Deployable ZOOM lens range extender

Abstract

A zoom lens magnification extender comprising a primary mirror with a central aperture through which the zoom lens images a scene of interest, and a concave reflective surface facing the scene of interest, and a convex secondary mirror facing the primary mirror, the focal lengths and distance apart of the primary and secondary mirrors being such that the magnification extender is afocal, reducing the diameter of am incident beam of illumination, without affecting its divergence. A pivot axis enables pivoting the secondary mirror out of the line of sight of the zoom lens. The primary and secondary mirrors are rigidly connected in a pivotable structure or the secondary mirror may be mounted on an arm and pivoted around the pivot axis independently of the primary mirror, such that the secondary mirror is pivoted out of the line of sight of the zoom lens while the primary lens remains stationary.

Description

[0001] DEPLOYABLE ZOOM LENS RANGE EXTENDER

[0002] FIELD

[0003] The present disclosure describes technology related to the field of zoom lenses, especially the use of magnification extenders to achieve a larger range of effective focal lengths, and especially for achieving longer range imaging.

[0004] BACKGROUND

[0005] Zoom lenses are used for a variety of applications, such as commercial, surveillance, and security applications, in a variety of wavelength ranges, from UV to infrared. Such lenses enable imaging to be performed over a wide range of distances, and are available commercially as catalogue-item independent units, having selected ranges and apertures, which are usable with any other image manipulation devices or systems. The demand for zoom lenses with extended zoom ratios, meaning extended ranges of effective focal lengths (EFLs), is always increasing, since such lenses would enable imaging to be performed over an even broader range of distances.

[0006] One solution to this requirement is shown in US Patent 7,586,678, to A. Bergeron et al, for “Optical Imaging System for Obtaining Multi-Field of View Image”, which includes two separate co-axial Cassegrain telescopes, one providing a wide field-of-view image and the other a narrow field-of-view image. However, this is a complex optical arrangement, and unlike a real zoom lens assembly, only supplies two separate effective focal lengths with separate ranges. US Patent Application 2009 / 0225406 to C. Voigt et al, for “Optical Telescope”, describes a system for enhanced viewing of objects into separate simultaneous frequency bands of light, IR and visible. The IR band includes a turret carousel having a number of different discrete focusing lenses, while the visible band includes a built-in collimating and switchable zoom lens assembly for imaging at a wide range of focal distances.

[0007] There is a limit to the range that can be obtained in a zoom lens, arising from the limitations of providing an acceptable modulation transfer function (MTF) over the whole range, because of the limitations of optical design with a limited number of lenses. Consequently, magnification extenders are known and used to enable the zoom lens to cover the same range ratio as the un-extended zoom lens, but extended in overall this range coverage by the range extension factor. For use with zoom lenses, magnification extenders are front mounted, which makes them convenient and simple to mount on the zoom lens, and to remove from the zoom lens. Such front mounted magnification extenders are also known as teleside converters. Consequently, the effective focal length can be changed by the magnification extender, but without changing the focal ratio of the zoom. The magnification extenders can also be termed range extenders, to reflect their practical function, and either phrase may be used interchangeably in this disclosure, and be thuswise claimed.

[0008] The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.

[0009] SUMMARY

[0010] The present disclosure attempts to provide novel systems and methods that overcome at least some of the disadvantages of prior art systems and methods for increasing the range of zoom lenses. Since the major cost of an imaging system is generally the detector array, whose cost, depending on the wavelengths detected and the resolution provided, can reach several tens of thousands of dollars, it is important to enable the use of a single detector array to cover as broad a range of fields of view as is possible. While the zoom lens itself does this to a significant extent, typically up to a zoom range of the order of 20 times, the use of a magnification extender can extend the overall range covered by the zoom lens, typically by up to another multiple of 4, such that the extended range zoom lens assembly should be able to cover an ultra-wide zoom range, of from a close, super-wide field of view, to a long distance, super-narrow field of view, expectantly covering an effective focal length range of 80, or even more. The present disclosure describes novel zoom lens extender systems which enable cost-effective range extension to be achieved, while still maintaining the range ratio of the original zoom lens.

[0011] While prior art zoom lenses have proven highly useful, a number of shortcomings have been identified. For example, achieving very high zoom ratios using only refractive optics in the magnification extender can be difficult and expensive, due to the large size and weight of the required refractive optics. While it is important to maintain both the shorter effective focal lengths (EFL) and the longer effective focal lengths, the long range optical configuration can affect the performance at short focal lengths. In light of the foregoing, there is an ongoing need for a system for use with a zoom lens, having an extended zoom ratio without affecting the short range performance, and without the use of large refractive optics.

[0012] When adding an extender on a zoom lens, both the wide and the narrow fields are magnified. However, as will be shown, two problems can arise from use of such a magnification extender.

[0013] (i) The original wide field-of-view (FOV) of the zoom lens may be degraded.

[0014] (ii) Because of effect (i) above, the narrower than expected, wide-FOV, makes it necessary to enlarge the diameter of the extender front lens. This makes the lens larger, heavier and significantly more expensive. In many cases, the widest FOV possible after magnification is not even achieved.

[0015] Methods and systems for overcoming both of these problems are described in the present disclosure, with full details of these methods and systems being shown in the Detailed Description section of the disclosure.

[0016] The novel methods and systems of the present disclosure are based on the use of reflective optics in the magnification extender, rather than refractive optics which are used almost exclusively in the zoom lens itself. This in itself is a departure from much conventional practice, since while mirror-based telescopes are very much preferred for long range imaging, such as in astronomical applications, they are not usually suitable or efficient for wide field imaging. The reason for the non-preferred use of mirror-based telescopes for wide field imaging, is because such telescopes may result in cropping even more of the wide field view than lens-based telescopes, unless large diameter mirrors are used, which may be unduly difficult in use. However, the use of mirrors-based telescopes rather than lenses, for applications such as in imaging systems, presents a significant advantage in cost and weight, which is considered to be more important and useful than the limitations which may be placed on the wide field of view performance of the zoom lens. A further advantage of the use of reflective optics is the relative independence of the telescope performance, as a function of the wavelength being used for the imaging process. Therefore, the use of a mirror-based retractable telescope as the magnification extender of a zoom lens provides significant advantages in size, weight, maneuverability and cost, compared with prior art refractive magnification extenders. The advantages of the telescope being afocal will become evident from the description thereof in the Detailed Description section hereinbelow. Not every element of a complex optical system has the same sensitivity with regard to the accuracy of its positional placement and angular alignment. This is particularly so with regard to high magnification systems, such as the use of the magnification extender telescope of the present application, with a complex optical system, such as a wide range zoom lens. In general, such a telescope is designed as an integral part of the complete optical system, and most switchable high magnification systems are thus designed as self-contained complete systems. In such systems, it is usually the main element that has the highest power in the system. In the case of a conventional telescopic refractive system, that is the entry lens, or in the case of a reflective telescope, the primary mirror. Therefore, that main element, besides having the optimum optical quality, also has to have the highest positional and alignment accuracy in the system, relative to the other elements of the system, or more specifically, relative to the next element of the system. Translated into practical terms, that means that the distance and orientation of that main element relative to the other elements of the system, must be achieved, because of the very high magnification being used, with extremely accurate tolerances, in order to provide the required performance at the very high magnification demanded from such a telescope. The above mentioned distance and orientation of that main element relative to the other elements of the system, refers in the presently described system, respectively to the distance between the primary mirror and the secondary mirror, and the angular alignment of the two on the axis of the system.

[0017] A further novel feature of the methods and systems of the present disclosure is in the manner in which the range extending telescope is deployed or retracted from the zoom lens optical path. Because of the extremely high location precision required for very long focal length telescopes, the lighter and the more easily handled the telescope, the greater the ease and precision with which the telescope can be positioned. According to this aspect of the systems of the present disclosure, instead of inserting and removing the entire telescope from the optical path to the zoom lens, only the secondary mirror of the telescope is inserted or withdrawn from the optical axis, and since it is of substantially smaller weight and size than the primary mirror, that reduction in weight and size enables achieving a significant increase in the ease and accuracy of the positioning of the entire telescope. To achieve the accuracy required, the secondary lens can be mounted on a pivotable structure with well-defined latching positions to define the required end position of the lens, enabling repeatable, accurate and speedy deployment between the two alternate positions, deployment and retraction, by a simple rotation motion. On the other hand, the movement of the secondary mirror independently of the primary mirror, while being a mechanically simpler task, introduces a major technological problem which may counteract the advantages of the simpler mechanical structure for moving just the secondary mirror. The problem arises from the above-mentioned precision required in maintaining the predetermined designed distance between the primary and secondary mirrors. This distance needs a high level of precision and mechanical stability in order to ensure accurate imaging of the scene of interest, especially at the longest EFL’s used. Consequently, mechanical separation of the two mirrors requires mechanical rigidity and accuracy of the movable secondary mirror that may outweigh the advantages of a lighter and simpler rotation mechanism for the secondary mirror alone. Detection in real time of any small vibrations or movements of the secondary mirror, and use of the detected signals to provide a feedback to correct the secondary mirror motion to cancel out the vibration, can overcome this problem, but each system application should be carefully analyzed to determine whether these added costs and complexity can compete with the mechanical stability provided by having the primary mirror and the secondary mirror mechanically and rigidly connected to each other in one rotatable structural unit.

