Patent Description:
A device having the features of the preamble of claim <NUM> is know from <CIT>. The Article "<NPL>) describes an MTF test bench with an integrated thermal chamber that allows measuring several sample sizes in a temperature range from -<NUM> degrees Celsius to +<NUM> degrees Celsius using a temperature stable design which includes an insulating vacuum.

The invention is defined by a device having the features of claim <NUM>. Sub-claims are directed to advantageous embodiments of the invention.

This document describes one or more aspects of a device for determining an optical characteristic of a camera. In one example, a device comprises a housing configured to receive a test fixture that retains a camera for determining an optical characteristic of the camera at a desired temperature. The housing comprises a first segment and a second segment removably attached to the first segment to create a chamber. The first segment is configured to attach to the test fixture. The first segment defines a first orifice located in a first side of the first segment, the first orifice being configured to direct a flow of a gas out of the chamber. The second segment defines a second orifice located in a first side of the second segment to direct the flow of the gas into the chamber. The first orifice and the second orifice are positioned to enable an inlet flow direction of the gas into the chamber be normal to an outlet flow direction of the gas out of the chamber. The second segment further defines an aperture located in a second side of the second segment positioned opposite the test fixture to define a field of view that includes a camera target.

This document further refers to a method which is not claimed but helps to understand the invention. The method includes adjusting, with a processor, a rotation angle of a test fixture about an optical axis of a camera retained by the test fixture. The test fixture and camera are disposed within a housing. The housing includes a first segment and a second segment removably attached to the first segment creating a chamber. The first segment is configured to attach to the test fixture and defines a first orifice located in a side of the first segment. The first orifice is configured to direct a flow of a gas out of the chamber. The second segment defines a second orifice located in a first side of the second segment to direct the flow of the gas into the chamber. The second segment also defines an aperture located in a second side of the second segment. The aperture is positioned opposite the test fixture to define a field of view that includes a camera target. The aperture is configured to receive a lens barrel of the camera, thereby enabling a determination of an optical characteristic of the camera. The method also includes receiving image data from the camera representing a captured image of the camera target in the field of view of the camera. The method also includes adjusting a position of the camera target in the field of view of the camera and determining the optical characteristic of the camera, based on the camera target, when a temperature of the camera is at a camera-temperature set point.

This summary is provided to introduce aspects of a device for determining an optical characteristic of a camera, which is further described below in the Detailed Description and Drawings. For ease of description, the disclosure focuses on vehicle-based or automotive-based systems, such as those that are integrated on vehicles traveling on a roadway. However, the techniques and systems described herein are not limited to vehicle or automotive contexts, but also apply to other environments where cameras can be used to detect objects. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.

The details of one or more aspects of a device for determining an optical characteristic of a camera are described in this document with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:.

The techniques of this disclosure relate to a device for determining an optical characteristic of a camera. A modulation transfer function (MTF) is a measure of an image quality characteristic of the camera and is an industry-accepted metric for characterizing advanced driver-assistance systems (ADAS) cameras for automotive applications. The typical way to test the MTF characterization of a camera image includes sampling image data from several different positions or locations across a field of view of the camera.

ADAS cameras are expected to operate over a temperature range of -<NUM>° Celsius to <NUM>° Celsius, and the performance is verified through laboratory testing using instrumentation that may not be rated to operate in the specified temperature range. The MTF testing can be accomplished at the specified temperature range by enclosing the camera in an environmental chamber that is mounted to a test stand specifically designed for MTF testing. The environmental chamber is capable of holding the camera at a predetermined temperature set-point while the MTF measurements are made at various points in the camera's field of view of. The environmental chamber receives conditioned air through an inlet orifice and circulates the air around the camera to transfer heat to or from the camera to achieve the camera temperature set-point. The conditioned air then exits from the environmental chamber and into the test cell. The environmental chamber has an aperture that exposes a lens of the camera to the test stand so that the camera can focus on a moveable target used for MTF testing across the entire field of view of the camera.

This disclosure introduces a device for determining an optical characteristic of a camera. Described is an environmental chamber for determining MTF measurements at all locations within the field of view of the camera. A method of determining the MTF using the environmental chamber is also disclosed. MTF measurements can be determined for any camera field position and indexed automatically to improve testing efficiencies, all while maintaining the camera at a desired temperature set-point.

