DE102019131001B3 - Lens, use of a lens and measuring system - Google Patents

Abstract

The invention includes a hybrid fixed focal length lens comprising four lenses. Two lenses are made of glass and two lenses are made of plastic. The lens is suitable for use in a LIDAR measuring system.

Description

Technical area

The invention relates to an objective with a fixed focal length. Such an objective is particularly suitable for use in a measuring system for transit time detection of a light beam (LIDAR). LIDAR is the abbreviation for light detection and ranging. LIDAR lenses mostly work in a very small wavelength range in the near infrared, typically 800-2000nm wavelength. Lasers are often used for lighting. In this case, the lenses must be able to compensate for the narrow bandwidth of the laser source and any drift in the wavelength with the temperature.

State of the art

Out WO 2017/180277 A1 a sensor with a SPAD array is known. The SPAD array can comprise avelance photodiodes (APD) as well as bipolar or field effect transistors in order to activate a bias line by line.

Out CN 205829628 U a LIDAR system with a VCSEL array and a SPAD array is known.

Out WO2017 / 164989 A1 an integrated lighting and detection system for LIDAR-based three-dimensional image recording is known. An objective with four lenses is proposed. A pulsed laser light source is proposed for illumination. In one embodiment, an array of several LIDAR measuring devices, consisting of laser emitters and detectors, is used. However, such a procedure is very complex.

Out WO2016 / 204844 A1 a LIDAR system with electrically adjustable light direction elements is known.

Out US 2016/0161600 A1 a LIDAR system with a SPAD array as a detector is known. Laser beams are used for illumination, which are controlled by means of integrated photonic circuits using optical phase arrays.

Out WO2015 / 189024 A1 a vehicle LIDAR system is known with a solid-state laser and a deflectable mirror.

Out WO2015 / 189025 A1 a vehicle LIDAR system is known with a pulse laser and a deflectable mirror and a CMOS image sensor.

Out WO 2015/126471 A2 a LIDAR device is known with an array of emitter / detector units.

Out US 2007/0181810 A1 a vehicle LIDAR system is known with a VCSEL array for lighting.

Out US 2014/0049842 A1 an imaging objective with four lenses is known which can be used for cameras in vehicles or for surveillance. The disadvantage is that the imaging properties can be temperature-dependent if two of the lenses are made from inexpensive plastic.

Object of the invention

The object of the invention is to provide an inexpensive, bright lens which can be operated over a wide temperature range and has the best possible image-side telecentricity and low F-theta distortion.

In particular, the objective should be suitable for LIDAR systems with detector arrays, for example SPAD arrays. In particular, the objective should be suitable for LIDAR systems without moving parts. In addition, the lens can be suitable as an imaging lens or as a projection lens.

Solution of the task

The object is achieved by an objective according to claim 1, a use according to claim 10 and a measuring system according to claim 11.

Advantages of the invention

The lens is inexpensive to manufacture and particularly suitable for LIDAR applications. It is characterized by passive athermalization, high light intensity, good telecentricity on the image side and low F-theta distortion. It can also be suitable for other applications as an imaging lens or as a projection lens.

description

An objective according to the invention has a fixed focal length F. It includes at least a first lens ( 5 ) with a first focal length f ₁ made of a first plastic, a second lens with a second focal length f ₂ made of a second plastic, a third lens with a third focal length f ₃ made of a first glass and a fourth lens with a fourth focal length f ₄ a second glass. The indices of the focal lengths are selected according to the number of the respective lens. As is known, the reciprocal of each focal length is its refractive power. A refractive power can thus be assigned to each of the lenses.

According to the invention, the refractive power D _{3 =} 1 / f _{3 of} the third lens is positive and the refractive power D ₄ = 1 / f _{4 of} the fourth lens is also positive.