[0018] The various embodiments of the extended zoom lens described herein provide versatile solutions to zoom lenses for imaging systems of all wavelengths, while minimizing the overall size and weight of the extended zoom lens.

[0019] There is thus provided in accordance with an exemplary implementation of the systems and devices described in this disclosure, a magnification extender for extending the effective focal length of a zoom lens, the extender comprising:

[0020] (i) a primary mirror having an axis, a central aperture through which the zoom lens can image a scene of interest along a line of sight, and a concave reflective surface adapted to face the scene of interest;

[0021] (ii) a secondary mirror having a diameter smaller than that of the primary mirror, and a convex reflective surface, the secondary mirror being positioned such that its reflective surface is directed towards the primary mirror, the focal lengths and distance apart of the primary and secondary mirrors being such that when the primary and secondary mirrors are aligned collinearly, the magnification extender is afocal, reducing the diameter of a beam of illumination impinging on the primary mirror, without affecting the divergence of the beam of illumination; and (iii) a pivot axis adapted to enable pivoting of at least the secondary mirror out of the line of sight of the zoom lens. In such a magnification extender, the primary mirror and the secondary mirror may be rigidly connected in a structure which can be pivoted around the pivot axis. Alternatively, the secondary mirror may be mounted on an arm which can be pivoted around the pivot axis independently of the primary mirror, such that the secondary mirror can be pivoted out of the line of sight of the zoom lens while the primary lens remains stationary.

[0022] In such a magnification extender, the pivoting of at least the secondary mirror out of the line of sight of the zoom lens enables the zoom lens to image the scene of interest without extended magnification. On the other hand, the positioning of at least the secondary mirror axially with the line of sight of the zoom lens enables the zoom lens to image the scene of interest with extended magnification.

[0023] In any of the above described magnification extenders according the diameter of the secondary mirror should be such that at least the major part of the beam of illumination reflected by the secondary mirror impinges on an input lens of the zoom lens. Additionally, the aperture of the primary mirror should have a diameter such that the beam of illumination reflected by the secondary mirror is configured to pass therethrough.

[0024] Furthermore, the structure rigidly connecting the primary mirror and the secondary mirror, maintains the mutually relative position and orientation of the secondary mirror and the primary mirror. In that case, the pivot axis may be disposed such that it passes through the optical axis of the zoom lens and a central region of the primary mirror, such that the primary mirror is configured to pivot while keeping its central region on-axis with the zoom lens. Additionally, the complete magnification extender may pivot about the pivot axis. Then, the complete magnification extender should be adapted to pivot sufficiently that the secondary mirror moves off the axis of the zoom lens by at least the radius, at the longitudinal position of the secondary mirror, of the field of view of the zoom lens, when the zoom lens is set at its minimum focal length.

[0025] In any of these embodiments, the pivot axis is disposed such that it enables the secondary mirror to move off the axis of the zoom lens by at least the radius of the field of view of the zoom lens, at the longitudinal position of the secondary mirror, when the zoom lens is set at its minimum focal length. Furthermore, the secondary mirror can be tilted sufficiently that it does not block any part of the line of sight of the zoom lens.

[0026] In any of the above described magnification extenders the structure may further comprise an actuator, positioned such that the magnification extender is pivoted around the pivot axis by the actuator. The structure may further comprise at least one mechanical buffer positioned such that the pivoting of the magnification extender to its deployed position ensures that the optical axis of the magnification extender is collinear with the optical axis of the zoom lens. In such a case, the structure may further comprise at least one latch to ensure that the magnification extender remains latched in its deployed position collinear with the optical axis of the zoom lens.

[0027] In any of the above described magnification extenders, the line of sight of the zoom lens is collinear with its optical axis.

[0028] There is further provided according to yet another implementation of the systems of the present disclosure, a magnification extender for use with a zoom lens adapted to image a scene of interest, the extender comprising:

[0029] (i) a primary mirror having a concave reflective surface, the primary mirror being located off-axis of the zoom lens, and

[0030] (ii) a secondary mirror having a convex reflective surface with a diameter smaller than that of the primary mirror, and positioned, when the magnification extender is actuated, on the optical axis of the zoom lens, and with its reflective surface directed such that it reflects a beam of light converging from the primary mirror towards the zoom lens, wherein at least one part of the magnification extender is mounted on a structure rotatable around a pivot axis such that on rotation, the at least one part of the magnification extender changes its angular orientation from a first orientation on-axis with the zoom lens, to a second orientation, in which the at least one part of the magnification extender is unaligned with the axis of the zoom lens.

[0031] In such a magnification extender, the focal lengths and distance apart of the primary mirror and the secondary mirror should be such that the magnification extender is afocal, so that the diameter of a beam of illumination impinging on, and being reflected by the primary mirror, is reduced, without affecting the divergence of the beam of illumination. In either of the two previously described cases, the at least one part of the extender may comprise the primary mirror and the secondary mirror, while the structure maintains the mutually relative position and orientation of the secondary mirror and the primary mirror. In that case, the complete magnification extender rotates about the pivot axis. If so, the complete magnification extender may be adapted to rotate sufficiently that the secondary mirror moves off the axis of the zoom lens by at least the radius, at the longitudinal position of the secondary mirror, of the field of view of the zoom lens, when the zoom lens is set at its minimum focal length. In any of these immediately preceding described magnification extenders, the at least one part of the magnification extender may comprise the secondary mirror but not the primary mirror, the structure being a rotatable arm holding the secondary mirror, the primary mirror remaining stationary.

[0032] There is even further provided according to yet another implementation of the systems of the present disclosure, a lens assembly, comprising:

[0033] (i) a zoom lens secured to a support structure, wherein the zoom lens has a zooms lens optical axis,

[0034] (ii) a magnification extender rotatably attached to the support structure, the magnification extender including a primary reflector and a secondary reflector aligned along an extender optical axis and secured to an extender structure, wherein the magnification extender is configured to undergo a change in angular orientation around a pivot axis from a second angular orientation having the magnification extender rotated to an angle with the zoom lens optical axis, to a first angular orientation with the zooms lens optical axis and the extender optical axis substantially collinear.

[0035] Such a lens assembly may further comprise an extender actuator configured to cause the magnification extender to undergo a change in angular orientation around the pivot axis between the first angular orientation and the second angular orientation. In that situation, the extender actuator may include a linear actuator. Alternatively, the extender actuator may include a rotary actuator.

[0036] In any of the above described lens assemblies, the extender actuator may include a latching mechanism configured to secure the magnification extender to the support structure in either the first angular orientation or the second angular orientation. The assembly may then further comprise a first latching mechanism configured to detachably secure the magnification extender to the support structure in the first angular orientation, or additionally a second latching mechanism configured to detachably secure the magnification extender to the support structure in the second angular orientation.

[0037] Furthermore, the zoom lens optical axis may substantially collinear with an incident light optical axis, or it may be offset from an incident light optical axis.

[0038] There is even yet further provided according to another implementation of the systems of the present disclosure, a lens assembly, comprising:

[0039] (i) a support structure having a pivot member with a pivot axis,

[0040] (ii) a zoom lens secured to the support structure, wherein the zoom lens has a zooms lens optical axis,

[0041] (iii) a primary reflector secured to the support structure, the primary reflector having a primary reflector optical axis,

[0042] (iv) a magnification extender rotatably attached to the pivot axle, wherein the magnification extender includes a secondary reflector having a secondary reflector optical axis, wherein the magnification extender is configured to undergo a change in angular orientation around the pivot axis from a second angular orientation having the magnification extender rotated to an angle with the zoom lens optical axis, to a first angular orientation having the zooms lens optical axis, the primary reflector optical axis, and the secondary reflector optical axis substantially collinear.

[0043] Such a lens assembly may further comprise an extender actuator configured to cause the magnification extender to undergo a change in angular orientation around the pivot axis between the first angular orientation and the second angular orientation. In that case, the extender actuator may include a linear actuator or a rotary actuator. In either of those cases, the extender actuator may include a latching mechanism configured to secure the magnification extender to the support structure in either the first angular orientation or the second angular orientation.

[0044] Additionally, such lens assemblies may further comprise at least one of a first latching mechanism configured to detachably secure the magnification extender to the support structure in the first angular orientation, and a second latching mechanism configured to detachably secure the magnification extender to the support structure in the second angular orientation.

[0045] In any such lens assemblies, the zoom lens optical axis may be substantially collinear with an incident light optical axis, or it may be offset from an incident light optical axis.