<FIG> illustrates an example device <NUM> for determining an optical characteristic of a camera <NUM>. One such characteristic is the MTF, which is a measure of an image quality of the camera <NUM>, which will be explained in more detail below. In an example implementation, the device <NUM> is an environmental chamber placed on a test stand <NUM> designed to determine the MTF of the camera <NUM>. In the examples disclosed herein, the test stand is a ProCam Test R&D test stand manufactured by TRIOPTICS GmbH, Wedel, Germany. It will be appreciated that the device <NUM> can be applied to other test stands used to measure optical characteristics of cameras. The camera <NUM> (see <FIG>) can be located inside the environmental chamber with a view through an aperture <NUM> to a collimator <NUM> on the test stand <NUM> that houses a back-lit target <NUM>. The collimator simulates target distances from about one meter (<NUM>) to infinity that can be experienced by the camera <NUM> in the field, and the target <NUM> is a cross-type reticle (see <FIG>) generated with collimated light to form a test image for the camera <NUM> to capture for analysis by the test equipment. The reticle image can be optically focused by the test equipment to simulate a desired physical distance of the test image in relation to the camera <NUM>.

The environmental chamber can maintain a temperature of the environment to which the camera <NUM> is exposed and receives conditioned air from an air conditioning unit via a hose <NUM> attached to the device <NUM>. The hose <NUM> can be insulated to reduce heat transfer between the hose and the environment to reduce the overshoot and undershoot temperature settings of the air conditioning unit. Cameras for automotive applications are required to function at temperatures ranging from -<NUM> degrees Celsius (°C) to <NUM>, and in some applications up to temperatures of <NUM>. The camera <NUM> may be any camera <NUM> suitable for use in automotive applications, for example, ADAS applications and/or occupant detection applications. The camera <NUM> includes optics that may include one or more fixed-focus lenses. The camera <NUM> includes an image sensor comprised of a two-dimensional array of pixels organized into rows and columns that define a resolution of the camera <NUM>. The pixels may be comprised of a Charge Coupled Device (CCD) and/or a Complementary Metal Oxide Semiconductor (CMOS) that convert light into electrical energy based on an intensity of the light incident on the pixels.

In general, the MTF varies inversely with both a spatial frequency of the image features, and with the focused distance from an optical axis <NUM> or boresight of the camera <NUM>. Typically, a larger MTF is considered a desirable feature of the camera <NUM>. The MTF of the camera <NUM> is a measurement of the camera's <NUM> ability to transfer contrast at a particular resolution from the object to the image and enables the incorporation of resolution and contrast into a single metric. For example, as line spacing between two parallel lines or line pairs on a test target decreases (i.e., the spatial frequency increases), it becomes more difficult for the camera lens to efficiently transfer the change in contrast to an image sensor of the camera <NUM>. In another example, for a test target having a given spacing between line pairs and imaged at two positions in a field of view <NUM> (FOV <NUM>), the camera has more difficulty resolving the line pairs for the target imaged a distance away from the optical axis. As a result, the MTF decreases, or an area under a curve of a plot of the MTF decreases.

The MTF is a modulus or absolute value of an optical transfer function (OTF), and the MTF can be determined in various ways depending on the type of target <NUM> used. Target types can include slant-edge targets <NUM> and point-source or pin-hole targets <NUM>. The MTF can be determined based on the type of target <NUM> and the camera application. In an example, the MTF is a two-dimensional Fourier transform (see <FIG>) of the imaging system's line spread function (LSF) taken from an edge spread function (ESF) of the slant-edge target <NUM>.

<FIG> illustrate example plots of an edge spread function, a line spread function, a modulation transfer function, and an example image of a slant-edge target used to develop the example plots. Slant-edge targets <NUM>, as illustrated in <FIG> as the image of the slant-edge target captured by the camera <NUM>, may be used to measure the MTF and are defined by an International Organization for Standardization (ISO) <NUM> requirement for spatial resolution measurements of cameras. The LSF (see <FIG>) is a normalized spatial signal distribution in the linearized output of the imaging system resulting from imaging a theoretical and infinitely thin line. The ESF (see <FIG>) is a normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a theoretical and infinitely sharp edge. The LSF is determined by taking a first derivative of the ESF.

