WO2017174867A1

WO2017174867A1 - Wide angle lens for capturing a panorama image

Info

Publication number: WO2017174867A1
Application number: PCT/FI2017/050203
Authority: WO
Inventors: Mika Aikio
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 2016-04-06
Filing date: 2017-03-23
Publication date: 2017-10-12
Anticipated expiration: 2018-10-06

Abstract

An imaging device (100,500) comprises: - an anamorphic unit (10) to form a virtual image (VMG1) of a cylindrical viewing region (SRF1), and - a focusing unit (20) to form a real image (IMG1) of the auxiliary virtual image (VMG1), wherein the anamorphic unit (10) comprises two or more refractive lenses (LNS11, LNS12) which have been selected such that the horizontal refractive power (P_x,C) of the imaging device (100) is greater than 1.5 times the vertical refractive power (P_y,C) of the imaging device (100), and the anamorphic unit (10) is arranged to form the virtual image (VMG1) by refracting light (B0_k) received from the cylindrical viewing region (SRF1) such that the aspect ratio(Δϕ/ΔΦ) of the virtual image (VMG1) is lower than the aspect ratio (Δϕ'/ΔΦ') of the viewing region (SRF1).

Description

WIDE ANGLE LENS FOR CAPTURING A PANORAMA IMAGE

FIELD

The present invention relates to an imaging device suitable for capturing a panorama image.

BACKGROUND

It is known that a panorama image may be captured by using a fish eye lens and an image sensor. The aspect ratio of the image sensor may be e.g. equal to 4:3, whereas the aspect ratio of the panorama image may be e.g. greater than 3:1 . The panorama image may cover e.g. less than 40 % of the active area of the image sensor when capturing the panorama image with the fish eye lens and with the image sensor.

Referring to the comparative example shown in Fig. 8, a wide angle lens of Prior Art may provide a circular optical image, and a rectangular portion of an image sensor may be arranged to capture a rectangular portion of said circular image. The circular optical image may correspond e.g. to a field of view of 170°. The rectangular portion of the circular image may correspond e.g. to a horizontal field of view having an angular width of 165°, and to a vertical field of view having an angular height of 40°. The ratio of the height H_R of the rectangular portion to the height H_s of the active area of the image sensor may be e.g. less than 0.40.

SUMMARY

Some variations may relate to a wide angle lens. Some variations may relate to an imaging device, which comprises a wide angle lens. Some variations may relate to a method for imaging. According to an aspect, there is provided an imaging device (100,500), comprising:

- an anamorphic unit (10) to form a virtual image (VMG1 ) of a cylindrical viewing region (SRF1 ), and

- a focusing unit (20) to form a real image (IMG1 ) of the auxiliary virtual image (VMG1 ),

wherein the anamorphic unit (10) comprises two or more refractive lenses (LNS1 1 , LNS12) which have been selected such that the horizontal refractive power (Px_,c) of the imaging device (100) is greater than 1 .5 times the vertical refractive power (P_y,c) of the imaging device (100), and the anamorphic unit (10) is arranged to form the virtual image (VMG1 ) by refracting light (B0_k) received from the cylindrical viewing region (SRF1 ) such that the aspect ratio (Δφ'/ΔΘ') of the virtual image (VMG1 ) is lower than the aspect ratio (Δφ/ΔΘ) of the viewing region (SRF1 ).

According to an aspect, there is provided a method for forming a real image (IMG1 ) of a viewing region (SRF1 ), the method comprising:

- forming a virtual image (VMG1 ) of the viewing region (SRF1 ) by using an anamorphic unit (10), and

- forming a real image (IMG1 ) of the auxiliary virtual image (VMG1 ) by using a focusing unit (20),

wherein the anamorphic unit (10) comprises two or more refractive lenses (LNS1 1 , LNS12) which have been selected such that the horizontal refractive power (Px_,c) of the imaging device (100) is greater than 1 .5. times the vertical refractive power (P_y,c) of the imaging device (100), and the anamorphic unit (10) is arranged to form the virtual image (VMG1 ) by refracting light (B0_k) received from the cylindrical viewing region (SRF1 ) such that the aspect ratio (Δφ'/ΔΘ') of the virtual image (VMG1 ) is lower than the aspect ratio (Δφ/ΔΘ) of the viewing region (SRF1 ).

Further aspects are defined in the claims.

An imaging apparatus may comprise the imaging device and an image sensor. The imaging apparatus may be arranged to capture a panorama image of the viewing region by forming an optical image on the image sensor such that the optical image may cover e.g. more than 95% of the active area of the image sensor, wherein the aspect ratio of the viewing region may be e.g. at least 50% higher than the aspect ratio of the image sensor. Thus, the pixels of the image sensor may be used in a more effective manner, so as to improve the spatial resolution of the captured image. In particular, the optical image may cover an increased number of detector pixels of the image sensor in the vertical direction.

The imaging device may provide a high anamorphic compression ratio. By using the imaging device, the fill factor of the image sensor may be high. The optical image may cover e.g. more than 95% of the active area of the image sensor when capturing a panorama image, wherein the aspect ratio of the panorama image may be e.g. in the range of 3:1 to 7:1 , and the aspect ratio of the image sensor may be e.g. in the range of 1 :1 to 2:1 . By using the imaging device, the distortion aberration of the optical image in the vertical direction may be low, when compared with the object surface.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following examples, several variations will be described in more detail with reference to the appended drawings, in which

Fig. 1 a shows, by way of example, in a cross-sectional top view, an imaging device, which comprises an anamorphic unit,

Fig. 1 b shows, by way of example, in a cross-sectional top view, propagation of a light ray through the elements of the imaging device,

Fig. 1 c shows, by way of example, in a cross-sectional side view, propagation of a light ray through the elements of the imaging device, Fig. 2 shows, by way of example, in a three-dimensional view, the imaging device,

Fig. 3a shows, by way of example, in a three-dimensional view, capturing an image of a viewing region by using the imaging device,

Fig. 3b shows, by way of example, in a three-dimensional view, capturing an image of a cylindrical object surface by using the imaging device,

Fig. 4 shows, by way of example, forming an optical image of the object surface, Fig. 5a shows, by way of example, mapping functions for conversion of a vertical input angle into a vertical image coordinate,

Fig. 5b shows, by way of example, curves which indicate the geometric distortion at different positions of the optical image,

Fig. 5c shows, by way of example, image points located on a horizontal line, on a vertical line, and on a diagonal line,

Fig. 6 shows, by way of example, forming a panorama image from a digital image,

Fig. 7 shows, by way of example, an imaging apparatus, which comprises the imaging device, and Fig. 8 shows a comparative example where an image sensor overlaps a circular image formed by a fish eye objective.

DETAILED DESCRIPTION Referring to Fig. 1 a, the imaging device 100 may comprise an anamorphic unit 10 and a focusing unit 20. The anamorphic unit 10 may receive input light B0 from a viewing region VREG1. The input light B0 may comprise a plurality of input beams BOo, B0i, B0k. The anamorphic unit 10 may receive input light beams BOo, B0i, BOk. e.g. from one or more objects 01 , 02, 03 (Fig. 3a). The anamorphic unit 10 may provide an auxiliary virtual image VMG1 (Fig. 4) by providing intermediate light beams B1₀, B1 i, B1 _k. The anamorphic unit 10 may provide the intermediate light beams B1₀, B1 i, B1 _k by refracting light of the input beams B0i, BOk. The anamorphic unit 10 may provide deflected intermediate beams B1 i, B1 _k by refracting light of the input beams B0i, BOk, and the anamorphic unit 10 may provide an axial intermediate beam B0i, by refracting light of an axial input beam BOo. The anamorphic unit 10 may cause mainly a horizontal change in the direction of the deflected beams B1 i, B1 _k. The direction of a light beam may be defined by an azimuth angle and by an elevation angle. The anamorphic unit 10 may refract light such that the azimuth angle of the deflected beams B1 i, B1 _k is substantially smaller than the azimuth angle of the input beams B0i, BOk. The azimuth angle of a light beam means the angle between the direction of the light beam and the vertical plane defined by the optical axis AXO of the imaging device 100. The elevation angle of the light beam means the angle between the direction of the light beam and the horizontal plane defined by the optical axis AXO.

