OBJECTIVE, USE OF AN OBJECTIVE AND MEASUREMENT SYSTEM

Abstract

The invention relates to a hybrid objective with fixed focal length, which has a total of four lenses. Two lenses consist of glass and two lenses consist of plastic. The objective is suitable for use in a LID AR measurement system.

Claims

1. An objective with a fixed focal length F, comprising at least a first lens with a first focal length f.sub.1 made of a first glass, a second lens with a second focal length f.sub.2 made of a first plastic, a third lens with a third focal length f.sub.3 made of a second glass, and a fourth lens with a fourth focal length f.sub.4 made of a second plastic, wherein the first lens is designed as a meniscus with a negative refractive power D.sub.1=1/f.sub.1, the third lens has a positive refractive power D.sub.3=1/f.sub.3>0, the sum D.sub.3+D.sub.4 of the refractive power D.sub.3=1/f.sub.3 of the third lens (8) and the refractive power D.sub.4=1/f.sub.4 of the fourth lens is positive, the fourth lens has at least one aspheric surface, and wherein $.Math.\frac{f_2}{f_4}+1.Math.\le 0.1\mathrm{and}/\mathrm{or}.Math.\frac{1}{f_2}+\frac{1}{f_4}.Math.\le \frac{0.015}{F}.$

2. The objective as claimed in claim 1, wherein the first lens and/or the second lens have at least one aspheric surface.

3. The objective as claimed in claim 1, wherein the first lens, the second lens, the third lens, and the fourth lens are arranged one after the other in a z direction in the beam path, or wherein at a light source, the fourth lens, the third lens, the second lens, and the first lens are arranged one after the other in the −z direction in the beam path.

4. The objective as claimed in claim 1, wherein a stop is arranged between the second lens and the third lens.

5. The objective as claimed in claim 1, wherein it has a focal length F of between 2 mm and 5 mm and/or in that the focal length f.sub.1 of the first lens is between −20 times and −4 times the focal length F of the objective and/or in that the focal length f.sub.3 of the third lens is between 2 and 5 times the focal length F of the objective and/or in that the focal length f.sub.4 of the fourth lens is between 2 and 10 times the focal length F of the objective and/or in that the focal length f.sub.4 of the fourth lens is between 0.8 and 3 times the focal length f.sub.3 of the third lens.

6. The objective as claimed in claim 1, wherein it is designed to be approximately telecentric on the image side, wherein the image-side telecentricity error is less than 5°.

7. The objective as claimed in claim 1, wherein the objective has a photographic luminous intensity of at least 1:1.3.

8. The objective as claimed in claim 1, wherein the objective comprises a bandpass filter for separating the signal light of the light source from ambient light, in particular from daylight, or is operable together with a bandpass filter arranged outside the objective.

9. The objective as claimed in claim 1, wherein the objective is operable as a projection objective and/or in that the objective is operable as an imaging objective.

10. The use of an objective as claimed in claim 1 for a measurement system for at least one time-of-flight detection of at least one light beam.

11. A measurement system, comprising at least one objective as claimed in claim 1, at least one light source, and at least one matrix sensor.

12. The measurement system as claimed in claim 1, wherein the light source is a laser beam source or an LED and in that the light source is operated in a pulsed manner and in that the pulse length is between 1 ns and 1 ms.

13. The measurement system as claimed in claim 1, wherein the matrix sensor is a SPAD array and/or in that the light source is a VCSEL array or an LED array.

Description

[0054] The figures show the following:

[0055] FIG. 1 shows a first exemplary embodiment.

[0056] FIG. 2 shows the beam path of the first exemplary embodiment.

[0057] FIG. 3 shows a second exemplary embodiment.

[0058] FIG. 4 shows a measurement system according to the invention.

EXEMPLARY EMBODIMENTS

[0059] The invention will be explained below using exemplary embodiments.

[0060] FIG. 1 shows a first exemplary embodiment. An objective 1 with a fixed focal length F is shown. The objective has an optical axis 3. The optical axis is in the z direction. In the figures, the image plane is disposed on the right, i.e. in the z direction, while the object plane is situated to the left of the objective. The objective comprises a first lens 5, a second lens 6, and a third lens 8, and a fourth lens 12. The lenses are arranged sequentially in the z direction in the order mentioned.

[0061] The first lens is produced from a first glass. The first lens is a spherical meniscus lens with negative refractive power, i.e. it has two opposing spherical optical surfaces.