<FIG> illustrate example plots of a progression from the ESF to the MTF. An aspect of the determination of the MTF measurement is that the edges of the slant-edge target <NUM> being imaged by the camera <NUM> are oriented off-axis from horizontal and vertical axes of the camera's <NUM> FOV <NUM>. That is, the edges of the target <NUM> are not aligned or overlaid with the horizontal and vertical reference axes of the FOV <NUM> so that the boundary from light to dark does not align with the rows and columns of pixels (e.g., the pixel axes) of the image sensor of the camera <NUM>. This off-axis alignment may be achieved by rotating the target <NUM> relative to the FOV <NUM> in a range from about <NUM>-degrees to about <NUM>-degrees relative to the horizontal axis of the FOV <NUM>, and in a range from about <NUM>-degrees to about <NUM>-degrees relative to the vertical axis of the FOV <NUM> (hereafter referred to as the desired off-axis measurement range). This range of rotation is needed due to the MTF measurement using two planes of focus; a sagittal plane (horizontal plane) and a tangential plane (vertical plane) that is orthogonal or normal to the sagittal plane. When the edges of the target <NUM> are less than about <NUM>-degrees to the reference axes of the FOV <NUM> to sample the sagittal plane and/or sample the tangential plane, the Fourier transform calculation goes to infinity, and the MTF measurement cannot be made. On the other hand, when the edges of the target are greater than about <NUM> degrees to the horizontal and vertical reference axes, the MTF calculation may combine the horizontal plane with the vertical plane and confound the MTF measurement.

<FIG> is a perspective view illustrating the device <NUM> separated from the test stand <NUM> where, for illustration purposes, a portion of the device <NUM> is shown as a transparent layer to reveal the camera <NUM>. The device <NUM> includes a housing <NUM> configured to receive a test fixture <NUM> that retains the camera <NUM> for determining the MTF. The test fixture <NUM> can be mounted to the test stand <NUM> and can be rotated about a rotational axis through a rotation angle <NUM> of at least ninety degrees and up to <NUM> degrees. The optical axis <NUM> of the camera <NUM> defines a line of rotational symmetry of the camera <NUM> and can be aligned with the rotational axis of the test fixture <NUM> during installation of the camera <NUM>. Aligning the optical axis <NUM> with the rotational axis enables the measurement of the MTF at all points in the FOV <NUM> of the camera <NUM> by rotating the camera <NUM> to a specific angle and moving the collimator <NUM> to position the target <NUM> at a desired point or angle in the FOV <NUM>. The illustrations used herein show the optical axis <NUM> aligned with the rotational axis, and it will be understood that the line depicting the optical axis <NUM> also depicts the rotational axis of the test fixture <NUM>.

The housing <NUM> can rotate with the test fixture <NUM> and camera <NUM> through the angle of at least <NUM> degrees when determining the MTF. In some examples, the test fixture <NUM>, camera <NUM>, and housing <NUM> are rotated through the rotation angle <NUM> of <NUM> degrees to test the MTF over approximately half of the FOV <NUM>. In addition to the rotation of the test fixture <NUM> about the optical axis <NUM> of the camera <NUM>, an objective arm on the test stand <NUM> that retains the collimator <NUM> can rotate or swing about an axis perpendicular to the optical axis <NUM>. The combination of the rotation of the test fixture <NUM> and the swinging objective arm enables the entire FOV <NUM> of the camera <NUM> to be mapped for the MTF measurement.

Referring back to <FIG>, the housing <NUM> includes a first segment <NUM>, hereafter a base <NUM>, and a second segment <NUM>, hereafter a cover <NUM>, removably attached to the base <NUM>. The base <NUM> is configured to attach to the test fixture <NUM> so that a relative movement between the base <NUM> and the test fixture <NUM> is minimized, enabling the base <NUM> to rotate with the test fixture <NUM>. The attachment can be made via threaded fasteners inserted through holes in a floor of the base that interface with corresponding threaded holes in the test fixture <NUM>. The cover <NUM> creates a chamber into which the camera <NUM> is placed. For the purposes of illustrating the test fixture <NUM> and the camera <NUM>, the cover <NUM> is shown as a transparent layer in <FIG>. The cover <NUM> can be attached to the base <NUM> via fasteners that enable rapid attachment and detachment. The detachability of the cover <NUM> enables access to the chamber and is advantageous for mounting the camera <NUM> to the test fixture <NUM> or adjusting a position of the camera <NUM> after the base <NUM> has been installed onto the test stand <NUM>.

The base <NUM> defines a first orifice <NUM> or port through one side of the base <NUM>. The first orifice <NUM> is illustrated in <FIG> on a right side of the base <NUM>, in other examples, the first orifice <NUM> is on a left side of the base <NUM>. The first orifice <NUM> is positioned proximate to the floor of the base and can direct a flow of a gas out of the chamber, as will be described in more detail below.

