Variable zoom imaging device

Abstract

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

Description

[Technical field]

[0001] The present disclosure relates to a variable zoom imaging device. More specifically, the present disclosure relates to an optical imaging system for use with a high-resolution optical sensor that enables high-quality variable zoom in a cost-effective manner. This application claims priority to U.S. Provisional Application No. 63 / 066,935, filed August 18, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] An optical imaging system forms an image in an image field (typically an image plane) of an object located in an object field. 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 and their positioning relative to each other and to the object field and image field form an image by collectively recombining light rays emanating from each point in the object field at a corresponding point in the image field. Thus, the optical imaging system generates a spatial distribution of light in the image field that corresponds to the spatial features of the object in the object field. In particular, the image corresponds to how the spatial features of the object affect the incident light differently (e.g., reflection, transmission, diffraction, scattering, and / or attenuation). In some cases, the object is illuminated by ambient light 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 this illumination light to generate the image. The spatial extent of the points in the object field that are imaged onto the image field is called the object field, and similarly, the spatial extent of the points in the image is called the image field.

[0003] In general, 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 in the image field of the rays that are recombined by the optical imaging system at each point in the image field. For example, the image-side numerical aperture NA can be expressed as n·sinθ, where θ is the angle formed between the most oblique ray (i.e., the marginal ray) entering the image field and the optical axis, and n is the refractive index of the medium immediately preceding the image field. The aperture stop of an optical imaging system is the element in the system that sets this numerical aperture NA by preventing rays outside this angular range from reaching the image field.

[0004] The magnification m' of an optical imaging system relative to an image in the image field is a measure of how much the lateral dimension of each feature in the image in the image field increases (or decreases) relative to the lateral dimension of each feature in the object. Thus, an object feature having a lateral dimension D is reproduced in an image having a lateral dimension equal to m'·D. It is often desirable to provide an optical imaging system with a range of different magnifications selectable by a user. For example, a user may wish to view an object over a large object field at a lower magnification m'1, and then view a subset of this object field at a higher magnification m'2, i.e., "zoom" to that subset of the object field. Minimum magnification m=m min From the maximum magnification m´=m´ max An imaging system that provides a range of magnifications m, ranging from z = m´ / m´, has a zoom ratio of min and the maximum zoom ratio z max =m´ max / m´ min Define z max An optical imaging system with >1 can be called a variable zoom system.

[0005] Conventionally, variable zoom optical systems include systems that have one or more optical imaging elements that move relative to one another to provide variable magnification, and systems that have a turret that inserts one of several different optical modules into the optical path to provide variable magnification. Optically, this variable magnification is achieved by increasing the object-side numerical aperture while decreasing the object field, while keeping the image-side numerical aperture fixed.

[0006] To capture and store a digital representation of an image of an object produced by an optical imaging system, an optical sensor (also referred to herein as a "detector" or "camera") having an array of detector elements may be positioned over the image area. Each detector element generates an electrical signal corresponding to a measurement of the intensity of light incident on that detector element (or, in some examples, a measurement of the intensity of light incident on the detector element for each of multiple colors of light). Image processing circuitry is coupled to the array of detector elements and processes the electrical signals to store a digital representation of the image. Current technological advances allow for high-resolution optical sensors that provide a very large lateral density of distinct detector elements. In fact, the number of detector elements can be much greater than the typical number of pixels required for the digital representation. As a result, some prior art imaging systems implement a "digital zoom", whereby different magnifications m of the object in the final digital representation are obtained simply by generating the digital representation with a corresponding subset of the entire set of detector elements. Specifically, a minimum zoom corresponds to sampling detector elements across the entire array of detector elements in the image field of the optical system, and a larger zoom corresponds to sampling detector elements that are present only in a smaller contiguous subset of the image field of the optical system. Summary of the Invention

[0007] The inventors have recognized several problems with prior art zoom systems. Systems implementing optical zoom require moving parts, which can degrade performance by increasing the likelihood of vibration, image wander, or focus shift during zooming, as well as reducing robustness. They also typically require more elements and / or more complex elements, thereby increasing manufacturing and design costs. On the other hand, systems implementing digital zoom suffer from a mismatch between the design of the optical imaging system and the detector element sampling across the zoom range.

[0008] For example, assuming a detector has an array of 10,000×10,000 detector elements and a desired resolution for the digital representation of the image is 1000×1000, the zoom range can in principle be from 1 to 10 using digital zoom. Specifically, at the lowest zoom, each pixel of the digital representation is mapped onto a corresponding 10×10 subarray of detector elements, and at the highest zoom, each pixel of the digital representation is mapped onto a single corresponding detector element in a 1000×1000 subarray within the entire array of detector elements. However, this difference in detector array sampling for different zooms imposes different constraints on the optical imaging system, since the resolution of the 1000×1000 digital representation may not be better than the resolution of the optical image produced on the detector array by the optical imaging system. Thus, if the lateral dimension of the detector elements is p, then at the lowest zoom, the optical imaging system only needs to provide enough resolution to produce an optical image with a feature size as small as about 10·p, but at the highest zoom, it needs to provide enough resolution to produce a feature size as small as about p.

[0009] Thus, to provide a high-quality digital representation of an image over the entire zoom range using digital zoom alone, an optical imaging system must provide sufficient resolution for the highest digital zoom setting. At the same time, the optical imaging system must capture the ray bundles from the entire object field corresponding to the lowest zoom, which increases the complexity of the optical imaging system, such as requiring more and / or larger optical imaging elements. This is because the complexity of an optical imaging system generally increases with each increase in object field and image-side NA. For example, it is easier to design an optical system to generate an image of a relatively small area with a coarse resolution than to design an optical system to generate an image of a relatively large area with a fine resolution. To do the former, a greater number of optical elements, larger optical elements, and / or more complex optical elements are generally required to direct the corresponding larger ray bundles from each of a greater number of points in the larger object field.

