DESC:TECHNICAL FIELD
[0001] The present invention relates a continuous zoom lens system in a mid-wave infrared (MWIR) spectral region having large zoom ratio (43X).

BACKGROUND
[0002] Conventional zoom lens systems have large number of optical lens elements, resulting in significantly lowering the overall transmission. In a conventional zoom lens system, the zoom lens has three lens groups. The first lens group relays an outside scene to an intermediate plane. The second lens group varies magnification of the relayed image. The second lens group includes two diffractive optical elements. The third lens group compensates for focus shift and focuses.
[0003] In another conventional zoom lens system, a four-element infrared lens is disclosed. Yet another conventional zoom lens system, discloses about the IR Zoom lens device having two independently moving parts to keep the lens device in focus.
[0004] In conventional zoom lens systems, lenses are manufactured with critical materials that include but not limited to Znse/Zns, CaF2, and AMTIR. Such critical materials are not abundantly available making the manufacturing process complex.
[0005] Further, conventional zoom lens systems have limitation of low zoom ratio, limitation of not having long focal length at narrow field of view (NFOV), limitation of having one or discrete field of views, limitation of not having relay group lenses, limitation of undesirable large track length and size, limitation of applicability only to spectral regions like visible and long wavelength infrared (LWIR), and limitation of incomplete correction of optical aberrations, most notably chromatic and spherical Aberrations.
[0006] Therefore, there is still a need for zoom lens system that address or overcomes one or more aforementioned problems.

SUMMARY
[0007] This summary is provided to introduce concepts related to zoom lens system. This summary is neither intended to identify essential features of the present invention nor is it intended for use in determining or limiting the scope of the present invention.
[0008] Accordingly, an aspect of the present invention discloses a zoom lens system in a medium-wave infrared (MWIR) spectral region, said zoom lens system comprising: a single fixed aspherical lens made of silicon for bending and collecting thermal radiation rays from a target for correcting an aberration; a single negative variator lens made of germanium having an aspherical surface for changing a magnification of said zoom lens system by axially translating said variator lens along a colinear optical axis of said zoom lens system, for correcting coma and off-axis aberrations in a field of view (FOV) simultaneously, negating a blurring of an image formed due to translation of an image plane; a plurality of compensator lenses divided into a first compensator lens having a positive silicon lens and a second compensator lens having a germanium lens and a plurality of silicon lenses, said first and second compensator lenses configured to restore a final image to said image plane by initiating a nonlinear translation of said first and second compensator lenses in relation to said variator lens translation into a fixed zoom position; a relay lens having a single fixed germanium lens for constant re-imaging and focusing in relation to a range by axially translating said relay lens along said colinear optical axis, for a zoom bore sight adjustment in relation to a signal generated by a sensor in real-time, thereby minimizing an objective lens diameter, controlling misalignment and maintaining a cold shield efficiency; a plurality of cam barrels having a field of view (FOV) barrel and a focus barrel with plurality of bearings, each said plurality of cam barrels for rotating simultaneously to configure said zoom position by translating said variator lens, said first and second compensator lenses and said relay lens relatively in a path along said colinear optical axis maintaining an optical alignment; and a lens control card for controlling translation of said variator lens, said first and second compensator lenses, said relay lens by rotation of said plurality of cam barrels relative to said zoom position simultaneously adjusting focus in relation to said range for configuring continuous change in said field of view (FOV) from a narrow field of view (NFOV) to a wide field of view (WFOV), with a 43X continuous zoom ratio in real-time with zero lag.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0009] The detailed description is described with reference to the accompanying figures.
[0010] Fig. 1 illustrates a front view of a continuous zoom lens system, according to implementation of proposed aspect of the present disclosure.
[0011] Figs. 2 illustrates the continuous zoom lens system with a thermal imager and a zoom lens assembly, according to implementation of system of the present disclosure.
[0012] Fig. 3 illustrates a continuous zoom lens optical layout, according to implementation of proposed system of the present disclosure.