[0062] The second lens 6 is produced from a first plastic. The second lens 6 is designed as a bi-aspheric diverging lens. In this exemplary embodiment, the second lens 6 is designed such that the object-side surface 9 (on the left in the illustration) is concave in a central region 10 (indicated with a bracket in the figure) and convex in a peripheral region 11.

[0063] The third lens 8 is produced from a second glass. The third lens 8 is a spheric converging lens.

[0064] The fourth lens 12 is designed as a bi-aspheric converging lens. It is produced from a second plastic. The second plastic here is the same as the first plastic.

[0065] A spacer 13 is arranged between the second lens 6 and the third lens 8. The spacer has an opening which acts as a stop 14. The opening is formed from a first cone frustum lateral surface 15 and a second cone frustum lateral surface 16. The intersection edge of the cone frustum lateral surfaces is an intersection edge 17, which represents the aperture. The stop is designed as an intersection edge. In a modification of the exemplary embodiment that is not shown in the figures, the stop can also be designed as a stop ring. In a further modification of the exemplary embodiment that is not shown in the figures, the stop is selected in the plane of a contact surface 7 of the second lens. It is then possible to make this surface such that it absorbs light and to use it as a stop.

[0066] A filter 18 is additionally provided, which separates the signal light from the ambient light.

[0067] FIG. 2 shows the beam path of the first exemplary embodiment. In this figure, the hatching of the lenses has been omitted in order to be able to better show the light beams 4, which represent the beam path 2. An image sensor for recording an image or a matrix sensor for detecting the time of flight of a light beam is arranged in the image plane 21.

[0068] The optical design is implemented according to Table 1 below:

TABLE-US-00001 TABLE 1 Radius of curvature Thickness/ Radius in No. Type Comment KR in mm distance in mm Material mm 1 STANDARD Object ∞ ∞ Air 0.000000 2 STANDARD Lens 1 29.264432 1.000000 Glass 1 (n = 1.5168) 13.421635 3 STANDARD 6.788618 5.450270 Air 6.680311 4 ASPHERE Lens 2 −13.088044 2.819898 Polymer 1 (n = 1.5300) 6.072270 5 ASPHERE 9.829847 2.770944 Air 2.800000 6 STANDARD Stop ∞ 1.447852 Air 2.350000 7 STANDARD Lens 3 82.915075 4.386519 Glass 2 (n = 1.9037) 4.289719 8 STANDARD −8.242710 0.221858 Air 5.275803 9 ASPHERE Lens 4 9.030488 5.000000 Polymer 2 (n = 1.5300) 5.679712 10 ASPHERE −9.938689 4.524408 Air 5.912429 11 STANDARD Filter ∞ 0.378000 n = 1.5000 4.382981 12 STANDARD Image ∞ 0.000000 4.325120

[0069] The first column gives a sequential number of a surface and is numbered from the object side. The “Standard” type designates a planar or spherically curved surface. The “ASPHERE” type designates an aspheric surface. A surface can be understood to mean an interface or lens surface. It should be noted that the object plane (no. 1), a stop (no. 6), and the image plane (no. 12) are additionally considered to be surfaces. Surfaces 2, 3, 4, 5, 7, 8, 9 and 10 are lens surfaces. These surfaces are denoted in FIG. 2 by the respective number as Surf 2, Surf 3, Surf 4, Surf 5, Surf 7, Surf 8, Surf 9 and Surf 10.

[0070] The Radius of curvature KR column indicates the radius of curvature of the respective surface. In the case of an aspheric surface, this is understood to mean the paraxial radius of curvature. In the table, the sign of a radius of curvature is positive if the shape of a surface is convex toward the object side, and the sign is negative if the shape of a surface is convex toward the image side. The specification—in the Radius of curvature column means that it is a planar surface. The distance between the i-th surface and the (i+1)-th surface on the optical axis is specified in the “Thickness/distance” column. The specification—in this column in no. 1 means that the object distance is infinite, i.e. an objective focused at infinity. For rows 2, 4, 7 and 9, this column gives the center thickness of the first, second, third and fourth lenses, respectively. In the Material column, the material between the respective surfaces is specified with the respective refractive index n. The refractive index n refers to a design wavelength for which the objective is designed. The design wavelength can for example be between 700 nm and 1100 nm or between 1400 nm and 1600 nm, for example at 905 nm, 915 nm, 940 nm, 1064 nm or 1550 nm. The Radius column specifies the outer radius of the respective surface. In the case of the stop (no. 6), that is the aperture. In the case of the lens surfaces, this is the maximum usable distance of the light beams from the optical axis, which, in the equation below, corresponds to the maximum value h for the respective surface.

