Variable zoom imaging device

Abstract

Disclosed is a variable zoom imaging device, comprising: i) an imaging optical device configured to form an image of an object located in an object region in an imaging region; ii) an adjustable aperture stop for adjustably setting a numerical aperture NA of the image formed by the imaging optical device; iii) an electronic detector including an array of detector elements located in the imaging region to detect the image; and iv) an image processing circuit coupled to the electronic detector to generate a digital representation of the image based on signals from at least some of the detector elements. For each of a plurality of different numerical apertures of the image set by the adjustable aperture stop, the image processing circuit generates a digital representation having a different magnification m of the object.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of U.S. Provisional Application No. 63 / 066,935, filed on August 18, 2020, under 35 U.S.C.§119, the entire content of which is incorporated herein by reference. Technical field

[0003] The present disclosure relates to a variable - zoom imaging device. More specifically, the present disclosure relates to an optical imaging system used with a high - resolution optical sensor, which can achieve high - quality variable zoom in a cost - effective manner. Background art

[0004] An optical imaging system forms an image of an object located in an object region in an image region (usually on an image plane). The optical imaging system includes one or more optical imaging elements, such as lenses or curved mirrors. Within the framework of geometric optics, the properties of each optical imaging element, its position relative to each other, and each of the object region and the image region together cause the light rays emitted from each point in the object region to recombine at the corresponding point in the image region, thereby forming an image. Thus, the optical imaging system generates a spatial distribution of light in the image region, which corresponds to the spatial characteristics of the object in the object region. Specifically, the image corresponds to how the spatial characteristics of the object differently affect (e.g., reflect, transmit, diffract, scatter, and / or attenuate) the incident light. In some cases, ambient light illuminates the object to generate the light rays captured by the optical imaging system to form the image, while in other cases, an illumination source is specifically used to generate illumination light and form the image. The spatial extent of the points in the object region that are imaged onto the image region is called the object field, and similarly, the spatial extent of the points in the image is called the image field.

[0005] Generally, the degree to which an optical imaging system can reproduce small features in the image field depends on the image - side numerical aperture NA of the optical imaging system, which corresponds to the angular range of the light rays recombined by the optical imaging system at each point in the image region at the imaging region. For example, the image - side numerical aperture NA can be expressed as n·sinθ, where θ is the angle formed between the most inclined light ray (i.e., the marginal ray) incident on the image region and the optical axis, and where n is the refractive index of the medium immediately preceding the image region. The aperture stop of an optical imaging system is the element in the system that sets this numerical aperture NA by preventing any light rays outside this angular range from reaching the image region.

[0006] The magnification m' of an optical imaging system with respect to an image in an image region is a measure of the degree to which the lateral dimension of each feature in the image in the image region is increased (or decreased) relative to the lateral dimension of the object. Thus, a feature of an object with a lateral dimension D will be reproduced in the image with a lateral dimension equal to m'·D. Typically, it is desirable to provide an optical imaging system with different magnification ranges that can be selected by a user. For example, after viewing an object on a large object field at a lower magnification m'1, the user may wish to view a subset of the object field at a greater magnification m'2, i.e., the user may want to "zoom" into a subset of the object region. Providing an imaging system with different magnifications m that vary from a minimum magnification m = m min to a maximum magnification m' = m' max defines a zoom ratio z = m' / m' min and a maximum zoom ratio z max = m' max / m' min . An optical imaging system with z max > 1 can be referred to as a variable zoom system.

[0007] Traditionally, variable zoom optical systems include systems having one or more optical imaging elements that move relative to each other to provide variable magnification, and systems including having a turret to insert one of several different optical modules into the optical path to provide variable magnification. Optically, such variable magnification is achieved by fixing the image-side numerical aperture while reducing the object field and increasing the object-side numerical aperture.

[0008] To obtain and store a digital representation of an image of an object produced by an optical imaging system, an optical sensor having an array of detector elements (also referred to herein as a "detector" or "camera") can be located on the image region. Each detector element generates an electrical signal that corresponds to a measure of the light intensity incident on that detector element (or, in some cases, for each of a plurality of colors of light, a measure of the light intensity incident on that detector element). Image processing circuitry is coupled to the array of detector elements to process the electrical signals and store a digital representation of the image. Current technological advancements have enabled high-resolution optical sensors that provide a very large lateral density of different detector elements. In fact, the number of detector elements can be much greater than the typical number of pixels required for the digital representation. Thus, some prior art imaging systems implement "digital zoom," whereby different magnifications m of the object in the final digital representation are simply obtained by generating a digital representation from a corresponding subset of the entire set of detector elements. Specifically, the minimum zoom corresponds to sampling detector elements throughout the entire detector element array in the image field of the optical system, while greater zooms correspond to sampling only detector elements located within successively smaller subsets of the image region of the optical system. SUMMARY OF THE INVENTION

[0009] The inventors have recognized certain problems in existing zoom systems. Systems that implement optical zoom require moving parts, which reduces robustness during zooming and increases the likelihood of vibration, image drift, or focus shift, degrading performance. It generally also requires a greater number of components and / or more complex components, increasing the cost of manufacturing and design. On the other hand, systems that implement digital zoom suffer from a mismatch between the design of the optical imaging system and the sampling of detector elements across the zoom range.

[0010] For example, assume that the detector has an array of 10,000×10,000 detector elements and the desired resolution of the digital representation of the image is 1000×1000. Then, in principle, the zoom range using digital zoom can be from 1 to 10. Specifically, at the lowest zoom, each pixel of the digital representation maps to a 10×10 sub-array of the corresponding detector element, while at the highest zoom, each pixel of the digital representation maps to a single corresponding detector within a 1000×1000 sub-array across the entire detector element array. However, this difference in detector array sampling for different zooms places different constraints on the optical imaging system because the resolution of the 1000×1000 digital representation may not be better than the resolution of the optical image produced by the optical imaging system on the detector array. Thus, if the lateral dimension of the detector element is p, then at the lowest zoom, the optical imaging system only needs to provide a resolution sufficient to generate an optical image with a feature size as small as approximately 10·p, but at the highest zoom, the optical imaging system needs to provide a resolution sufficient to generate a feature size as small as approximately p.