[0013] Fig. 4 illustrates modulation transfer function (MTF) curves at a narrow field of view (NFOV) and a wide field of view (WFOV), according to implementation of the proposed system of the present disclosure.
[0014] Fig. 5 illustrates spot diagrams at narrow field of view (NFOV) and wide field of view (WFOV), according to implementation of the proposed system of the present disclosure.
[0015] Fig. 6 illustrates schematics of Narcissus Ray-Tracing, according to implementation of the proposed system of the present disclosure.
[0016] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION
[0017] In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures are shown in diagram form to facilitate describing the invention. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into several applications.
[0018] In general, the present invention claims a zoom lens system in a medium-wave infrared (MWIR) spectral region, said zoom lens system comprising: a single fixed aspherical lens made of silicon; a single negative variator lens made of germanium having an aspherical surface; a plurality of compensator lenses divided into a first compensator lens having a positive silicon lens and a second compensator lens having a germanium lens and a plurality of silicon lenses; a relay lens having a single fixed germanium lens; a plurality of cam barrels having a field of view (FOV) barrel and a focus barrel with plurality of bearings; and a lens control card for controlling translation of said variator lens, said first and second compensator lenses, said relay lens by rotation of said plurality of cam barrels relative to said zoom position simultaneously adjusting focus in relation to said range for configuring continuous change in said field of view (FOV) from a narrow field of view (NFOV) to a wide field of view (WFOV), with a 43X continuous zoom ratio in real-time with zero lag.
[0019] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these details. One skilled in the art will recognize that embodiments of the present disclosure, some of which are described below, may be incorporated into a number of systems.
[0020] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present disclosure and are meant to avoid obscuring of the present disclosure.
[0021] Furthermore, connections between components and/or modules within the figures are not intended to be limited to direct connections. Rather, these components and modules may be modified, re-formatted or otherwise changed by intermediary components and modules.
[0022] References in the present disclosure to “embodiment” or “implementation” mean that a particular feature, structure, characteristic, or function described in connection with the embodiment or the implementation is included in at least one embodiment or implementation of the invention. The appearances of the phrase “in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
[0023] While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail, a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiment illustrated. Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
[0024] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. The skilled person will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. All the terms and expressions in the description are only for the purpose of the understanding and nowhere limit the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein may be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness. Terms first, second, front, rear, top, bottom, colinear, optical axis, plurality, at least, adjacent, farther and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0025] Referring to figures 1-6, discloses a zoom lens system (100), a single fixed aspherical lens (120), a single negative variator lens (130), a first compensator lens (140a), a second compensator lens (140b), a relay lens (150), a plurality of cam barrels (160), a focus motor and a field of view motor (170).
[0026] According to an aspect, the present invention discloses zoom lens system (100) in a medium-wave infrared (MWIR) spectral region. The zoom lens system (100) comprises a single fixed aspherical lens (120) made of silicon for bending and collecting thermal radiation rays from a target for correcting an aberration; a single negative variator lens (130) made of germanium having an aspherical surface for changing a magnification of said zoom lens system (100) by axially translating said variator lens (130) along a colinear optical axis of said zoom lens system (100), for correcting coma and off-axis aberrations in a field of view (FOV) simultaneously, negating a blurring of an image formed due to translation of an image plane; a plurality of compensator lenses divided into a first compensator lens (140a) having a positive silicon lens and a second compensator lens (140b) having a germanium lens and a plurality of silicon lenses, said first and second compensator lenses (140a, 140b) configured to restore a final image to said image plane by initiating a nonlinear translation of said first and second compensator lenses (140a, 140b) in relation to said variator lens (130) translation into a fixed zoom position; a relay lens (150) having a single fixed germanium lens for constant re-imaging and focusing in relation to a range by axially translating said relay lens (150) along said colinear optical axis, for a zoom bore sight adjustment in relation to a signal generated by a sensor in real-time, thereby minimizing an objective lens diameter, controlling misalignment and maintaining a cold shield efficiency; a plurality of cam barrels (160) having a field of view (FOV) barrel and a focus barrel with plurality of bearings, each said plurality of cam barrels (160) for rotating simultaneously to configure said zoom position by translating said variator lens (130), said first and second compensator lenses (140a, 140b) and said relay lens (150) relatively in a path along said colinear optical axis maintaining an optical alignment; and a lens control card for controlling translation of said variator lens (130), said first and second compensator lenses (140a, 140b), said relay lens (150) by rotation of said plurality of cam barrels (160) relative to said zoom position simultaneously adjusting focus in relation to said range for configuring continuous change in said field of view (FOV) from a narrow field of view (NFOV) to a wide field of view (WFOV), with a 43X continuous zoom ratio in real-time with zero lag.