A second orifice <NUM> is defined by the cover <NUM> and located through a first side <NUM> of the cover <NUM>, hereafter a front <NUM> of the cover <NUM>, to direct the flow of the gas into the chamber. The second orifice <NUM> is positioned proximate to a second side <NUM>, hereafter a top <NUM> of the cover <NUM>, such that the second orifice <NUM> and the first orifice <NUM> are positioned at different elevations relative to the test fixture <NUM>.

To be clear, the rotational axis that is aligned with the optical axis <NUM> defines a plane <NUM> parallel to the inlet flow direction. The second orifice <NUM> and the first orifice <NUM> are located on a same side of the plane <NUM> and are shown in <FIG> on the right side of the housing <NUM>. This arrangement of the second orifice <NUM> and the first orifice <NUM> enables an inlet flow direction of the gas into the chamber to be normal to an outlet flow direction of the gas out of the chamber, which enables a circulating gas flow around the camera <NUM>, as will be explained in more detail below.

An area of the first orifice <NUM> is equal to the area of the second orifice <NUM> to minimize a pressure drop through the chamber that may occur due to restrictions in the outlet or due to header losses at the inlet. The areas of the orifices can be any area, and in the example illustrated in <FIG>, the area is approximately <NUM> square centimeters (<NUM><NUM>) for each orifice. The areas of the orifices may also be adjusted based on a flow rate of the gas through the chamber to maintain a desired backpressure of the chamber, as the backpressure can affect the flow dynamics of the gas within the chamber.

<FIG> is the same perspective view as in <FIG>, with the cover <NUM> illustrated as nontransparent. A fitting <NUM> is attached to the cover <NUM> and can direct the flow of the gas through the second orifice <NUM> into the chamber. The fitting <NUM> is configured to receive the hose <NUM> (see <FIG>) that delivers the gas to the device <NUM>, which in the examples disclosed herein is air. The air can be conditioned using an air conditioning unit by heating or cooling the air to a desired temperature before the air enters the hose. The air temperature can be based on the test requirements, and the air may also be humidified.

An angle of the fitting <NUM> may be about <NUM> degrees relative to the front <NUM> of the cover <NUM>, and the fitting <NUM> is oriented such that an inlet end <NUM> of the fitting <NUM> is facing toward a floor of the test cell. This orientation is advantageous in reducing a build-up of condensation within the fitting <NUM> that may otherwise occur with different orientations; the condensation will descend toward the floor of the test cell within the hose. This orientation is also beneficial for reducing a torque applied by a weight of the hose <NUM> to the housing <NUM> that can restrict the ability of the test stand <NUM> to rotate the housing <NUM> to the required angles for testing the MTF.

The fitting <NUM> includes a lip <NUM> configured to retain the hose such that the hose can rotate freely around the fitting <NUM> as the housing <NUM> is rotated about the rotational axis of the test fixture <NUM>. The rotation of the hose relative to the fitting <NUM> reduces a torque on the fitting <NUM> that can restrict the ability of the test stand <NUM> to rotate the housing <NUM> to the required angles for testing the MTF. The hose can be retained on the fitting <NUM> via a hose clamp placed above the lip <NUM> or other retention devices, for example, corrugations in the hose can engage around the lip <NUM> to prevent the hose from separating from the fitting <NUM>.

<FIG> is a cross section of the cover <NUM> through a center of the aperture <NUM>. The aperture <NUM> is located in the top <NUM> of the cover <NUM> and is positioned opposite the test fixture <NUM> to define the FOV <NUM> that includes the camera target <NUM> in the collimator <NUM>. The test stand <NUM> can move or rotate the collimator <NUM> through an arc so that the target <NUM> can be placed at different points or angles in the FOV <NUM>. The aperture <NUM> is sized, shaped, and arranged to receive a lens barrel <NUM> of the camera <NUM> enabling the determination of the MTF, and in the examples illustrated in <FIG>, the FOV <NUM> is in a range of about <NUM> degrees to about <NUM> degrees.

The aperture <NUM> is further defined by a conical section <NUM> attached to the cover <NUM> that protrudes or extends into the chamber toward the test fixture <NUM> and camera <NUM>. The conical section <NUM> may be formed integral to the cover <NUM> or may be attached as a separate component of the cover <NUM>. The conical section <NUM> defines an annulus <NUM> or open ring between the lens barrel <NUM> and a leading edge of the conical section providing a clearance between the lens barrel <NUM> and the conical section <NUM>. In the example illustrated in <FIG>, the annulus <NUM> is in a range from about one millimeter (<NUM>) to about <NUM> and can vary based on a diameter of the lens barrel <NUM>. Minimizing the annulus <NUM> is advantageous for maintaining the temperature within the chamber and reducing a flow of air from the chamber through the annulus <NUM> that may create optical aberrations during the MTF measurements. Optimizing a size of the annulus <NUM> to enable a relatively small air flow rate through the annulus <NUM> may be advantageous to reduce fogging of the camera lens that may be caused by humidity in the surrounding room air.