[0011] Therefore, in order to provide a high-quality digital representation of imaging across the full zoom range using only digital zoom, the optical imaging system must provide a resolution sufficient to reach the highest digital zoom setting. At the same time, the optical imaging system must capture a light beam from the entire object field corresponding to the lowest zoom, increasing the complexity of the optical imaging system, which requires many and / or larger optical imaging elements. This is because the complexity of the optical imaging system generally increases with each increase in the object field and the image-side NA. For example, it is easier to design an optical system to produce an image of a relatively small area with a coarse resolution than to design an optical system to produce an image of a relatively large area with a fine resolution. To achieve the latter, generally a greater number of optical elements, larger optical elements, and / or more complex optical elements are required to direct a corresponding larger light beam from each of a greater number of points in a larger object field.

[0012] To address these issues, the inventors disclose a system that combines digital zoom with a simpler optical imaging system. The system includes a variable aperture diaphragm to adjust the image-side numerical aperture NA according to the desired resolution at the digital zoom setting. At the lowest zoom, the aperture diaphragm is set to the minimum NA, and the optical imaging system is designed to capture a light beam from the entire object field at this minimum NA to produce an optical image on the detector. At higher zooms, the aperture diaphragm opening is set to a larger NA to provide the necessary resolution for a (smaller) sub-region of the object field corresponding to the higher zoom. The optical imaging system is designed to capture a light beam from this sub-region of the object field at this larger NA to produce an optical image on the detector. On the other hand, to simplify the design of the optical imaging system, the optical imaging system is not designed to capture all the light beams from the object field outside this sub-region at this larger NA. Although this may result in a blurry image on some parts of the detector, those parts will correspond to detector elements outside the sampling region of the digital representation of the detector used to produce the optical image at these higher zooms. This significantly reduces the design constraints on the optical imaging system, thereby reducing cost and complexity while still producing a digital image of the object with the desired resolution over the entire zoom range.

[0013] Accordingly, more specifically, the following embodiments are disclosed.

[0014] Generally, in one aspect, a variable zoom imaging device is disclosed. The variable zoom imaging device includes: i) imaging optics configured to form an image of an object located in an object region in an imaging region; ii) an adjustable aperture diaphragm for adjustably setting the numerical aperture NA of the image formed by the imaging optics; iii) an electronic detector including an array of detector elements located in the imaging region to detect the image; and iv) an image processing circuit coupled to the electronic detector to generate a digital representation of the image based on signals from at least some of the detector elements. For each of a plurality of different numerical apertures of the image set by the adjustable aperture diaphragm, the image processing circuit generates the digital representation with a different magnification m of the object, where the different magnifications m range from a minimum magnification m = m min to a maximum magnification m = m max , to define a zoom ratio z = m / m min and a maximum zoom ratio z max = m max / m min .

[0015] Embodiments of the variable zoom imaging device may include any of the following additional features.

[0016] The imaging optical device is fixed to provide a constant magnification from the object region to the image region.

[0017] The zoom ratio z represented by the number can vary inversely with the field region spanned by the detector element for generating the number. For example, the sizes of different numerical apertures can be set by an adjustable aperture diaphragm to increase with a corresponding increase in the zoom ratio z of the number representation. Additionally, in some embodiments, the sizes of the different numerical apertures set by the adjustable aperture diaphragm can increase linearly with a corresponding increase in the zoom ratio z of the number representation within a zoom ratio range greater than 1. For example, the numerical aperture NA of an image set by the adjustable aperture diaphragm can be given by where p is the maximum lateral dimension of the detection element and λ is the central wavelength of the light used to form the image on the detector.

[0018] The number representation can include at least one intensity value at each pixel in an N1×N2 pixel array, where N1 and N2 are positive integers. For example, both N1 and N2 can be greater than or equal to 400.

[0019] The array of detector elements of the electronic detector can include an array at least as large as an M·N1×M·N2 array, where M is a positive integer greater than or equal to z max For example, z max can be greater than or equal to 3. In some embodiments, the image processing circuit determines the intensity value of each pixel in the N1×N2 array by one or more signals from detector elements in a corresponding sub - array of M / z×M / z detector elements to generate the number representation with the zoom ratio z. In some other embodiments, the image processing circuit determines the intensity value of each pixel in the N1×N2 array by only one signal from detector elements in a corresponding sub - array of M / z×M / z detector elements to generate the number representation with the zoom ratio z. In yet some other embodiments, the image processing circuit determines the intensity value of each pixel in the N1×N2 array by a weighted average of the signals from detector elements in a corresponding sub - array of M / z×M / z detector elements to generate the number representation with the zoom ratio z. Additionally, in some embodiments, the sub - arrays of detector elements corresponding to the pixels in the number representation are repetitively spaced apart from each other within the field region spanned by the detector elements for generating the number representation.

[0020] Generally, in some embodiments, the image processing circuit determines the intensity value of each pixel in the N1×N2 array by one or more signals among the signals of the detector elements in the corresponding sub-arrays from one or more detector elements, to generate the digital representation with a zoom ratio z, wherein the number of detector elements in each corresponding sub-array decreases as the numerical aperture NA set adjustably by the aperture stop increases.

[0021] The imaging optics may include a first set of optics that guides light from an object to a pupil defined by an aperture stop and a second set of optics that guides light from the pupil to an image region. The variable zoom imaging device may further include a light source configured to illuminate the object and thereby provide light to the imaging optics to form an image of the object. For example, the light source may be a coherent laser. Additionally, in certain embodiments, the variable zoom imaging device may further include an interferometer assembly including a beam splitter and a reference surface, wherein the light source is further configured to illuminate the reference surface, and the beam splitter is configured to coherently combine the light from the object and the reference surface such that the image formed by the imaging optics on the imaging region is an interference image.

[0022] In certain embodiments, the area of the array of detector elements is between 0.25 cm 2 and 10 cm 2 .

[0023] In certain embodiments, the minimum magnification is between 1 / 10 and 1 / 5, such as in the case where the variable zoom imaging device is a Fizeau interferometer. In certain other embodiments, the minimum magnification is between 1 / 2 and 5, such as in the case where the variable zoom imaging device is a microscope interferometer.