According to the invention, the focal lengths are chosen such that the magnitudes of the focal lengths | f ₁ | of the first lens and | f ₂ | of the second lens are more than 7 times the focal length F of the lens and / or the amount of the sum of the refractive powers | D ₁₊ D ₂ | from the refractive power D ₁ = 1 / f _{1 of} the first lens and the refractive power D ₂ = 1 / f _{2 of} the second lens is less than 0.125 times the refractive power D = 1 / F of the objective. The first condition can be expressed as follows: | f ₁ |> 7F and | f ₂ |> 7F. The second condition can be expressed as follows: | 1 / f ₁ + 1 / f ₂ | <0.125 / F. According to the invention, at least one of these conditions is met. The focal lengths can advantageously be chosen so that both conditions are met. A particularly good passive athermalization of the lens can then be achieved.

The focal length of a lens can be the focal length with respect to paraxial (in the sense of on-axis) rays in an external medium of the refractive index 1 be understood.

According to the invention, the first lens and the second lens together have at least two aspherical surfaces. The first lens and / or the second lens can advantageously be designed as biaspherical lenses, particularly advantageously both of the lenses mentioned.

An aspherical lens can be a lens with at least one aspherical optical surface. The first lens can also be designed as a biaspherical lens. A biaspherical lens can be understood as a lens that has two opposing aspherical optical surfaces. The first lens can have at least one free-form surface.

The third lens and the fourth lens can advantageously be designed as spherical lenses. A spherical lens can be understood to be a lens that has two opposing spherical optical surfaces. A spherical lens can also be called a bispherical lens. One of the spherical surfaces can be a plane surface. A plane surface can be understood as a spherical surface with an infinite radius of curvature.

It can also be advantageous if the third lens and the fourth lens are spherical lenses, and the first and second lenses are aspherical lenses, i. are each formed with at least one aspherical surface. The first lens can particularly advantageously be designed as a biaspherical lens. Both the first lens and the second lens can very particularly advantageously be designed as biaspherical lenses.

The first lens, the second lens, the third lens and the fourth lens can advantageously be arranged one after the other in a z direction in the beam path. The image plane of the objective can be arranged in the z direction after the fourth lens. An object plane can be arranged in front of the first lens. Then it can Lens be an imaging lens. An image sensor for recording an image or a matrix sensor for detecting the transit time of light beams can be arranged in the beam path after the fourth lens, advantageously in the image plane of the objective. The light rays can propagate from the object to the image plane with a component in the z direction.

A light source, the fourth lens, the third lens, the second lens and in the first lens can likewise advantageously be arranged one after the other in a -z direction in the beam path. Then the lens can be used to illuminate objects or scenes that are located in the -z direction from the first lens. The light rays can propagate from the light source with a component in the -z direction to the object to be illuminated or the scene. A scene can be understood as a number of objects that are to be detected and / or illuminated in a specific solid angle range.

A diaphragm can advantageously be arranged between the first lens and the second lens. The screen can be an opening in a screen component. The screen component can be designed in an annular manner. The screen component can simultaneously be designed as a spacer between the second and the third lens. Through this choice of the diaphragm plane between the first and the second lens, the telecentricity error and / or the distortion can be reduced and / or the vignetting can be minimized or avoided.
Of the first lens and the second lens, one lens can advantageously have a positive refractive power and the other lens can have a negative refractive power. The first lens can particularly advantageously have a negative refractive power and the second lens a positive refractive power.

The first lens can advantageously have a concave and a convex optical surface, and the concave surface and the convex surface can be arranged one after the other in the z direction. In the case of an imaging lens, the concave surface can be the surface of the first lens on the object side or the surface of the lens on the light entry side. In the case of a projection lens, the concave surface can be the surface of the first lens facing away from the light source or the surface of the lens on the light exit side. The concave surface of the first lens which is on the outside with respect to the objective can have the advantage that the surface cannot be so easily soiled or scratched in comparison to an outside convex surface. It is also easier to clean.

The second lens can advantageously have a concave and a convex optical surface and the convex surface and the concave surface can be arranged one after the other in the z direction.

