The present invention is directed to wide angle lens assemblies and camera objectives especially as claimed in the independent claims.

Wide angle lens assemblies generally comprise a first lens group with a negative focal length. A second lens group of the assem ^¬ bly has a positive focal length. Besides meniscus lenses, the assemblies need at least one aspherical lens to correct aberra ^¬ tion.

US 2011/0109974 suggests to arrange an aspherical lens as the second lens in the first group. Such an arrangement demands a relatively large aspherical lens. As aspherical lenses are ex ^¬ pansive to produce, such a system results in relatively high production costs.

It is an object of the present invention to overcome the draw- backs of the state of the art, in particular it is an object to provide a lens assembly which can be produced cost efficiently and which nevertheless provides a reliable aberration correc ^¬ tion. The objects are solved with the invention as defined in the claims, in particular with a wide angle lens assembly for a cam ^¬ era, comprising a first group and a second group of lenses. The first group is adapted to be arranged closer to an iris of the camera than the second group. The first group comprises multi- pie, preferably five, lenses with a negative focal length. The second group comprises at least three lenses, which are prefera ^¬ bly cemented and at least one aspherical lens. The first group comprises one aspherical lens distanced from the other lenses of the first group adapted to be arranged further away from the iris than the other lenses of the first group.

By arranging the aspherical lens distanced from the other lenses, at least the diagonal size of the aspherical lens can be reduced. Therewith, less material is needed, manufacturing is easier and costs can be reduced. Preferably, also a size orthog ^¬ onal to the diagonal size of the aspherical lens can be reduced by arranging the aspherical lens distanced from the other lenses.

The aspherical lens in the second group is used to correct high order aberration. The lenses of the first group have a negative focal length. The lenses of the second group have a positive focal length.

Preferably, the aspherical lens of the first group is distanced such that the diagonal size of the aspherical lens is equal to or less than half the diagonal size of an image sensor of the system with which the assembly will be used. Therewith, the costs of the assembly can be further reduced.

The surface (directed away from the iris) of the aspherical lens of the first group is preferably distanced by about 30-40 mm, more preferably about 34.5 mm from a the surface (directed to the iris) of the lens of the first group closest to the iris, when the focus is set to infinity. Therewith, the costs can be further reduced. In a preferred embodiment, the first group comprises a second aspherical lens. The second aspherical lens is preferably ar ^¬ ranged closest to the distanced aspherical lens. Preferably, the distanced aspherical lens comprises two aspheri ^¬ cal surfaces. The second aspherical lens comprises preferably only one aspherical surface. The aspherical surface of the sec ^¬ ond aspherical lens is preferably pointing towards the distanced aspherical lens.

An aspherical lens comprising only one aspherical surface is cheaper in production than an aspherical lens comprising two aspherical surfaces. As the non-distanced aspherical lens of the first group prefera ^¬ bly comprises only one aspherical lens, the costs are kept rela ^¬ tively low.

With a second aspherical lens the aberration can be more accu- rately corrected. By arranging the second aspherical lens clos ^¬ est to the other aspherical lens, the diagonal size of the sec ^¬ ond aspherical lens can be kept at a minimum. Therewith, the ad ^¬ ditional costs are kept at a minimum. The first group is preferably adapted to be fixedly arranged with respect to the iris.

By arranging the first group fixedly with respect to the iris, the aspherical lens (es) is arranged at a constant distance with respect to the iris.

If the first group is not fixedly arranged, the image height of a principal ray and a lens aperture tends to be bigger. There- with, the aspherical lens also has to be bigger in order to cor ^¬ rect the aberration. By arranging the first group fixedly with respect to the iris, the size and therewith the costs of the as ^¬ pherical lens can be further reduced.

Preferably, the second group is adapted to be moveably arranged with respect to the iris such that a focus is adjustable by mov ^¬ ing the second group with respect to the iris. To adjust the focus, lenses have to be axially moved. By making the second group moveable with respect to the iris, the size of the aspherical lens can be reduced.

Preferably, the second group further comprises four extra lenses. The aspherical lens of the second group is preferably arranged between the three preferably cemented lenses and the four extra lenses.