[0024] In certain embodiments, the area of the object region imaged onto the array of detector elements is between 0.04 cm 2 and 10,000 cm 2 .

[0025] The adjustable aperture stop may be continuously adjustable. Alternatively, the adjustable aperture stop may be discretely adjustable for each of a plurality of discrete settings. For example, the adjustable aperture stop may be a mechanical aperture stop or an electronic aperture stop. Additionally, for example, the aperture stop may provide a nominal circular opening to define the numerical aperture. Or, for example, the aperture stop may provide a nominal rectangular opening to define the numerical aperture.

[0026] The variable zoom imaging device may further include a user control interface configured to electronically adjust the adjustable aperture diaphragm in response to a user input of a zoom ratio. For example, the user control interface also causes the image control circuit to set the magnification of the detector for the object in response to a user input of a zoom ratio. Additionally, for example, the image control circuit may be configured to set the magnification of the detector for the object by adjusting the sampling of the detector elements used to generate the digital representation.

[0027] In some embodiments, when the adjustable aperture diaphragm is set to the largest one of a plurality of different numerical apertures, for the full field region of the object corresponding to the full field region across all detector elements in the array, the diameter of the imaging optics need not be large enough to pass all the light rays from the object. However, in this embodiment, when the adjustable aperture diaphragm is set to the smallest one of a plurality of different numerical apertures, for the full field region of the object, the diameter of the imaging optics may be large enough to pass all the light rays from the object.

[0028] In some embodiments, when the adjustable aperture diaphragm is set to the largest one of a plurality of different numerical apertures, the imaging optics does not produce a diffraction-limited image over the full field region across all detector elements in the array. However, in this embodiment, when the adjustable aperture diaphragm is set to the smallest one of a plurality of different numerical apertures, the imaging optics may produce a diffraction-limited image over the full field region. Additionally, for example, when the adjustable aperture diaphragm is set to the largest one of a plurality of different numerical apertures, the imaging optics may produce a diffraction-limited image over the maximum zoom field region, where the maximum zoom field region is equal to the area of the full field region divided by z max . The imaging optics producing a diffraction-limited image of that numerical aperture NA over a given field of view (“FOV”) in the image region means that: for coherent illumination, the imaging optics is capable of producing features in that image region at a spatial period d as small as in any place of the FOV.

[0029] Generally, in another aspect, an optical imaging system for use with a variable zoom imaging device that implements digital zoom is disclosed. The optical imaging device includes: i) imaging optics configured to form an image of an object located in an object region in an imaging region; and ii) an adjustable aperture diaphragm for adjustably setting the numerical aperture NA of the image formed by the imaging optics. The imaging optics is designed to form the image as a diffraction-limited image for each of a plurality of continuously increasing numerical apertures NA of the image corresponding to continuously decreasing fields of view of the object in the object region set by the adjustable aperture diaphragm.

[0030] Embodiments of the optical imaging system may further include any of the above features for the variable zoom imaging device.

[0031] All documents mentioned herein, if any, are incorporated by reference in their entirety. In case of conflict with the present disclosure and any document incorporated by reference, the present disclosure shall prevail.

[0032] Details of one or more embodiments of the present disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present disclosure will be apparent from the specification, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1A is a schematic diagram of a variable zoom imaging device for a lower first magnification.

[0034] Figure 1B is by the variable zoom imaging device for a lower first magnification Figure 1A schematic diagram of digital sampling implemented.

[0035] Figure 2A is a schematic diagram of a variable zoom imaging device for a higher second magnification.

[0036] Figure 2B is by the variable zoom imaging device for a higher second magnification Figure 1A schematic diagram of digital sampling implemented.

[0037] Figures 3 to 5 is a ray trace diagram of an exemplary imaging optical system for imaging an object onto a sensor, where the system has a collimator, an aperture stop, and an eyepiece, and the thin lens approximation is used for the collimator and the eyepiece.

[0038] Figures 6 to 7 is Figures 3 to 5 ray trace diagram of the eyepiece portion of the system depicted in, which compares the light beams of the full field of view and a smaller aperture stop (as Figure 6 shown) with the light beams of a one-third field of view size system (resulting in a 3-fold (3x) magnification of the digital representation presented by the sensor) and an aperture stop 3 times larger (as Figure 7 shown).

[0039] Figures 8 to 10 is a ray trace diagram of a 6-lens eyepiece using real lens elements.

[0040] Figure 11 is a ray trace diagram of a 5-lens eyepiece using real lens elements and implementing a simplified optical design of the present invention to achieve diffraction-limited imaging for a variable zoom system for implementing digital zoom.

[0041] Figure 12 is Figures 8 to 10 a ray trace diagram of the complete optical system of the eyepiece shown, and includes a 3-lens collimator.

[0042] Figure 13 With Figure 14 is Figure 11 a ray trace diagram of the complete optical system of the eyepiece shown, and further includes a 2-lens collimator. The complete optical system implements the optical design simplification of the present invention to achieve diffraction-limited imaging of a variable zoom system for implementing digital zoom. Figure 13 shows full field-of-view imaging at 1100 pixel resolution, while Figure 14 shows one-third field-of-view imaging at 1100 pixel resolution, where the pixel dimension is Figure 13 one-third of the pixel dimension in

[0043] Figure 15 is Figure 13 With Figure 14 a schematic diagram of an optical imaging system, which further includes a laser source as an illumination source to irradiate an object via a beam splitter.

[0044] Figure 16 is Figure 15 a schematic diagram of an optical imaging system, which is further implemented as an interferometric optical imaging system by including a reference element, such that the image of the object formed on the sensor interferes with the reference wavefront to generate an interference image of the object.