[0010] To solve these problems, the inventors disclose a system that combines digital zoom with a much simpler optical imaging system that includes a variable aperture stop to adjust the image-side numerical aperture NA according to the resolution required by the digital zoom setting. At the lowest zoom, the aperture stop is set to a minimum NA and the optical imaging system is designed to capture the ray bundle from the entire object field at this minimum NA to generate an optical image on the detector. At higher zooms, the aperture stop opening is set to a larger NA to provide the required resolution for a (smaller) sub-area of ​​the object field corresponding to the higher zoom. The optical imaging system is designed to capture the ray bundle from this sub-area of ​​the object field at this larger NA to generate 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 of the ray bundle from the object field outside this sub-area at this larger NA. This may generate a blurred image in certain parts of the detector, but those parts correspond to detector elements that are outside the sampling area of ​​the detector used to generate the digital representation of 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 digital images of objects having the desired resolution throughout the entire zoom range.

[0011] More generally, the following embodiments are therefore disclosed: In general, in one aspect, a variable zoom imaging device is disclosed that includes: i) imaging optics configured to form an image at an image field of an object positioned at an object field; ii) an adjustable aperture stop that adjustably sets a numerical aperture NA for an image formed by the imaging optics; iii) an electronic detector including an array of detector elements positioned at the image field to detect the image; and iv) an image processing circuit coupled to the electronic detector for generating a digital representation of the image based on signals from at least some of the detector elements. The image processing circuit generates the digital representation having a different magnification m of the object for each of a plurality of different numerical apertures for the image set by the adjustable aperture stop, the different magnifications m being m=m min From the minimum magnification of m=m max The zoom ratio z=m / m min and the maximum zoom ratio z max =m max / m min This section stipulates:

[0012] Embodiments of the variable zoom image capture device may include any of the following additional features. The imaging optics may be fixed to provide a constant magnification of the object field relative to the image field.

[0013] The zoom ratio z of the digital representation may vary inversely proportional to the field of view spanned by the detector elements for generating the digital representation. For example, the sizes of the different numerical apertures may be set by the adjustable aperture stop to increase corresponding to an increase in the zoom ratio z for the digital representation. Furthermore, in certain embodiments, the sizes of the different numerical apertures set by the adjustable aperture stop may increase linearly corresponding to an increase in the zoom ratio z for the digital representation over a range of zoom ratios greater than 1. For example, the numerical aperture NA for the image set by the adjustable aperture stop may be:

[0014]

number

[0015] The digital representation may include at least one intensity value for each pixel in an N1×N2 pixel array, where N1 and N2 are positive integers. For example, N1 and N2 may each be 400 or greater.

[0016] The array of detector elements in the electronic detector may include an array at least as large as an M N1 by M N2 array, where M is z max A positive integer greater than or equal to z. For example, max may be 3 or more. In a particular embodiment, the image processing circuit generates the digital representation with a zoom ratio z by determining the intensity value for each pixel in the N1×N2 array from one or more of the signals from the detector elements in the corresponding subarray of M / z×M / z detector elements. In another particular embodiment, the image processing circuit generates the digital representation with a zoom ratio z by determining the intensity value for each pixel in the N1×N2 array from only one of the signals from the detector elements in the corresponding subarray of M / z×M / z detector elements. In yet another particular embodiment, the image processing circuit generates the digital representation with a zoom ratio z by determining the intensity value for each pixel in the N1×N2 array from a weighted average of the signals from the detector elements in the corresponding subarray of M / z×M / z detector elements. Also, in a particular embodiment, the subarrays of the detector elements corresponding to the pixels in the digital representation are repeatedly spaced apart from one another within the field of view spanned by the detector elements for generating the digital representation.

[0017] Generally, in certain embodiments, the image processing circuit generates the digital representation having a zoom ratio z by determining the intensity value of each pixel in the N1 x N2 array from one or more of the signals from the detector elements in a corresponding sub-array of one or more detector elements, the number of detector elements in each corresponding sub-array decreasing with increasing numerical aperture NA that is adjustably set by the aperture stop.

[0018] The imaging optics may include a first set of optics that directs light from the object to a pupil defined by the aperture stop, and a second set of optics that directs light from the pupil to an image area. The variable zoom imaging device may further include a light source configured to provide light to the imaging optics for illuminating the object to form the image of the object. For example, the light source may be a coherent laser. Also, in certain embodiments, the variable zoom imaging device may further include an interferometer component including a beam splitter and a reference surface. The light source is further configured to illuminate the reference surface, and the beam splitter is configured to coherently combine light from the object and the reference surface such that the image formed by the imaging optics on the image area is an interference image.

[0019] In a particular embodiment, the area of ​​the array of detector elements is 0.25 cm 2 ~10cm 2 It is. In a specific embodiment, when the variable zoom imaging device is a Fizeau interferometer, etc., the minimum magnification is 1 / 10 to 1 / 5. In another specific embodiment, when the variable zoom imaging device is a microscope interferometer, etc., the minimum magnification is 1 / 2 to 5.

[0020] In a particular embodiment, the area of ​​the object region imaged onto the array of detector elements is 0.04 cm 2 ~10,000cm 2 It is. The adjustable aperture stop may be continuously adjustable. Alternatively, the adjustable aperture stop may be discretely adjustable to each of a plurality of discrete settings. For example, the adjustable aperture stop may be a mechanical aperture stop or an electronic aperture stop. Also, for example, the aperture stop may provide a nominally circular aperture to define a numerical aperture. Alternatively, for example, the aperture stop may provide a nominally rectangular aperture to define a numerical aperture.

[0021] The variable zoom imager may further include a user control interface configured to electronically adjust the adjustable aperture stop in response to a user input for the zoom ratio. For example, the user control interface may cause the image control circuitry to set a magnification of the object by the detector in response to the user input for the zoom ratio. Further, for example, the image control circuitry may be configured to set the magnification of the object by the detector by adjusting a sampling of the detector elements used to generate the digital representation.

[0022] In certain embodiments, the imaging optics need not be of a diameter large enough to pass all ray trajectories from the object for a full field area of ​​the object corresponding to a full field area across all of the detector elements in the array when the adjustable aperture stop is set to the largest of a plurality of different numerical apertures, however, in such embodiments, the imaging optics may have a diameter large enough to pass all ray trajectories from the object for a full field area of ​​the object when the adjustable aperture stop is set to the smallest of a plurality of different numerical apertures.