The imaging device 100 may be arranged to form an optical image IMG1 on an image sensor DET1. An imaging apparatus 500 may comprise the imaging device 100 and the image sensor DET1. The imaging device 100 may form an image IMG1 of a viewing region VREG1 on the image sensor DET1. The viewing region VREG1 may comprise an object 01. The viewing region VREG1 may be represented by a cylindrical object surface SRF1 (Fig. 3b). A part of the object surface SRF1 may represent the object 01.

The anamorphic unit 10 may provide an auxiliary image VMG1 , which is shrunk in one dimension (1 D) when compared with the original scene SRF1. The anamorphic unit 10 may provide anisotropic image compression. The anamorphic unit 10 may provide an intermediate light beam B1 as the optical output of the anamorphic unit 10. The anamorphic unit 10 may provide intermediate light B1 , which comprises the intermediate beams B1₀, B1 i, B1 _k. The intermediate light beams B1₀, B1 i, B1 _k may together represent an auxiliary image VMG1 .

For example, an observer could view the auxiliary image VMG1 in a situation where the anamorphic unit 10 would operate without the focusing unit 20 so that the intermediate light beam may impinge on the eye of the observer. Light refracted by the anamorphic unit 10 may be coupled to the focusing unit 20. The optical output of the anamorphic unit 10 may be coupled into the focusing unit 20. The focusing unit 20 may receive an intermediate light beam B1 provided by the anamorphic unit 10. The focusing unit 20 may form an image IMG1 of the auxiliary virtual image VMG1 on the image sensor DET1 by focusing light of the intermediate beams B1₀, B1 1 , B1 _k. The focusing unit 20 may provide isotropic scaling. The focusing unit 20 may provide the image IMG1 by compressing (i.e. scaling) the auxiliary image VMG1 by a scale factor that is the same in the direction SX and in the direction SY. The lenses of the focusing unit 20 may have circular symmetry (i.e. axial symmetry) with respect to the optical axis AX0. The focusing unit 20 may be e.g. a camera objective.

The focusing unit 20 may provide the optical real image IMG1 from the auxiliary virtual image VMG1 by radially compressing (i.e. scaling) the auxiliary image VMG1 . The anamorphic unit 10 may comprise two or more refractive optical elements LNS1 1 , LNS12, ... The optical elements LNS1 1 , LNS12 of the anamorphic unit 10 may be selected such that the horizontal refractive power of the imaging device 100 is greater than e.g. 150% of the vertical refractive power of the imaging device 100.

The refractive power P of an optical unit is equal to the inverse of the focal length f of said optical unit, i.e. P=1/f. The anamorphic unit 10 may provide a deflected light beam B1 _k by refracting light of an input beam BO_k. The anamorphic unit 10 may provide the deflected light beam B1 _k such that the azimuth angle of the light beam B1 _k is substantially smaller than the azimuth angle of the light beam BO_k. The anamorphic unit 10 may provide the deflected light beam B1 _k such that the elevation angle of the light beam B1 _k is substantially equal to the elevation angle of the light beam BO_k. The ratio of the elevation angle of the deflected beam B1 _k to the elevation angle of the input beam BO_k may be substantially greater than the ratio of the azimuth angle of the deflected beam B1 _k to the azimuth angle of the input beam BO_k. The azimuth angle means the angle between the direction of the light beam and the vertical plane. The elevation angle means the angle between the direction and the horizontal plane. The vertical plane is defined by the directions SX and SZ. The horizontal plane is defined by the directions SY and SZ. The direction SZ is shown e.g. in Fig. 2.

The anamorphic unit 10 may have a first focal length f_{X A} for refraction in the horizontal plane defined by the directions SX and SZ. The anamorphic unit 10 may have a second focal length f_{Y A} for refraction in the vertical plane defined by the directions SY and SZ. The anamorphic unit 10 may have a horizontal refractive power P_{x A}, which may be defined by the equation P_x,A⁼1/fx,A- The anamorphic unit 10 may have a vertical refractive power P_{y A}, which may be defined by the equation P_{y A} =1/fy,A- For example, the focal length f_{y A} may be infinite, and the vertical refractive power P_{y A} may be substantially equal to zero, respectively.

The horizontal refractive power P_{x A} may be substantially equal to the vertical refractive power P_{y A}. In particular, the anamorphic unit 10 may be substantially afocal, wherein the focal length f_{y A} may be substantially infinite and also the focal length f_{x A} may be substantially infinite. The use of an afocal anamorphic unit 10 may provide efficient coupling of light into the focusing unit 20 and/or may reduce aberrations e.g. in a situation where the focusing unit 20 is arranged to provide a sharp image of an object located at infinity (i.e. when the focus of the focusing unit 20 is set at infinity). Alternatively, the horizontal refractive power P_{x A} may be different from the vertical refractive power P_y,A. For example, the vertical refractive power P_{y A} may be substantially equal to zero, wherein the horizontal refractive power P_X,A may be different from the vertical refractive power P_y,A.

The focusing unit 20 may have a focal length f_B. The focusing unit may have a focal length f_{X B} for refraction in in the horizontal plane defined by the directions SX and SZ. The focusing unit may have a focal length f_{Y B} for refraction in the vertical plane defined by the directions SY and SZ. The focal length f_{X B} of the focusing unit 20 may be equal to the focal length f_{Y B}. The focal lengths fx,B and ίγ,Β may be equal to the focal length f_B. The focusing unit 10 may have a horizontal refractive power P_{x B}, which may be defined by the equation P_X,B=1 /fx,B- The focusing unit 10 may have a vertical refractive power Py,_B, which may be defined by the equation P_Y,B=1 /fx,B- The vertical refractive power P_{y B} of the unit 20 may be equal to the horizontal refractive power Ρχ,Β of the unit 20. The horizontal refractive power (P_X,B) of the focusing unit (20) may be equal to the vertical refractive power (P_Y,B) of the focusing unit (20) in a situation where the focusing unit (20) is operated without the anamorphic unit (10).

The imaging device 100 may have a first focal length f_{x c} for refraction in the horizontal plane, and a second focal length f_{Y C} for refraction in the vertical plane. The imaging unit 100 may have a horizontal refractive power P_{x C}, which may be defined by the equation P_x,c=1 /fx,c, and a vertical refractive power Py,c which may be defined by the equation P_{y C} =1 /f_y,c- The focal length fx_,c may be different from the focal length f_y,c, and the horizontal refractive power P_x,c may be different from the vertical refractive power P_{y C}.