[0027] According to an embodiment of the present invention, said lens control card generates signals to translate said variator lens (130) towards an image side, said first compensator lens (140a) towards an object side, and said second compensator lens (140b) towards said image side relatively for zooming from a wide-angle end to a telephoto end and translate said relay lens (150) for focusing relative to said zoom position.
[0028] According to the embodiment of the present invention, said lens control card has a control printed circuit board (PCB) in communication with a power supply board via a RS422 serial communication interface for generating a plurality of command signals initiating supply voltages to translate said focus motor (170) and said field of view motor (170) to said zoom position based on an input signal generated from a field-programmable gate array (FPGA) board received by said control printed circuit board (PCB) interfacing a plurality of calibrated differential encoders and a plurality of motor encoders.
[0029] According to the embodiment of the present invention, said zoom lens system (100) as claimed in any one of preceding claims 1-3, wherein said zoom lens system (100) has: a focal length of 20-860mm for f/5.5 cooled detectors with a compact maximum aperture size of 160 mm; a compact track length of 220-230 mm; a cold shield efficiency of 100%; at least 0.4 MTF (Modulation Transfer Function) at a spatial frequency of 17lp/mm for said narrow field of view (NFOV); a cooled 640×512 sensor with a cooling sterling focal plane array (FPA); said wide field of view (WFOV) of 27° and said narrow field of view (NFOV) of 0.63°; operational performance capacity at 3.7-4.8 µm; only one DOE lens surface for configuring image contrast; a back focal length of 16 mm; a thermal range from -30°C to +55°C; a bore sight of at most 5 pixels with no internal compensation; a maximum RMS dispersion spot radius of 13 microns; and a minimum narcissus induced temperature difference (NITD) contribution for said narrow field of view (NFOV) satisfying YNI=0.1, thereby reducing narcissus effect in said image.
[0030] According to the embodiment of the present invention, said single fixed aspherical lens (120) is located at a front end of a housing (110), said single negative variator lens (130) is located distantly from said front end, adjacent said single fixed aspherical lens (120).
[0031] According to the embodiment of the present invention, said plurality of compensator lenses (140a, 140b) are located colinear to each other and distantly farther from said front end.
[0032] According to the embodiment of the present invention, said first compensator lens (140a) is located distantly adjacent to said single negative variator lens (130).
[0033] According to the embodiment of the present invention, said germanium lens of said second compensator lens (140b) is located distantly adjacent first to said first compensator lens (140a) and said plurality of plurality of silicon lenses of said second compensator lens (140b) is located distantly adjacent second to said first compensator lens (140a).
[0034] According to the embodiment of the present invention, said relay lens (150) is located at a rear end of said housing (110) and each said plurality of cam barrels (160) are mounted on top of said housing (110).
[0035] According to the embodiment of the present invention, said single fixed lens, said variator lens (130), said first and second compensator lenses (140a, 140b), said relay lens (150) located within a predetermined tolerance of 30µm at a magnification level.
[0036] Referring Fig. 1 illustrates a front view of a zoom lens system (100), according to implementation of proposed aspect of the present disclosure. In the present exemplary embodiment, opto-mechanical module includes an anterior group (120). The Anterior fix group has one large diameter front fixed aspherical singlet lens (120), which is made with silicon. Front fixed lens (120) is used to collect the thermal radiation from the target. It plays major role to bend the rays for optimal aberration correction.