[0023] In certain embodiments, the imaging optics does not produce a diffraction-limited image across the entire field region across all of the detector elements in the array when the adjustable aperture stop is set to the largest of the multiple different numerical apertures. However, in such embodiments, the imaging optics may produce a diffraction-limited image across the entire field region when the adjustable aperture stop is set to the smallest of the multiple different numerical apertures. Also, for example, the imaging optics may reduce the area of ​​the entire field region by z max An imaging optics system that produces a diffraction-limited image for a given field of view ("FOV") in the image field, for a numerical aperture NA, means that the imaging optics can produce features in the image field that have a small spatial period d, comparable to d=λ / NA, anywhere in the FOV due to coherent illumination.

[0024] In general, in another aspect, an optical imaging system for use with a variable zoom imager implementing digital zoom is disclosed. The optical imaging system includes: i) imaging optics configured to form an image in an image field of an object located in an object field; and ii) an adjustable aperture stop that adjustably sets a numerical aperture NA for 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 successively increasing numerical apertures NA for the image that are set by the adjustable aperture stop corresponding to successively decreasing fields of view of the object in the object field.

[0025] Embodiments of the optical imaging system may further include any of the features described above for the variable zoom imaging device. All documents referenced herein, if any, are incorporated by reference in their entirety. In the event of a conflict between this disclosure and any document incorporated by reference, the present disclosure will control.

[0026] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims. Like reference symbols in the various drawings indicate like elements. [Brief description of the drawings]

[0027] [Figure 1A] FIG. 1A is a schematic diagram of a first variable zoom imaging device for low magnification. [Figure 1B] FIG. 1B is a schematic diagram of the digital sampling performed by the variable zoom imager of FIG. 1A for a first, lower magnification. [Figure 2A] FIG. 2A is a schematic diagram of a second variable zoom imaging device for high magnification. [Figure 2B] FIG. 2B is a schematic diagram of the digital sampling performed by the variable zoom imager of FIG. 1A for a second, higher magnification. [Diagram 3] FIG. 3 is a ray tracing diagram of an exemplary imaging optical system for imaging an object onto a sensor, the system having a collimator, an aperture stop, and an eyepiece, and using a thin lens approximation for the collimator and eyepiece. [Figure 4] FIG. 4 is a ray tracing diagram of an exemplary imaging optical system for imaging an object onto a sensor, the system having a collimator, an aperture stop, and an eyepiece, and using a thin lens approximation for the collimator and eyepiece. [Diagram 5] FIG. 5 is a ray tracing diagram of an exemplary imaging optical system for imaging an object onto a sensor, the system having a collimator, an aperture stop, and an eyepiece, and using thin lens approximations for the collimator and eyepiece. [Figure 6] FIG. 6 is a ray tracing diagram of the eyepiece portion of the system shown in FIGS. 3-5, and FIGS. 6 and 7 compare the ray bundles for a full object field and smaller aperture stop (as shown in FIG. 6) with a 1 / 3 object field size (which results in three times the magnification of the digital representation rendered by the sensor) and a three times larger aperture stop (as shown in FIG. 7). [Figure 7] FIG. 7 is a ray tracing diagram of the eyepiece portion of the system shown in FIGS. 3-5, while FIGS. 6 and 7 compare the ray bundles for a full object field and smaller aperture stop (as shown in FIG. 6) with a 1 / 3 object field size (which results in three times the magnification of the digital representation rendered by the sensor) and a three times larger aperture stop (as shown in FIG. 7). [Figure 8] FIG. 8 is a ray tracing diagram of a six-lens eyepiece using real lens elements. [Figure 9] FIG. 9 is a ray tracing diagram of a six-lens eyepiece using real lens elements. [Figure 10] FIG. 10 is a ray tracing diagram of a six-lens eyepiece using real lens elements. [Figure 11] FIG. 11 is a ray tracing diagram of a five-lens eyepiece using actual lens elements and implementing the optical design simplifications of the present invention to enable diffraction-limited imaging for a variable zoom system implementing digital zoom. [Figure 12] FIG. 12 is a ray tracing diagram of the overall optical system for the eyepiece shown in FIGS. 8-10, including a three-lens collimator. [Figure 13] FIG. 13 is a ray tracing diagram of the entire optical system for the eyepiece shown in FIG. 11 including a two-lens collimator, the entire optical system implementing the optical design simplifications of the present invention that enable diffraction-limited imaging of a variable zoom system that implements digital zoom, FIG. 13 showing imaging of the entire object field at 1100 pixel resolution. [Figure 14] FIG. 14 is a ray tracing diagram of the entire optical system for the eyepiece shown in FIG. 11 including a two-lens collimator, the entire optical system implementing the optical design simplifications of the present invention that enable diffraction-limited imaging of a variable zoom system implementing digital zoom, FIG. 14 showing imaging of a ⅓ object field (pixel size ⅓ of the pixel size of FIG. 13) at 1100 pixel resolution. [Figure 15]FIG. 15 is a schematic diagram of the optical imaging system of FIGS. 13 and 14 further including a laser source as an illumination source for illuminating an object through a beam splitter. [Figure 16] FIG. 16 is a schematic diagram of the optical imaging system of FIG. 15 further implemented as an interferometric optical imaging system by including a reference element such that an image of the object formed on the sensor interferes with a reference wavefront to generate an interferometric image of the object. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Image zoom is an important feature in many optical systems. Zooming in on an image provides the user with better lateral resolution than a smaller image size would provide. A well-designed zoom system increases the available resolution in direct proportion to the zoom ratio. This is typically done by fixing the numerical aperture of the imaging ray bundle on the sensor while increasing the object space numerical aperture while decreasing the lens field of view. The emergence of new ultra-high resolution sensors provides an alternative method for image zoom ("digital" zooming) for a subset of applications where the required number of resolution elements in the entire image is significantly less than the number of sensor elements in the entire sensor. However, as mentioned above, digital zoom generally suffers from a mismatch between the design of the optical imaging system and the detector element sampling across the entire digital zoom range.