Figs. 1 b and 1 c show, by way of example, propagation of a light ray RAY1 through the optical elements of the device 100. The marginal light ray RAY1 impinging on an optical element may intersect the input surface of said optical element at an intersection point IC. For example, the marginal ray RAY1 may intersect the first six elements LNS1 1 , LNS12, LNS13, LNS14, LNS15, LNS21 at intersections points ICi , IC₂, IC₃, IC₄, IC₅, IC₆. h_x,_q may denote the horizontal distance (in the direction SX) between the optical axis AXO and the intersection point on the input surface of a q element. h_{y q} may denote the vertical distance (in the direction SY) between the optical axis

AXO and the intersection point on the input surface of the q element. h_x,i , h_x,2, h_x,3, h_x,4, h_x,5, h_x,6 may denote the horizontal distances h_x,_q for the intersection points of the first six elements LNS1 1 , LNS12, LNS13, LNS14, LNS15, LNS21 . h_y,i , h_y,₂, h_y,₃, h_y,₄, h_y,₅, h_y,₆ may denote the vertical distances hy,_q for the intersection points of the first six elements LNS1 1 , LNS12, LNS13, LNS14, LNS15, LNS21 . The light ray RAY1 may be parallel with the optical axis AXO. The position and the direction of the ray RAY1 may be selected such that the horizontal distance h_x,i is different from zero and/or such that the vertical distance h_y,i is different from zero. The path of the ray RAY1 and the positions h_{x k}, h_{y k} of the intersection points may be determined e.g. by ray tracing. Weighting coefficients w_{x q} and w_{y q} for the q^th element be defined by using the horizontal distances h_x,i , h_x,_q and the vertical distances h_y, i , h_y,_q e.g. as follows:

_ ^hy,q

wy.q = h ^{(1 b)}

Thus, the weighting coefficient w_{x q} for the refractive power of an element associated with the index q may be proportional to the horizontal distance between the ray RAY1 and the axis AXO at the location of said element. The weighting coefficient w_{y q} for the refractive power of an element associated with the index q may be proportional to the vertical distance between the ray RAY1 and the axis AXO at the location of said element. The weighting coefficients w_x, i and w_y, i for the first element of the anamorphic unit 10 (i.e. the lens LNS1 1 ) may be equal to one (i.e. w_x, i =hx,

). The horizontal refractive power P_{x C} of the imaging device 100 may be equal to the weighted sum of the horizontal refractive powers P_x,_q of the anamorphic unit 10 and the horizontal refractive powers P_x,_q of the focusing unit 20:

Px,C = ^" x,q (1 C)

The symbol N may denote the number of the optical elements of the anamorphic unit 10. The symbol M may denote the number of the optical elements of the focusing unit 20. The first summation (from q=1 to q=N) in equation 1 c may take into account the contribution of the elements of the anamorphic unit 10. The second summation (from q=N+1 to q=N+M) may take into account the contribution of the elements of the focusing unit 20.

The vertical refractive power P_{y C} of the imaging device 100 may be equal to the weighted sum of the vertical refractive powers P_y,_q of the anamorphic unit 10 and the horizontal refractive powers P_y,_q of the focusing unit 20:

The horizontal refractive power P_{x C} of the imaging device 100 may be equal to the weighted sum of the horizontal refractive power P_x,A Of the anamorphic unit 10 and the horizontal refractive power P_{x B} of the focusing unit 20:

The vertical refractive power P_{y C} of the imaging device 100 may be equal to the weighted sum of the vertical refractive power P_y,A Of the anamorphic unit 10 and the vertical refractive power P_{y B} of the focusing unit 20: Py,C = P_y,A + ( _y,B - P_y,_Bj (1f)

The weighting coefficient w_{x B} of the focusing unit 20 may be equal to the weighting coefficient w_{x q} of the first lens LNS21 of the focusing unit 20. The weighting coefficient w_{y B} of the focusing unit 20 may be equal to the weighting coefficient w_{y q} of the first lens LNS21 of the focusing unit 20. In particular, the weighting coefficient w_x,_B may be e.g. equal to h_x,₆/h_x,i, and the weighting coefficient w_y,_B may be e.g. equal to h_y,₆/h_y,i . The anamorphic unit 10 may steer the light transmitted through the anamorphic unit 10 such that ratio (h_x,_N+i/h_x,i) of the horizontal weighting coefficients may be substantially different from the ratio (h_y,_N+i/h_y,i) of the vertical weighting coefficients. Consequently, the horizontal refractive power P_x,c of the imaging device 100 may be substantially different from the vertical refractive power P_{y C} of the device 100 in a situation where the horizontal refractive power P_{x B} of the focusing unit 20 coupled to the anamorphic unit 10 is equal to the vertical refractive power P_{y B} of the focusing unit 20.

The lenses may be selected e.g. such that the ratio h_x,₆/h_x,i is e.g. greater than 1 .5 times the ratio h_y,₆/h_y,i . The lenses may be selected e.g. such that the ratio h_x,_N+i/h_x,i is e.g. greater than 1 .5 times the ratio h_y,_N+i/h_y,i . The weighting coefficient w_{x B} may be e.g. greater than 1 .5 times the weighting coefficient w_{y B}. The vertical refractive power P_{y A} of the anamorphic unit 10 may be substantially equal to zero, and the vertical refractive power P_{y C} of the imaging device 100 may be substantially equal to the vertical refractive power Py B of the focusing unit 20. The anamorphic unit 10 may comprise two or more refractive optical elements LNS1 1 , LNS12. The horizontal refractive power P_{x A} of the anamorphic unit 10 may be equal to the weighted sum of the horizontal refractive powers P_x,i, P_x,2, ... , P_x,_q,,--- , P_X,N of the individual optical elements LNS1 1 , LNS12, LNS13, ... of the anamorphic unit 10:

The vertical refractive power P_YA of the anamorphic unit 10 may be equal to the weighted sum of the vertical refractive powers P_y,i, P_y,2,... , P_Y,_Q,,--- , P_Y,N of the individual optical elements LNS11, LNS12, LNS13,... of the anamorphic unit 10:

Py,A=∑w_y,_q-P_y,_q (2b)

q=l The anamorphic unit 10 may comprise e.g. 5 elements LNS11, LNS12, LNS13, LNS14, LNS15 shown in Fig.1a, and the horizontal refractive power Px_A of the anamorphic unit 10 may be calculated according to the following equation:

N

∑^Wx,q-^Px,q

q=l

1 _| ^hx,2/^hx,l _| ^hx,3^/hx,l _| ^hx,4/^hx,l _| ^hx,5^/hx,l fx,LNSll ^fx,LNS12 ^fx,LNS13 ^LNSM ¹x,LNS15

(2c)

The optical elements of the anamorphic unit 10 may be selected such that the horizontal refractive power P_xC of the imaging device 100 is greater than e.g.1.5 times the vertical refractive power P_{y C} of the imaging device 100:

Px,C>l-5-Py,c (3a)

The light ray RAY1 may be coupled from the anamorphic unit 10 into the focusing unit 20 such that the anamorphic unit 10 defines the horizontal distance h_x6 and the vertical distance h_y6 between the between the light ray RAY1 and the axis AXO at the location of the first element (LNS21 ) of the focusing unit 20. The anamorphic unit 10 may define the position (h_x,₆, h_{y 6}) of the intersection point (\Ce) where the light ray RAY1 meets the input surface of the focusing unit 20. The weighting coefficients w_x,_B, w_{y B} may be calculated e.g. based on the distances h_x,₆, h_y,₆.

The optical elements of the anamorphic unit 10 may be selected e.g. according to the following equation (3b):

+ W_y,B - Py,B

(3b)

Equation (3b) may be obtained from equation (3a) e.g. by using the equations (1 e), (1f), (2a) and (2b). The weighting coefficient w_x,_B may be different from the weighting coefficient w_{y B} so that the imaging device 100 may provide anamorphic compression also in a situation where the anamorphic unit 10 is afocal and the focusing unit 20 is axially symmetric.