[0071] In the following two tables (Table 2, Table 3), the coefficients of the aspheric surfaces are given for the respective surface number.

TABLE-US-00002 TABLE 2 No. C.sub.2 in mm−1 C.sub.4 in mm−3 C.sub.6 in mm−5 C.sub.8 in mm−7 4 0.0000000E+00 3.8946765E−03 −1.9916747E−04   9.3959964E−06 5 0.0000000E+00 7.2821395E−03 7.6976794E−04 −4.1404616E−04 9 0.0000000E+00 −3.2477297E−04  4.4136483E−05 −5.1107094E−06 10 0.0000000E+00 1.2815739E−03 3.1453468E−05 −4.9419416E−06

TABLE-US-00003 TABLE 3 No. C.sub.10 in mm−9 C.sub.12 in mm−11 C.sub.14 in mm−13 C.sub.16 in mm−15 4 −3.2268213E−07   7.3829174E−09 −9.9657773E−11   5.9756551E−13 5 9.9825464E−05 −1.0939844E−05 4.9478924E−07  0.0000000E+00 9 3.8726105E−07 −1.7725428E−08 4.2761827E−10 −4.3462716E−12 10 3.6159105E−07 −1.4520099E−08 2.6777834E−10 −1.8307264E−12

[0072] In the numerical values of the aspheric data, “E−n” (n: integer) means “×10−n” and “E+n” means “×10n”. Furthermore, the aspheric surface coefficients are the coefficients C.sub.m with m=2 . . . 16 in an aspheric expression represented by the following equation:

[00003]$Zd=\frac{h^2}{KR+\sqrt{K{R}^2-\left(1+k\right)h^2}}+{.Math.}_{m=2}^{16}{C}_m.Math.h^m,$

[0073] Zd is the depth of an aspheric surface (i.e. the length of a perpendicular from a point on the aspheric surface at a height h to a plane touching the vertex of the aspheric surface and perpendicular to an optical axis), h is the height (i.e. a length from the optical axis to the point on the aspheric surface), KR is the paraxial radius of curvature, and C.sub.m denotes the aspheric surface coefficients given below (m=2 . . . 16). Unspecified aspheric surface coefficients, here all with an odd-numbered index, are to be assumed to be zero. The coordinate h is to be used in millimeters, as is the radius of curvature; the result Zd is obtained in millimeters. The coefficient k is the conicity coefficient, which in the present exemplary embodiment is zero for all surfaces.

[0074] The focal length of the first lens is f.sub.1=−17.7 mm, that of the third lens is f.sub.3=8.7 mm. The focal length of the second lens is f.sub.2=−10.3 mm, that of the fourth lens is f.sub.4=9.95 mm. The objective has a focal length F of 2.78 mm.

[0075] In a modification of this exemplary embodiment, the objective is focused at a finite object distance. This can be accomplished by changing the image width. For this purpose, the distance in line no. 10 can be increased accordingly.

[0076] In a further modification (not shown), the objective can be used as a projection objective. For this purpose, a light source is arranged in the plane 21, rather than the sensor. A scene located in the negative z direction, identified as the −z direction in FIG. 1, upstream of the objective can then be illuminated.

[0077] FIG. 3 shows a second exemplary embodiment. This will be described in the following paragraphs. In this figure, the hatching of the lenses has been omitted in order to be able to better show the light beams 4, which represent the beam path 2. In accordance with the statements given under the first exemplary embodiment, the optical design of the second exemplary embodiment is implemented according to Table 4 below:

TABLE-US-00004 TABLE 4 Radius of Thickness/ curvature KR distance Radius in No. Type Comment in mm in mm Material mm 1 STANDARD Object ∞ ∞ Air 0.000000 2 STANDARD Lens 1 21.700000 1.000000 Glass 1 (n = 1.5168) 11.006013 3 STANDARD 5.900000 5.890000 Air 5.834891 4 ASPHERE Lens 2 −12.300000 1.000000 Polymer 1 (n = 1.5300) 4.874867 5 ASPHERE 14.200000 4.900000 Air 3.630000 6 STANDARD Stop ∞ 0.886000 Air 3.433203 7 STANDARD Lens 3 31.200000 3.150000 Glass 2 (n = 1.9037) 4.191108 8 STANDARD −10.500000 1.660000 Air 4.595297 9 ASPHERE Lens 4 7.400000 5.000000 Polymer 2 (n = 1.5300) 4.800000 10 ASPHERE −37.700000 4.570000 Air 4.800000 11 STANDARD Filter ∞ 0.500000 n = 1.5000 4.225592 12 STANDARD Image ∞ 0.000000 4.232742

[0078] The coefficients of the aspheric surfaces given in the following tables (Table 5, Table 6) (asphere-type surfaces with the respective number given in Table 4 above) were used:

TABLE-US-00005 TABLE 5 No. C.sub.2 in mm−1 C.sub.4 in mm−3 C.sub.6 in mm−5 C.sub.8 in mm−7 4 0.00000E+00 6.66623E−03 −4.20535E−04  1.52374E−05 5 0.00000E+00 8.56409E−03 −1.23883E−04 −2.27136E−05 9 0.00000E+00 1.22214E−04  1.25206E−05 −2.08983E−06 10 0.00000E+00 2.13660E−03 −7.95143E−05  1.52434E−05

TABLE-US-00006 TABLE 6 No. C.sub.10 in mm−9 C.sub.12 in mm−11 C.sub.14 in mm−13 C.sub.16 in mm−15 4 −3.32951E−07  3.16413E−09 0.00000E+00 0.00000E+00 5  2.40847E−06 −6.93424E−08 0.00000E+00 0.00000E+00 9  1.78721E−07 −8.46345E−09 2.09208E−10 −2.23688E−12  10 −1.56245E−06  9.49397E−08 −3.08630E−09  3.87340E−11

[0079] Unspecified aspheric surface coefficients, here all with an odd-numbered index, are to be assumed to be zero. The conicity coefficients k of all surfaces are also equal to zero in this example.

[0080] The focal length of the first lens is f.sub.1=−16.285 mm, that of the third lens is f.sub.3=9.278 mm. The focal length of the second lens is f.sub.2=−12.453 mm, that of the fourth lens is f.sub.4=12.307 mm. The objective of this second exemplary embodiment has a focal length F of 3.302 mm.

[0081] The stop is designed as an intersection edge. In a modification of the exemplary embodiment that is not shown in the figures, the stop can also be designed as a stop ring. In a further modification of the exemplary embodiment that is not shown in the figures, the stop is selected in the plane of a contact surface 7 of the second lens. It is then possible to make this surface such that it absorbs light and to use it as a stop.

[0082] In a modification of this exemplary embodiment, the objective is focused at a finite object distance. This can be accomplished by changing the image width. For this purpose, the distance in line no. 10 can be increased accordingly.

[0083] In a further modification (not shown), the objective can be used as a projection objective. For this purpose, a light source is arranged in the plane 21, rather than the sensor. A scene located in the negative z direction, identified as the −z direction in FIG. 3, upstream of the objective can then be illuminated.

[0084] The design wavelength of the first and second exemplary embodiments is 905 nm. Modifications of the exemplary embodiments can also be used with other wavelengths stated in the description.

[0085] FIG. 4 shows a measurement system according to the invention. The measurement system 19 comprises a transmitter objective 22, a receiver objective 23, a light source 20, and a matrix sensor 21. The light source illuminates one or more objects 24 with transmitter light 25. The matrix sensor detects the time of flight of the reflected light 26.

REFERENCE SIGNS

[0086] 1. Objective [0087] 2. Lens arrangement with beam path [0088] 3. Optical axis [0089] 4. Light beam [0090] 5. First lens [0091] 6. Second lens [0092] 7. Contact surface [0093] 8. Third lens [0094] 9. Object-side surface of the second lens [0095] 10. Central region [0096] 11. Peripheral region [0097] 12. Fourth lens [0098] 13. Spacer [0099] 14. Stop [0100] 15. First cone frustum lateral surface [0101] 16. Second cone frustum lateral surface [0102] 17. Intersection edge [0103] 18. Filter [0104] 19. Measurement system [0105] 20. Light source [0106] 21. Matrix sensor [0107] 22. Transmitter objective [0108] 23. Receiver objective [0109] 24. Object [0110] 25. Transmitter light [0111] 26. Reflected light