[0029] An embodiment of the present invention includes an imaging system in which the size of the aperture stop increases in proportion to 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 to maintain diffraction-limited imaging over the field of view specified by the currently selected zoom ratio. This zoom system embodiment can be much simpler than standard optical zooms, which require complex cam mechanisms to move multiple optical elements to adjust zoom while maintaining focus. Furthermore, in at least some embodiments, the zoom system only needs to adjust the size of the aperture stop while changing the viewing area of ​​the sensor. Furthermore, the zoom system can avoid image wander observed in many mechanically actuated optical zoom systems while maintaining focus.

[0030] Exemplary embodiments of the variable zoom imaging system 100 of the present invention are shown in FIGS. 1A and 2A for a first low magnification m1 (FIG. 1A) and a second high magnification m2 (FIG. 2A). The variable zoom imaging system 100 is configured to generate an image on an image field 150 of an object 115 on an object field 110. As will be explained further below, the magnifications m1, m2 relate to the final digital representation of the image and are in contrast to the optical magnification m' of the image of the object in the image field, which is constant in the variable zoom imaging system 100 of the present invention shown in FIGS. 1A and 2A. In addition to the optical elements, the variable zoom imaging system 100 includes an electronic detector 145 with an array of N×N detector elements (also referred to herein as a high-resolution sensor) configured to detect the image by measuring light intensity values ​​at each of the detector elements. An image processing circuit 155 is electrically coupled to the detector 145 and stores and processes the intensity values ​​to provide a digital representation of the image. The image processing circuit 155 is electrically coupled to the user interface 190, receives commands therefrom, and provides the digital representation to the user interface 190. The optical elements of the variable zoom imaging system 100 extend along an optical axis 105 corresponding to the z-axis and include a first optical module 130 (also referred to herein as a "collimator") of the one or more optical elements, a second optical module 140 (also referred to herein as an "eyepiece") of the one or more optical elements, and an aperture stop 135 positioned between the first optical module 130 and the second optical module 140. The optical elements in the optical modules 130, 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 xy plane, as does the array of detector elements of the detector 145. Aperture stop 135 provides a variable aperture for varying the image-side numerical aperture NA of the optical imaging system and is operatively coupled to user interface 190 to allow a user to control the image-side numerical aperture NA. The aperture also limits the object-side numerical aperture, which is equal to the image-side numerical aperture NA multiplied by the magnification m.

[0031] The collimator 130 and the eyepiece 140 form an optical imaging system for generating an optical image of the object 115 on the object region 110 on the image region 150. Specifically, the characteristics (e.g., dimensions and refractive power) of each optical element in the optical imaging system and their positioning relative to each other and to the object region and image region cause light rays emanating from each point in the object region to collectively recombine at a corresponding point in the image region to form an image. This is shown diagrammatically in each of Figures 1A and 2A for 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, which define the object field and the image field (A in Figure 1A). 1O and A 1I In FIG. 2A, A 2O and A 2I There are two other sets of corresponding points at the outer edge of the ray bundle (denoted by 110 in FIG. 1A and FIG. 2A ). The central ray 125 of the ray bundle emerging from each point in the object region 110 is called the chief ray and is shown by a solid arrow in FIG. 1A and FIG. 2A . The optical imaging system in FIG. 1A and FIG. 2A is a telecentric system because the chief ray passing through the center of the aperture provided by the aperture stop 135 is perpendicular to each of the object region 110 and the image region 150. The outermost rays 120 (FIG. 1A ) and ray 220 (FIG. 2A ) of the ray bundle emerging from each point in the object region 110 are called marginal rays and are shown by dashed arrows in FIG. 1A and FIG. 2A . The edge of the aperture provided by the aperture stop 135 coincides with the path of the marginal rays and defines the range of angles at which the marginal rays leave the object region 110 and enter the image region 150.

[0032] To configure the variable zoom imaging system 100 to operate at a first, lower magnification m1 (as shown in FIG. 1A ), the user interface 190 provides a smaller opening to the ray bundle by the variable aperture stop 135, thereby resulting in a smaller angle θ1 of the marginal rays 120 entering the image field 150 relative to the optical axis 105, resulting in 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 FIG. 2A ), the user interface 190 provides a larger opening to the ray bundle by the variable aperture stop 135, thereby resulting in a larger angle θ2 of the marginal rays 220 entering the image field 150 relative to the optical axis 105, resulting in a larger image-side numerical aperture NA2. In a particular embodiment, eyepiece 140 has an effective focal length of f, and aperture stop 135 and image field 150 are located at the front and back focal planes of eyepiece 140, respectively, such that the marginal ray angle θ incident on the image field satisfies the equations tan θ=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's opening parallel to the xy plane. For example, for a circular aperture stop positioned perpendicular to the optical axis, r is the radius of the aperture stop's opening. In the limit of smaller angles θ, which are common in many imaging systems, the equation for NA simplifies to NA=n·r / f.

[0033] Importantly, the different magnifications m1, m2 of the variable zoom imaging system 100 correspond to different aperture stop openings, while the optical elements of the collimator 130 and eyepiece 140 remain the same and do not move relative to each other or to the object and image fields, thereby providing a very stable and robust system. Rather, digital zoom is used to provide the different magnifications, as shown diagrammatically in Figures 1B and 2B, respectively. Specifically, Figures 1A and 1B diagrammatically illustrate the sampling by image processing circuitry 155 of multiple detector elements of detector 150 to generate digital representation 195. For ease of illustration, digital representation 195 in these figures is shown as having values ​​across a 3x3 pixel array, and the detector is shown as having an array of 9x9 detector elements.

[0034] 1B, at a first, low magnification m1, the intensity value at each pixel in the digital representation 195 is derived from one or more values ​​in a spatially corresponding block of 3×3 detector elements in the detector 145. For example, the intensity value may simply correspond to the intensity value of a central detector element in the block of 3×3 detector elements, may correspond to an average of the intensity values ​​in the block of 3×3 detector elements, may correspond to a weighted average of the intensity values ​​in the block of 3×3 detector elements (e.g., the central detector element is weighted more heavily than the surrounding detector elements), or may correspond to a more complex function of the intensity values ​​in the block of 3×3 detector elements. In any case, the digital representation is based on the image field dimension A 1I , and therefore the scale of the digital representation is determined by the object field dimension A. 1O Corresponds to.