The vertical refractive power P_{y A} of the anamorphic unit 10 may also be e.g. smaller than 10% of the vertical refractive power P_{y C} of the imaging device 100:

^Py,A < 0.10 P. y,c (3c) The anamorphic unit 10 may comprise at least one negative refractive lens LNS1 1 and at least one positive refractive lens (e.g. LNS 15). The refractive powers of the lenses of the anamorphic unit 10 may be selected such that equations (3b) and (3c) are fulfilled. The first refractive lens of the anamorphic unit 10 may be e.g. a negative cylindrical meniscus lens LNS1 1 . The negative cylindrical meniscus lens LNS1 1 may have a first cylindrical convex surface and a second cylindrical concave surface, wherein the radius of curvature of the second cylindrical surface may be smaller than the radius of curvature of the first cylindrical surface. The convex surface of the first lens LNS1 1 may receive the light beams BO_k from the viewing region VREG1 . All other lenses of the anamorphic unit 10 may be located between the lens LNS1 1 and the real image IMG1 . All other lenses of the imaging device 100 may be located between the lens LNS1 1 and the real image IMG1 .

The anamorphic unit 10 may comprise e.g. a combination of a cylindrical negative meniscus lens LNS1 1 , and a bi-concave cylindrical lens LNS12. The lenses LNS1 1 , LNS12 may provide anamorphic compression by causing mainly a horizontal change in the direction of light. The lenses LNS1 1 , LNS12 may provide a refracted beam by refracting light of an input beam BO_k such that the azimuth angle of the refracted beam is substantially smaller than the azimuth angle of the input beam BO_k, wherein the elevation angle of the refracted beam may be substantially equal to the elevation angle of the input beam BO_k. The azimuth angle means the angle between the direction of a light beam and the vertical plane. The elevation angle means the angle between the direction and the horizontal plane. The ratio of the elevation angle of the refracted beam to the elevation angle of the input beam BO_k may be substantially greater than the ratio of the azimuth angle of the refracted beam to the azimuth angle of the input beam BO_k.

The anamorphic unit 10 may further comprise a lens LNS13 to correct aberrations. The lens LNS13 may be e.g. a cylindrical positive meniscus lens LNS13. The lens LNS13 may have a first cylindrical concave surface and a second cylindrical convex surface, wherein the radius of curvature of the second surface may be smaller than the radius of curvature of the first surface.

The anamorphic unit 10 may optionally comprise one or more lenses LNS14, LNS15 to match the optical output of the anamorphic unit 10 with the viewing region of the focusing unit 20. Without using the lens LNS14 and/or LNS15, some peripheral light beams provided by the lens LNS13 could be outside the angular viewing region of the focusing unit 20. The lens LNS13 and the lens LNS15 may at least partly compensate the effect of the negative refractive power of the lenses LNS1 1 , LNS12, LNS14. The lens LNS14 may at least partly compensate chromatic aberration caused by the lens LNS15. The lens LNS14 may least partly compensate geometric distortion.

The anamorphic unit 10 may comprise lenses LNS1 1 , LNS12, LNS13, LNS14, LNS15. The lenses LNS1 1 , LNS1 , and LNS14 may be negative lenses. The lenses LNS13, LNS15 may be positive lenses. Also the lenses LNS13, LNS14, LNS15 may be cylindrical lenses. The lenses LNS1 1 , LNS1 , and LNS14 may be negative cylindrical lenses, and the lenses LNS13, LNS15 may be positive cylindrical lenses. Light refracted by the lens LNS1 1 may be coupled to the lens LNS12. Light refracted by the lens LNS12 may be coupled to the lens LNS13. Light refracted by the lens LNS13 may be coupled to the lens LNS14. Light refracted by the lens LNS14 may be coupled to the lens LNS15. Light refracted by the lens LNS15 may be coupled to the focusing unit 20.

The focusing unit 20 may comprise e.g. two or more axially symmetric lenses LNS21 , LNS22, LNS23, LNS24, LNS25. The lens LNS21 , LNS22, LNS23, LNS24, and/or LNS25 may be axially symmetric. The axially symmetric surfaces of the lenses LNS21 , LNS22, LNS23, LNS24, LNS25 may be spherical, aspherical or planar. The focusing unit 20 may provide focused light B2 by focusing the intermediate light B1 . The focusing unit 20 may provide focused light beams B2₀, B2i , B2_k by focusing light of the intermediate beams B1₀, B1 i , B1 _k. The focusing unit 20 may provide the real image IMG1 by providing the focused light beams B2₀, B2_k.

SX, SY and SZ denote orthogonal directions. The direction SX may be called e.g. as the horizontal direction, and the direction SY may be called e.g. as the vertical direction. The direction SZ may be called e.g. as the axial direction or as the longitudinal direction. The directions SX, SY, SZ may be defined by the device 100. The direction SY does not need to be parallel to the direction of gravity, and the direction SX does not need to be perpendicular to the direction of gravity. The imaging device 100 may have an optical axis AXO. The optical axis AXO may be parallel to the direction SZ. The anamorphic unit 10 may exhibit symmetry with respect to a plane defined by the directions SY and SZ. The anamorphic unit 10 may also exhibit symmetry with respect to a plane defined by the directions SX and SZ.

The direction of an axial input beam BOo may remain substantially unaltered.

Figs. 1 a and 1 b shows, in a top view, the imaging device 100. The viewing direction of Figs. 1 a and 1 b is perpendicular to the horizontal plane defined by the directions SX and SZ. Fig. 2 shows a three dimensional view of the imaging device 100.

Table 1 shows, by way of example, suitable dimensions for the surfaces of the imaging device 100. Table 2 shows, by way of example, suitable optical materials for the optical elements of the imaging device 100. The materials listed in Table 2 may be used in the device of Table 1 .

Table 1 . Suitable dimensions of the surfaces of the imaging device 100.

Element Surface Surface Radius of Thickness Radius of

number type curvature in (mm) curvature in

# direction SY direction SX

(mm) (mm)

S F1 0 CYLINDRICAL INF 5000 5000

LNS11 1 CYLINDRICAL INF 2 55.63

LNS11 2 CYLINDRICAL INF 15.85 18.57

LNS12 3 CYLINDRICAL INF 3.79 -124.76

LNS12 4 CYLINDRICAL INF 8.00 101.00

LNS13 5 CYLINDRICAL INF 7.82 -67.46

LNS13 6 CYLINDRICAL INF 11.74 -55.22

LNS14 7 CYLINDRICAL INF 11.17 -22.20 LNS14 8 CYLINDRICAL INF 0.20 -98.76

LNS15 9 CYLINDRICAL INF 14.54 5372.56

LNS15 10 CYLINDRICAL INF 2.00 -40.65

LNS21 11 SPHERICAL 18.36 2.97 18.36

LNS21 12 SPHERICAL 111 0.44 111

LNS22 13 SPHERICAL 6.62 1.97 6.62

LNS22 14 SPHERICAL 4.55 3.89 4.55

AS1 15 STOP INF 1.69 INF

LNS23 16 SPHERICAL -8.64 1.00 -8.64

LNS23 17 SPHERICAL 13.74 4.66 13.74

LNS24 17 SPHERICAL 13.74 4.66 13.74

LNS24 18 SPHERICAL -9.41 0.50 -9.41

LNS25 19 SPHERICAL 64.55 2.61 64.55

LNS25 20 SPHERICAL -25.22 1.00 -25.22

Window A 21 PLANE INF 1.00 INF

Window A 22 PLANE INF 13.28 INF

Window B 23 PLANE INF 1.00 INF

Window B 24 PLANE INF 0.55 INF

DET1 25 PLANE INF INF

The lenses LNS23 and LNS24 may together form a doublet lens (i.e. they may have the common surface #17). Window A and window B may refer to protective windows, which may be optionally positioned e.g. between the lens LNS25 and the detector DET1 . SRF1 denotes the object surface. DET1 means the image sensor. INF means infinite radius. The glass types may refer to the glass type designations specified by the company Schott AG on the date of filing of this application.