[0046] Finally, some reference numbers in parentheses have been added to the independent claims of the application, and to some of those dependent claims which recite additional claim features. This has been done, in view of the complexity of some of the claims, solely in order to increase the clarity of the claims, by identifying recited claim elements with exemplary elements in the drawings or the description, and is not intended in any way to interpret or limit the scope of the claims.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The presently claimed invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings, in which:

[0049] Fig. 1 is a schematic drawing of the optical elements of a conventional exemplary refractive magnification extender for mounting on the front of a zoom lens;

[0050] Fig. 2 illustrates schematically, the ray tracing output of an optical design program of an exemplary magnification extender of the present disclosure, mounted at the input of a zoom lens;

[0051] Fig. 3 illustrates one example of how the magnification extender shown in Fig. 2 may be implemented practically;

[0052] Fig. 4 illustrates how the primary and secondary mirrors of the range expander of Fig. 3, are firmly attached by a mechanical supporting assembly, such that the entire magnification extender pivots as a single unit around the pivoting center;

[0053] Fig. 5 illustrates how a simpler method of deactivating the magnification extender than that of Fig. 4, can be achieved by tilting only the secondary mirror off-axis of the zoom lens field of view; Fig. 6 illustrates schematically, one way of overcoming the problem arising from the use of on-line reflective telescopes, by using an equivalent off-axis telescope for achieving the range extension;

[0054] Fig. 7 illustrates the off-axis arrangement of the magnification extender 100 of Fig. 6, showing more details of the elements of this arrangement;

[0055] Fig. 8 is a listing showing the physical properties and the optical performance results expected by comparison of three types of magnification extender (i) a refractive element extender, (ii) an on-axis reflective extender, and (iii) an off-axis reflective extender;

[0056] Fig. 9 shows a mechanical mounting arrangement for enabling the rotation of the complete magnification extender;

[0057] Fig. 10 shows a detailed view of the embodiment of the pivot assembly shown in Fig. 9;

[0058] Fig. 11 shows a cross-sectional side view of the extended zoom lens assembly shown in Fig. 9, including the actuator assembly;

[0059] Fig. 12 shows a view of the extended zoom lens assembly of Fig. 4, in which the complete magnification extender has been rotated from the deployed orientation around the pivot axis to the retracted orientation by an actuator;

[0060] Fig. 13 shows an exemplary mechanical structure for implementing the magnification extender embodiment shown in Fig. 5, of the alterative method of retracting the magnification extender, by tilting only the secondary mirror;

[0061] Fig. 14 is a view of the magnification extender of FIG. 13, from the bottom (relative to the drawing) in order to show the pivoting systems used in this embodiment;

[0062] Fig. 15 illustrates the extended zoom lens assembly of Fig. 7, but showing one exemplary structure by which the primary and secondary mirrors of the magnification extender are maintained in their correct mutual positions; and

[0063] Fig. 16 shows the magnification extender of Figs. 7 and 15, but with the magnification extender in the retracted position.

[0064] DETAILED DESCRIPTION

[0065] Before describing in detail, the essential parts of the zoom lens magnification extenders of the present application, it is important to note that the presently described systems differ from most of such complete telescopic systems, in which the telescope is an integral part of the imaging system. In those cases, no importance need be placed on whether the telescope provides a collimated output beam, or is converging or even diverging, so long as the optical design of the imaging system components generates a focal plane at the plane of the imaging array. Such prior art systems have generally thus been designed to provide optimal performance for the specification demanded of the entire system, where the zoom lens is designed as part of the entire imaging system.

[0066] In contrast to such complete imaging systems, the presently described telescopic system is intended for use as a magnification extender for a zoom lens, which can maintain its designed optical properties such as its focal range, without dependence on the optical design of the telescopic system. In order to achieve this optical independence, the presently described magnification extension systems must be afocal, namely providing an output beam which is parallel to the input beam, but having a reduced diameter such that the output beam can enter the zoom lens, whose performance it is intended to extend. The major optical property of such an afocal telescope, is that the diameter of the incident beam of light is changed without affecting the divergence of the beam. Since the input beam to the telescopic system is parallel light, coming from optical infinity, the output of the presently described telescopic system is also a parallel collimated beam. The operational advantage of such a design is that the zoom lens does not need to be located with any unusual level of accuracy relative to the magnification extender, but can simply be positioned behind the output of the magnification extender, without the need to align it with high accuracy relative to the optical axis of the magnification extender. This is because the parallel beam emitted by the magnification extender is no different from the point of view of its optical direction and divergence, than the beam of the view being surveilled by the zoom lens. Moving a zoom lens laterally does not change the quality of the view being inspected, though it does of course, change the point of the terrain being viewed by the lens, by the amount of lateral movement. Tilting a zoom lens too does not change the quality of the view being inspected, though it does of course change the point of the terrain being viewed, especially for the long focal length settings, where small orientation changes of the extender could move the image generated by a significant part of the screen being viewed, or even more. In a similar manner, when used with a magnification extender, the axial and longitudinal position of the zoom lens relative to the magnification extender is not highly critical, so long, of course, as the image beam from the required region being viewed by the telescopic magnification extender, is input to the zoom lens. Furthermore, the afocal collimated output of the telescope means that the zoom lens and telescope do not have to be optically designed to match each other, but that the telescopic beam extender can be used with any zoom lens which is physically matched to the available space provided at the output of the telescope, or further beyond the output. Thus, the afocal magnification extender of the present specification can be used with any independent zoom lens, without the zoom lens requiring to be positioned with a very high level of accuracy, longitudinally or laterally relative to the magnification extender optical axis, apart from the obvious requirement that the zoom lens does view the desired remote position to be imaged. The magnification extender can therefore be considered as being a modular assembly, intended for operation with any zoom lens having a suitable physical dimensions, The need for the magnification extender of the present application to be afocal, is thus an important property, enabling its use with any desired zoom lens, provided that the mechanical dimensions of the zoom lens are suited to those of the magnification extender.

[0067] As previously mentioned in the summary section of this disclosure, two different embodiments of the telescopic magnification extenders are described, one in which the complete telescopic assembly is tilted out of the line of sight of the zoom lens, and the other in which only the secondary mirror is tilted off-axis. Because of the above-described afocal characteristic of the magnification extenders described in this application, and because of the very high positional and orientation accuracy required of the two elements of the telescope, the embodiment in which the complete telescopic assembly is tilted out of the line of sight of the zoom lens, has an advantage over the embodiment in which only the secondary mirror is tilted off-axis. In the former case, the single motion that needs to be controlled, namely the tilt angle around a single axis, can be performed without changing any of the optical properties of the telescopic assembly itself, and particularly the distance apart of the mirrors of the assembly, and their mutual orientation. This is an important optical advantage in the presently described afocal magnification extenders, since the mutual positions and orientations of the two elements are fixed, reducing the need in the second embodiment for the very high accuracy positioning of the secondary mirror required to maintain the performance of the complete telescopic assembly. Even in the latter case, methods are described hereinbelow of ensuring very high accuracy location and orientation of the secondary mirror relative to the primary mirror Reference is first made to Fig. 1 which is a drawing of the optical elements of an exemplary refractive magnification extender for mounting on the front of a zoom lens (not shown in Fig.l). The exemplary extender shown has a x4 range extension, suitable for mounting on a f / 4 zoom lens having a 15-300mm range. The zoom range after magnification extension should therefore be 60- 1200mm. However, in order to maintain the f / 4 requirement, a four times increase in the lens diameters is required. Calculating the diameter of the input lens of the magnification extender for the 1200 mm EFL, the diameter becomes 1200 / 4 = 300mm. This itself results in a costly input lens, because of the cost of the IR refractive material and the lens generation. However, because of limitations of the entrance angle of the light at the input aperture of the zoom lens itself, for the wide angle end of the zoom range, the zoom range becomes more limited, and the input lens of the magnification extender must be enlarged.

[0068] A compromise increase of the lens diameter to 366 mm has been used in this example lens, in order to fulfill limitations generated by this problem. This in itself is a moderate increase, but more seriously, the wide field EFL has to be limited to 100mm, instead of the planned 60mm, which reduced the usable range by 33%. Thus, the overall final zoom range became 100- 1200mm, i.e. a xl2 overall zoom range instead of the x20 zoom range originally planned. A significant limitation is thus necessary when using a refractive magnification extender.

[0069] In order to use such a refractive image extender, it has been the practice of inserting or removing the magnification extender manually in small and portable systems, and utilizing simple attachment devices to maintain the correct position of the magnification extender relative to the axis of the zoom lens. However, for infra red refractive imaging devices with the very large EFL’s required in the field, coupled with the input aperture sizes required, this becomes a difficult task, since the weight of the above described magnification extender with the 366mm. diameter input lens of an infra red transparent material, would be of the order of 15 kg. Furthermore, the alignment accuracy required is such that any sort of simple mechanical attachment devices used for such long EFL ranges, would be totally inadequate. As an example to illustrate the extreme requirements needed for alignment of a long focal length magnification extender, for a 1200 mm EFL extended zoom lens system, the angle of the field of view is of the order of 0.5°. Using a high-resolution imaging device, having 1280 x 1024 xlOp pixels, each pixel has an angular field of view covering as little as one or perhaps a very few prad. Therefore, a seemingly small inaccuracy in the mechanical angular positioning of the magnification extender, could mean misalignment of the object being viewed at the maximum range, of as much as half of the entire image screen.