[0035] 2B, at a second, higher 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 a 3×3 block of detector elements in the center of the detector 145. In this case, the digital representation is 3×3 pixels in size 1×1000×1000 pixels wide, with the image field dimension A being 10×1000×1000 pixels wide. 2I , and therefore the scale of the digital representation is derived from detector elements in only the central third of the total area of ​​the detector on the image field 150 corresponding to the object field dimension A 2O Based on the exemplary depictions of FIG. 1B and FIG. 2B, this corresponds to A 1O As a result, in this exemplary depiction, the second, higher magnification m2 is three times larger than the first, lower magnification m1.

[0036] Of course, in practical embodiments, the resolution of the detector will provide many more detector elements, for example detector elements at least as large as 1000×1000 or even 10,000×10,000 or more. As a result, in further embodiments, more gradations of digital zoom are possible, with successively larger magnifications for the digital representation being based on sampling successively smaller areas of the array of detector elements provided by the detector. To optically accommodate this increasing digital magnification, the variable aperture stop is set to increase the NA by correspondingly increasing the aperture stop, and the area of ​​the optical image on the detector that is captured by the digital representation (i.e., dimension A i The image field of view (having a resolution of 100 s x 100 s) is made to be diffraction limited for image features having sizes on the order of the block of detector elements corresponding to each pixel in the digital representation, while the quality of the optical image on the detector outside this region does not need to be high quality since the digital representation does not sample those regions, resulting in relaxed design constraints on the optical imaging system.

[0037] For example, if we assume that the image resolution required for digital representation is N×N pixels, then the desired range of zoom factor z is z min =1 to z max=M, where M is a positive integer. In further embodiments, the detector is selected to have a resolution provided by an array of at least M·N×M·N detector elements. For example, in one embodiment where the zoom ratio is 1, the entire detector array is read and then subsampled to select every Mth pixel in every Mth row to derive a value for each pixel in the N×N digital representation of the optical image. The image processing circuitry, through communication with the user interface, can vary this sampling to provide higher zoom ratios. For example, instead of sampling every Mth pixel in every Mth row to provide a zoom ratio z equal to 1, the image processing circuitry may sample every (Mm)th pixel in every (Mm)th row to provide a zoom ratio z equal to M / (Mm), where m is from 0 to M−1, and the image processing circuitry reads only a central portion of the detector array sufficient to provide an N×N digital representation at this sampling. These integer sampling intervals can be used to sample unique detector elements. For example, if M=3, integer values ​​of m=0, 1, 2 correspond to sampling 3×3, 2×2, and 1×1 pixel blocks, corresponding to zoom ratios z of 1, 1.5, and 3, respectively. However, intermediate zoom ratios may also be selected by interpolating detector elements. Furthermore, as discussed above with respect to Figures 1B and 2B, the image processing circuitry may derive an intensity value at each pixel in the digital representation from one or more intensity signals in a spatially corresponding (Mm)×(Mm) block of detector elements by averaging, weighted averaging, or more complex processing of these detector element signals.

[0038] To provide an optical image that takes advantage of the resolution provided by the sampling of detector elements and allows a diffraction-limited image to be captured by the digital representation of each such zoom ratio, the image-side numerical aperture NA, which is set by a variable aperture stop (e.g., under control by a user interface), is

[0039]

number

[0040] where p is the smallest lateral dimension of a detector element and λ is the central wavelength of the light used to form the image on the detector. More generally, including non-integer sampling, NA can be expressed as:

[0041]

number

[0042] As a result, optical imaging systems have a continuously smaller image field of view A corresponding to increased digital zoom. I For a given zoom ratio, the image quality on the detector outside the image field does not matter because those regions are not required to generate the digital representation for that zoom ratio. This is an important advantage to the optical designer of the imaging optics because the field size for which the optical imaging system needs to be corrected decreases inversely with the size of the aperture stop opening. For example, at 2x zoom, the aperture is twice as large as at 1x, but the field is half as large. This tradeoff of aperture stop size versus field size makes the optical system easier to design than if one had to design a primary optical imaging system with the full field size and full resolution as would typically be required for a conventional digital zoom system that is intended to be diffraction limited. Also, an advantage of this approach over an optical continuous zoom or a series of zoom relay lenses on a turret is that there are no moving optical elements other than the aperture stop. This avoids the tight assembly and alignment tolerances required to minimize image position and focus shifts during zooming.

[0043] It also greatly improves the user experience. For example, since there is no moving lens, the image position on the camera is by definition fixed between different zoom positions. And since the focus does not shift with zoom, 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. Furthermore, since the raw pixel lateral calibration between the object and the camera does not change with zoom ratio, a single calibration at any zoom position is sufficient to calibrate all zoom positions. Furthermore, subsampling of the detector element array at lower zooms can provide a higher instrument transfer function ("ITF") because the individual detector element size is small compared to the distance between the sampled detector elements.

[0044] In further embodiments, the relationship between the image-side numerical aperture NA and the zoom ratio z may differ somewhat from that shown in equations (1) or (2) above. For example, equations (1) and (2) assume coherent illumination of the object. To account for incoherent illumination, the general formula for the Abbe resolution limit,

[0045]

number

[0046] where d is the smallest spatial period resolvable in the image and NA' is the numerical aperture of the illumination of the object. This illumination numerical aperture NA' varies from NA'=0 for coherent illumination to NA'=NA for incoherent illumination that fills the image-side numerical aperture. Equations (1) and (2) correspond to this Abbe formula for coherent illumination that resolves the smallest spatial period corresponding to a given zoom setting z.

[0047]

number

[0048] Furthermore, equations (1) and (2), whether modified to account for incoherent illumination or not, do not take into account oversampling, which results in a numerical aperture somewhat larger than that required to resolve the minimum spatial period corresponding to a given digital zoom setting. Thus, in other embodiments, the image-side numerical aperture NA, whether modified to account for incoherent illumination or not, can be somewhat larger than that given by equations (1) and (2). However, what is important is that the image-side numerical aperture NA generally increases in response to an increase in the zoom ratio z.