Table 2. Suitable optical materials of the elements of the imaging device 100.

Element Glass type LNS11 N-LAK34

LNS12 N-SK4

LNS13 N-LASF41

LNS14 N-BAF10

LNS15 N-LASF46A

LNS21 N-BAF52

LNS22 N-SK16

LNS23 N-SF56

LNS24 N-LAF36

LNS25 N-LAK14

Window A N-BK7

Window B B270

In case of the device specified in Tables 1 and 2, the horizontal field of view may be substantially equal to 179°, and the vertical field of view may be substantially equal to 29.8°. The operating wavelength range may be e.g. in the range of 486 nm to 656 nm. The F-number may be substantially equal to 2.8. The effective focal length f_{x c} may be substantially equal to 4.85 mm, and the effective focal length f_{Y C} may be substantially equal to 18.5 mm. The full width of the image formed on the detector may be substantially equal to 12.8 mm, and the full height of the image formed on the detector may be substantially equal to 9.6 mm.

Referring to Fig. 3a, the imaging device 100 may form an image IMG1 of a viewing region VREG1 on the image sensor DET1 . The viewing region VREG1 may comprise one or more objects 01 , O2, O3. An object 01 may comprise an object point P_k, which may emit or reflect light BOk towards the input aperture of the lens element LNS1 1 . The light sent from the object point Pk to the lens element LNS1 1 may be understood to constitute an input light beam BOk. The direction of the input light beam BOk may be specified by angles (φκ,θκ). The azimuth angle φk may denote an angle between the direction of the input light beam BOk and a vertical reference plane defined by the directions SY and SZ. The elevation angle 9k may denote an angle between the direction of the input light beam BOk and a horizontal reference plane defined by the directions SX and SZ. The entrance pupil of the device 100 may be defined by an aperture stop AS1 of the focusing unit 20. The aspheric unit 10 does not need to comprise an aperture stop. The entrance pupil may also be called e.g. as the input pupil. The aperture stop AS1 of the focusing unit 20 may be e.g. substantially circular, and entrance pupil of the device 100 may be substantially elliptical. The shape of the perimeter of the input aperture of the lens element LNS1 1 may substantially correspond to the shape of a projection of an ellipse on the curved input surface of the element LNS1 1 .

The image IMG1 of the viewing region VREG1 may comprise sub-images SUB1 , SUB2, SUB3. The sub-image SUB1 may be an image of the object O1 . The sub-images SUB2, SUB3 may be images of the objects O2, O3.

The viewing region VREG1 may have an angular width Δφ and an angular height ΔΘ. The active light-detecting surface of the image sensor DET1 may be in a plane defined by directions SU and SV. The direction SU may be parallel to the direction SX, and the direction SV may be parallel to the direction SY.

Referring to Fig. 3b, the viewing region VREG1 may comprise a cylindrical object surface SRF1 . The object surface SRF1 may represent the viewing region VREG1 . The angular width of the object surface SRF1 may be equal to the angular width of the viewing region VREG1 , and the angular height of the object surface SRF1 may be equal to the angular height of the viewing region VREG1 , when viewed by the imaging device 100. The imaging device 100 may be arranged to form a sharp image IMG1 of the cylindrical surface SRF1 . The imaging device may form a real optical image of a cylindrical object surface on a planar image sensor. The cylindrical object surface may have a predetermined radius of curvature. The imaging device may form a sharply focused real image of the cylindrical object surface on the planar image sensor.

The object surface SRF1 may comprise an object 01 . The object surface SRF1 may comprise a portion O1 , which represents an object. The image IMG1 may comprise a sub-image SUB1 of an object O1 . The object O1 may have an object point P_k. The image IMG1 may comprise an image P"_k of the object point P_k. The image The position of the image point P"_k may be specified e.g. by coordinates (Uk,v_k). The cylindrical surface SRF1 may have a radius L₀ of curvature. The distance between the cylindrical surface SRF1 and the first lens LNS1 1 may be equal to L₀. The cylindrical surface SRF1 may have a circumferential length As and a height Ay. The cylindrical surface SRF1 may have an aspect ratio As/Ay. The position of the object point P_k may be specified e.g. by coordinates (s_k,y_k) or by the angular coordinates (φκ,θκ).

The optical real image IMG1 of the cylindrical surface SRF1 may cover a large part of the active area of the image sensor DET1 . For example, the image IMG1 may cover more than 95% of the active area of the image sensor DET1 . The fill factor of the image sensor DET1 may be e.g. higher than 95%. The fill factor of the image sensor DET1 may mean the ratio of the area covered by the image IMG1 to the area of the active area.

The imaging device 100 may have a first focal length f_{x c} for refraction in the horizontal plane defined by the directions SX and SZ. The imaging device 100 may have a second focal length f_{Y C} for refraction in the vertical plane defined by the directions SY and SZ. The second focal length f_{Y C} may be greater than the first focal length f_{x c}. The ratio (fy.c/fx.c) of the focal lengths may be e.g. in the range of 3.0 to 6.0. The ratio (fy.c/fx.c) may also be called e.g. as the anamorphic compression ratio of the imaging device 100. The anamorphic compression ratio (fy.c/fx.c) may be e.g. in the range of 3.0 to 6.0.

The dimensions W_DETI, h_DETi of the active area of the image sensor DET1 defines the maximum dimensions of the optical image IMG1 , which can be captured by the image sensor DET1 . The relationship between the angular dimensions of the object surface SRF1 and the dimensions of the optical image IMG1 may be approximated e.g. by the following equations:

(4a)

The image IMG1 formed by the imaging device 100 may match with the image sensor DET1 when the focal lengths fx and fy fulfill the equations (4a) and (4b). The focal lengths fx and fy may be given e.g. by the following equations:

(5a)

The lenses of the imaging device 100 may be selected such that the imaging device 100 provides the focal lengths fx,c and fy,c determined by the equations (5a) and (5b).

For example, the object surface SRF1 may have angular dimensions Δφ=180°, and Δθ=30°, and the active area of the image sensor DET1 may have dimensions W_DETI= 2.8. mm and h_DETi=9.6 mm. The corresponding focal lengths fx_,c = 4.07 mm, and fy_,c = 17.91 mm may be calculated from the equations (5a) and (5b). The imaging device 100 may be arranged to operate such that the focal length f_{x c} = 4.07 mm, and fy_,c = 17.91 mm. In this example, the aspect ratio of the active area is 4:3, and the angular height ΔΘ of the viewing region is 16.67% of the angular width Δφ of the viewing region.

Fig. 4 illustrates how the image IMG1 may be formed from light received from the cylindrical surface SRF1 . The cylindrical surface SRF1 may have an angular width Δφ and an angular height ΔΘ. The optical axis AX0 of the imaging device 100 may intersect the cylindrical surface SRF1 at the point Po. The upper edge of the surface SRF1 may have an angular coordinate ΘΜΑΧ- The right side of the surface SRF1 may have an angular coordinate ΦΜΑΧ- The angular width Δφ may be equal to 2-φ_ΜΑχ- The height ΔΘ may be equal to 2-ΘΜΑΧ- The length As may be equal to Ι_₀ - ΦΜΑΧ- The height Ay may be equal to L₀-tan(9MAx)- The surface SRF1 may have an aspect ratio Δφ/ΔΘ.