Dimensions of the aperture <NUM> and a distance, X, of a camera lens <NUM> to the top <NUM> of the cover <NUM> can be determined based on the angle of the FOV <NUM>. For example, the diameter of the aperture <NUM> in the top <NUM> of the cover <NUM>, shown as parameter Y in <FIG>, can be determined by the equation, Y = <NUM>*X*tan(B), where X is the distance from the top <NUM> of the cover <NUM> to a vertex or highest point of the camera lens, and B is a half-angle of the FOV <NUM>. Knowing the FOV <NUM> of the camera <NUM> being tested, the user may fabricate or select the cover <NUM> with the appropriate diameter, Y, of the annulus <NUM> so that the cover <NUM> does not occlude the FOV <NUM> during measurement of the MTF. In the scenario where the diameter, Y, and the FOV <NUM> are predetermined, the distance, X, can be solved by rearranging the equation. For example, given Y = <NUM> and B = <NUM> degrees, X = <NUM>. In this example, the apex of the camera lens <NUM> cannot exceed a depth of <NUM> below the top <NUM> of the cover <NUM> to maintain a clear or un-occluded FOV <NUM>.

<FIG> is an exploded view of the device <NUM> showing the camera <NUM> mounted to the test fixture <NUM>. A cap <NUM> or plug can be used to seal the aperture <NUM> to inhibit thermal losses while the camera <NUM> is being held at the test temperature set-point, then removed to measure the MTF. The cap <NUM> can include a skirt that inserts into the aperture <NUM> or can have a flat surface that seals against the top <NUM> of the cover <NUM>. The skirt can have a clearance fit with vertical sides of the aperture <NUM>, and the cap can include opposing ramped sections that engage corresponding opposing mounting lugs formed into the top <NUM> of the cover <NUM>, as illustrated in <FIG>. The cap <NUM> can be rotated about the optical axis <NUM> to engage the ramped sections with the mounting lugs to seal the aperture <NUM>.

The base <NUM> and cover <NUM> can include insulation layers <NUM> attached to internal or external surfaces, and in the example illustrated in <FIG>, the insulation layers <NUM> line the internal surfaces of both the base <NUM> and cover <NUM> (not shown). In this example, the insulation layers have a thickness of approximately <NUM> and have an R-value, or a capacity of the insulating material to resist heat flow, in the range of R = <NUM> to R = <NUM>. As the R-value increases, the insulating ability of the material also increases.

The base <NUM> and cover <NUM> can be formed of a polymer material, for example, Acrylonitrile butadiene styrene (ABS), nylon, or polyetherimide that is marketed under the name of ULTEM ®, manufactured by SABIC, Riyadh, Saudi Arabia. The material can be selected based on the temperature range determined by the testing requirements. The base <NUM> and cover <NUM> can be injection molded or fabricated via additive manufacturing or 3D-printing, and in the example illustrated in <FIG>, the base <NUM> and cover <NUM> are 3D-printed from ABS, resulting in the fitting <NUM>, the aperture <NUM>, and the mounting lugs, being integrally formed with the cover <NUM>.

Walls of the housing <NUM> are configured to circulate the flow of air around the camera <NUM> before exiting the chamber, and at least two sides or walls of the base <NUM> are arranged at <NUM>-degree angles relative to the inlet flow direction, as illustrated in <FIG>. The placement of the walls having the <NUM>-degree angles also provides clearance between the device <NUM> and the test stand <NUM>, enabling the housing <NUM> to be rotated without interference from the test stand <NUM>.

<FIG> illustrate flow modeling of three different positions of the first orifice <NUM> in the cover <NUM>. <FIG> shows the flow dynamics with the first orifice <NUM> centered on the front <NUM> of the cover <NUM>. This placement enables the air flow to directly impinge on the camera <NUM> before exiting the chamber at the second orifice <NUM> on the lower-right side of the device <NUM>. This placement of the first orifice <NUM> results in erratic flow patterns within the chamber and can also create aberrations in the MTF measurements.