[0070] Consequently, a completely new conception is required for the mechanical deployment and removal of a magnification extender used for high resolution telescopic sights, having a very long EFL. The new concept must be able to speedily insert or remove the magnification extender, and to ensure that its position when deployed is rigid, robust and with extremely high positional and angular accuracy. Because of the large field of view of the zoom lens when used for the near field short EFL imaging, a large motion is required in order to ensure that the magnification extender is completely out of the maximum field of view of the zoom lens.

[0071] In the range extending attachments of the present application, these problems are tackled and solved by a combination of novel and inventive opto-mechanical arrangements. In the first place, instead of refractive optics, whose costs and weight grow excessively with lens diameter, the present magnification extenders use reflective optics, generally in the form of an afocal Cassegrain telescope 20, as shown in Fig. 2. The use of reflectors, not only reduces the weight of the optical elements needed, but also substantially reduces the costs of systems for operation in the IR, since reflective optical elements are significantly less costly than refractive IR optical elements, and are generally independent of the wavelength of the light being used for the imaging.

[0072] Reference is now made to Fig. 2, which illustrates schematically, the ray tracing output of an optical design program, for an exemplary magnification extender of the present disclosure, in the form of an on-axis afocal Galilean or Cassegrain telescope 20, mounted at the input lens of a zoom lens 23. The telescope converts the large diameter input illumination 25 into a parallel beam having a smaller diameter 27, enabling entry into the input aperture 21 of the zoom lens. Since the telescope output to the zoom lens is a collimated parallel beam 27, the telescope is afocal, its effect being the implementation of an effectively longer focal length of the zoom lens, by virtue of an increased angular magnification of the entire focusing system. The entire focusing system is the term used for the magnification extender telescope with the zoom lens in line. It is to be understood though that a deflection mirror could be used for the telescope output beam, if the telescope and zoom lens are to be disposed in an orientation other than being in-line. In Fig. 2, in order to make the beam conversion process clearer, only the outer rays of the input illumination 25 are shown, whereas in practice, the illumination from the scene being viewed will take up the whole of the beam diameter.

[0073] Additionally, the deploying and retracting mechanisms are implemented in the form of rigid mechanical optical element supports, as shown in Figs. 8 to 15 hereinbelow, which enable the reflective optical elements to be inserted into position and removed by means of a pivoting rotational motion. The mechanical accuracy with which the extender is angularly positioned relative to the optical axis of the zoom lens, is ensured by using mechanical actuators and location or latching devices, for ensuring the required rotational motion and positional accuracy. Further details of such methods and mechanisms for generating the rotational motion, and for ensuring the accuracy of the final positioning of the magnification extender, are given in the detailed description of examples of the type of mechanical structures which can be used to practically implement the outline optical concepts illustrated in Figs. 3 to 5.

[0074] Referring now back to Fig. 2, the Cassegrain reflective type of telescope 20, receiving the illumination beam 25 from the scene being imaged, has an aperture 21 in the primary mirror 22, enabling the positioning of the input aperture of the zoom lens 23 to be located right within or close to the aperture of the primary mirror, such that the primary mirror itself, does not need to be laterally moved to avoid interfering with the input beam to the zoom lens itself. Thus a small tilt of the primary mirror 22, as will be further explained hereinbelow, does not move the position of the aperture of the primary lens away from the input of the zoom lens, which would then cause blockage of the imaging beam entering the zoom lens. The secondary mirror 24, will need to be moved out of the imaging beam when the magnification expander is retracted, allowing just the non-extended zoom lens alone to image the scene.

[0075] Two different mechanical arrangements are proposed for implementing the pivoting mechanism, neither of which interferes with the passage of the input beam through the center aperture of the primary reflector of the telescope. In a first arrangement, as will be shown in Fig. 4 hereinbelow, the primary and secondary mirrors are connected as one integral mechanical assembly, and the pivoting mechanism swings the entire reflective magnification extender between either the deployed position on the axis of the zoom lens, or in the retracted position, out of the axis of the zoom lens. Thus, the primary mirror simply tilts while remaining on the axis of the zoom lens, while the secondary mirror swings entirely out of the axis. However, this arrangement requires the pivoting assembly to also rotate the heavy primary mirror, which makes the pivoting system bulky, though not as much so as a tilting mechanism with refractive optics elements.

[0076] In a second arrangement, as shown in Fig. 5 hereinbelow, the primary mirror remains fixed in its position, while only the secondary mirror is rotated out of the axis of the zoom lens. The second arrangement requires a mechanism that rotates only the mount of the small secondary lens. Moving only a comparatively light optical element, such as the secondary lens, is the simpler of the two arrangements, is more cost-effective, and is a second novel and inventive feature of the presently described invention.

[0077] With the extender deployed on-axis of the zoom lens, the extra-long EFL range enabled by the magnification extender, is activated. With the magnification extender, or just its secondary mirror, pivoted away from the axis of the zoom lens, the original zoom lens with its wide field of view can be readily used without interference by the magnification extender.

[0078] Reference is now made to Fig. 3, which illustrates schematically, how the magnification extender shown in Fig. 2 may be implemented practically. Fig. 3 shows the optical elements of a magnification extender 100 deployed in line with the zoom lens assembly 150. In Figs. 3 to 5, only the optical elements themselves are shown without any supporting or mounting features, in order to explain the optical imaging aspects of the implementations. The zoom lens 150, having a field of view 154, is shown mounted behind the central aperture 342 of the primary mirror 340, which is a large diameter annular concave mirror. The secondary mirror 360 is a convex mirror, mounted at the distance from the primary mirror that will generate a parallel beam of diameter suited to the input lens aperture of the zoom lens. This is ensured in the optical design by selection of the primary mirror diameter and focal length, the virtual focal length of the secondary mirror and the distance apart of the mirrors. The magnification extender telescope then executes the increase of the EFL of the zoom lens in accordance with the optical design shown in Fig. 2. The primary lens optical axis is marked APR, the secondary lens optical axis is marked ASR, the zoom lens optical axis is marked Az, while the incident illumination direction is marked Ai. As is evident from the geometry of the telescope optics, the incident illumination is only incident on the primary mirror on the annulus around the secondary lens.

[0079] Reference is now made to Fig. 4, which illustrates how both the primary mirror 340 and the secondary mirror 360 of the range expander of Fig. 3, are pivoted around the pivoting axis Ap, as a single unit. The pivoting axis is located near the entrance aperture of the zoom lens 150 and accurately on the axis Az of the zoom lens. When in the off-axis pivoted position of Fig. 4, the zoom lens images its field of view directly, through the center aperture 342 of the primary mirror of the magnification extender telescope, such that no part of the magnification extender optics blocks any part of the imaged scene. An exemplary mechanical supporting assembly for pivoting the complete magnification extender, and enabling accurate and stable pivoting, is shown schematically in Fig. 8 hereinbelow.

[0080] Reference is now made to Fig. 5, which illustrates how a simpler method of deactivating the magnification extender can be achieved, by tilting only the secondary mirror 360 off-axis of the zoom lens axis Az, and out of the zoom lens field of view 154. The primary mirror 340 remains fixed in its position relative to the zoom lens 150, with the zoom lens again imaging the scene through the aperture 342 in the primary mirror. The secondary mirror has been tilted out of the axis Azof the line of sight of the zoom lens, by an angle a such that it does not block any part of the imaged scene. The advantage of this arrangement is that, because of the comparatively light weight and size of the secondary mirror 360, the mechanically attachment assembly for pivoting the secondary lens out of the optical axis can be made much lighter and simpler than that of the mechanical connecting tilting assembly required by the arrangement on Fig. 4. This mechanical mounting assembly will be illustrated in Fig-8.

[0081] In Fig. 5, the pivot axis has been shown in the same on-axis position as that of the embodiment of Fig. 4. However, it is to be understood that since the pivoting structure does not operate on the position or angular orientation of the primary mirror 340, the pivot does not have to pass through the central region of the primary mirror, but can be at located at any other convenient location, so long as it enables the secondary mirror 360 to drop out of the field of view of the zoom lens located within or behind the aperture in the primary mirror.

[0082] However, there is one disadvantage in use of the telescope shown in Figs. 2 to 5, using the on axis configuration. Such on-axis magnification extenders collect the information from the view to be imaged, only over an annularly shaped area around the hole in the primary mirror, since the output aperture of the telescope has to project the output image information through the primary mirror to input the image information to the zoom lens. Using only annular imaging of the field of view, can result in a reduced image quality over parts of the operational range of the telescope, in comparison to the quality obtained with the use of the complete field of view, as is achieved with the refractive lens magnification extender of Fig. 1. This reduction in image quality, arising from the missing illumination information from the center of the field of view, may be observed by noticing a reduction of the MTF of the range extended zoom lens at various ranges of the extender. This is compared with a less marked change in the MTF of the extender and zoom lens combination, when a full aperture refractive element extender is used.