The aspect ratio of the surface SRF1 may be e.g. greater than 3:1 , greater than 4:1 , greater than 5:1 , or even greater than 6:1 . The aspect ratio of the surface SRF1 may be e.g. in the range of 3 to 5. The aspect ratio of the surface SRF1 may be e.g. in the range of 3 to 7 (i.e. in the range of 3:1 to 7:1 ).

The horizontal field of view Δφ may be e.g. in the range of 120° to 180°. The horizontal field of view Δφ may even be greater than 180°. The vertical field of view ΔΘ may be e.g. in the range of 40° to 60°. The vertical field of view may be e.g. in the range of 15% to 34% of the horizontal field of view. The value 15% may substantially correspond to the aspect ratio 7 (1 /0.15=6.7), and the value 34% may substantially correspond to the aspect ratio 3 (1 /0.34=2.9).

The angular width Δφ of the viewing region may be e.g. in the range of 120° to 160°, and the angular height ΔΘ of the viewing region may be e.g. in the range of 15% to 34% of the angular width Δφ of the viewing region. The angular width Δφ of the viewing region may be e.g. in the range of 160° to 220°, and the angular height ΔΘ of the viewing region may be e.g. in the range of 15% to 34% of the angular width Δφ of the viewing region. The angular width Δφ of the viewing region may be e.g. in the range of 220° to 270°, and the angular height ΔΘ of the viewing region may be e.g. in the range of 15% to 34% of the angular width Δφ of the viewing region.

The angular width Δφ of the viewing region may be e.g. in the range of 120° to 270°, and the angular height ΔΘ of the viewing region may be e.g. in the range of 15% to 34% of the angular width Δφ of the viewing region.

The fill factor of the image sensor may be e.g. higher than 95%, corresponding to the horizontal and vertical field of view. The aspect ratio of the image sensor may be e.g. in the range of 1 :1 to 2:1 .

The aspect ratio of the image sensor may be e.g. 4:3 or 16:9. The aspect ratio of the view region may be e.g. substantially equal to 7:1 , 6:1 , 5:1 , 4:1 , or 3:1 .

The anamorphic unit 10 may be arranged to form a virtual image VMG1 of the cylindrical surface SRF1 by refracting light received from the surface SRF1 . The virtual image VMG1 may be a sharp image. The anamorphic unit 10 may be arranged to form a substantially sharp virtual image VMG1 of the cylindrical surface SRF1 by refracting light received from the surface SRF1 .

The virtual image VMG1 may have an angular width Δφ' and an angular height Δθ'. The virtual image VMG1 may have an image point ΡΌ, which corresponds to the central object point P₀. The virtual image VMG1 may have an image point P'_k, which corresponds to the object point P_k. . The virtual image VMG1 may comprise a sub-image SUB1 ' of the object O1 . The virtual image VMG1 may have an aspect ratio Δφ'/ΔΘ'. The aspect ratio Δφ'/ΔΘ' may be e.g. smaller than 2. The anamorphic unit 10 may be interpreted to provide the virtual image VMG1 by straightening the curved surface SRF1 , and by compressing the straightened surface SRF1 in the direction SX. The focusing optics 20 may "see" the virtual image VMG1 through the anamorphic unit 10. The anamorphic unit 10 may provide the virtual image VMG1 such that the vertical scaling factor ΔΘ7ΔΘ is substantially equal to one. The anamorphic unit 10 may provide the virtual image VMG1 such that the horizontal scaling factor Δφ'/Δφ is substantially smaller than one. The anamorphic unit 10 may provide the virtual image VMG1 such that the horizontal scaling factor Δφ'/Δφ is substantially smaller than the vertical scaling factorABVAB.

The focusing unit 20 may form the real image IMG1 of the virtual image VMG1 by focusing light refracted by the anamorphic unit 10. The focusing unit 20 may be understood to provide the real image IMG1 by radially compressing the virtual image VMG1 towards the axis AX0. Depending on the properties of the focusing optics 20, the virtual image IMG1 may be planar or slightly curved so that the real image IMG1 may be substantially planar. The image IMG1 may have a width Au and a height Δν. The position of the image point P"_k may be specified by coordinates Uk,v_k. The coordinates Uk,v_k may specify the position of the image point P"_k with respect to a reference point. In particular, the coordinates u_k,v_k may specify the position of the image point P"_k with respect to the central point P"₀. The optical axis AX0 may intersect the image sensor DET1 at the central point P"₀.

The image sensor DET1 may have a width WDETI 3nd a height hoEn■ The image sensor DET1 may have an aspect ratio W_DETI/ ΠΟΕΤΙ - The aspect ratio WDETI h_DETi may be e.g. smaller than 2. For example, the aspect ratio W_DETI/ h_DETi may be e.g. 4:3 or 16:9.

The image IMG1 of the surface SRF1 may cover e.g. more than 80% of the active area of the image sensor DET1 . The image IMG1 may cover 100% of the active area of the image sensor DET1 . The width Au of the image IMG1 may be greater than 80% of the width W_DETI of the image sensor DET1 , and the height Δν of the image IMG1 may be greater than 80% of the height h_DETi of the image sensor DET1 . The image IMG1 of the surface SRF1 may cover e.g. more than 80% of the active area of the image sensor DET1 such that the width Au of the image IMG1 is equal to the width W_DETI of the image sensor DET1 , or the height Δν of the image IMG1 is equal to the height h_DETi of the image sensor DET1 . The image IMG1 of the surface SRF1 may cover e.g. more than 95% of the active area of the image sensor DET1 such that the width Au of the image IMG1 is equal to the width W_DETI of the image sensor DET1 , and the height Δν of the image IMG1 is equal to the height h_DETi of the image sensor DET1 .

The image sensor DET1 may convert the real optical image IMG1 into a digital image DIMG1 . The image sensor DET1 may capture the image IMG1 . The object surface SRF1 may have an (angular) aspect ratio Δφ/ΔΘ, and the optical image IMG1 may have an aspect ratio Au/Av. The ratio (Δφ/ΔΘ)/(Δυ/Δν) of these aspect ratios may be called e.g. as the anamorphic compression coefficient of the imaging device 100. The anamorphic compression coefficient may be e.g. in the range of 3.0 to 5.0.

The dimensions of the optical elements of the anamorphic unit 10 and the focusing unit 20 may be selected e.g. such that the anamorphic compression coefficient is in the range of 3.0 to 5.0 in a situation where the angular width Δφ of the viewing region is in the range of 120° to 180°, and the angular height ΔΘ of the viewing region is in the range of 15% to 34% of the angular width Δφ of the viewing region.

The dimensions of the optical elements of the anamorphic unit 10 and the focusing unit 20 may be selected e.g. such that the anamorphic compression coefficient is in the range of 3.0 to 5.0 in a situation where the angular width Δφ of the viewing region is in the range of 160° to 270°, and the angular height ΔΘ of the viewing region is in the range of 15% to 34% of the angular width Δφ of the viewing region. The dimensions of the optical elements of the anamorphic unit 10 and the focusing unit 20 may be selected e.g. such that the anamorphic compression coefficient is in the range of 3.0 to 5.0 in a situation where the angular width Δφ of the viewing region is in the range of 120° to 270°, and the angular height ΔΘ of the viewing region is in the range of 15% to 34% of the angular width Δφ of the viewing region.

The modulation transfer function of the imaging apparatus may depend on the modulation transfer function of the imaging device 100 and on the modulation transfer function of the image sensor DET1 . The modulation transfer function of the image sensor DET1 may depend on the height and width of the detector pixels of the image sensor DET1 .