The extra lenses correct the remaining aberration. An arrange- ment with three cemented lenses, four extra lenses and an as ^¬ pherical lens has been shown to efficiently correct high order aberration and the remaining aberration.

Preferably, a middle lens of the preferably three cemented lens of the second group is biconvex.

Alternatively, the middle lens might be biconcave.

The biconvex lens in the middle allows a close arrangement of the three lenses. In wide angle assemblies, the light which has passed the first group and is incident on the second group has still a large angle. For this reason the second group is prefer ^¬ ably of the "negative lead type" and/or the three cemented lenses of the second group have a negative refracting power. In order to minimize chromatic aberration, both, lenses with a neg ^¬ ative refracting power and with a positive refracting power, should be used. In this regard, the use of three cemented lenses of the second group is advantageous to minimize performance changes because of the clearance between the lenses. To distrib ^¬ ute the refracting power equally, the positive refracting power lens is preferably arranged on the middle as a biconvex lens. Then, securing a symmetric imaging and minimizing aberration is possible.

Preferably, the assembly further comprises a third group of lenses between the first and the second group. The third group preferably comprises three cemented lenses. The third group of lenses corrects chromatic aberration.

In lens systems, chromatic aberration occurs because of differ ^¬ ent wave lengths of different colors. These different wave lengths are differently shifted by lenses. In order to correct this chromatic aberration, a third group of lenses might be pre ^¬ sent between the first and the second group of lenses.

Therewith, the colors on the image are not shifted and occur more naturally.

A middle lens of the further three cemented lenses of the third group is preferably biconcave.

The biconcave lens in the middle allows a close arrangement of the three lenses.

The two outer lenses are preferably biconvex. The use of three cemented lenses of the third group again is advantageous to min- imize performance changes because of a clearance between the lenses. Cemented biconcave middle lens and biconvex outer lenses aid in securing a symmetric imaging and achieving a refracting power equally.

D _r

0.3 <_≥^< 0.85 The lens assembly is preferably arranged such that Y , wherein D _GaSp is a maximum radius among the aspherical lenses of the first group and Y is a half diagonal size of an image sensor of the system. This is a standard setting for an assembly having an aspherical lens with a diagonal size, which is less than half of a sensor of the system. Therewith, the costs can be reduced.

0.3 < < 0.75

The lens assembly is preferably arranged such that TL _r wherein lc _asp is a distance between a surface of the distanced as- pherical lens of the first group directed away from the iris and a surface directed to the iris of the lens of the first group closest to the iris, when the system is set to an infinity fo ^¬ cus. TL is the distance between a surface directed away from the iris of the lens of the system arranged most distanced from the iris and said surface of said lens of the first group closest to the iris, when the focus is set to infinity. The smaller lc _asp is, the smaller the aspherical lens can be designed.

The lens assembly is preferably arranged such that f

J G2,tr _P iet _r wherein fGi,tr _P iet is a focal length of the three lenses closest to the iris of the first group and fG2,tr _P iet is a focal length the three lenses closest to the iris of the second group . The formula describes a focal length rate for the three cemented lenses closest to the iris of the first group and second group. With a focal length rate close to 1, the symmetric imaging is secured around the iris. Therewith, the chromatic aberration and distortion is easily corrected.

The lens assembly is preferably arranged such that , wherein fc2, asp is a focal length of the aspherical lens of the second group and f _G 2 is a focal length of the second group as a whole .

With the preferred ratio, the aspherical lens of the second group takes all refracting power of the second group. The as ^¬ pherical lens can correct all remaining aberration except for a chromatic aberration.

The invention is also directed to a camera objective comprising an iris and a lens assembly as described herein

The objective with a lens assembly as described herein provides the advantages of the assemblies described herein. The description is in the following described with reference to schematic drawings, which show non-limiting examples of the in ^¬ vention .

The figures schematically show:

Fig. 1: A lens assembly according to the invention; Fig. 2: An alternative lens assembly according to the invention; Fig. 3a: A Ray Fan of the embodiment of Figure 1 at infinity; Fig. 3b: A Ray Fan of the embodiment of Figure 1 with a magnifi ^¬ cation of-0.075.