<FIG> shows the flow dynamics with the first orifice <NUM> located on a left side of the front <NUM> of the cover <NUM>. This placement directs the air flow to pass around a back side of the camera <NUM> before exiting the chamber. This placement improves the flow efficiency and a heat transfer from the air to the camera <NUM> compared to the central placement shown in <FIG>. Efficiencies in the heat transfer can be determined based on the time to reach a temperature set-point, with higher efficiencies resulting in shorter times to the set-point.

<FIG> shows the flow dynamics with the first orifice <NUM> located on a right side of the front <NUM> of the cover <NUM>, as illustrated in <FIG>. This placement directs the air flow to circulate around the back side of the camera <NUM> and then around a front side of the camera <NUM> before exiting the chamber. This placement results in improved air circulation and improved heat transfer from the air to the camera <NUM> compared to the placement in <FIG>.

<FIG> illustrates a test system <NUM> to determine the MTF, where the device <NUM> further includes a processor <NUM> or controller in communication with the test fixture <NUM> and the camera <NUM>. The processor <NUM> can be attached to the housing <NUM> or can be located remotely from the housing <NUM>. The processor <NUM> may be implemented as a microprocessor or other control circuitry such as analog and/or digital control circuitry. The control circuitry may include one or more applicationspecific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs) that are programmed to perform the techniques or may include one or more general-purpose hardware processors programmed to perform the techniques in accordance with program instructions in firmware, memory, other storage, or a combination thereof. The processor <NUM> may also combine custom hard-wired logic, ASICs, or FPGAs with custom programming to accomplish the techniques. The processor <NUM> may include a memory or storage media (not shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The EEPROM stores data and allows individual bytes to be erased and reprogrammed by applying programming signals. The processor <NUM> may include other examples of non-volatile memory, such as flash memory, read-only memory (ROM), programmable read-only memory (PROM), and erasable programmable read-only memory (EPROM). The processor <NUM> may include volatile memory, such as dynamic random-access memory (DRAM) or static random-access memory (SRAM). The one or more routines may be executed by the processor to perform steps for determining the MTF based on signals received by the processor <NUM> from the camera <NUM> and the test fixture <NUM> as described herein.

The processor <NUM> can adjust the rotation angle <NUM> of the test fixture <NUM> about the optical axis <NUM> of the camera <NUM> to position the camera <NUM> for measuring the MTF at all points in the FOV <NUM>. The processor <NUM> can send signals to motors or rotary actuators in the test stand <NUM> that control the rotation of the test fixture <NUM> retaining the camera <NUM>. The processor <NUM> can also send signals to the test stand <NUM> to position the target <NUM> in a plane that is normal to lines of sight of the camera <NUM> at any position within the FOV <NUM> by swinging the objective arm that retains the collimator <NUM>, as illustrated in <FIG>. For example, the target <NUM> can be positioned by the test stand <NUM> by swinging the objective arm such that the target <NUM> is perpendicular to any line of sight. Positioning the target <NUM> normal to the line of sight reduces errors in the measurement of the MTF because the target <NUM> is most accurately sampled by measuring the target <NUM> normal to a field angle radius or line of sight. The test stand <NUM> is configured to position a center of the target <NUM> at a same radial distance from the camera <NUM> at all positions in the FOV <NUM> by moving the target <NUM> along an arc from one position to the next with the radius of the arc remaining constant.

The processor <NUM> can receive image data from the camera <NUM> representing captured images of the camera target <NUM> in the FOV <NUM> of the camera <NUM> and adjust the position of the target <NUM> in the FOV <NUM>. The processor <NUM> can determine the MTF of the camera <NUM> based on the camera target <NUM> at the adjusted positions in the FOV <NUM> when a temperature of the camera is at a camera-temperature set point. The camera temperature can be determined by one or more thermocouples attached to the camera <NUM> that may be shielded from the air flow impinging on the thermocouple. The thermocouples may be located in a space between the camera <NUM> and the test fixture <NUM>, where the air flow is minimized. Additional thermocouples can be placed in the chamber as a reference for determining the air temperature entering the device <NUM>.