[0083] Reference is now made to Fig. 6, which illustrates schematically, one way of overcoming the problem arising from the use of on-line reflective telescopes, by using an equivalent off- axis telescope 60 to achieve the range extension. Fig. 6 shows the ray tracing output of an optical design program of such a magnification extender, in the form of an off-axis afocal telescope, similar to a S chief spiegler (skewed or oblique mirror) type of telescope. However, since such an off-axis telescope is afocal, it outputs a parallel image beam 62 for inputting into the zoom lens 63. As with the on-axis magnification extenders previously described, this telescope converts the large input illumination beam 61 into a parallel beam 62 reflected from the secondary mirror 65, having a smaller diameter enabling its entry into the input aperture of the zoom lens 63. Since the telescope output is a collimated parallel beam 62, the telescope is afocal, its effect being the implementation of an effectively longer focal length of the zoom lens, by virtue of an increased angular magnification of the entire focusing system of magnification extender and zoom lens. The off-axis magnification extender has the advantage over the previously described on-axis extenders, in that the primary mirror 64 collects the illumination from the imaged scene over the whole of the diameter of the mirror, resulting in the elimination of the optical quality reduction arising from the use of the annular beam collection of the on-line magnification extenders of Fig. 2 to Fig. 5.

[0084] Reference is now made to Fig. 7, which illustrates the off-axis arrangement of the magnification extender 100 of Fig. 6, showing more details of the elements of this arrangement.

[0085] The first angular orientation AOs (also referred to herein as the “deployed orientation”) of an this embodiment of an optical arrangement for an extended zoom lens assembly 500 that includes a magnification extender 600 configured to extend the effective focal length (EFL) of the zoom lens 150 having the field-of-view 154 and an optical axis Az shown in FIGS 3- 5. In the illustrated embodiment, the magnification extender 600 is provided as a reflective afocal telescope with an “off-axis” configuration, where the optical axis Al of the incident light is offset from the optical axis Az of the zoom lens 150. In the illustrated embodiment, the magnification extender 600 includes at least one primary reflector 640 having an optical axis APR and at least one secondary reflector 660 having an optical axis ASR. The primary reflector 640 includes a primary reflector substrate 642, having a perimeter 644, a concave primary reflector surface 646. In the illustrated embodiment, the secondary reflector 660 includes at least one secondary reflector substrate 662 having a perimeter 664 and at least one convex secondary reflector surface 666. The morphology of the primary reflector surface 646 and the secondary reflector surface 666 may be provided as any of many configurations, radii, focal lengths, etc. The material used in the primary reflector substrate 642 and the secondary reflector substrate 662 may be any of a wide variety of materials used for reflective optics. In this illustrated deployed orientation, the optical axis ASR of the second reflector element 660, and the optical axis of the primary reflector 640 are aligned at mutual angles, such that the light reflected along the zoom lens axis Az, is parallel to the light 10 entering the extender along axis Ai. The magnification extender 600 also has a pivot axis Ap around which the magnification extender 600 rotates relative to the zoom lens 150. In this deployed orientation, the magnification extender 600 is configured to receive the light rays Ai incident on the primary reflector 640 where they are reflected to the secondary reflector 660 that in turn reflects them to the zoom lens 150.

[0086] However, in spite of the above described advantages of the off-axis magnification extender of Figs. 6 and 7, such an optical arrangement also has a number of disadvantages, some practical, and others relating to the optics of the telescope. Firstly, the asymmetric location of the primary mirror 640 renders the assembly somewhat larger in size than the on-axis design, and hence, somewhat more cumbersome to handle. Additionally, this asymmetry may make the production and calibration of the magnification extender, more difficult. More importantly, the asymmetric arrangement of the optical beam paths generate some geometric aberrations, such as coma and astigmatism, which can be corrected, but which do lead to a reduction in overall image quality.

[0087] However, reflective magnification extenders, both of the on-axis type of Fig. 2 to Fig. 5, and the off-axis type of Figs. 6 and 7, have a common disadvantage which arises from the presence of the secondary mirror 360 or 660 on-axis, between the input of the zoom lens and the scene being imaged. This anomaly arises because of what is known as “image mixing”. This phenomenon occurs because for some ranges, the input aperture of the zoom lens obtains light information of the scene to be imaged, both from the light reflected by the secondary mirror of the magnification extender, as is intended in the normal use of the magnification extender, but also by seeing part of the field of view 154 from around the outer periphery of the secondary lens of the magnification extender. This combination of illumination from two separate sources, each having different magnifications, results in a disturbance to the main image, as obtained through the magnification extender, by the addition of extraneous image illumination from the direct peripheral view, and this addition results in a degradation of the quality of the main image. This effect is most marked when the zoom lens is used at short EFL settings, since such short EFL settings represent imaging of the widest field of view, and hence a higher likelihood of obtaining illumination from around the secondary lens of the magnification extender.

[0088] The practical outcome of this phenomenon is that it is often problematic to use the entire range of a reflective magnification extender, since the wider FOV settings of the extended zoom lens, may result in “image mixing”, and in an image quality which falls below that expected of the extended zoom lens. In such situations, instead of having overlapping ranges for the EFL of the zoom lens assembly with and without the magnification extender deployed, there is a gap in the coverage range of EFL’s, between the longest EFL which the zoom lens alone can achieve, and the shortest EFL having sufficient optical quality, which the zoom lens assembly with the magnification extender, can achieve.

[0089] To illustrate how this phenomenon is observed with the magnification extender installed, as the zoom lens moves from the longest EFL setting, down to a wider field of view, at a certain EFL region, the image begins to become less sharp and somewhat confused. This occurs when the zoom lens input begins to capture illumination directly from the scene being imaged, which comes, because of the larger FOV angle, from outside the edges of the secondary mirror, instead of from the secondary mirror itself. This directly viewed image information is mixed with the image generated by illumination passing through the magnification extender.

[0090] A common method of practically overcoming this anomaly, is to use digital multiplication of the image information in that part of the range of EFL values, missing from the region where acceptable optical images are obtained. Such use of digital manipulation enables a continuous range of EFL imaging to be obtained, thus overcoming the problem of image mixing. However, for the uncorrected magnification extender, the result remains as a gap in coverage of the EFL’s, between the longest EFL which the zoom lens alone can cover, and the shortest EFL which provides an acceptable image quality of the zoom lens with the magnification extender installed. For example, a commonly used zoom lens has an EFL range of 20-275mm. When fitted with a magnification extender providing a 3.6 times range magnification, such that an EFL of 1000 mm can be achieved, it would be expected that the minimum EFL of the zoom lens with range extension, would be of the order of 50mm. (15 x 3.6 mm.). However, a predetermined criterion for image quality may determine that below 550 mm EFL, the quality of the image using the magnification extender, is insufficient for its intended function, such that the zoom lens has a gap for EFL’s in the region between 275 mm and 550 mm. As previously stated, this gap can be compensated for by the use of digital multiplication of the image obtained.

[0091] Reference is now made to Fig. 8, which is a listing showing the physical properties and the optical performance results expected by comparison of three types of magnification extender (i) a reflective extender in which the secondary mirror only is tilted off-axis, (ii) a reflective extender in which the entire telescope is tilted off-axis, and (iii) a refractive element extender. The exemplary beam extender used for the reflective cases, is the above described extender for a zoom lens having an EFL range of 20 to 275 mm. The table clearly shows some of the various phenomena described hereinabove. Thus, for instance, it is observed that the standard refractive range extended zoom lens is able to cover the full intended range of both the original zoom lens and the zoom lens with the extended range. This is in contrast to the reflective extenders, where the presence of the “image mixing” phenomenon necessitates the use of the zoom lens in two separate EFL ranges with a gap between them. The table is not intended to provide exact details of what the systems of the present application will achieve, but is intended to provide a comparison of the possibly potential advantages availed by the systems of the present application.

[0092] The most notable features of the table are the physical properties of the three different types. As is observed, the weight of the reflective extenders is around half of that of the refractive extender, while the expected cost is less than half. Part of this cost reduction comes because of the substantially lower cost of the mirror materials than that of the lens elements, and part of the cost reduction arises because, while the reflective systems only require precision optical generation of two surfaces - the two mirror surfaces - the refractive systems require the precision generation of 4 or 6 lens surfaces. Additionally, the lower weight of the elements may result in a reduction in the complexity of the mechanical supports for the pivotal elements of the extenders.

[0093] Reference is now made to Fig. 9 to Fig. 15, which show various mechanical arrangements proposed for use in rotating either the entire magnification extender, or just the secondary mirror, into or out of the beam entry path of the zoom lens. Figs. 9 to 15 are shown in much more detail than Figs. 3 to 5, and Fig. 7, in order to clearly show the constructural details of the mechanics. The guiding principle in the mechanical structure of the systems, is to provide, with minimum weight and components, a rigid support system, to reduce vibration or unwanted motion of the extender elements, both relative to each other, and relative to the zoom lens.