Fig. 5a shows, by way of example, mapping from the tangent tan(9k) of the vertical angular position 9k of an object point P_k to the vertical position v_k of the corresponding image point P"_k. The image point P"_k may be the image of the object point P_k. The vertical position v_k of the image point P"_k may depend on the vertical angular position 9k, and also (to a lesser extent) on the horizontal angular position φk of the object point P_k. The vertical position v_k of the image point P"_k may be expressed by a mapping function

where the vertical position v_k depends on the angle φk and on the tangent tan(9k) of the angle 9k.

The dashed curve of Fig. 5a shows the vertical position

of the image point P"_k as the function of the tangent tan(9k) of the vertical angular position 9k when the object point P_k is at the right edge

of the object surface SRF1 . The solid curve of Fig. 5a shows the vertical position

of the image point P"_k as the function of the tangent tan(9k) of the vertical angular position 9k when the object point P_k is on a vertical line at the center ^k=0) of the object surface SRF1 .

The relationship between the tangent tan(9k) of the vertical angular position 9k and the vertical position v_k may be nearly linear at each object point of the object surface SRF1 within the viewing region VREG1 , i.e. when - ΦΜΑΧ≤ΦΙ<≤⁺ΦΜΑΧ, and when -9_MAx≤9k≤+9_MAx- The curves of Figs. 5a and 5b may illustrate image distortion e.g. in an embodiment, where the width As of the cylindrical object surface SRF1 may be e.g. 15.0 m, the height Ay of the object surface SRF1 may be e.g. 2.6 m, and the radius L₀ of curvature may be e.g. 5.0 m. The corresponding angular width Δφ of the object surface SRF1 may be e.g.

The width WDETI of the light-detecting area of the image sensor DET1 may be e.g. equal to 1 2.8 mm, and the height h_DETi of the light-detecting area may be e.g. equal to 9.6 mm. The aspect ratio of the image sensor DET1 may be e.g. 4:3.

Fig. 5b shows, by way of example, the relative vertical distortion (v_k- Vk,REF) Vk,REF caused by the mapping from an object point P_k to the corresponding image point P"_k. Vk.REF denotes an ideal vertical position of an image point of the object point P_k without distortion. The ideal vertical position v_K,REF may be calculated e.g. according to the following equation:

Vk,REF = ^fY,C - ^tan(^ek ) (6)

9_k may denote the input elevation angle of the input beam received from the object point P_k. The curves of Fig. 5b may be interpreted to illustrate how much the curves of Fig. 5a deviate from a straight line.

The relative difference between vertical magnification (d97d9) at a corner of the real image (IMG1 ) and vertical magnification (d9"/d9) at the center of the real image (IMG1 ) may be e.g. smaller than 5%.

The imaging device 100 may provide substantially constant vertical magnification for several different object points (P_k) which are located on the cylindrical object surface SRF1 . The imaging device 100 may provide substantially sharp image points (P'V) for the different object points (P_k) which are located on the cylindrical object surface SRF1 .

Input azimuth angle means the azimuth angle of an input beam, and input elevation angle means the elevation angle of the input beam. The parameters of the surfaces of the lenses of the anamorphic unit 10 may be selected e.g. such that the modulation transfer function (MTF) of the imaging device 100 at a predetermined spatial frequency is higher than 50% for each input azimuth angle (φκ) which is in the range of 0° to Δφ/2 when the input elevation angle 9k = 0°, and such that the modulation transfer function (MTF) of the imaging device (500) at the predetermined spatial frequency (vi) is higher than 50% for each input azimuth angle (φκ) which is in the range of 0° to Δφ/2 when the input elevation angle 9k is equal to the maximum value ΔΘ/2. Δφ denotes the angular width and ΔΘ denotes the angular height of the viewing region VREG1 . The modulation transfer function (MTF) at the predetermined spatial frequency may have a first value MTF1 when φκ=0^ο, 9k = 0°. The modulation transfer function (MTF) at the predetermined spatial frequency may have a second value MTF2 when φι<=Δφ/2, 9k = ΔΘ/2. The parameters of the surfaces of the lenses of the anamorphic unit 10 may be selected e.g. such that the sum MTF1 +MTF2 is maximized.

Fig. 5c shows a horizontal line LIN 1 , a vertical line LIN2, and a diagonal line LIN3 positioned on the optical image IMG1 . The lines LIN1 , LIN2, and LIN3 may intersect the center P"₀ of the image IMG1 . The lines LIN1 , LIN2, and LIN3 may intersect the optical axis AX0 of the imaging device 100, and the lines LIN1 , LIN2, and LIN3 may be perpendicular to the axis AX0. The dimensions and materials of the optical elements of the imaging device 100 may be selected such that optical performance of the imaging device 100 is optimized for image points P'V which are on the diagonal line LIN3. The optical performance may be optimized for image points P'V which are on the diagonal line LIN3 outside the center P"₀. The optical performance may be optimized for image points P'V which are on the diagonal line LIN3 close to the corner point (Au/2,Av/2) of the image IMG1 . The optical performance may be optimized for image points which are on the line LIN1 outside the center P"o, for image points which are on the line LIN2 outside the center, and also for image points which are on the line LIN3 outside the center.

The parameters of the surfaces of the lenses of the anamorphic unit 10 may be selected e.g. such that the minimum value of the modulation transfer function (MTF) at the predetermined spatial frequency is maximized for image points, which are located on the diagonal LIN3 of the image IMG1 . Referring to Fig. 6, the apparatus 500 may comprise a data processor CNT1 , which may be configured to form a panorama image PAN1 from the digital image DIMG1 captured by the image sensor DET1 . The data processor CNT1 may be configured to form the panorama image PAN1 e.g. by scaling the digital image DIMG1 by a first scaling coefficient in the horizontal direction and by scaling the digital image DIMG1 by a second different scaling coefficient in the horizontal direction. The optical image IMG1 may be slightly distorted when compared with the cylindrical object surface SRF1 . Consequently, also the digital image DIMG1 captured by the image sensor DET1 may be slightly distorted when compared with the cylindrical object surface SRF1 . The data processor CNT1 may be configured to correct the distortion of the digital image DIMG1 . Referring to Fig. 7, the imaging apparatus 500 may comprise the imaging device 100 and the image sensor DET1 . The imaging apparatus 500 may optionally comprise a memory MEM1 for storing the digital image DIMG1 captured by the image sensor DET1 . The imaging apparatus 500 may optionally comprise a data processor CNT1 for processing the digital image DIMG1 . The data processor CNT1 may be configured to form an image PAN1 from the digital image DIMG1 . The image PAN1 may be a panorama image. The aspect ratio of the image PAN1 may be e.g. greater than or equal to 3:1 . The imaging apparatus 500 may optionally comprise a memory MEM2 for storing the image PAN1 . The imaging apparatus 500 may optionally comprise a memory MEM3 for storing computer program code PROG1 . The imaging apparatus 500 may optionally comprise a user interface UIF1 for receiving input from a human user. The user interface UIF1 may comprise e.g. a touch screen and/or keys for selecting operating parameters of the imaging apparatus 500. The user interface UIF1 may comprise e.g. a display for displaying the digital image DIMG1 and/or the image PAN1 . The imaging apparatus 500 may optionally comprise a communication unit RXTX1 for sending image data DIMG1 and/or PAN1 . The communication unit RXTX1 may communicate data e.g. by wireless communication, via an electric cable, and/or via an optical cable. The communication unit RXTX1 may communicate data e.g. with a mobile phone network. The communication unit RXTX1 may communicate data e.g. with the Internet. COM1 denotes a data transmission signal.