[0045] The same reference symbols in each figure represent the same elements. Detailed Description

[0046] Image zoom is an important feature in many optical systems. Zooming in on an image provides the user with better lateral resolution at a smaller image size. A well-designed zoom system will increase the available resolution in proportion to the zoom ratio. This is typically achieved by fixing the numerical aperture of the imaging light beam on the sensor while reducing the lens field of view and increasing the object space numerical aperture. The emergence of new very high-resolution sensors has provided an alternative method ("digital" zoom) for image zoom for a subset of the following applications, where the number of resolution elements required throughout the image is significantly less than the number of sensor elements throughout the sensor. However, as described above, digital zoom typically suffers from a mismatch between the design of the optical imaging system and the detector element sampling throughout the digital zoom range.

[0047] Embodiments of the present invention include an imaging system, wherein the size of the aperture stop increases proportionally with the desired zoom ratio, and the field of view is adjusted by sampling a proportionally smaller area of the sensor. The optical system is designed such that the imaging remains diffraction-limited within the field of view specified by the currently selected zoom ratio. Embodiments of this zoom system can be much simpler than standard optical zoom, which requires complex cam mechanisms to move multiple optical elements to adjust the zoom while maintaining focus. Additionally, in at least some embodiments, it only requires adjusting the size of the aperture stop while changing the display area of the sensor. Further, it can maintain focus and avoid image drift observed in many mechanically-driven optical zoom systems.

[0048] Representative embodiments of the variable zoom imaging system 100 of the present invention are shown in FIGS. 1 and 2 for a lower first magnification m1 ( Figure 1A ) and a higher second magnification m2 ( Figure 2A ). The variable zoom imaging system 100 is configured to produce an image of an object 115 located in object region 110 on image region 150. As will be described further below, magnifications m1 and m2 are with respect to the final digital representation of the image and are opposite to the optical magnification m' of the image of the object in the image region, where for Figure 1A and Figure 2AFor the variable zoom imaging system 100 of the present invention shown in [description], the optical magnification m' is constant. In addition to its optical components, it further includes an electronic detector 145, which includes an N×N detector element array (also referred to herein as a high-resolution sensor), and the array is configured to detect an image by measuring the light intensity values at each detector element. The image processing circuit 155 is electrically coupled to the detector 145 to store and process the intensity values to provide a digital representation of the image. The image processing circuit 155 is electrically coupled to the user interface 190 to receive commands from the user interface and provide the digital representation to the user interface 190. The optical components of the variable zoom imaging system 100 extend along the optical axis 105 corresponding to the z-axis, and include a first optical module with one or more optical elements 130 (also referred to herein as "collimators"), a second optical module with one or more optical elements 140 (also referred to herein as "eyepieces"), and an aperture stop 135 located between the first optical module 130 and the second optical module 140. The optical elements within the optical modules 130 and 140 may include, for example, lenses and / or curved mirrors. In this embodiment, both the object region 110 and the image region 150 extend parallel to the x-y plane, and so does the detector element array of the detector 145. The aperture stop 135 provides a variable aperture opening to change the image-side numerical aperture NA of the optical imaging system, and is operably coupled to the user interface 190 such that the user can control the image-side numerical aperture NA. The aperture opening will also limit the object-side numerical aperture, which is equal to the image-side numerical aperture NA multiplied by the magnification m.

[0049] The collimator 130 and the eyepiece 140 form an optical imaging system for generating an optical image of the object 115 located on the object region 110 on the image region 150. Specifically, the properties (e.g., dimensions and optical powers) of each optical element within the optical imaging system and their positions relative to each other, along with each of the object region and the image region, together cause the light rays emitted from each point in the object region to recombine at the corresponding points in the image region, thereby forming an image. This is schematically shown in Figure 1A with Figure 2B for each of Figure 1A three points on the object region 110 and three corresponding points on the image region 150. There is a set of corresponding points on the optical axis 105, and there are two other sets of corresponding points at the outer edges of the object field and the image field (represented by A 1O and A 1I in Figure 2A and represented by A 2O and A 2I in Figure 1A and Figure 2A . The central ray 125 of the light ray bundle emitted from each point in the object region 110 is called the chief ray, and is depicted by solid arrows in Figure 1A withFigure 2A The optical imaging system is a telecentric system because the chief ray passing through the center of the opening provided by the aperture stop 135 is perpendicular to each of the object region 110 and the image region 150. The outermost rays 120 (in Figure 1A ) and 220 (in Figure 2A ) of the light beam emitted from each point of the object region 110 are referred to as marginal rays and are depicted by dashed arrows in Figure 1A and Figure 2A . The edge of the opening provided by the aperture stop 135 coincides with the path of the marginal rays and defines the angle at which the marginal rays are emitted from the object region 110 and incident on the image region 150.

[0050] To configure the variable zoom imaging system 100 to operate at a first lower magnification m1 (as shown in Figure 1A ), the user interface 190 causes the variable aperture stop 135 to provide a smaller opening for the light beam, resulting in a smaller angle θ1 of the marginal ray 120 incident on the image region 150 relative to the optical axis 105 and a smaller image-side numerical aperture NA1. Conversely, to configure the variable zoom imaging system 100 to operate at a second higher magnification m2 (as shown in Figure 2A ), the user interface 190 causes the variable aperture stop 135 to provide a larger opening for the light beam, resulting in a larger angle θ2 of the marginal ray 220 incident on the image region 150 relative to the optical axis 105 and a larger image-side numerical aperture NA2. In some embodiments, the eyepiece 140 has an effective focal length f, and the aperture stop 135 and the image region 150 are located in the front focal plane and the rear focal plane of the eyepiece 140, respectively. In this case, the angle θ of the marginal ray incident on the image region satisfies the formula tanθ = r / f, and NA = n·sin[arctan(r / f)], where r is the distance from the optical axis 105 to the edge of the aperture stop opening parallel to the x-y plane. For example, for a circular aperture stop positioned perpendicular to the optical axis, r is the radius of the aperture stop opening. In the limit of small angles θ, which is common in many imaging systems, the expression for NA simplifies to NA = n·r / f.