The processor <NUM> can determine the MTF at room temperature after the camera <NUM> is installed on the test fixture <NUM> at all points in the FOV <NUM>. The processor can then determine the MTF after the camera <NUM> has reached the set-point temperature of <NUM> and soaks or holds at the set-point temperature for a period of at least ten minutes to ensure the camera temperature is stable. The cap <NUM> can be installed on the cover <NUM> to retain heat within the housing <NUM> as the temperature of the camera is adjusted, then removed for the MTF measurements. Removing the cap <NUM> can result in a relatively small temperature drop, for example, in a range of <NUM> to <NUM>, and is enabled by the insulative properties of the housing <NUM> and the geometry of the aperture <NUM> that minimizes flow out of the aperture <NUM>. A ramp rate from room temperature to the set-point temperature of <NUM> can occur in the range of <NUM> minutes to <NUM> minutes and is enabled by the insulative properties of the housing <NUM>. The air conditioning unit can be set to a higher temperature than the camera temperature set-point, for example, <NUM> to <NUM> above the set-point temperature, to overcome heat losses in the system <NUM>.

The processor <NUM> can then determine the MTF at all points in the FOV <NUM> when the camera has reached the camera-temperature set point of -<NUM>, and after the camera <NUM> soaks at this set-point temperature for at least ten minutes. The ramp rate from <NUM> to the set-point temperature of -<NUM> can be in the range of <NUM> minutes to <NUM> minutes, and the air conditioning unit can be set to a lower temperature than the camera temperature set-point, for example, <NUM> to <NUM> below the set-point temperature, to overcome heat gains in the system <NUM>.

The air conditioning unit can be manually controlled to achieve the desired camera set-point temperatures or can be controlled by the processor <NUM>. The air flow rate delivered by the air conditioning unit can be in a range of about <NUM> meters per second (<NUM>/s) and can vary based on the testing requirements and desired temperature ramp rates.

<FIG> is an example of an overall process flow <NUM> starting at <NUM> with attaching the test fixture <NUM> to the test stand <NUM> and ending at <NUM> with repeating the MTF measurements on other cameras <NUM>. In this example, at <NUM>, the test fixture <NUM> is attached to the test stand <NUM>. At <NUM>, the camera <NUM> and thermocouples are attached to the test fixture <NUM>. A wiring harness connects the camera <NUM> and thermocouples to the processor <NUM>. At <NUM>, the base <NUM> of the housing <NUM> is placed over the test fixture <NUM> and camera <NUM> and is attached to the test fixture <NUM> using fasteners.

At <NUM>, the test stand <NUM> and the camera <NUM> are powered up and the camera viewing software used to measure the MTF is launched. At <NUM>, software used to operate the test stand is launched and test settings for the MTF testing are initialized.

At <NUM>, the optical axis <NUM> of the camera <NUM> is aligned with the rotational axis of the test stand <NUM>, and at <NUM>, the performance of the camera <NUM> is measured to verify functionality of the camera <NUM> and the system <NUM> before closing the housing <NUM>.

At <NUM>, the camera <NUM> is powered off, and at <NUM>, the cover <NUM> is attached to the base <NUM> of the housing <NUM> and the air hose is installed on the fitting <NUM>.

At <NUM>, the air conditioning unit is powered on and set to the first temperature set-point. At <NUM>, the camera thermocouple temperature is monitored, and when the thermocouple has reached the temperature set-point, at <NUM>, the camera <NUM> is soaked at the temperature set-point for <NUM> minutes.

At <NUM>, the camera <NUM> is powered on and the MTF measurements are conducted at all points in the FOV <NUM>, as determined by the test specification. The camera can be rotated about the optical axis <NUM> through <NUM> degrees to <NUM> degrees, and the target <NUM> can be moved across the entire FOV <NUM> to capture all the images at the specified test points.

Once the MTF measurements are completed, at <NUM>, the air conditioning unit is set to room temperature, and once the temperature of the camera <NUM> has reached room temperature, at <NUM>, the cover <NUM> and camera <NUM> are removed, and the testing is repeated with another camera <NUM>.

<FIG> illustrates example methods <NUM> performed by the system <NUM>. For example, the processor <NUM> configures the system <NUM> to perform operations <NUM> through <NUM> by executing instructions associated with the processor <NUM>. The operations (or steps) <NUM> through <NUM> are performed but not necessarily limited to the order or combinations in which the operations are shown herein. Further, any of one or more of the operations may be repeated, combined, or reorganized to provide other operations.

Step <NUM> includes ADJUST ROTATION ANGLE. This can include adjusting, with the processor <NUM>, the rotation angle <NUM> of the test fixture <NUM> about the optical axis <NUM> of the camera <NUM> retained by the test fixture <NUM>, as described above. The camera <NUM> is placed within the insulated housing <NUM> that includes the cover <NUM> removably attached to the base <NUM>. The base <NUM> is attached to the test fixture <NUM>, enabling the housing <NUM> to rotate with the test fixture <NUM> through the rotation angle <NUM> of at least <NUM> degrees and up to <NUM> degrees, as described above. The processor <NUM> adjusts the rotation angle <NUM> so that the MTF of the camera <NUM> can be measured at all points in the FOV <NUM> of the camera, as described above.