The apparatus 500 may comprise at least one processor CNT1 , a memory MEM3 including computer program code PROG1 stored in the memory MEM3. The computer program code PROG1 may be configured to, with the at least one processor CNT1 , cause the apparatus 500 to perform at least one of the following:

- capturing a digital image DIMG1 ,

- forming a panorama image PAN1 from the digital image DIMG1 ,

- storing the digital image DIMG1 and/or the panorama image PAN1 in a memory, and/or

- transmitting the digital image DIMG1 and/or the panorama image PAN1 . The imaging device 100 may provide a wide viewing region. The imaging device 100 may be e.g. positioned at a corner of a building or vehicle. A first wall may meet a second wall at the corner such that the angle between the walls is substantially equal to 270°. The horizontal angular width Δφ of the viewing region of the imaging device 100 may cover the full 270° angle between said walls.

The imaging device 100 or apparatus 500 may be used e.g. as a part of a surveillance system, as part of a navigation system, or as a part of a machine vision system. A surveillance system may comprise the imaging device 100 or the apparatus 500 for capturing a panorama image of an environment. A navigation system may comprise the imaging device 100 or the apparatus 500 for capturing a panorama image of an environment. The imaging device 100 or the apparatus 500 may be attached e.g. to a vehicle. The captured image may be compared with image data e.g. in order to determine the position of the imaging device 100 with respect to the environment. The captured image may be compared with image data e.g. in order to determine the position of the vehicle with respect to the environment. A machine vision system may comprise the imaging device 100 or the apparatus 500 for capturing a panorama image of a product. The panorama image may be analyzed in order to control the manufacturing process of the product. An imaging apparatus 500 may be attached to a vehicle, in particular to a car. The imaging apparatus 500 may capture a digital image DIMG1 of the environment of the vehicle, and the digital image DIMG1 and/or the panorama image PAN1 may be displayed to the driver of the vehicle by using the user interface UIF1 .

The imaging device 100 may be used as a part of a laser distance measuring device.

The image sensor DET1 may be e.g. a CMOS sensor or a CCD sensor. The imaging device 100 or apparatus 500 may be arranged to capture a video of the viewing region. The video may comprise one or more digital images DIMG1 captured by the image sensor DET1 .

An imaging apparatus 500 may be arranged to operate as an image projector. The image sensor DET1 may be replaced with a two-dimensional light modulator, and the surface SRF1 may operate as a projection screen. The light modulator may be e.g. a digital micro mirror device, a liquid crystal modulator, or an array of light emitting diodes. The imaging apparatus 500 may comprise the imaging device 100 and the light modulator. The light modulator may be arranged to form an image, and the imaging device 100 may be arranged to project the image on the surface SRF1 . In an embodiment, the anamorphic unit 10 may be manufactured, stored, and/or transported separately from the focusing unit 20. A digital camera CAM1 may comprise the focusing unit 20 and the image sensor DET1 . The anamorphic unit 10 may be provided as a separate unit, which may be attached to the digital camera. The anamorphic unit 10 may be attached e.g. to the digital camera by an end user of the apparatus 500.

In an embodiment, the digital image DIMG1 may be stored in a memory and/or displayed to a viewer without digitally correcting the distortion. Thanks to the anamorphic unit, the relative vertical distortion of the digital image DIMG1 may be so small that a human viewer may recognize the images of the objects also without digitally correcting the distortion. The digital image DIMG1 may comprise an image of a linear object such that the image of the linear object may be substantially linear without digitally correcting the distortion. The aspheric unit 10 may be attached to a digital camera, and the digital images DIMG1 provided by the digital camera may be stored and/or used without a need to install new software to the camera.

Fig. 8 shows a prior art solution for capturing a panorama image. For the person skilled in the art, it will be clear that modifications and variations of the devices and the methods according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.

Claims

1 . An imaging device (100,500), comprising:

wherein the anamorphic unit (10) comprises two or more refractive lenses (LNS1 1 , LNS12) which have been selected such that the horizontal refractive power (P_x,c) of the imaging device (100) is greater than 1 .5 times the vertical refractive power (P_y,c) of the imaging device (100), and the anamorphic unit (10) is arranged to form the virtual image (VMG1 ) by refracting light (B0_k) received from the cylindrical viewing region (SRF1 ) such that the aspect ratio (Δφ'/ΔΘ') of the virtual image (VMG1 ) is lower than the aspect ratio (Δφ/ΔΘ) of the viewing region (SRF1 ).

2. The device (100,500) of claim 1 wherein the anamorphic unit (10) is afocal.

3. The device (100,500) of claim 1 or 2 wherein the first refractive lens (LNS1 1 ) of the device (100,500) on the object side of the device (100,500) is a negative cylindrical meniscus lens.

4. The device (100,500) according to any of the claims 1 to 3 wherein the horizontal refractive power (P_X,B) of the focusing unit (20) is equal to the vertical refractive power (P_Y,B) of the focusing unit (20) in a situation where the focusing unit (20) is operated without the anamorphic unit (10).

5. The device (100,500) according to any of the claims 1 to 4 wherein the anamorphic unit (10) comprises a first negative cylindrical meniscus lens (LNS1 1 ), and a second bi-concave negative cylindrical lens LNS12.

6. The device (100,500) according to any of the claims 1 to 5 wherein the anamorphic unit (10) comprises one or more lenses (LNS14, LNS15) arranged to match the optical output of the anamorphic unit 10 with the viewing region of the focusing unit 20.

7. The device (100,500) according to any of the claims 1 to 6, wherein the angular width (Δφ) of the viewing region (SRF1 ) is in the range of 120° to 270°, and the angular height (ΔΘ) of the viewing region (SRF1 ) is in the range of 15% to 34% of the angular width (Δφ) of the viewing region (SRF1 ).

8. The device (100,500) according to any of the claims 1 to 7, wherein the aspect ratio (Δφ/ΔΘ) of the viewing region (SRF1 ) is in the range of 3:1 to 7:1 .

9. The device (500) according to any of the claims 1 to 8 comprising an image sensor (DET1 ), wherein the imaging device (100) is arranged to form the real image (IMG1 ) on the image sensor (DET1 ), and the aspect ratio (w_DETi hDETi ) of the active area of the image sensor (DET1 ) is lower than or equal to 2:1 .

10. The device (500) of claim 9, wherein the real image (IMG1 ) covers more than 95% of the active area of the image sensor (DET1 )

1 1 . The device (500) of claim 9 or 10, wherein the image sensor (DET1 ) is arranged to provide a digital image (DIMG1 ), and the device (500) comprises a data processor (CNT1 ), which is configured to provide a panorama image (PAN1 ) by correcting distortion of the digital image (DIMG1 ).

12. The device (500) according to any of the claims 1 to 1 1 , wherein the relative difference between vertical magnification (d97d9) at a corner of the real image (IMG1 ) and vertical magnification (d9"/d9) at the center of the real image (IMG1 ) is smaller than 5%.

13. A method for forming a real image (IMG1 ) of a viewing region (SRF1 ), the method comprising:

- forming a real image (IMG1 ) of the auxiliary virtual image (VMG1 ) by using a focusing unit (20), wherein the anamorphic unit (10) comprises two or more refractive lenses (LNS1 1 , LNS12) which have been selected such that the horizontal refractive power (Px_,c) of the imaging device (100) is greater than 1 .5 times the vertical refractive power (P_y,c) of the imaging device (100), and the anamorphic unit (10) is arranged to form the virtual image (VMG1 ) by refracting light (B0_k) received from the cylindrical viewing region (SRF1 ) such that the aspect ratio (Δφ'/ΔΘ') of the virtual image (VMG1 ) is lower than the aspect ratio (Δφ/ΔΘ) of the viewing region (SRF1 ).

14. The method of claim 13, wherein the anamorphic unit (10) is afocal, and the first refractive lens (LNS1 1 ) of the anamorphic unit (10) is a negative cylindrical meniscus lens.