In cooperation with the aforementioned design of the first lens, this can be advantageous for the optical quality of the lens.

The fourth lens can advantageously have a concave and a convex optical surface. The convex surface and the concave surface can advantageously be arranged one after the other in the z direction. The concave surface can therefore face the image plane in the case of an imaging lens or the light source in the case of a projection lens.

The objective can advantageously have a focal length F between 7 mm and 20 mm.

The first glass and the second glass can be different glasses. The first and the second glass can differ in the thermal expansion and / or in the refractive index and / or in the temperature dependence of the refractive index. Alternatively, however, it is also advantageously possible to use the same type of glass as the first and second glass. Optical glasses such as BK7 or borosilicate glass can be used for this. Highly refractive glasses, for example dense flint glasses (SF glasses), lathanum-containing flint or crown glasses (for example LaF, LaSF or LaK glasses) or barium-containing flint or crown glasses (for example BaF or BaSF or BaK glasses) can be particularly suitable. Both glasses can advantageously have a refractive index of more than 1.8. The first and second glasses can be high index Lathanium flint glasses. The same type of glass can advantageously be used as the first and second glass.

The first plastic and the second plastic can be different plastics. The first and the second plastic can differ in the thermal expansion and / or in the refractive index and / or in the temperature dependence of the refractive index. Alternatively, however, it is also possible, and in some cases even particularly advantageous, to use the same type of plastic as the first and second plastic. A plastic can be understood as a polymer. A transparent, ie be a clear polymer. Polycarbonate, COP, Zeonex, COC (Topas) or OKP can be particularly suitable. PMMA can also be suitable.

The objective can have an optical axis. The optical axis can be referred to as the z-axis.

The objective according to the invention comprises four lenses. It can advantageously include exactly four lenses. In addition, it can comprise further elements, for example a ring diaphragm, filter, polarizer, etc. The objective according to the invention is cheaper to manufacture compared to objectives with more than four lenses. The further elements can advantageously be used without refractive power, i. E. be designed without curvature of the optical interfaces.

The lens can advantageously be designed to be approximately telecentric on the image side. This can be understood to mean that the image-side telecentricity error is less than 5 °, particularly advantageously less than 3 °, very particularly advantageously less than 1 °. Ideally, a telecentricity error of less than 0.7 ° can be achieved. This design of the objective can be particularly advantageous if a filter, for example a bandpass filter, is arranged between the fourth lens and the image plane. Such an advantageous arrangement can also comprise an image sensor for image recording or a matrix sensor for detection of the transit time of a light beam, which can be arranged in the image plane. With such an arrangement of the objective and the filter, an inhomogeneity of the illumination of the image plane as a result of different angles of incidence on the filter can be avoided. The requirements for the angle acceptance range of the filter can be reduced in comparison to a non-telecentric lens. This can make the filter less expensive. An image-side telecentricity error can be understood as the angular deviation between the optical axis and the main rays between the last lens and the image sensor. The rays that intersect with the optical axis in the diaphragm plane can be referred to as main rays. If there is no diaphragm, the main rays can be assumed to be the rays with the mean angle with respect to the ray bundles that strike the image plane at a specific point.

The objective can advantageously have a photographic light intensity of at least 1: 1. The photographic light intensity can be described as the maximum aperture ratio of the lens. The reciprocal of the photographic light intensity can be referred to as the f-number. The condition can also be expressed in such a way that the f-number should be less than 1.

The lens can advantageously include a bandpass filter for separating the signal light of the light source from ambient light, in particular from daylight. A bandpass filter can, however, also be arranged outside the objective in the beam path. The bandpass filter can advantageously be arranged directly in front of the image sensor or matrix sensor.

The lens can be operated as a projection lens. However, it can also be operated as an imaging lens.