The housing <NUM> includes the first orifice <NUM> that directs the flow of conditioned air out of the housing <NUM> and the second orifice <NUM> that directs the conditioned air into the housing <NUM>. The inlet air flow direction is normal to the outlet air flow direction, and the orifices are arranged so that the air circulates around the camera <NUM> before exiting the housing <NUM>, as described above. The cover <NUM> includes the aperture <NUM> that is positioned opposite the test fixture <NUM> and camera <NUM> and defines the FOV <NUM> that includes the target <NUM> used for determining the MTF of the camera <NUM>. The aperture <NUM> is sized to receive the lens barrel <NUM> of the camera <NUM>, and the geometry of the aperture <NUM> reduces the flow of air out of the housing <NUM> from around the lens barrel <NUM> during testing, as described above.

Step <NUM> includes RECEIVE IMAGE DATA. This can include receiving, with the processor <NUM>, image data from the camera <NUM> representing the captured image of the camera target <NUM> in the FOV <NUM> of the camera <NUM>, as described above. The camera <NUM> can capture images of the target <NUM> at different magnifications of the collimator that represents target distances from <NUM> meter to infinity, as described above. The images can be stored in the memory of the processor <NUM> for determining the MTF. The target <NUM> can be the slant-edge target <NUM> or pin-hole target <NUM> that is back-lit to improve the sharpness of the image captured by the camera <NUM>.

Step <NUM> includes ADJUST TARGET POSITION. This can include adjusting, with the processor <NUM>, the position of the camera target <NUM> in the FOV <NUM> of the camera <NUM>. The processor <NUM> can send signals to the test stand <NUM> to move the collimator <NUM>, retaining the target <NUM> through an arc to different points in the FOV <NUM>. The test stand <NUM> positions the center of the target <NUM> at the same radial distance from the camera <NUM> at all positions in the FOV <NUM> when moving the target <NUM> along the arc from one position to the next by maintaining a constant arc radius, as described above. The position of the target <NUM> can be adjusted in any increments, for example, in increments of <NUM> degree across the range of the FOV <NUM>.

Step <NUM> includes DETERMINE OPTICAL CHARACTERISTIC. This can include determining the optical characteristic of the camera or the MTF based on the camera target <NUM> when a temperature of the camera <NUM> is at the camera-temperature set point, as described above. The MTF can be determined over a temperature range of -<NUM> to <NUM>, and in some applications up to temperatures of <NUM>. The temperature of the camera <NUM> is held or soaked at each temperature set-point for at least ten minutes before measuring the MTF to ensure a stable camera temperature. The time to ramp the camera-temperature set point from room temperature to -<NUM> or from room temperature to <NUM> is about fifteen minutes to about twenty minutes, and the time to adjust the camera-temperature set point from -<NUM> to <NUM>, or from <NUM> to -<NUM>, is about thirty minutes to forty minutes. The processor <NUM> uses known software for determining the MTF based on the type of target <NUM> retained in the collimator <NUM>.

Claim 1:
A device (<NUM>) comprising:
a housing (<NUM>) configured to receive a test fixture (<NUM>) that retains a camera (<NUM>) for determining an optical characteristic of the camera (<NUM>) at a desired temperature, wherein:
the housing (<NUM>) comprises a first segment (<NUM>) and a second segment (<NUM>) removably attached to the first segment (<NUM>) to create a chamber,
the first segment (<NUM>) is configured to attach to the test fixture (<NUM>);
the first segment (<NUM>) defines a first orifice (<NUM>) located in a first side of the first segment (<NUM>), the first orifice (<NUM>) being configured to direct a flow of a gas out of the chamber;
the second segment (<NUM>) defines a second orifice (<NUM>) located in a first side (<NUM>) of the second segment (<NUM>) to direct the flow of the gas into the chamber;
the first orifice (<NUM>) and the second orifice (<NUM>) are positioned to enable an inlet flow direction of the gas into the chamber be normal to an outlet flow direction of the gas out of the chamber;
and
the second segment (<NUM>) further defines an aperture (<NUM>) located in a second side (<NUM>) of the second segment (<NUM>) positioned opposite the test fixture (<NUM>) to define a field of view that includes a camera target.