[0051] Importantly, although different magnifications m1 and m2 of the variable zoom imaging system 100 correspond to different aperture stop openings, the optical elements within each of the collimator 130 and the eyepiece 140 remain the same and do not move relative to each other or relative to the object region and the image region, thereby providing a very stable and robust system. In contrast, digital zoom is used to provide different magnifications, as schematically shown in Figure 1B and Figure 2B . Specifically, Figure 1A and Figure 1BSchematically shows the sampling of the detector elements of detector 150 by imaging processing circuit 155 to produce digital representation 195. For ease of illustration, digital representation 195 in these figures is depicted as having values spanning a 3×3 pixel array, and the detector is depicted as having a 9×9 detector element array.

[0052] As Figure 1B shown, at a lower first magnification m1, the intensity value at each pixel in digital representation 195 is derived from one or more values in a spatially corresponding 3×3 detector element block in detector 145. For example, the intensity value can simply correspond to the intensity value of the central detector element in the 3×3 detector element block; it can correspond to the average of the intensity values in the 3×3 detector element block; it can correspond to a weighted average of the intensity values in the 3×3 detector element block (e.g., where the weight of the central detector element is greater than that of the surrounding detector elements); or it can correspond to a more complex function of the intensity values in the 3×3 detector element block. In any case, the digital representation is derived from detector elements across the entire area of the detector spanning the image region 150, which corresponds to image field dimension A 1I , and thus, the scale of the digital representation corresponds to object field dimension A 1O .

[0053] On the other hand, as Figure 2B shown, at a higher second magnification m2, the intensity value at each pixel in the 3×3 digital representation 195 is derived from the intensity value of the corresponding detector element in the 3×3 detector element block at the center of detector 145. In this case, the digital representation is derived only from detector elements in the central one-third of the entire area of the detector spanning the image region 150, which corresponds to image field dimension A 2I , and thus, the scale of the digital representation corresponds to object field dimension A 2O , based on Figure 1B and Figure 2B 's illustrative description, object field dimension A 2O is one-third of A 1O . As a result, for this illustrative description, the higher second magnification m2 is three times larger than the lower first magnification m1.

[0054] Of course, in actual embodiments, the resolution of the detector provides many more detector elements, such as at least 1000×1000, or even as large as or greater than 10,000×10,000. Thus, in further embodiments, there can be more levels of digital zoom, where successive larger magnifications in digital representation are based on sampling successively smaller regions of the detector element array provided by the detector. To optically accommodate this increased digital magnification, the variable aperture diaphragm is set to correspondingly increase the aperture diaphragm, thereby increasing the NA, such that the region (i.e., having dimension A i of the image field) captured by the digital representation in the optical image on the detector is diffraction-limited with respect to an image feature having a size on the order of the number of detector element blocks corresponding to each pixel in the digital representation. On the other hand, the quality of the optical image outside this region on the detector does not have to be high quality, since the digital representation does not sample these regions, thereby reducing the design constraints on the optical imaging system.

[0055] For example, assume that the desired image resolution for the digital representation is N×N pixels, and the desired range of the zoom ratio z is from z min =1 to z max =M, where M is a positive integer. Then, in further embodiments, the detector is selected to have a resolution provided by a detector element array of at least M·N×M·N. For example, in one embodiment with a zoom ratio of 1, the entire detector array is read and then subsampled such that every Mth pixel on every Mth row is selected to derive the value of each pixel in the N×N digital representation of the optical image. Through communication with the user interface, the image processing circuit can change this sampling to provide a higher zoom ratio. For example, instead of sampling every Mth pixel on every Mth row to provide a zoom ratio equal to 1, the image processing circuit can sample every (M-m)th pixel on every (M-m)th row to provide a zoom ratio z equal to M / (M-m), where m ranges from 0 to M-1, and the imaging processing circuit only reads the central portion of the detector array sufficient to fill the N×N digital representation in this sampling. Using these integer sampling intervals, specific detector elements can be sampled. For example, assume M = 3, then the integer values of m = 0, 1, 2 will correspond to sampling 3x3, 2x2, and 1x1 pixel blocks respectively, which correspond to zoom ratios z of 1, 1.5, and 3 respectively. However, intermediate zoom ratios can also be selected by interpolating detector elements. Additionally, as described above with respect to Figure 1B and Figure 2BAs described, the imaging processing circuit can also derive the intensity value at each pixel in the digital representation from one or more intensity signals in an (M - M)×(M - M) detector element block corresponding spatially by averaging, weighted averaging, or more complex processing of these detector element signals.

[0056] To provide the resolution afforded by sampling with detector elements and enable a diffraction - limited image to be captured in digital representation at each such zoom ratio, the image - side numerical aperture NA set by the variable aperture stop (e.g., under the control of a user interface) can be given by the following formula:

[0057]

[0058] where p is the minimum lateral dimension of the detector element and λ is the central wavelength of the light used to form the image on the detector. More generally, including for non - integral sampling, NA can be set according to:

[0059]

[0060] Thus, for successively smaller image fields A corresponding to increasing digital zoom I , the optical imaging system only needs to be designed to be diffraction - limited at a larger NA. For a certain zoom ratio, the image quality outside the image field on the detector that is not diffraction - limited will be immaterial because the digital representation at that zoom ratio does not require these regions. This is a significant advantage for the optical designer of the imaging optical system because the field size within which the optical imaging system needs to be corrected is inversely proportional to the size of the aperture stop opening. For example, at 2x zoom, the aperture stop is twice as large as at 1x zoom, but the field is 1 / 2 as large. This trade - off between aperture stop size and field size makes it easier to design the optical system than to design a primary optical imaging system with the full field size and full resolution typically required for a conventional digital zoom system that purports to be diffraction - limited. Moreover, compared to optical continuous zoom on a turret or a series of zoom relay lenses, the advantage of this method is that there are no moving optical elements other than the aperture stop. This avoids the strict assembly and alignment tolerances required to minimize image position shift and focus shift during zoom.

[0061] The user experience has also been significantly improved. For example, since there is no moving lens, the image position on the camera is fixed by definition between different zoom positions. In addition, the focus does not shift with zoom, so the user can zoom to the maximum magnification and focus the image, and be confident that the focus will not shift when switching to a lower zoom. In addition, the original pixel lateral calibration between the object and the camera does not change with the zoom ratio, so a single calibration at any zoom position is sufficient to calibrate all zoom positions. In addition, subsampling of the detector element array at lower zoom can result in a higher instrument transfer function (ITF), because the size of a single detector element is small compared to the distance between the sampled detector elements.