[0049] Optical imaging systems implementing features of the present invention can be designed using conventional optical design software known in the art, such as Synopsys' Code V® optical design software or similar software from Zemax LLC. Simplified optical designs resulting from the present invention are now illustrated in Figures 3-14. These figures include ray trace diagrams generated from such optical design software, showing the propagation of chief rays and in some cases marginal rays for several object points for various designs of imaging optical systems.

[0050] The cost of manufacturing an optical imaging system is generally determined by the number of optical elements and their size and precision. Therefore, the cost is controlled by minimizing the number of elements, reducing their size, and allowing looser tolerances on the surfaces and their alignment. In many cases, optical imaging systems are designed as telecentric imaging systems. In a telecentric imaging system designed for magnification or demagnification, there are typically two lens groups, which are separated to have a common focal point between the two lens groups. The aperture stop of the system is placed at this point. By placing the stop where the two focal points coincide, the chief rays on both the object side and the image side of the lens are parallel to the optical axis. In the embodiment of Figures 1A and 2A, these two lens groups correspond to the collimator 130 and the eyepiece 140.

[0051] FIG. 3 shows a simple telecentric optical imaging system that uses a thin lens approximation to generate an image of an object on a sensor (i.e., a detector with an array of detector elements). A telecentric optical imaging system includes a collimator and an eyepiece that share a common focal point, with an aperture positioned at that focal point. The size of the lens determines the field of view (object field of view A in the embodiment of FIGS. 1A and 2A). O The field of view is determined by a combination of the aperture stop size (corresponding to the field of view angle θ) and the aperture stop size. As shown in Figure 4, a smaller field of view requires a smaller lens size. Furthermore, as shown in Figure 5, increasing the aperture stop size requires a larger lens size because the optical system must capture a larger angular range of light rays emanating from each object point in the object field.

[0052] Focusing now on just the eyepiece portion of the system, Figures 6 and 7 compare the ray bundle for a full object field and smaller aperture stop (as shown in Figure 6) with the ray bundle for a 1 / 3 object field size system (resulting in a 3x magnification to the digital representation rendered by the sensor) and a 3x larger aperture stop (as shown in Figure 7). In particular, in the system of Figure 6, the ray bundle requires a larger diameter of the eyepiece but results in a relatively small beam footprint on the eyepiece, while in the system of Figure 7, a smaller diameter is required but the beam footprint is large, substantially covering this smaller diameter. As a result, in this 3x zoom state, the eyepiece needs to be of high quality only over a small area in the center of the eyepiece.

[0053] 8-10 show the same principle with an actual eyepiece formed by multiple lens elements. Specifically, FIG. 8 shows a 6-element eyepiece designed to provide 3300 pixel resolution over the full field of view of the sensor. In contrast, FIG. 9 shows the same system but with the aperture size reduced to provide only 1100 pixel resolution, resulting in a much smaller ray bundle footprint on the lens elements of the eyepiece. Finally, FIG. 10 shows a system with the same 3300 pixel resolution as FIG. 6 but with 1 / 3 the object field of view (resulting in a 3x magnification for the digital representation rendered by the sensor), which shows a similar (or even smaller) ray bundle footprint to that of FIG. 9.

[0054] By reducing the diameter of the lenses required between Figures 8 and 9, the cost of the eyepiece is reduced. Further simplification and cost reduction is also possible, as an eyepiece that meets these imaging specifications no longer requires six elements. For example, a new eyepiece is shown in Figure 11, where the number of elements is reduced from six to five.

[0055] In addition, the large collimator used with the eyepiece of Figure 8 requires three elements to achieve 3300 pixel imaging performance over the entire object field, as shown in Figure 12, which presents the overall system layout, whereas the collimator used with the eyepiece shown in Figure 11 and shown in Figures 13 and 14, which present the overall system layout, requires only two elements, resulting in further cost savings. Figure 13 shows a system of the present invention imaging the entire object field at 1100 pixel resolution, while Figure 14 shows a system with 1100 pixel resolution, but with pixel dimensions that are one third of those of Figure 13, imaging one-third the object field (resulting in a three times magnification for the digital representation rendered by the sensor).

[0056] The overall system layout shown in Figures 12-14 includes a beam splitter element (illustrated as a rectangular element) along the light path between the collimator and the aperture stop position. The purpose of the beam splitter is to combine light from an illumination source (e.g., a laser source) for illuminating an object (e.g., a test part under inspection) to produce a beam that is imaged onto the sensor by the collimator and eyepiece. The overall system including these additional elements is shown in Figure 15. Specifically, light from the laser source is focused by a laser focus lens, then reflected by the beam splitter and passes through a two-lens collimator to illuminate the 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 two-lens collimator through the beam splitter and an aperture stop that defines the image-side numerical aperture of the system and is located at the focus of the two-lens collimator. The light that passes through the aperture stop is then focused by a five-lens eyepiece to form an optical image of the object on the sensor that is used to capture a digital representation of the object.

[0057] In other embodiments, different illumination configurations can be used. For example, the illumination source may illuminate the object at an angle from the side or from behind, or ambient light may be used to illuminate the object. As mentioned 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 features of a certain size.

[0058] Additionally, in other embodiments, the variable zoom imaging system can be configured as an interferometric system as shown diagrammatically in FIG. 16, which further includes a reference element relative to the system of FIG. 15, which reflects illumination light back through a five-element eyepiece to interfere with light from the test part and form an interferometric image of the test part on the sensor, which can be processed by image processing circuitry to generate a digital representation of the interferometric image. For example, as is known in the art, interferometric imaging can be used to provide surface height information about the test part within the object region being imaged. Specifically, in FIG. 16, the reference element is a transmissive flat located just in front of the object, which reflects a small portion of the illumination light back to the sensor to interfere with illumination light reflecting from the object.

[0059] The embodiments of the invention can have many different implementations. For example, the absolute magnification provided by the optical imaging system can be greater than 1 (i.e., magnification) or less than 1 (i.e., demagnification). For example, in certain embodiments, the minimum magnification can be between 1 / 10 and 1 / 5, suitable for imaging optics in a Fizeau interferometer. In another example, in certain embodiments, the minimum magnification can be between 1 / 2 and 5, suitable for imaging optics in a microscope interferometer. Also, for example, the area of ​​the array of detector elements can be less than 0.25 cm. 2 ~10cm 2 In this regard, the area of ​​the object region imaged onto the array of detector elements may also vary over a wide range depending on the implementation, such as anywhere between 0.04 cm 2 ~10,000cm 2The amount of the ion exchange resin may vary over a wide range, such as anywhere between 100 and 1500 .