Figure 1 shows a wide angle lens assembly 1 according to the in- vention. The assembly comprises a first group 2, a second group 3 and a third group 4 of lenses. The first group 2 is arranged closest to an iris (not shown) in an objective. The second group 3 is arranged most distanced to the iris in an objective. The first group 1 comprises five lenses. The lenses of the first group 2 have a negative focal length. Four lenses are arranged close to each other. One fifth lens 7 comprises two aspherical surfaces and is arranged distanced from the other four lenses. The lens 8 closest to the distanced aspherical lens 7 of the other four lenses comprises one aspherical surface facing the distanced aspherical lens 7. The aspherical lenses correct aber ^¬ ration .

The second group 3 of lenses comprises three cemented lenses 5 as a first sub-group coming from the iris side. The lenses of the second group 3 have a positive focal length. The middle lens 10 of the three cemented lenses is biconvex. The cemented lens 3 are adapted to correct high order aberration. The second group 3 further comprises an aspherical lens 6 next to the three cement- ed lenses 5. Four additional lenses are arranged on the other side of the aspherical lens 6 to correct any remaining aberra ^¬ tion.

The third group 4 comprises three cemented lenses. A middle lens 9 of the three lenses is biconcave. The three lenses are adapted to correct chromatic aberration. In use, the second group 3 is movable with respect to the in order to adjust a focus. The first group 2 is fixedly

ranged with respect to the iris. The distance between the surface (directed away from the iris) of the distanced aspherical lens 7 and the surface (directed to ^¬ wards the iris) of the lens of the first group closest to the iris is 34,3 mm .

[Table 1.] Specifications of embodiment 1.

Typical specifications of the assembly of Figure 1 are disclosed in the following tables.

Radius Thick nd vd

Obj infinity DO

1 53.12 4.5 1.516800 64.17

2 35.36 5.2

3 44.31 4 1.846660 23.78

4 27.63 5.6

5 40.03 5 1.516800 64.17

6 20.4 3.15

7 22.8 3 1.689000 52.8

8* 10.38 14.3

9* 38.762 3 1.689000 52.8

10* 22.614 4.6

11 24.771 5 1.592700 35.45

12 -10.29 1.5 1.772500 49.62

13 22.86 3.4 1.717360 29.5

14 -65.65 2.5

15 (stop) infinity Dl

16 57.82 1.5 1.903660 31.31

17 11.89 5.3 1.717360 29.5

18 -12.14 1.5 1.903660 31.31

19 infinity 0.3

20* 31.365 5.9 1.689000 52.8

21 * -14.263 0.3

22 -44.25 1.6 1.903660 31.31

23 23.45 5.4 1.438750 94.96

24 -158.5 0.3

25 59.81 1.6 1.903660 31.31

26 26.41 10.6 1.456500 90.27

27 -20.07 38

28 infinity D2 29 infinity 2.5 1.516800 64.17

30 infinity D3

lmg infinity D4

The objective numbers the surfaces of the different lenses starting on the surface of the first group 2 arranged closest the iris in an objective. The *-symbol indicates aspherical sur- faces. Hence, numbers 1-10 are members of the first group 2, numbers 11-15 are members of the third group 4, and numbers 16- 30 are members of the second group 3.

"nd" is the refractive index of the material.

"vd" is the Abbe number.

[Table 2.] Zoom data and aspherical coefficient of embodiment 1 The aspherical coefficients of the aspherical surfaces of the embodiment of Figure 1 are the following:

K c D

8* -1.16357

9* 2.91586 -6.96482E-05 1.0731 1E-06 -5.1 1962E-09 5.49903E-12

10* 0.05500 -5.63447E-05 1.17687E-06 -6.04906E-09 -3.52658E-1 1

20* 2.76265 -2.69072E-05 2.03146E-07 -2.62322E-09 7.12078E-12

21 * -2.67095 -5.35187E-05 2.89171E-07 -9.97322E-10 -4.96553E-12

The zoom data of the embodiment of Figure 1 are the following for different zooms

m=0 m=-0.075

EFL/MAG 11.5 0.075

FOV 62.98 62.269

F/# 4.002 4.181

DO Infinity 128.60360

Dl 4.20000 2.64163

D2 0.30000 1.85837

D3 0.50001 0.50001

D4 0.00840 0.06879 The distance between second and third lens on embodiment 2 is longer than the distance between second and third lens on embod ^¬ iment 1.

