.11 mm-1 or comply with T_STD / CT < 0.10 mm-1.

8. The lens assembly (100) of claim 1, wherein T_STD / CT < 0.05 mm-1 .

9. The lens assembly (100) of claim 1, wherein f1 / EFL<0.9 or <0.85.

10. The lens assembly (100) of claim 1, wherein a focal length f5 of lens element L5 fulfills |f5 / EFL|>8.0 or |f5 / EFL|>6.0 or |f5 / EFL|>4.0.

11. The lens assembly (100) of claim 1, wherein a focal length f6 of lens element L6 fulfills |f6 / EFL| > 45.0 or |f6 / EFL| > 30.0 or |f6 / EFL| > 15.0.

12. The lens assembly (100) of claim 1, wherein a normalized gap standard deviation constant G_STD of a gap between lens elements L1 and L2 complies with G_STD < 0.015.

13. The lens assembly (100) of claim 1, wherein a normalized gap standard deviation constant G_STD of a gap between lens elements L1 and L2 complies with G_STD < 0.01 or with G_STD < 0.007.

14. The lens assembly (100) of claim 1, wherein SDL =12mm and wherein FOV < 82.1 degrees.