Use of the objective for a measuring system for at least one transit time detection of at least one light beam can be advantageous. The measuring system can advantageously comprise at least one objective, at least one light source and at least one matrix sensor. The light source can be a laser beam source or an LED. The light source can be operated in a pulsed manner. The pulse length can be between 1ns and 1ms.

The measuring system can be characterized in that the matrix sensor is a SPAD array and / or that the light source is a VCSEL array or an LED array.

The objective can comprise one or more spacers each arranged between two lenses. The spacers can advantageously be made from polycarbonate or from a glass fiber reinforced plastic. It can alternatively be made of a metal such as e.g. Be made of aluminum or beam.

The objective can have a focal length, a pixel size, a modulation transfer function and a distortion in the image plane. The focal length of the lens and / or at least one of the optical properties image point size, modulation transfer function, image size, distortion in the image plane can be independent of temperature at a first wavelength over a temperature range without the use of active components. This can be referred to as passive athermalization.

The passive athermalization can be achieved by the above-mentioned selection of the lens materials in connection with the above-mentioned restrictions of the focal length ratios.

The lens can be designed for a single wavelength (design wavelength), for example that of a specific laser radiation, for example 780nm, 808nm, 880nm, 905nm, 915nm, 940nm, 980nm, 1064 or 1550nm. However, the objective can also be designed for a certain bandwidth, for example for the visible wavelength range or the near infrared range, or for several discrete wavelengths. The bandwidth provided can also be, for example, 20 nm to 50 nm in order to be able to compensate, for example, a thermal wavelength drift of a diode laser provided for illumination.

The lens can be operated as a projection lens. For example, a laser beam can be projected linearly or flat into a room section.

The lens can be operated as an imaging lens. A light beam reflected from an object, for example a laser beam which has been reflected from a point on the object, can be projected onto a point on the detector. The transit time of this light beam can be detected with the detector.

In a preferred embodiment, the objective can be used simultaneously as a projection objective and as an imaging objective. The laser beam to be projected can be coupled into the beam path by means of a beam splitter arranged in the beam path between the objective and the detector.

The use of an objective with a fixed focal length F for a measuring system for at least one transit time detection of at least one light beam can be advantageous. The light beam can be a laser beam. The light beam can be emitted from a light source. The light source can be an optically pumped solid-state laser or an electrically pumped diode laser. The light source can be arranged on a vehicle together with the objective according to the invention and a detector. The light source can be designed such that individual light pulses can be emitted. A photoelectric detector can be provided to detect the transit time of the light beam. The detector can be designed as an avalanche photodiode, for example as a single photon avalanche diode (abbreviated SPAD; English single-photon avalanche diode). The detector can comprise several avalanche photodiodes. These can be implemented as a SPAD array.

A measuring system according to the invention comprises at least one lens according to the invention, at least one light source and at least one matrix sensor. The light source can emit at least one signal light. This can differ in wavelength from the ambient light. The light source can advantageously be a laser light source. It can be an infrared laser. Alternatively, the light source can be an LED.

The light source can be operated in a pulsed manner. The pulse length can be between 1ns and 1ms.

In a further embodiment, the light source can comprise a plurality of light-emitting elements which can be operated independently of one another. The light source can be designed as a VCSEL array or an LED array. The light source can be operated in which at least two of the light-emitting elements emit light pulses at different times.

The matrix sensor can be a SPAD array.

• 1 zeigt ein erstes Ausführungsbeispiel.
• 2 zeigt den Strahlengang des ersten Ausführungsbeispiels.
• 3 zeigt ein erfindungsgemäßes Messsystem.

The figures show the following:

• 1 shows a first embodiment.
• 2 shows the beam path of the first embodiment.
• 3 shows a measuring system according to the invention.

Embodiments

The invention is explained below using exemplary embodiments.

1 shows a first embodiment. A lens is shown 1 with a fixed focal length F. The lens has an optical axis 3 on. The optical axis lies in the z direction. In the figures is the image plane on the right, ie arranged in the z direction, while the object plane is to the left of the lens. The objective includes a first lens 5 a second lens 8th and a third lens 11 and a fourth lens 12 . The lenses are arranged one after the other in the specified order in the z direction.