[0094] Fig. 9 now shows a perspective view of an exemplary embodiment which attempts to achieve those aims for the extended zoom lens assembly 100 shown in Fig. 3 in the angular orientation where the optical axis AE and the optical axis Az are substantially collinear. In this illustrated embodiment, the extended zoom lens assembly 100 includes the zoom lens 150, only partly visible as it is sitting within the aperture 342 of the primary mirror 340, the magnification extender 300, an extender structure 400, and a mounting structure 250, which should be adapted for mounting to the system on which the zoom lens is being used. In this embodiment, the zoom lens 150 is secured to at least one lens mounting plate 200. The primary reflector 340 and the secondary reflector 360 of the magnification extender 300 are mounted to the extender structure 400. In the illustrated embodiment, the extender structure 400 includes a primary reflector retainer 402 and a secondary reflector retainer 404 secured relative to each other by a first vertical support member 406, a second vertical support member 408, a first lateral support member 410, and a second lateral support member 412. The terms vertical and lateral relate to the orientations of the drawing of Fig. 9. In the illustrated embodiment, the primary reflector retainer 402 is has an arcuate shape with a channel formed therein, with the channel sized to receive and securely retain the primary reflector 340 therein. In the illustrated embodiment, the primary reflector retainer 402 engages at least a portion of the perimeter 344 of the primary reflector 340, though in other embodiments the primary reflector retainer 402 may engage the primary reflector surface and / or the rear surface 352 of the secondary reflector 360. In the illustrated embodiment, the secondary reflector retainer 404 has a passage formed therein, wherein the passage is sized to receive the secondary reflector 360 therein so it can be securely retained by the secondary reflector retainer 404. In the illustrated embodiment, the first vertical support member 406 and the second vertical support member 408 extend from the primary reflector retainer 402 to opposing sides of the secondary reflector retainer 404. The first lateral support member 410 attaches the top quadrant of the secondary reflector retainer 404 to an upper portion of the primary reflector retainer 402. In the illustrated embodiment, the second lateral support member 412 includes two pieces, wherein each piece attaches to the primary reflector retainer 402 and extends to and is fastened to one of the first vertical support member 406 and second vertical support member 408, or to the bottom quadrant of the of the secondary reflector retainer 404. In the illustrated embodiment, the secondary reflector retainer 404 may be detachably secured to the first vertical support member 406 and the second vertical support member 408 so that the secondary reflector retainer 404 may be removed and replaced with a different secondary reflector retainer 404 that holds an alternate secondary reflector 360. Those skilled in the art will appreciate that the extender structure 400 may include any variety of support members configured to securely retain the primary reflector 340 relative to the secondary reflector 360.

[0095] The extender support structure 250 may further include at least one extender support 260 that includes at least one support member 262 having an optional relief 264 formed therein. In the illustrated embodiment, one end of the extender support 260 is secured to the extender support member 252, and a positioning or latching mechanism 370 is incorporated into the other end, as will be shown and described hereinbelow in relation to Fig. 11.

[0096] The extended zoom lens assembly 100 further includes one or more pivot support members 230 secured to opposing sides of the extender support member 252, though only one of the pivot support members 230 is visible in FIG. 9. Each of the pivot support members 230 has a pivot passage 232 formed therein, wherein the pivot passages 232 are sized to receive a pivot axis Ap therein. The pivot support members 230 are secured to the extender support member 252 by means of screws 234 or fasteners. For the purposes of this disclosure, the pivot support members 230 may be considered to be part of the extender support structure 250.

[0097] The embodiment of the extended zoom lens assembly 100 shown in FIG. 9 has the extender support member 252 in a substantially vertical orientation and the optical axis Az of the zoom lens 150 disposed in a horizontal orientation substantially perpendicular to the extender support member 252. Those skilled in the art will appreciate that the extender support member 252 may be in disposed in any angular orientation and the optical axis Az may be disposed at any angle relative to the extender support member 252.

[0098] FIG. 10 now shows a detailed view of the embodiment of the pivot assembly 420 shown in FIG. 9. The pivot assembly 420 is used to provide rotational support to the magnification extender 300 when it undergoes changes in angular orientation relative to the extender support member 252. In the illustrated embodiment, the pivot assembly 420 includes a pivot axis Ap, a pivot member or axle 422, a pivot adaptor 424, and a pivot retainer 426. The pivot adaptor 424 is secured to the primary reflector retainer 402 to provide support for the pivot axle 422. In this embodiment, because of the position of the pivot axis Ap relative to the primary reflector 340 and the zoom lens 150, the pivot assembly 420 cannot use a single pivot axle extending from one side of the extender structure 400 across to the other side of the extender structure 400. As such separate pivot axles 422 are required, one on each side of the primary reflector retainer 402. The each pivot axle 422 is secured to a pivot adaptor 424 to provide the mechanical support for the entire magnification extender 300 and the pivot retainer 426 is fastened to the pivot axle 422 to rotationally secure the pivot axle 422 to the pivot support member 230. The pivot assembly 420 described above is only one of any variety of pivot assemblies that may be used to provide rotational support to the magnification extender 300 when it undergoes changes in angular orientation relative to the extender support structure 250.

[0099] In the illustrated embodiment, the extended zoom lens assembly 100 includes a biasing member 430 to help retain, or at least partially retain the magnification extender 300 in either the deployed orientation or the retracted orientation by applying a biasing force to the extender structure 400. In the illustrated embodiment, the biasing member 430 is an extension spring having a biasing member axis AB with a first end that is secured to the extender support member 252 or other structure by a first biasing member retainer 432 and a second end secured to a second biasing member retainer 434 that is secured to the pivot adaptor 424 or other structure of the primary reflector retainer 402 or the extender structure 400. When the magnification extender 300 is in the deployed orientation, the biasing member axis AB is oriented on a first side of the pivot axis Ap (e.g., above the pivot axis Ap in the deployed orientation shown in FIGS. 9 and 10). When the magnification extender 300 is in the retracted orientation as shown in FIG. 12, the biasing member axis AB is oriented on a second side of the pivot axis Ap (e.g., below the pivot axis Ap). This arrangement of the biasing member 430 may be referred to as “over center” configuration that enables the biasing member 430 to exert a biasing force on the magnification extender 300, both when the magnification extender 300 is in the deployed orientation and when it is in the retracted orientation. The biasing force is intended to hold the magnification extender firmly against a mechanical stop that defines the correct position of the magnification extender in either position.

[0100] Reference is now shown to FIG. 11 which shows a cross-section side view of the embodiment of the extended zoom lens assembly 100 shown in FIG. 9, with the magnification extender 300 in the deployed orientation AOi so that the optical axis AE of the magnification extender 300 and the optical axis Az of the zoom lens 150 are as substantially collinear as is required to meet the accuracy requirements of the complete optical arrangement. As shown, the zoom lens 150 is mounted on the lens mounting plate 200 and passes through the passage 202 so that the zoom lens mounting plate 200 may be secured to the extender support member 252 such as by a plurality of fasteners. The extender support 260 includes a relief 264 formed therein, and the extender support 260 is secured to the extender support member 252, such as by one or more fasteners. At least one first latching mechanism 370 may be provided that is configured to lock or latch the magnification extender 300 in the deployed orientation. In the illustrated embodiment, the first latching mechanism 370 includes a magnetic latching device 372 and a shock absorbing device 374. The magnetic latching device 372 includes a first magnet 376 secured to the extender support 260, and a second magnet 378 secured to the primary reflector retainer 402, so that when the magnification extender 300 is deployed from the retracted orientation, it will be latched accurately in place. In one embodiment, the first magnet 376 and the second magnet 378 may be permanent magnets. In another embodiment, the first magnet 376 and the second magnet 378 may comprise one permanent magnet and one electromagnet so that the magnification extender 300 may be latched and unlatched electrically. The extended zoom lens assembly 100 may include a second extender locking assembly 390 positioned so that the magnification extender 300 may be latched in the retracted orientation, though the accuracy required for the retracted position is accordingly less. It is also to be understood that even if latching devices are not used, the angular position of the rotatable magnification extender should be able to rotate exactly to its defined deployed position by at least one buffer stop, onto which the structure makes contact to define its accurate orientation relative to the optical axis.

[0101] The extended zoom lens assembly 100 may include any of a variety of actuators configured to change the angular orientation of the magnification extender 300 from the deployed orientation to the retracted orientation, and vice versa. Though not shown in detail, at least one linear actuator 450 may be provided that causes the magnification extender 300 to undergo the change in angular orientation from the deployed orientation to the retracted orientation. The actuator may be of a number of different implementations, the common feature being the ability to control the motion to a high level of accuracy, and to do so without appreciable backlash. In the illustrated embodiment, the actuator 450 may have a fixed portion mounted on the pivot support member 230, and a movable portion coupled to the primary reflector retainer 402. The actuator 450 may extend through the passage 258 formed in the extender support member 252.