[0037] In the present exemplary embodiment, opto-mechanical module includes a variator group (130). The variator group has only one negative optical element in the form of a single negative germanium lens (130). The magnification of the zoom system is changed by axially shifting a component, called the variator or variator group. The change in magnification is always accompanied by a blurring of image due to shift of the image plane. The main power of this group comes from the germanium element and the aspherical surface is used here to correct the coma and off-axis aberrations in all FOV’s simultaneously.
[0038] In the present exemplary embodiment, opto-mechanical module includes a compensator group. The compensator group is divided into two groups one is compensator-1 (140a), which is comprises the one positive silicon lens and compensator-2 (140b), which is comprises two lenses one of Germanium and other of Silicon, which reduces the sensitivity of the optical and mechanical components. compensator group achieves desired optimum performance with easily producible tolerances. Compensator Group is used to restore the image shift into a fixed position in all zoom conditions. Accordingly, in the present invention the final image is then restored to the original image plane by moving another lens component, called the compensator. This restoration of the final image usually demands a nonlinear movement of the compensator with respect to the variator.
[0039] In the present exemplary embodiment, opto-mechanical module includes a relay group (150) or focusing lens group or a re-imaging group (150). In the opto-mechanical arrangement of the lens system of the present invention, the compensator group is followed by the single fixed germanium lens. The re-imaging group minimizes the objective lens diameter while maintaining 100% cold shield efficiency. The lens arranged in this group also gives the allowance to control the misalignment. The image always is in focus with respect to range by axially moving the focusing lens group.
[0040] In the present exemplary embodiment, opto-mechanical module includes a plurality of cam barrels (160). In the present invention zoom (Magnification) is achieved by movement of the variator optics group and compensator optics group relatively as per the optical design paths. Since the zooming and focusing are to be achieved by pressing a button with in very little time and image has to stay focused at any of the positions, these stringent requirements need optical elements to be located within a tolerance of 30µm at any magnification level. These placements of the optical elements are catered by rotating two cam barrels simultaneously. Cam barrels (FOV barrel and Focus barrel) are used to move the variator, compensator and focussing groups into a specified zoom positions.
[0041] In the present exemplary embodiment, opto-mechanical module includes the control electronics module (120) includes a lens control card. In the system a control PCB takes +5V and +12V DC power input from a power supply board assembly. The power supply board assembly supplies required voltages to a focus motor and a field of view motor (180). The power supply board assembly incorporates a RS422 serial communication interface. Depending on the user input for focus or field of view change, a field programmable gate array (FPGA) board sends respective commands to Control PCB via power supply board assembly. Basing on these commands; the Control PCB moves the motors to appropriate positions. With the predefined commands the lens control card is used to move the variator, compensator and focussing groups into a specified zoom positions and also used to adjust the focus with respect to range.
[0042] Referring Figs. 2 through 2A and 2B illustrates the zoom lens system (100) with a thermal imager and a zoom lens system (100), according to implementation of system of the present disclosure. Accordingly, in the present exemplary embodiment, the present disclosure provides a zoom lens system (100) having a large zoom ratio (43X), a continuous zoom lens in MWIR spectral region. The zoom lens system has high resolution image quality and simple structure. The zoom lens system has only seven lenses with an IP 67 sealed front lens. The zoom lens system is light weight and is mostly made of abundant available materials mainly germanium, silicon, making it cost effective. The zoom lens system has high zoom ratio (43X) for f/5.5 cooled detectors. The zoom lens system is of compact size achieved by using telephoto configuration having maximum aperture size limited to 160mm. The zoom lens system requires long focal length to detect long range targets at near field of view. The zoom lens system has relay group lenses. The zoom lens system has short track length and size, works in medium-wave infrared (MWIR) spectral region. The zoom lens system has an aspherical singlet fixed lens to bend the rays for optimal aberration correction. The zoom lens system has active thermal compensation, high image contrast which is achieved using only one DOE lens surface. The zoom lens system has real-time bore sight adjustment with respect to sensor. The opto-mechanical design of the zoom lens system is upheld to preserve the excellent image performance at all zoom positions. The control electronics enabled the smooth change of Field of View and focus at all zoom positions within short time.