The first lens is made from a first plastic. The first lens is an aspherical lens.

The second lens 8th is made from a second plastic. The second lens 8th is designed as an aspherical lens.

The third lens 11 is made from a first glass. The third lens 11 is a spherical converging lens.

The fourth lens 12 is made from a second glass. The second glass here is the same as the first glass.

An aperture 15th is arranged between the first lens and the second lens.

There is also a filter 16 provided that separates the signal light from the ambient light.

The first lens has a concave optical surface ( 6th ) and a convex optical surface ( 7th ), where in the z direction the concave surface ( 6th ) and the convex surface ( 7th ) are arranged. The second lens has a concave optical surface ( 10 ) and a convex optical surface ( 9 ), with the convex surface ( 9 ) and the concave surface ( 10 ) are arranged. The fourth lens has a convex optical surface ( 13 ) and a concave optical surface ( 14th ), with the convex surface ( 13 ) and the concave surface ( 14th ) are arranged.

2 shows the beam path of the first embodiment. In this figure the hatching of the lenses is omitted to show the light rays 4th to be able to better represent which is the beam path 2 represent. In the image plane 19th an image sensor for image recording or a matrix sensor for transit time detection of a light beam is arranged.

The optical design is carried out according to the following table: No. Type comment Radius of curvature KR in mm Thickness / distance in mm material Radius in mm 1 DEFAULT object ∞ ∞ air 0.000000 2 ASPHERE Lens 1 -6.899608 5.738520 Polymer 1 (n = 1.5300) 9.000000 3 ASPHERE -7.963824 0.100000 air 9.291035 4th DEFAULT cover ∞ 0.100000 air 8,600,000 5 ASPHERE Lens 2 8.37E + 00 5.010700 Polymer 2 (n = 1.5300) 9.435361 6th ASPHERE 6.383210 5.953286 air 9.341767 7th DEFAULT Lens 3 -1306.627331 7.063166 Glass 1 (n = 1,846) 9.923505 8th DEFAULT -20.064594 0.100000 air 10,500,000 9 DEFAULT Lens 4 16.610978 6.000000 Glass 2 (n = 1,846) 10.250027 10 DEFAULT 3.65E + 01 7.347295 air 8.922798 11 DEFAULT filter ∞ 1,500,000 n = 1.5000 7.000000 12 DEFAULT image ∞ 0.000000 7.000000

The first column gives a consecutive number of an area and is numbered from the object side. The “Standard” type describes a flat or spherically curved surface. The "ASPHERE" type describes an aspherical surface. An interface or lens surface can be understood as a surface. It should be noted that the object plane (no. 1), a diaphragm (no. 4) and the image plane (no. 12) are also considered as a surface. The surfaces 2 , 3 , 5 , 6th , 7th , 8th , 9 and 10 are Lens surfaces. These areas are in 2 with the respective number designated as Surf 2 , Surf 3 , Surf 5 , Surf 6th , Surf 7th , Surf 8th , Surf 9 or Surf 10 .

The column radius of curvature KR indicates the radius of curvature of the respective surface. In the case of an aspherical surface, this is to be understood as the paraxial radius of curvature. In the table, the sign of a radius of curvature is given as positive if the shape of a surface is convex towards the object side and the sign is negative if the shape of a surface is convex towards the image side. The specification ∞ in the column radius of curvature means that it is a flat surface. The “Thickness / Distance” column shows the distance between the i-th surface and the (i + 1) -th surface on the optical axis. The indication ∞ in this column in number 1 means that it is an infinite object distance, ie a lens focused on infinity. For the lines 2 , 5 , 7th and 9 this column indicates the center thickness of the first, second, third and fourth lenses. In the Material column, the material between the respective surfaces is specified with the respective refractive index n. The refractive index n relates to a design wavelength for which the lens 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, 915 nm, 940 nm, 1064 nm or 1550 nm. The column Radius indicates the outer radius of the respective surface. In the case of the aperture (No. 4), this is the aperture. In the case of lens surfaces, this is the maximum usable distance between the light rays and the optical axis; in the following equation, this corresponds to the maximum value h for the respective surface.