[0062] In a further embodiment, the relationship between the image-side numerical aperture NA and the zoom ratio z may be somewhat different from the relationship shown in the above formulas (1) or (2). For example, formulas (1) and (2) assume coherent illumination of the object. To account for incoherent illumination, the general formula for the Abbe resolution limit can be considered:

[0063] d = λ / (NA + NA′) (3)

[0064] where d is the smallest spatial period resolvable in the image, and NA' is the numerical aperture for the object illumination. The variation of this illumination numerical aperture NA' is from NA' = 0 for coherent illumination to NA' = NA for incoherent illumination filling the image-side aperture. Formulas (1) and (2) correspond to this Abbe formula for coherent illumination, which is used to resolve the smallest spatial period corresponding to a given zoom setting z:

[0065]

[0066] For example, at maximum zoom, d = 2p, corresponding to the size of two detector elements. Thus, in other embodiments involving incoherent illumination, in the limit of incoherent illumination filling the image-side aperture, the expressions for the image-side NA in formulas (1) and (2) are at most reduced by one-half.

[0067] In addition, formulas (1) and (2), whether modified to account for incoherent illumination or not, do not account for any oversampling, under which the numerical aperture is slightly larger than that required to resolve the smallest spatial period corresponding to a given digital zoom setting. Thus, in other embodiments, the image-side numerical aperture NA may be slightly larger than that given by formulas (1) and (2), whether the formulas are modified to account for incoherent illumination or not. However, importantly, the image-side numerical aperture NA generally increases with the corresponding increase in the zoom ratio z.

[0068] The optical imaging system implementing the features of the present invention can be designed using common optical design software known in the art, such as Code V Optical Design Software from Synopsys or similar software from Zemax LLC. The simplification of the optical design resulting from the present invention will now be described in Figures 3 - 14 and Figures 3 - 14 which includes ray trace diagrams generated by such optical design software and shows the chief rays of several object points and in some cases the marginal rays propagation of various designs of the imaging optical system.

[0069] The cost of manufacturing an optical imaging system is generally determined by the number of optical elements, their size, and precision. Therefore, the cost is controlled by minimizing the number of elements, reducing their size, and allowing looser tolerances for the surfaces and their alignment. The optical imaging system is typically designed as a telecentric imaging system. In a telecentric imaging system designed for magnification or reduction, there are usually two separate groups of lenses such that they have a common focus between the two groups. The aperture stop of the system is located at this point. By positioning the stop at the position where the two foci coincide, the chief rays on the object side and the image side of the lens are parallel to the optical axis. In Figure 1A and Figure 2A 's embodiments, these two groups of lenses correspond to the collimator 130 and the eyepiece 140.

[0070] Figure 3 shows a simple telecentric optical imaging system using the thin lens approximation to generate an image of an object on a sensor (i.e., a detector having an array of detector elements). The telecentric optical imaging system includes a collimator and an eyepiece sharing a common focus, where the aperture is located at this focus. The size of the lens is determined by the combination of the field of view (corresponding to Figure 1A and Figure 2A 's embodiment's object field A O ) and the aperture stop size. As Figure 4 shows, a smaller field size will reduce the size of the required lens. In addition, as Figure 5 shows, increasing the aperture stop size will increase the size required for the lens because the optical system needs to capture a larger angular range of light rays emitted from each object point in the object field of view.

[0071] Now focusing only on the eyepiece part of the system, Figure 6 compares the light beams of the full object field and a smaller aperture stop (as Figure 7 shows) with the light beams of a one-third object field size system (resulting in a 3x magnification of the digital representation presented by the sensor) and a 3x larger aperture stop (as Figure 6 shows). It is worth noting that in Figure 7 shown, Figure 6In the system, the light beam requires an eyepiece with a larger diameter, but results in a relatively small beam footprint on the eyepiece, while in Figure 7 In the system, a smaller diameter is required, but the beam footprint is larger and substantially covers this smaller diameter. As a result, for this 3x zoom case, the eyepiece only needs to have higher quality in a small area at the center of the eyepiece.

[0072] Figures 8 - 10 Shows the same principle of a real eyepiece formed by multiple lens elements. Specifically, Figure 8 Shows a 6-element eyepiece designed to provide 3300 pixel resolution across the full field of view of the sensor. In contrast, Figure 9 Shows the same system, but with the aperture size reduced to provide only 1100 pixel resolution, and resulting in a smaller beam footprint on the lens elements of the eyepiece. Finally, Figure 10 Shows the same system with the same 3300 pixel resolution as in Figure 6 but with one-third of the object field (resulting in a 3x magnification of the digital representation presented by the sensor), which shows a beam footprint similar (or even smaller) to that of Figure 9 .

[0073] By reducing the diameter of the lens required between Figure 8 and Figure 9 , the cost of the eyepiece is reduced. Since the eyepiece meeting these imaging specifications no longer requires 6 components, further simplification and cost reduction are also possible. For example, Figure 11 Shows the new eyepiece, where the number of elements has been reduced from 6 to 5.

[0074] In addition, the large collimator used with the eyepiece in Figure 8 requires 3 elements to achieve the imaging performance of 3300 pixels across the entire object field as shown in Figure 12 to provide a complete system layout. On the other hand, the collimator used with the eyepiece in Figure 11 and as shown in Figure 13 and Figure 14 to provide a complete system layout only requires 2 components, which further saves cost. Figure 13 Shows the inventive system imaging the full object field at 1100 pixel resolution, and Figure 14 Shows the system imaging one-third of the object field (resulting in a 3x magnification of the digital representation presented by the sensor) at 1100 pixel resolution, but with pixel dimensions that are Figure 13 one-third of those of

[0075] Figures 12 - 14The complete system layout depicted includes a beam splitter element (depicted as a rectangular assembly) along the optical path between the collimator and the aperture stop positions. The purpose of the beam splitter is to couple light from an illumination source (e.g., a laser source) to illuminate an object (e.g., a test part being inspected) to generate light that is imaged by the collimator and the eyepiece onto the sensor. The complete system including these additional components is shown in Figure 15 . Specifically, light from the laser source is focused by a laser focusing lens and then reflected by the beam splitter and passed through a 2-lens collimator to illuminate an object (e.g., a test part) in the object field. Light emitted from the test part in response to this illumination light is then imaged by the 2-lens collimator through the beam splitter and the aperture stop, which defines the image-side numerical aperture of the system and is located at the focal point of the 2-lens collimator. The light passing through the aperture stop is then focused by a 5-lens eyepiece to form an optical image of the object on the sensor, which is used to capture a digital representation of the object.