[Table 3.] RDN data of embodiment 2

The specifications of the embodiment of Figure 2 are therefore different :

S# Radius Thick nd vd Note

obj infinity DO

Group

1 51.085 4.50 1.516800 64.2

1

2 35.751 1.98

3 37.644 4.00 1.846660 23.78

4 25.400 10.31

5 50.872 4.50 1.516800 64.2

6 21.453 1.08

7 22.800 3.00 1.689000 52.8

8* 10.381 15.15

9* 38.762 3.00 1.689000 52.8

10* 22.614 4.51

11 22.404 5.00 1.592700 35.45

12 -10.328 1.50 1.772500 49.62

13 23.944 3.40 1.717360 29.5

14 -124.212 2.00

15(stp) infinity Dl

Group

16 54.249 1.50 1.903660 31.31

2

17 11.817 5.30 1.717360 29.5

18 -12.523 1.50 1.903660 31.31

19 infinity 0.10

20* 31.365 5.90 1.689000 52.8

21 * -14.263 0.18

22 -43.893 1.60 1.903660 31.31

23 26.242 5.40 1.438750 94.96

24 -235.496 0.10

25 53.239 1.60 1.903660 31.31

26 24.371 10.60 1.456500 90.27

27 -20.310 D2

28 infinity 2.50 1.516800 64.2 Filter

29 infinity D3

img infinity D4

[Table 4.] Zoom data and aspherical coefficients of embodiment 2. Aspherical coefficients:

K A B C D E

8* -1.16357 O.OOOOOE+00 O.OOOOOE+00 O.OOOOOE+00 O.OOOOOE+00

9* 2.91586 -6.96482E-05 1.0731 1E-06 -5.1 1962E-09 5.49903E-12

10* 0.05500 -5.63447E-05 1.17687E-06 -6.04906E-09 -3.52658E-1 1

20* 2.76265 -2.69072E-05 2.03146E-07 -2.62322E-09 7.12078E-12

21 * -2.67095 -5.35187E-05 2.89171E-07 -9.97322E-10 -4.96553E-12

Zoom Data:

m=0 m=-0.075

EFL/MAG 11.4752 0.07533

FOV 62.888 61.52

F/# 4.01 4.307

DO infinity 132.31819

Dl 4.13851 1.81749

D2 38.01266 40.33367

D3 0.54100 0.44489

D4 -0.04100 0.05511

[Table 5.] Comparison of embodiments.

A comparison of the embodiment of Figure 1 and Figure 2 is shown in the table below:

Embodi ^¬ Embodi ^¬ ment 1 ment 2

D _Gasp : maximum radius of first group 2 includ ^¬

16.82 17.25 ing aspherical lens 7

Y: half diagonal size of image sensor 21.7 21.7 l casp - distance between a surface of the dis ^¬ tanced aspherical lens 7 of the first group 2

directed away from the iris and a surface di ^¬

34.3 34.559 rected to the iris of the lens of the first

group 2 closest to the iris when the focus is

set to infinity.

TL: distance between a surface directed away

from the iris of the lens of the assembly 1

arranged most distanced from the iris and the 103.25 101.84 surface of the lens of the first group 2

closest to the iris when the focus is set to

infinity.

fGi , trpiet - focal length of three cemented

lenses closest to the iris of the first group 63.271 72.111

2

fG2, trpiet - focal length of three cemented

lenses 5 closest to the iris of the second -66.43 -73.648 group 3

fG2, asp - Focal length of the aspherical lens 6

14.957 14.957 of the second group 3

f _G 2 '. Focal length of the second group 3 as a

29.783 28.529 whole

Formula (1) o 3 < ^Dg " ^sp < 0 85 0.33 0.34

Y

Formula (2) o 3 < < 0 75 0.70 0.70

TL

Formula (3) 1 1 < ^ ^GX ^ ^let < 0 9 -0.95 -0.98

fci,trplet

Formula (4) l o < ^ ^G2 ' ^asp < 1 5 0.50 0.52

ί Gl 3a shows the Ray Fan on infinity and magnification of -0.075 of embodiment 1. 3b shows the Ray Fan on infinity and magnification of -0.075 of embodiment 2.