[0102] One solution could be to use a controlled motor, applied to a screw mechanism, the screw rotating within an internally threaded opening, generating linear motion between the screw and the threaded opening. The threaded opening could be on the primary reflector retainer 402, such that rotation of the screw by the motor results in linear motion of the primary reflector retainer 402, which is translated into a rotating motion of the primary reflector around the pivot axis Ap. In such an embodiment, the housing of the threaded opening should be pivoted on the primary reflector retainer 402, to enable its angle to change as the retainer tilts relative to the extender support member 252. Use of such a screw actuator, or indeed of any actuator providing closely controlled motion, may obviate the need for any latching device or stop buffers for defining the angular end position of the primary reflector retainer 402, since the rotational position of the retainer can be accurately determined by the controlled motion of the screw, on condition that the screw-thread pair has a level of backlash that will not degrade the angular accuracy of the retainer position.

[0103] The actuating motor could be any motor having accurately controlled rotation, such as a stepping motor, or a conventional motor having an angular encoder to provide a feedback control signal to limit its rotation to the required amount, or a conventional motor operated with a feedback control signal from a linear encoder measuring the linear motion of the screw or of the retainer itself. Other alternatives could be piezoelectric actuators, whose accuracy is very high. Those skilled in the art will appreciate that the extended zoom lens assembly 100 may include any type or number of actuators.

[0104] As alternative to the controlled electrical actuators described hereinabove, it is also possible to deploy and retract the magnification extender manually, using latching devices such as those previously described, to accurately define the angular position required of the magnification extender, especially in its deployed position.

[0105] FIG. 12 now shows a view of one embodiment of the mechanical arrangement of the extended zoom lens assembly 100 shown in FIG. 4, in which the complete magnification extender 300, including both the primary mirror and the secondary mirror, has been rotated from the deployed orientation around the pivot axis Ap to the retracted orientation by the actuator 450 so that the optical axis AE and the optical axis Az are angularly separated by an angle a in the retracted orientation. The zoom lens 150 remains in its original position attached to the extender support structure 250 and images the view of interest through the aperture in the primary reflector. The size of the aperture is such that the tilt of the primary reflector does not affect the ability of the zoom lens itself to image its complete intended field of view. Other details are shown in accordance with the feature numbering in FIGS. 9 and 11.

[0106] FIGS. 13 and 14 now show an alternative exemplary mechanical arrangement proposed for use in rotating only the secondary mirror 360, into or out of the beam entry path of the extended zoom lens assembly 100. Such a tilting motion of only the secondary mirror has been shown schematically in FIG. 5. Since the secondary mirror 360 is significantly smaller and lighter than the primary mirror 340, a simpler and more manageable rotation mechanism can be used, than that required for tilting the whole of the magnification extender, as was shown in FIG. 4, for instance.

[0107] The exemplary embodiment of FIGS. 13 and 14 illustrate a different mechanical structure than the type used in FIGS 9 to 12, where the whole magnification extender is tilted as a single consolidated unit. The secondary mirror itself requires a well defined, sturdy, mechanical support and positioning structure, having good stability against small vibrational movements. If this is not achieved, at the very high magnifications achieved by these systems, small motions of the secondary mirror would render the images obtained to be severely degraded. Therefore, the supporting arm of the secondary mirror must have a cross section sufficiently sturdy that it provides the required robustness. However, if it were necessary to rotate such a comparatively heavy support arm out of the beam path, and to return it accurately to its defined position when reinserted into the optical path, the advantages of rotating the small and light secondary mirror may be largely nullified. Therefore, the embodiment shown in FIGS. 13 and 14 uses a novel support and tilting arrangement, in which the secondary mirror support arm is made of two separate components, the first being a comparatively thin arm for holding and tilting the secondary mirror itself out of the beam path when required, and a significantly more sturdy positioning arm, whose function is to accurately define the position of the secondary mirror when it is deployed into the beam path. In this mechanical arrangement, the secondary mirror support arm is rotated out of the beam path in one plane, using a lightweight movement mechanism, while the heavier support and positioning arm is tilted in a second plane, in this case, an orthogonal plane to that of the tilt of the secondary mirror itself. Referring now in detail to the exemplary embodiment shown in FIG. 13, the magnification extender is built on an external support member 252, with the zoom lens 150 rigidly supported on that member. The primary mirror 340 is mounted in the primary reflector retainer 402 and to the support member 252 using support members 231. However, unlike the embodiment shown in FIGS. 9 to 12, where the primary mirror 340 and its retainer 402 are mounted on a pivot in the support member 230, in the embodiment of FIG. 13, the primary mirror and its retainer are rigidly mounted to the support members 231. Attached to the external support member 252, is a base plate 470, whose function is to support the pivoting mechanism of the secondary mirror 360. The secondary mirror itself is clamped onto a secondary mirror motion arm 472, which is rotatable into and out of the beam axis by means of a pivot 473 mounted in the base plate 470. An actuating mechanism (not shown in FIGS. 13 and 14) is used in order to tilt the secondary mirror into and out of the beam axis. The deployed position of the secondary mirror 360 is defined by means of the support and positioning arm 480, which has a V-groove 482 in a face facing the edge of the secondary mirror, such that when the actuating mechanism returns the secondary mirror to its operating position in the beam path, its position is accurately defined within the V-groove. The position of the secondary mirror firmly against the V-groove can be ensured by the use of magnets (not shown in the drawings) or by means of a biasing mechanism such as a spring (not shown in the drawings) acting on the secondary mirror motion arm 472. Though such a V-groove 482 is an accurate method of defining the location of the secondary mirror, it is to be understand that any other method or mechanism which is capable of accurately locating the mirror is equally suitable for use in this magnification extender embodiment, and the locating system is not intended to be limited to the V-groove arrangement shown in FIGS. 13 and 14. The position of the secondary mirror 360 is also dependent on the alignment of the support arm 480 relative to the beam axis. This position is assured by the position of the support arm base plate 484 in essentially complete contact with the base plate 470 of the entire magnification extender, such that the position of the V-groove 482 is accurately defined relative to the base plate 470, and hence relative to the external support member 252, and hence the optical axis of the magnification extender.

[0108] The relative robustness shown of the support and positioning arm 480 compared to the secondary mirror motion arm 472 is determined by their function and method of attachment to the telescope structure. The two arms have rotational axes having orthogonally opposite positions, and different robustness. Thus, the strong support and positioning arm 480, has a long rotational pin axis 490 on which it rotates in a vertical direction (relative to the direction of the view of Figs. 13 and 14), providing it with high robustness against rotating laterally, and a rigid, well-defined stop plate 470 to determine when it has rotated vertically (in the drawings) into the in-line position on the optical axis of the primary mirror. On the other hand, the mirror holder 472, which is substantially lighter than the support and positioning arm 480, has only a short rotational axis 473, which less positional accuracy in the vertical direction, but uses the V-groove 482 in the support and positioning arm 480, to provide not only a well defined vertical position on-axis of the primary mirror, but also a well defined lateral position on-axis of the primary mirror, against the walls of the V-groove, such that the position of the secondary mirror relative to the primary mirror is ensured, both the bidirectional on-axis position, and at the correct longitudinal distance from the primary mirror. By that means, a combination of very high positional and repeatable accuracy is obtained, together with ease of moving the secondary mirror into and out of deployment.

[0109] Reference is now made to FIG. 14, which is a view of the magnification extender of FIG. 13, from the bottom (relative to the drawing), in order to show the pivoting systems used in this embodiment. The numbering of the components shown in FIG. 14 is identical to those of FIG. 13, and therefore need not be repeated for FIG. 14. Since, in the embodiment shown in FIG. 13, even when the secondary mirror 360 is pivoted away from the optical axis OA of the system, its support arm 480 remains in the field of view of the zoom lens 150, and would therefore substantially degrade the quality of the image generated by the zoom lens, 150. Therefore, it is also necessary to move the support arm 480 from the proximity of the optical axis of the system, and right out of the field of view of the zoom lens. In the exemplary embodiment of FIG. 14, this is achieved by attaching the support arm base plate 484 to the external support member 252, by means of a pivot axis 490, such that the support arm can be swung away from the optical axis OA. The activation mechanism for performing this motion can be similar to that shown in FIG. 11, and is not shown is FIG. 14. Also visible in FIG. 14 is the bottom end of the pivot 473 for rotating the secondary mirror motion arm 472.

[0110] It is to be appreciated that the implementation shown in FIGS. 13 and 14 is not understood to be the only method of achieving the required tilting motion of the secondary mirror, but that any form of tilting mechanism can equally well be used in order to tilt the secondary mirror into and out of the beam path, and that this aspect of the invention is not intended to be limited by what is shown in FIGS. 13 and 14. The magnification extenders so far described in the detailed description, have been of the afocal Galilean or Cassegrain telescope type, using a primary mirror with an aperture in which the zoom lens sits, as shown in the optical designation of FIG. 2. Another embodiment of the extended zoom lens assembly 500 includes a different optical arrangement, as shown in FIGS. 15 to 16, wherein the mirrors of the magnification extender are oriented in a so- called off-axis or oblique mirror afocal configuration, such as is shown in the ray tracing drawing of FIG. 6, and the detailed drawing of FIG. 7.