[0043] According to the embodiment, referring figures 1-6, the zoom lens system has aspherical and diffractive optical elements and has only seven lenses in total. Said first compensator and second compensator lenses reduce sensitivity of said the optical and mechanical components to achieve the optimum performance with easily producible tolerances. According to the embodiment, the zoom lens system is designed and configured for smooth cam movements using bearings which minimises burden on electrical motors. According to the embodiment, zooming and focusing is achieved by pressing a button within less time and image is required to stay focused any of the positions, therefore said fixed lens, variator lens, first and second compensator lenses are located within a tolerance of 30µm at any magnification level. According to the embodiment, said lens control card has PCB that takes +5V and +12V DC power input from the power supply board assembly.
[0044] According to the embodiment, the materials of germanium and silicon are selected while balancing the axial chromatic aberration, coma and off axis aberration of the system. In the present invention, for the purpose of compensating residual aberration generated by said fixed front single aspherical lens, structure of said relay group is designed using single silicon lens.
[0045] In the present exemplary embodiment, the zoom lens system (100) in the mid-wave infrared (MWIR) region has cooled 640×512 sensor with cooling sterling focal plane array (FPA). The system works at 3.7-4.8 µm and achieves the zoom of 20-860mm, large zoom ratio of 43X and F number of 5.5, thereby obtaining cold shield efficiency of 100% and modular transfer function (MTF) more than 0.4 at the spatial frequency of 17lp/mm which is close to the diffraction limit of 0.42. Thus, the zoom lens system of the present disclosure has a high-resolution image quality, a high zoom ratio (43X) for f/5.5 cooled detectors, a long focal length to detect the long-range targets, provision for live bore sight adjustment with respect to sensor, a high image contrast which is achieved using only one diffractive optical element (DOE) lens, telephoto configuration for achieving compact size of the system, active Thermal compensation, cost effective structure having lenses made of silicon, a fast field of view (FOV) change with retention of focus at infinity, light weight by using the minimum number of lenses and IP 67 Sealed front lens.
[0046] In the present exemplary embodiment, the present lens system has compact track length (220-230 mm) using only one binary surface out of 14 optical surfaces and only seven lenses in total. The system has only one DOE surface. The WFOV and NFOV is 27° and 0.63° respectively. The zoom ratio is 43X and it is Very high for f/5.5 cooled detectors. The present disclosure is based on abundantly available Ge and Si lenses. Manufacturing of lenses using Ge and Si lenses is simple when compared with other materials like ZnSe and Zns.
[0047] Referring Fig. 3 illustrates a zoom lens optical layout, according to implementation of proposed system of the present disclosure. In the present exemplary embodiment, the materials for lenses are selected balancing axial chromatic aberration, coma and off axis aberration of the system. For the purpose of compensating the residual aberration generated by the anterior (front) groups, the structure of the relay group is designed using single silicon lens. The total length of the system is 230 mm, and the back focal length is 16 mm.
[0048] According to the present exemplary embodiment, the zoom lens system of the present disclosure provides continuous changes in the field of view from the narrow field of view to the wide field of view. The present disclosure provides high zoom ratio. Generally, it is possible to observe the longer targets only at the longer focal lengths. Since the system is aimed to design in compact the maximum aperture size is limited to 160mm. With 160mm aperture size the achievable focal length is 860mm for F/# 5.5 detector. However, in general surveillance applications, a user feels more comfort when viewing the wider area which is provided through small focal lengths only. Therefore, in the present disclosure a lower side 20mm optimum focal length is provided to observe the wide field of view, thereby achieving high zoom ratio of 43X. in the present disclosure 43X zoom ratio is achieved by using the following methods of advanced optical elements like aspherical and DOE lens or adapting the telephoto configuration or splitting the compensator into two parts or placing the entrance pupil at the front surface or using the Germanium and Silicon materials combination or using highly optimized relay lens or using optimised variator and compensator movements or by balanced aberrations by considering minimum variation in surface sag profile.