The coefficients of the aspherical surfaces are given below. No. C ₂ in mm ^-1 C ₄ in mm ^-3 C ₆ in mm ^-5 C ₈ in mm ^-7 2 0.000000E + 00 1.984885E-05 -1.703411E-06 6.554599E-08 3 0.000000E + 00 6.508143E-04 -7.942826E-06 2.300400E-07 5 0.000000E + 00 4.784978E-04 -1.372895E-05 2.832933E-07 6th 0.000000E + 00 1.836502E-04 -2.472992E-06 1.930275E-08 No. C ₁₀ in mm ^-9 C ₁₂ in mm ^-11 C ₁₄ in mm ^-13 C ₁₆ in mm ^-15 k 2 -1.122241E-09 1.154834E-11 -6.624874E-14 1.588935E-16 -3.111840 3 -4.741868E-09 6.725617E-11 -5.270632E-13 1.793910E-15 -0.397414 5 -4.007099E-09 3.429747E-11 -1.591803E-13 3.052884E-16 -4.355210 6th -1.732452E-10 1.343126E-12 -6.083887E-15 1.131555E-17 -3.869062

In the numerical values of the aspherical data, “En” (n: integer) means “x10 ^-n ” and “E + n” means “x10 ⁿ ”. Furthermore, the aspherical surface coefficients are the coefficients C _m with m = 2..16 in an aspherical expression that is represented by the following equation: $$Zd=\frac{H^2}{K\mathrm{R.}+\sqrt{K{\mathrm{R.}}^2-\left(1+k\right){\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102019131001B3\_0002.png"\; state="\{\{state\}\}">H</figure-callout>}}^2}}+{\displaystyle {\sum }_{m=2}^{16}{\mathrm{C.}}_m\cdot H^m,wObei}$$

Zd is the depth of an aspherical surface (i.e. the length of a perpendicular from a point on the aspherical surface with a height h to a plane touching the apex of the aspherical surface and perpendicular to an optical axis), h is the height (i.e. a length from the optical axis to the point on that of the aspherical surface), KR is the paraxial radius of curvature, and C _m are the aspherical surface coefficients given below (m = 2 .. 16). Aspherical surface coefficients not specified, here all with an odd index, are assumed to be zero. The coordinate h is to be entered 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 specified in the last column.

The focal length of the first lens is f ₁ = -389mm, that of the second lens is f ₃ = 115mm. The focal length of the third lens is f ₂ = 24.8 mm, that of the fourth lens is f ₄ = 32.8 mm. The lens has a focal length F of 13.2mm. The design wavelength of the exemplary embodiment is 905 nm. Modifications of the exemplary embodiment can also be used for other wavelengths listed in the description.

In a modification of this exemplary embodiment, the objective is focused on a finite object distance. This can be done by changing the image distance. To do this, the distance in line no. 10 can be increased accordingly.

In a further modification, not shown, the objective can be used as a projection objective. Instead of the sensor in the plane 19th arranged a light source. Then a scene located in front of the lens in the negative z direction, which is identified in the figure as -z direction, can be illuminated.

3 shows a measuring system according to the invention. The measuring system 17th includes a transmitter lens 20th , a receiver lens 21st , a light source 18th and a matrix sensor 19th . The light source illuminates one or more objects 22nd with a transmitter light 23 . The matrix sensor detects the transit time of the reflected light 24 .

List of reference symbols

1.

lens

2.

Lens arrangement with beam path

3.

Optical axis

4th

Beam of light

5.