[0060] Also, in some embodiments, the adjustable aperture diaphragm provides a continuously adjustable aperture, while in other embodiments, the adjustable aperture diaphragm is discretely adjustable to each of a plurality of discrete settings. The adjustable aperture diaphragm may be mechanically or electronically actuated. Also, while the embodiments of Figures 1A and 2A have a user control interface configured to adjust the adjustable aperture diaphragm in response to a user input for the zoom ratio, in other embodiments, the aperture diaphragm may be manually adjusted. Typically, the aperture diaphragm opening is circular, although embodiments having a square or rectangular opening are also possible.

[0061] [range] As used in this specification and the appended claims, "a" or "an" includes plural referents unless the context clearly dictates otherwise, such as when the term "single" is used.

[0062] As used herein, the terms "adapted" and "configured" mean that an element, component, or other subject matter is designed and / or intended to perform a given function. Thus, use of the terms "adapted" and "configured" should not be interpreted to mean that a given element, component, or other subject matter is merely "capable of" performing a given function.

[0063] The phrases "at least one of" and "one or more of," as used herein in reference to a list of two or more entities, mean any one or more of the entities in the list of entities, and are not limited to at least one of each and every entity specifically listed in the list of entities. For example, "at least one of A and B" (or, equivalently, "at least one of A or B" or "at least one of A and / or B") may refer to A only, B only, or a combination of A and B.

[0064] The term "and / or" between a first entity and a second entity, as used herein, means one of: (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entities listed with "and / or" should be interpreted in the same manner, i.e., "one or more" of the entities so joined. Other entities other than the entities specifically identified by the "and / or" clause may optionally be present, whether related or unrelated to those entities specifically identified.

[0065] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions.

[0066] Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.

[0067] Moreover, although features may be described above as acting in particular combinations and may initially be claimed as such, one or more features from a claimed combination may, in some cases, be deleted from that combination, and the claimed combination may be directed to subcombinations or variations of the subcombinations.

[0068] Similarly, although operations are shown in the figures in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown, or in sequential order, or that all of the illustrated operations be performed, to achieve desired results. In certain situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the program elements and systems described may generally be integrated together in a single software product or packaged in multiple software products.

[0069] Above, specific embodiments of the present invention have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown or sequential order to achieve desirable results. In some implementations, multitasking and parallel processing may be advantageous.

[0070] Although several embodiments of the invention have been described, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A variable zoom imaging device an imaging optical system configured to form an image at an image region of an object located at an object region; an adjustable aperture diaphragm that adjustably sets a numerical aperture NA for the image formed by the imaging optical system; an electronic detector including an array of detector elements positioned in the image region to detect the image; an image processing circuit coupled to the electronic detector for generating a digital representation of the image based on signals from at least some of the detector elements; Equipped with the image processing circuit generates the digital representation having a different magnification m of the object for each of a plurality of different numerical apertures for the image set by the adjustable aperture stop; The different magnification m is m=m ｍｉｎ From the minimum magnification of m = m ｍａｘ The zoom ratio z = m / m ｍｉｎ and the maximum zoom ratio z ｍａｘ = m ｍａｘ / m ｍｉｎ This defines the following: the imaging optics does not produce a diffraction-limited image across a full field area across all of the detector elements in the array when the adjustable aperture stop is set to a maximum of the plurality of different numerical apertures; A variable zoom imaging device, wherein the imaging optical system produces a diffraction-limited image across the entire field of view when the adjustable aperture stop is set to a minimum one of the plurality of different numerical apertures.

2. The variable zoom imaging device of claim 1 , wherein the imaging optics are fixed to provide a constant magnification of the object field to the image field.

3. The variable zoom imaging device of claim 1 , wherein the zoom ratio z of the digital representation varies inversely with the field of view spanned by the detector elements used to generate the digital representation.

4. The variable zoom imaging device of claim 3 , wherein the sizes of the different numerical apertures set by the adjustable aperture stop increase with increasing zoom ratio z to the digital representation.

5. 5. The variable zoom imaging device of claim 4, wherein the sizes of the different numerical apertures set by the adjustable aperture stop increase linearly with increasing zoom ratio z to the digital representation over a range of zoom ratios greater than 1.

6. The numerical aperture NA for the image, as set by the adjustable aperture stop, is [0010] 5. The variable zoom imager of claim 4, wherein p is the maximum lateral dimension of a detector element and .lambda. is the central wavelength of light used to form said image on said electronic detector.

7. The digital representation is N １ ×N ２ (N １ and N ２ 5. The variable zoom imaging device of claim 4, further comprising at least one intensity value at each pixel in a pixel array where m is a positive integer.

8. N １ and N ２ 8. The variable zoom image pickup device according to claim 7, wherein each of the first and second sine waves is equal to or greater than 400.

9. The array of detector elements in the electronic detector has at least M.N １ ×M.N. ２ where M is an array of z ｍａｘ 8. The variable zoom image pickup apparatus according to claim 7, wherein the first and second inputs are each a positive integer equal to or greater than 1.

10. Z ｍａｘ 10. The variable zoom image capture device according to claim 9, wherein is 3 or more.

11. The image processing circuitry extracts the N signals from one or more of the signals from the detector elements in a corresponding subarray of M / z×M / z detector elements. １ ×N ２ 10. The variable zoom imaging apparatus of claim 9, wherein the digital representation having a zoom ratio z is generated by determining the intensity value for each pixel in an array of

12. The image processing circuitry derives the N signals from only one of the signals from the detector elements in the corresponding subarray of M / z×M / z detector elements. １ ×N ２ 12. The variable zoom imaging apparatus of claim 11, wherein the digital representation having a zoom ratio z is generated by determining the intensity value for each pixel in an array of

13. The image processing circuitry calculates the N signal from a weighted average of the signals from the detector elements in the corresponding subarray of M / z×M / z detector elements. １ ×N ２ 12. The variable zoom imaging apparatus of claim 11, wherein the digital representation having a zoom ratio z is generated by determining the intensity value for each pixel in an array of

14. 12. The variable zoom imaging device of claim 11, wherein the subarrays of detector elements corresponding to the pixels in the digital representation are repeatedly spaced apart from one another within the field of view spanned by the detector elements for generating the digital representation.