[0049] According to the present invention, for zooming from the wide-angle end to the telephoto end, the first lens unit (variator) is moved toward the image side, the second lens unit (companisator-1) is moved toward the object side and the third lens unit (companisator-2) is moved towards to image side. The focusing lens group is moved for focusing.
[0050] Referring Fig. 4 illustrates modulation transfer function (MTF) curves at a narrow field of view (NFOV) and a wide field of view (WFOV), according to implementation of the proposed system of the present disclosure. According to the present exemplary embodiment, the present disclosure provides high resolution image quality. This is by MTF (Modulation Transfer Function) being the main image quality evaluation parameter. The MTF curves of this system are shown in Figure-4 representing the MTF curves of NFOV & WFOV. These curves show that at the spatial frequency 17lp/mm, NFOV has MTF value near to 0.4, which are close to diffraction limited curve (0.42) for good image quality.
[0051] Referring Fig. 5 illustrates spot diagrams at narrow field of view (NFOV) and wide field of view (WFOV), according to implementation of the proposed system of the present disclosure. According to the present exemplary embodiment, the infrared zoom lens system is an imaging system. For imaging systems spot diagram are used to evaluate the image quality. The spot diagram represents the image formation of the rays from a point object. Figure-5, shows the maximum RMS dispersion spot radius for both NFOV & WFOV respectively, and the maximum RMS dispersion spot radius is near to 13 microns. This is less than a single pixel size of 15 microns. The evaluation results have shown that the system confirms to good image quality.
[0052] Referring Fig. 6 illustrates schematics of Narcissus Ray-Tracing, according to implementation of the proposed system of the present disclosure. According to the present exemplary embodiment, the present disclosure eliminates the Narcissus effect. Narcissus effect is the cooled detector window is a see itself. The cooled detector window will radiate some energy and this energy will reflect from refractive surfaces and focus at the FPA. These retro-reflections have the effect of reducing the background flux seen by the detector, if this background flux reduction varies over the FPA, then the effect will be a dark/bright spot at the centre of the picture. So it is necessary to analyse in the designing stage. Narcissus intensity for the whole detector area and ghost variations across every pixel is efficiently controlled by constraining the absolute values of YNI by using optical design program. In the narcissus analysis, YNI product is an important parameter. The effect of cold reflect can be neglected when YNI= 0.1. If the value of YNI is smaller, it may result in serious narcissus. Narcissus analysis result at NFOV position is presented in Figure-6, it shows that the Narcissus Induced Temperature Difference (NITD) contributions minimum for all the surfaces so their cold reflects effect can be negligible. With consideration of YNI=0.1, the narcissus effect in the image is reduced.
[0053] According to the present exemplary embodiment, the present disclosure provides suave CAM movement. The movements of the optical groups variator and compensator are obtained by an outer revolution cam, turning around the body along bearings surface tracks. Cam has two helicoidally machined ramps, fitted with two drive-rollers. Manufacturing of cam barrels plays very important role in achieving the critical design parameters like FOV and through zoom bore sight. These require critical dimensional stability and higher surface finish for achieving smooth discrete zooming movement. The relay lens is moved in the X-Y movement across the optical axis for the through zoom bore sight adjustment. With this feature the through zoom bore sight can be easily achieved with respect to sensor. configured for smooth cam movements (It is achieved by using the bearings) which minimises the burden on the electrical motors. The zoom mechanism not only moves the various optical groups with the correct rates of movement, but also precisely maintains optical alignment. These features are incorporated while design stage by considering the tolerance stack-up analysis. Movement of the cam barrels is catered by means of motor, for getting desired FOV position.