First lens

6th

Concave surface of the first lens

7th

Convex surface of the first lens

8th.

Second lens

9.

Convex surface of the second lens

10.

Concave surface of the second lens

11.

Third lens

12.

Fourth lens

13.

Convex surface of the fourth lens

14th

Concave surface of the fourth lens

15th

cover

16.

filter

17th

Measuring system

18th

Light source

19th

Matrix sensor

20th

Transmitter lens

21st

Receiver lens

22nd

object

23.

Transmitter light

24.

Reflected light

Claims (13)

Objective (1) with a fixed focal length F, comprising at least one first lens (5) with a first focal length f ₁ made of a first plastic, a second lens (8) with a second focal length f ₂ made of a second plastic, a third lens (11) with a third focal length f ₃ made of a first glass and a fourth lens (12) with a fourth focal length f ₄ made of a second glass, the refractive power D ₃ = 1 / f _{3 of} the third lens (11) is positive and the refractive power D ₄ = 1 / f _{4 of} the fourth lens (12) is positive and the first lens (5) and the second lens (8) together have at least two aspherical surfaces, with the amounts of the focal lengths f _{1 of} the first lens and f _{2 of} the second lens are more than 7 times the focal length F of the objective and / or the amount of the sum of the refractive powers | D ₁ + D ₂ | from the refractive power D ₁ = 1 / f _{1 of} the first lens and the refractive power D ₂ = 1 / f _{2 of} the second lens is less than 0.125 times the refractive power D = 1 / F of the objective. Objectively after Claim 1 , characterized in that the first lens (5) and / or the second lens (8) is designed as biaspherical lenses. Objective according to one of the preceding claims, characterized in that the first lens (5), the second lens (8), the third lens (11) and the fourth lens (12) are arranged one after the other in a z direction in the beam path , or thereby characterized in that a light source (18), the fourth lens (12), the third lens (11), the second lens (8) and the first lens (5) are arranged one after the other in the -z direction in the beam path . Objective according to one of the preceding claims, characterized in that a diaphragm (15) is arranged between the first lens (5) and the second lens (8). Objective according to one of the preceding claims, characterized in that it has a focal length F between 7mm and 20mm and / or that of the first lens (5) and the second lens (8) one lens has a positive refractive power and the other has a negative refractive power and / or that the first lens has a concave optical surface (6) and a convex optical surface (7) and the concave surface (6) and the convex surface (7) are arranged one after the other in the z direction and / or that the second Lens has a concave optical surface (10) and a convex optical surface (9) and the convex surface (9) and the concave surface (10) are arranged one after the other in the z direction. and / or that the fourth lens has a convex optical surface (13) and a concave optical surface (14) and the convex surface (13) and the concave surface (14) are arranged one after the other in the z direction. Objective according to one of the preceding claims, characterized in that it is designed to be approximately telecentric on the image side, the telecentricity error on the image side being less than 5 °. Objective according to one of the preceding claims, characterized in that the objective has a photographic light intensity of at least 1: 1. Objective according to one of the preceding claims, characterized in that the objective comprises a bandpass filter (16) for separating the signal light of the light source from ambient light, in particular from daylight, or can be operated together with a bandpass filter arranged outside the objective. Lens according to one of the preceding claims, characterized in that the lens can be operated as a projection lens and / or that the lens can be operated as an imaging lens. Use of an objective (1) according to one of the preceding claims for a measuring system (17) for at least one transit time detection of at least one light beam (4). Measuring system (17) comprising at least one objective (20, 21) according to one of the preceding claims, at least one light source (18) and at least one matrix sensor (19). Measuring system according to one of the preceding claims, characterized in that the light source (18) is a laser beam source or an LED and that the light source is operated in a pulsed manner and that the pulse length is between 1ns and 1ms. Measuring system according to one of the preceding claims, characterized in that the matrix sensor (19) is a SPAD array and / or that the light source (18) is a VCSEL array or an LED array.

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