[0076] In other embodiments, different illumination configurations may be used. For example, the illumination source may illuminate the object from the side or from the back at an angle, or ambient light may be used to illuminate the object. As described above, the illumination may be coherent (e.g., from a laser source) or incoherent, resulting in different requirements for the numerical aperture NA needed to resolve certain size features.

[0077] In addition, in other embodiments, a variable zoom imaging system may be configured as an interferometric system, as Figure 16 schematically shown in, which further includes a reference element in the system of Figure 15 to reflect the illumination light back through the 5-element eyepiece to the sensor so as to interfere with the light from the test part and form an interference image of the test part on the sensor, which can be processed by an image processing circuit to produce a digital representation of the interference image. For example, as is known in the art, interferometric imaging can be used to provide information about the surface height of a test part in the object region being imaged. Specifically, in Figure 16 , the reference element is a transmission flat located just in front of the object to reflect a small portion of the illumination light back to the sensor to interfere with the illumination light reflected from the object.

[0078] Embodiments of the present disclosure can have many different implementations. For example, the absolute magnification provided by an optical imaging system can be greater than 1 (i.e., magnified) or less than 1 (i.e., reduced). For example, in some embodiments, the minimum magnification will be between 1 / 10 and 1 / 5, such as applicable to the imaging optics in a Fizeau interferometer. In another example, in some embodiments, the minimum magnification will be between 1 / 2 and 5, such as applicable to the imaging optics in a microscope interferometer. Additionally, for example, the area of the detector element array can vary over a wide range depending on the implementation, e.g., between 0.25 cm 2 and 10 cm 2 in any range. Correspondingly, the area of the object region imaged onto the detector element array can also vary over a wide range depending on the implementation, e.g., between 0.04 cm 2 and 10,000 cm 2 in any range.

[0079] Furthermore, in some embodiments, the adjustable aperture stop provides a continuously adjustable aperture opening, while in other embodiments, the adjustable aperture stop is discretely adjustable for each of a plurality of discrete settings. The adjustable aperture stop can be mechanically or electronically driven. Additionally, while Figure 1A the Figure 2A embodiments have a user control interface configured to adjust the adjustable aperture stop in response to a user input of a zoom ratio, in other embodiments, the aperture stop can also be manually adjusted. Generally, the aperture stop is circular, but there may also be some embodiments with a square or rectangular aperture opening.

[0080] Range

[0081] It must be noted that as used herein and in the appended claims, unless the context clearly dictates otherwise, the singular forms "a," "an," and "the" include plural referents, e.g., when the word "single" is used.

[0082] As used herein, the terms "adapted" and "configured" mean that an element, component, or other subject is designed to and / or intended to perform a given function. Thus, the use of the terms "adapted" and "configured" should not be construed to mean that a given element, component, or other subject simply "can" perform a given function.

[0083] As used herein, the phrases "at least one" and "one or more," when referring to a list of more than one entity, mean any one or more of the entities in the list, and do not necessarily refer to at least one of each and every entity specifically listed in the list. For example, "at least one of A and B" (or equivalently, "at least one of A or B," or equivalently, "at least one of A and / or B") can refer to A alone, B alone, or a combination of A and B.

[0084] As used herein, the term "and / or" placed between a first entity and a second entity means one of the following: (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entities listed with "and / or" shall be construed in the same manner, i.e., as "one or more" entities so combined. Other entities may optionally exist in addition to the entities specifically identified by the "and / or" clause, whether related or unrelated to those specifically identified.

[0085] Although this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or the scope that may be claimed, but rather as descriptions of features specific to particular embodiments of a particular invention.

[0086] Certain features that are described in the context of separate embodiments in this specification may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments.

[0087] Furthermore, although the above features may be described as acting in certain combinations and even initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variant of a sub-combination.

[0088] Similarly, although operations are depicted in the figures in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or in a sequential order, or that all of the illustrated operations be performed, to obtain a desired result. In some cases, multitasking and parallel processing may be advantageous. Additionally, the separation of the various system components in the above embodiments should not be construed as requiring such separation in all embodiments, but rather that the described program components and systems can generally be integrated in a single software product or packaged into multiple software products.

[0089] Accordingly, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result. Also, the processes depicted in the figures need not be in the particular order or sequential order shown to achieve the desired result. In certain implementations, multitasking and parallel processing may be advantageous.

[0090] Although multiple embodiments of the present invention have been described, it should be understood that various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A variable zoom imaging device, comprising: Imaging optics configured to form an image of an object in an imaging region, the object being located in an object region; An adjustable aperture stop for adjustably setting a numerical aperture NA of the image formed by the imaging optics; A light source configured to illuminate the object and thereby provide light to the imaging optics to form the image of the object; An electronic detector including an array of detector elements located in the imaging region to detect the image; And An image processing circuit coupled to the electronic detector to generate a digital representation of the image based on signals from at least some of the detector elements; wherein, for each of a plurality of different numerical apertures of the image set by the adjustable aperture stop, the image processing circuit generates the digital representation having a different magnification m of the object; Among them, the different magnification factors m range from the minimum magnification factor m = m min to the maximum magnification factor m = m max , to define the zoom ratio z = m / m min and the maximum zoom ratio z max = m max / m min , wherein a zoom ratio z of the digital representation varies inversely with a field region across which the detector elements are used to generate the digital representation; wherein sizes of the different numerical apertures set by the adjustable aperture stop increase with a corresponding increase in the zoom ratio z of the digital representation; wherein sizes of the different numerical apertures set by the adjustable aperture stop increase linearly with a corresponding increase in the zoom ratio z of the digital representation within a zoom ratio range greater than 1; wherein, the numerical aperture NA of the image set by the adjustable aperture diaphragm is given by where p is the maximum lateral dimension of the detection element and λ is the central wavelength of the light used to form the image on the detector.