[0054] According to the present exemplary embodiment, the present disclosure provides active thermal compensation. Active thermal compensation is done by using the positive last lens which is used to compensate the image plane shift with respect to the temperature variations of optical and mechanical components. The optical system is designed to handle a thermal range from -30°C to +55°C. The performance over this thermal range is retained by repositioning of the focusing lens group.
[0055] According to the present exemplary embodiment, the zoom lens system of present disclosure has controlling bore sight. The important requirement of most IR zoom systems is very good bore sight. Zoom systems with good bore sight, the target will remain in all FOVs. It is a significant challenge moving zoom groups axially in the barrel up to 90mm in case of higher Zoom ratio. The tolerances and alignment scheme allows the bore sight to be less than 5 pixels, without any internal compensation. With compensation, this error will be able to be reduced further.
[0056] According to the embodiment, the optical design is of state of the art and is based on Aspherical and Diffractive Optical elements. The zoom lens system comprises innovative opto-mechanical and control electronics module PCB design. The system is optical aligned, and adjustment of various lenses is made possible through zoom bore-sighting and ease of production. The electronics module (PCB) has been developed for control of field of view (FOV) motor and focus motors. The electronics also calibrates the differential encoders and performs BITE of zoom lens on Power On. The electronics module caters for automatic focus at infinity, at various zoom positions and temperature compensation of focus. The electronics interfaces with motor encoders and also with the signal processing electronics.
[0057] There have been described and illustrated herein several embodiments of exemplary indicative implementation of the zoom lens system. It will be also apparent to a skilled person that the embodiments described above are specific examples of a single broader invention, which may have greater scope than any of the singular descriptions taught. There may be many alterations made in the description without departing from the scope of the invention. The present invention is simple in construction and design, integrated, portable, cost effective and easy to manufacture. While particular embodiments of the invention have been described, it is not intended that the invention be limited said configuration disclosed thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular structure specific type of arrangement of elements, type of configurations, numbers, have been disclosed, it will be appreciated that the embodiments may be manufactured with other design parameters and configurations as well. Accordingly, the electrical connections between the components, GUI interface, number, material type of lenses, cam movements and arrangement of elements, are not limited thereto and may be as per operational requirements and nowhere limits the scope of the invention. Known electrical connections, cam movements operation may be as per operational requirements and nowhere limits the scope of the invention. Thus, while particular structure with said configurations has been disclosed, it will be appreciated that the embodiments may be manufactured with other design parameters as well. Further, the methods and configuration of the system, are provided only for reference and for understating purpose of the invention. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” is used as the plain-English equivalent of the respective term “comprising” respectively.
,CLAIMS:
1. A zoom lens system (100) in a medium-wave infrared (MWIR) spectral region, said zoom lens system (100) comprising:
a single fixed aspherical lens (120) made of silicon for bending and collecting thermal radiation rays from a target for correcting an aberration;
a single negative variator lens (130) made of germanium having an aspherical surface for changing a magnification of said zoom lens system (100) by axially translating said variator lens (130) along a colinear optical axis of said zoom lens system (100), for correcting coma and off-axis aberrations in a field of view (FOV) simultaneously, negating a blurring of an image formed due to translation of an image plane;
a plurality of compensator lenses divided into a first compensator lens (140a) having a positive silicon lens and a second compensator lens (140b) having a germanium lens and a plurality of silicon lenses, said first and second compensator lenses (140a, 140b) configured to restore a final image to said image plane by initiating a nonlinear translation of said first and second compensator lenses (140a, 140b) in relation to said variator lens (130) translation into a fixed zoom position;
a relay lens (150) having a single fixed germanium lens for constant re-imaging and focusing in relation to a range by axially translating said relay lens (150) along said colinear optical axis, for a zoom bore sight adjustment in relation to a signal generated by a sensor in real-time, thereby minimizing an objective lens diameter, controlling misalignment and maintaining a cold shield efficiency;
a plurality of cam barrels (160) having a field of view (FOV) barrel and a focus barrel with plurality of bearings, each said plurality of cam barrels (160) for rotating simultaneously to configure said zoom position by translating said variator lens (130), said first and second compensator lenses (140a, 140b) and said relay lens (150) relatively in a path along said colinear optical axis maintaining an optical alignment; and
a lens control card for controlling translation of said variator lens (130), said first and second compensator lenses (140a, 140b), said relay lens (150) by rotation of said plurality of cam barrels (160) relative to said zoom position simultaneously adjusting focus in relation to said range for configuring continuous change in said field of view (FOV) from a narrow field of view (NFOV) to a wide field of view (WFOV), with a 43X continuous zoom ratio in real-time with zero lag.