15. The image processing circuitry extracts the N signals from one or more of the signals from the detector elements in a corresponding subarray of one or more detector elements. １ ×N ２ 8. The variable zoom imaging device of claim 7, wherein the digital representation having a zoom ratio z is generated by determining the intensity value of each pixel in an array of a plurality of subarrays, the number of detector elements in each corresponding subarray decreasing with increasing numerical aperture NA that is adjustably set by the adjustable aperture stop.

16. 2. The variable zoom imaging device of claim 1, wherein the imaging optical system includes a first set of optical systems that directs light from the object to a pupil defined by the aperture stop, and a second set of optical systems that directs light from the pupil to an image region.

17. The variable zoom imaging device of claim 1 , further comprising a light source configured to provide light to the imaging optics for illuminating the object and thereby forming the image of the object.

18. 20. The variable zoom imaging device of claim 17, further comprising an interferometer component including a beam splitter and a reference surface, the light source further configured to illuminate the reference surface, and the beam splitter configured to coherently combine light from the object and the reference surface such that the image formed on the image area by the imaging optics is an interference image.

19. The variable zoom imager of claim 17 , wherein the light source is a coherent laser.

20. The area of ​​the detector element array is 0.25 cm ２ ~10cm ２ 2. The variable zoom image pickup apparatus according to claim 1, wherein:

21. 2. The variable zoom image pickup apparatus according to claim 1, wherein the minimum magnification is 1 / 10 to 1 / 5.

22. 2. The variable zoom image pickup apparatus according to claim 1, wherein the minimum magnification is 1 / 2 to 5.

23. The area of ​​the object region imaged onto the array of detector elements is 0.04 cm ２ ~10,000 cm ２ 2. The variable zoom image pickup apparatus according to claim 1, wherein:

24. The variable zoom imaging device of claim 1 , wherein the adjustable aperture stop is continuously adjustable.

25. The variable zoom imaging device of claim 1 , wherein the adjustable aperture stop is discretely adjustable to each of a plurality of discrete settings.

26. The variable zoom imaging device of claim 1 , wherein the adjustable aperture stop is a mechanical aperture stop.

27. The variable zoom imaging device of claim 1 , wherein the adjustable aperture stop is an electronic aperture stop.

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

29. 30. The variable zoom imaging device of claim 28, wherein the user control interface causes the image processing circuit to set a magnification of the object by the electronic detector in response to the user input for the zoom ratio.

30. 30. The variable zoom imager of claim 29, wherein the image processing circuitry is configured to set the magnification of the object by the electronic detector by adjusting the sampling of the detector elements used to generate the digital representation.

31. The variable zoom imager of claim 1 , wherein the aperture stop provides a nominally circular aperture to define the numerical aperture.

32. The variable zoom imager of claim 1 , wherein the aperture stop provides a nominally rectangular aperture to define the numerical aperture.

33. 5. The variable zoom imaging device of claim 4, wherein the imaging optics does not have a diameter large enough to pass all ray trajectories from the object for a full field of view of the object corresponding to a full field of view across all of the detector elements in the array when the adjustable aperture stop is set to a maximum of the plurality of different numerical apertures.

34. 34. The variable zoom imaging device of claim 33, wherein the imaging optics has a diameter large enough to pass all ray trajectories from the object for the entire field of view of the object when the adjustable aperture is set to the smallest of the plurality of different numerical apertures.

35. The imaging optical system is configured to have an area of ​​the total field of view of z when the adjustable aperture stop is set to the maximum of the plurality of different numerical apertures. ｍａｘ 10. The variable zoom imaging device of claim 1, which produces a diffraction-limited image over a maximum zoom field area equal to an area divided by a factor of 10.

36. 36. The variable zoom imaging device of claim 35, wherein the imaging optical system produces a diffraction-limited image for the numerical aperture NA at a given field of view ("FOV") in the image region, meaning that the imaging optical system can produce features in the image region that have a small spatial period d equivalent to d=λ / NA anywhere within the FOV due to coherent illumination.

37. 1. An optical imaging system for use with a variable zoom imaging device implementing digital zoom, comprising: a) imaging optics configured to form an image in an image region of an object located in an object region; b) an adjustable aperture stop that adjustably sets a numerical aperture NA for the image formed by the imaging optical system; c) the imaging optics is designed to form the image as a diffraction-limited image for each of a plurality of successively increasing numerical apertures NA for the image set by the adjustable aperture stop corresponding to successively decreasing fields of view of the object in the object region; d) The optical imaging system, wherein the imaging optical system does not produce the image as a diffraction-limited image across a full field area across the entire image field when the adjustable aperture stop is set to a maximum of a plurality of different numerical apertures.

38. 38. The optical imaging system of claim 37, wherein the imaging optical system does not have a diameter large enough to pass all ray trajectories from the object for a full field of view of the object corresponding to a full field of view across the image field when the adjustable aperture stop is set to a maximum of a plurality of different numerical apertures.

39. 40. The optical imaging system of claim 38, wherein the imaging optical system has a diameter large enough to pass all ray trajectories from the object for the entire field of view of the object when the adjustable aperture stop is set to the smallest of a plurality of different numerical apertures.

40. 38. The optical imaging system of claim 37, wherein producing a diffraction-limited image for the numerical aperture NA in a given field of view ("FOV") in the image region means that the imaging optical system can produce features in the image region that have a small spatial period d equivalent to d=λ / NA anywhere in the FOV due to coherent illumination.

41. 38. The optical imaging system of claim 37, wherein the imaging optical system includes a first set of optical systems between the object region and the aperture stop, the first set of optical systems directing light from the object to a pupil defined by the aperture stop, and a second set of optical systems between the aperture stop and the image region, the second set of optical systems directing light from the pupil to the image region.

Images