2. The variable zoom imaging device according to claim 1, wherein, The imaging optics is fixed to provide a constant magnification from the object region to the image region.

3. The variable zoom imaging device according to claim 1, wherein, The digital representation includes at least one intensity value at each pixel in an N1×N2 pixel array, where N1 and N2 are positive integers.

4. The variable zoom imaging device according to claim 3, wherein, Both N1 and N2 are greater than or equal to 400.

5. The variable zoom imaging device according to claim 3, wherein, The array of detector elements of the electronic detector includes an array that is at least as large as an M·N1×M·N2 array, where M is a positive integer greater than or equal to z max and N2 is a positive integer.

6. The variable zoom imaging device according to claim 5, wherein, z max Greater than or equal to 3.

7. The variable zoom imaging device according to claim 5, wherein, The image processing circuit determines the intensity value at each pixel in the N1×N2 pixel array by one or more signals from detector elements in a corresponding sub-array of M / z×M / z detector elements to generate the digital representation having a zoom ratio z.

8. The variable zoom imaging device according to claim 7, wherein, The image processing circuit determines the intensity value at each pixel in the N1×N2 pixel array by only one signal from detector elements in the corresponding sub-array of M / z×M / z detector elements to generate the digital representation having a zoom ratio z.

9. The variable zoom imaging device according to claim 7, wherein, The image processing circuit determines the intensity value at each pixel in the N1×N2 pixel array by a weighted average of signals from detector elements in the corresponding sub-array of M / z×M / z detector elements to generate the digital representation having a zoom ratio z.

10. The variable zoom imaging device according to claim 7, wherein, Sub-arrays of detector elements corresponding to pixels in the digital representation are repeatedly spaced apart from each other within the field region across which the detector elements are used to generate the digital representation.

11. The variable zoom imaging device according to claim 3, wherein, The image processing circuit determines the intensity value of each pixel in the N1×N2 pixel array based on one or more signals in the signals of the detector elements in the corresponding sub-array from one or more detector elements to generate the digital representation with a zoom ratio z, wherein the number of detector elements in each corresponding sub-array decreases as the numerical aperture NA adjustably set by the adjustable aperture diaphragm increases.

12. The variable zoom imaging device according to claim 1, wherein, The imaging optical device includes a first set of optical devices that guides light from the object to the pupil defined by the adjustable aperture diaphragm and a second set of optical devices that guides light from the pupil to the image region.

13. The variable zoom imaging device according to claim 12 further includes an interferometer assembly, the interferometer assembly including a beam splitter and a reference surface, and wherein, The light source is further configured to irradiate the reference surface, and the beam splitter is configured to coherently combine the light from the object and the reference surface such that the image formed by the imaging optical device on the imaging region is an interference image.

14. The variable zoom imaging device according to claim 1, wherein, The light source is a coherent laser.

15. The variable zoom imaging device according to claim 1, wherein, The area of the array of detector elements is between 0.25 cm 2 and 10 cm 2 in size.

16. The variable zoom imaging device according to claim 1, wherein, The minimum magnification is between 1 / 10 and 1 / 5.

17. The variable zoom imaging device according to claim 1, wherein, The minimum magnification is between 1 / 2 and 5.

18. The variable zoom imaging device according to claim 1, wherein, The area of the object region imaged onto the array of detector elements is between 0.04 cm 2 and 10,000 cm 2 2 19. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm is continuously adjustable.

20. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm is discretely adjustable for each of a plurality of discrete settings.

21. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm is a mechanical aperture diaphragm.

22. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm is an electronic aperture diaphragm.

23. The variable zoom imaging device according to claim 1, further comprising a user control interface configured to electronically adjust the adjustable aperture diaphragm in response to a user input of the zoom ratio.

24. The variable zoom imaging device according to claim 23, wherein, The user control interface further causes the image control circuit to set the magnification of the detector for the object in response to a user input of the zoom ratio.

25. The variable zoom imaging device according to claim 24, wherein, The image control circuit is configured to set the magnification of the detector for the object by adjusting the sampling of the detector elements used to generate the digital representation.

26. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm provides a nominal circular opening to define the numerical aperture.

27. The variable zoom imaging device according to claim 1, wherein, The adjustable aperture diaphragm provides a nominal rectangular opening to define the numerical aperture.

28. The variable zoom imaging device according to claim 1, wherein, When the adjustable aperture diaphragm is set to the largest one of the plurality of different numerical apertures, for the full field region of the object corresponding to the full field region across all detector elements in the array, the diameter of the imaging optical device is not large enough to pass all the light rays from the object.

29. The variable zoom imaging device according to claim 28, wherein, When the adjustable aperture diaphragm is set to the smallest one of the plurality of different numerical apertures, for the full field region of the object, the diameter of the imaging optical device is large enough to pass all the light rays from the object.

30. The variable zoom imaging device according to claim 1, wherein, When the adjustable aperture diaphragm is set to the largest one of the plurality of different numerical apertures, the imaging optical device does not produce a diffraction-limited image on the full field region across all detector elements in the array.

31. The variable zoom imaging device according to claim 30, wherein, When the adjustable aperture diaphragm is set to the smallest one of the plurality of different numerical apertures, the imaging optical device produces a diffraction-limited image on the full field region.

32. The variable zoom imaging device according to claim 31, wherein, When the adjustable aperture diaphragm is set to the largest one of the plurality of different numerical apertures, the imaging optical device produces a diffraction-limited image on the maximum zoom field region, and the maximum zoom field region is equal to the area of the full field region divided by z max .

33. The variable zoom imaging device according to claim 32, wherein, The fact that the imaging optical device produces a diffraction-limited image with the numerical aperture NA over a given field of view ("FOV") in the image region means that, for coherent illumination, the imaging optical device is capable of producing features in the image region with a spatial period d as small as anywhere within the FOV.

Images