2. The zoom lens system (100) as claimed in claim 1, wherein said lens control card generates signals to translate said variator lens (130) towards an image side, said first compensator lens (140a) towards an object side, and said second compensator lens (140b) towards said image side relatively for zooming from a wide-angle end to a telephoto end and translate said relay lens (150) for focusing relative to said zoom position.

3. The zoom lens system (100) as claimed in claim 1 or 2, wherein said lens control card has a control printed circuit board (PCB) in communication with a power supply board via a RS422 serial communication interface for generating a plurality of command signals initiating supply voltages to translate said focus motor (170) and said field of view motor (170) to said zoom position based on an input signal generated from a field-programmable gate array (FPGA) board received by said control printed circuit board (PCB) interfacing a plurality of calibrated differential encoders and a plurality of motor encoders.

4. The zoom lens system (100) as claimed in any one of preceding claims 1-3, wherein said zoom lens system (100) has:
a) a focal length of 20-860mm for f/5.5 cooled detectors with a compact maximum aperture size of 160 mm;
b) a compact track length of 220-230 mm;
c) a cold shield efficiency of 100%;
d) at least 0.4 MTF (Modulation Transfer Function) at a spatial frequency of 17lp/mm for said narrow field of view (NFOV);
e) a cooled 640×512 sensor with a cooling sterling focal plane array (FPA);
f) said wide field of view (WFOV) of 27° and said narrow field of view (NFOV) of 0.63°;
g) operational performance capacity at 3.7-4.8 µm;
h) only one DOE lens surface for configuring image contrast;
i) a back focal length of 16 mm;
j) a thermal range from -30°C to +55°C;
k) a bore sight of at most 5 pixels with no internal compensation;
l) a maximum RMS dispersion spot radius of 13 microns; and
m) a minimum narcissus induced temperature difference (NITD) contribution for said narrow field of view (NFOV) satisfying YNI=0.1, thereby reducing narcissus effect in said image.

5. The zoom lens system (100) as claimed in any one of preceding claims 1-4, wherein said single fixed aspherical lens (120) is located at a front end of a housing (110), said single negative variator lens (130) is located distantly from said front end, adjacent said single fixed aspherical lens (120).

6. The zoom lens system (100) as claimed in any one of preceding claims 1-5, wherein said plurality of compensator lenses are located colinear to each other and distantly farther from said front end.

7. The zoom lens system (100) as claimed in any one of preceding claims 1-6, wherein said first compensator lens (140a) is located distantly adjacent to said single negative variator lens (130).

8. The zoom lens system (100) as claimed in any one of preceding claims 1-7, wherein said germanium lens of said second compensator lens (140b) is located distantly adjacent first to said first compensator lens (140a) and said plurality of plurality of silicon lenses of said second compensator lens (140b) is located distantly adjacent second to said first compensator lens (140a).

9. The zoom lens system (100) as claimed in any one of preceding claims 1-8, wherein said relay lens (150) is located at a rear end of said housing (110) and each said plurality of cam barrels (160) are mounted on top of said housing (110).

10. The zoom lens system (100) as claimed in any one of preceding claims 1-9, wherein said single fixed lens, said variator lens (130), said first and second compensator lenses (140a, 140b), said relay lens (150) located within a predetermined tolerance of 30µm at a magnification level.