[0111] Reference is now made to FIG.15, which illustrates the extended zoom lens assembly 500 of FIG.7, but showing one exemplary method and structure by which the primary mirror 640 and the secondary mirror 660 of the magnification extender 600, are maintained in their correct predetermined spatial and orientational mutual positions. An extender structure 700, and a mounting structure 750 are used for this purpose. In the illustrated embodiment, the extender support structure 750 includes at least one extender support member 752 having a relief 754 formed therein. The zoom lens 150 is secured to at least one lens mounting plate 800 that is positioned in the relief 754 and secured to the extender support member 752. The primary reflector 640 and the secondary reflector 660 of the magnification extender 600 are mounted to the extender structure 700. In the illustrated embodiment, the extender structure 700 includes a primary reflector retainer 702 and a secondary reflector retainer 704 secured relative to each other by at least one vertical support member 706, and at least one lateral support member 708. In the illustrated embodiment, the secondary reflector retainer 704 has a passage formed therein, wherein the passage is sized to receive the secondary reflector 660 therein so it can be securely retained by the secondary reflector retainer 704. In the illustrated embodiment, the vertical support member 706 and the lateral support member 708 extend from the primary reflector retainer 702 to opposing sides of the secondary reflector retainer 704. A biasing member such as a spring can be provided to help retain, or at least partially retain the magnification extender 600 in either the deployed orientation or the retracted orientation by applying a biasing force to the structure 600. The biasing member may most simply be an extension spring with a first end that is secured to the primary reflector retainer 702 and a second end secured to the extender support structure 750 or its extender support member 752. Those skilled in the art will appreciate that the extender structure 700 may include any variety of support members configured to securely retain the primary reflector 640 relative to the secondary reflector 660. Those skilled in the art will appreciate that the extender structure 700 can be constructed in a wide variety of ways. FIG. 15 has shown a side view of the embodiment of the extended zoom lens assembly 500 in the deployed orientation, where the secondary reflector 660 is positioned in the FOV 154 of the zoom lens 150. Reference is now made to FIG.16, which shows the magnification extender of FIGS. 7 and 15, but in the second angular orientation AOe, which is the retracted position. As is observed, the entire magnification extender 600, including the primary mirror 640 and the secondary mirror 660, connected by the mechanical frame 700, as shown in Fig. 15, are rotated about the pivot axis Ap, such that the secondary mirror 660 has dropped out of the field of view 154 of the zoom lens 150. The zoom lens can thus now operate without any magnification extension. Relevant methods and parts of the rotation and latching mechanisms of FIGS. 8 to 11, can be used to implement and control the rotation of the magnification extender 600 of the present embodiment.

[0112] In addition, in a further mechanical arrangement (not shown in the drawings) for moving the magnification extender to its retracted position, it is possible to rotate only the secondary mirror 660 off the axis of the zoom lens, on its own rotation arm, while the primary mirror 640 remains fixed relative to the zoom lens. The pivot axis Ap would then be operative to rotate only the arm holding the secondary mirror 660. This is a similar solution to that described in relation to Fig. 14 of the on-axis magnification extender, or similar to any of the equivalent mechanism mentioned in relation thereto.

[0113] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details have been set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. Furthermore, it is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.

Claims

CLAIMSWhat is claimed is:

1. A magnification extender (100) for extending the effective focal length of a zoom lens (150), the extender comprising: a primary mirror (340) having an axis (APR), a central aperture (342) through which the zoom lens can image a scene of interest along a line of sight, and a concave reflective surface (342) adapted to face the scene of interest; a secondary mirror (360) having a diameter smaller than that of the primary mirror, and a convex reflective surface, the secondary mirror being positioned such that its reflective surface is directed towards the primary mirror, the focal lengths and distance apart of the primary and secondary mirrors being such that when the primary and secondary mirrors are aligned collinearly, the magnification extender is afocal, reducing the diameter of a beam of illumination (Ai) impinging on the primary mirror, without affecting the divergence of the beam of illumination; and a pivot axis (Ap) adapted to enable pivoting of at least the secondary mirror out of the line of sight of the zoom lens.

2. A magnification extender according to claim 1, wherein the primary mirror and the secondary mirror are rigidly connected in a structure (400) which can be pivoted around the pivot axis.

3. A magnification extender according to claim 1, wherein the secondary mirror is mounted on an arm (472) which can be pivoted around the pivot axis independently of the primary mirror, such that the secondary mirror can be pivoted out of the line of sight of the zoom lens while the primary lens remains stationary.

4. A magnification extender according to any of claims 1 to 3, wherein the pivoting of at least the secondary mirror out of the line of sight of the zoom lens enables the zoom lens to image the scene of interest without extended magnification.

5. A magnification extender according to any of claims 1 to 3, wherein the positioning of at least the secondary mirror axially with the line of sight of the zoom lens enables the zoom lens to image the scene of interest with magnification extension.

6. A magnification extender according to any of the previous claims, wherein the diameter of the secondary mirror is such that at least the major part of the beam of illumination reflected by the secondary mirror impinges on an input lens of the zoom lens.

7. A magnification extender according to any of the previous claims, wherein the aperture of the primary mirror has a diameter such that the beam of illumination reflected by the secondary mirror is configured to pass therethrough.

8. A magnification extender according to any of the previous claims, wherein the structure rigidly connecting the primary mirror and the secondary mirror, maintains the mutually relative position and orientation of the secondary mirror and the primary mirror.

9. A magnification extender according to claim 8, wherein the pivot axis is disposed such that it passes through the optical axis of the zoom lens and a central region of the primary mirror, such that the primary mirror is configured to pivot while keeping its central region on-axis with the zoom lens.

10. A magnification extender according to claim 9, wherein the complete magnification extender pivots about the pivot axis.

11. A magnification extender according to claim 10, wherein the complete magnification extender is adapted to pivot sufficiently that the secondary mirror moves off the axis of the zoom lens by at least the radius, at the longitudinal position of the secondary mirror, of the field of view of the zoom lens, when the zoom lens is set at its minimum focal length.

12. A magnification extender according to any of the previous claims, wherein the pivot axis is disposed such that it enables the secondary mirror to move off the axis of the zoom lens by at least the radius of the field of view of the zoom lens, at the longitudinal position of the secondary mirror, when the zoom lens is set at its minimum focal length.

13. A magnification extender according to any of the previous claims, wherein the secondary mirror can be tilted sufficiently that it does not block any part of the line of sight of the zoom lens.

14. A magnification extender according to any of the previous claims, wherein the structure further comprises an actuator, positioned such that the magnification extender is pivoted around the pivot axis by the actuator.

15. A magnification extender according to any of the previous claims, wherein the structure further comprises at least one mechanical buffer positioned such that the pivoting of the magnification extender to its deployed position ensures that the optical axis of the magnification extender is collinear with the optical axis of the zoom lens.

16. A magnification extender according to claim 15, wherein the structure further comprises at least one latch to ensure that the magnification extender remains latched in its deployed position collinear with the optical axis of the zoom lens.

17. A magnification extender according to any of the previous claims, wherein the line of sight of the zoom lens is collinear with its optical axis (Az).

18. A magnification extender for use with a zoom lens (150) adapted to image a scene of interest, the extender comprising: a primary mirror (640) having a concave reflective surface (646), the primary mirror being located off-axis of the zoom lens; and a secondary mirror (660) having a convex reflective surface (666) with a diameter smaller than that of the primary mirror, and positioned, when the magnification extender is actuated, on the optical axis (Az) of the zoom lens, and with its reflective surface directed such that it reflects a beam of light converging from the primary mirror towards the zoom lens, wherein at least one part of the magnification extender is mounted on a structure (700) rotatable around a pivot axis (Ap) such that on rotation, the at least one part of the magnification extender changes its angular orientation from a first orientation on-axis with the zoom lens, to a second orientation, in which the at least one part of the magnification extender is unaligned with the axis Az of the zoom lens.

19. A magnification extender according to claim 18, wherein the focal lengths and distance apart of the primary mirror and the secondary mirror are such that the magnification extender is afocal, so that the diameter of a beam of illumination impinging on, and beingreflected by the primary mirror, is reduced, without affecting the divergence of the beam of illumination.

20. A magnification extender according to either of claims 18 or 19, wherein the at least one part of the extender comprises the primary mirror and the secondary mirror, and the structure maintains the mutually relative position and orientation of the secondary mirror and the primary mirror.

21. A magnification extender according to claim 20, wherein the complete magnification extender rotates about the pivot axis.

22. A magnification extender according to claim 21 , wherein the complete magnification extender is adapted to rotate sufficiently that the secondary mirror moves off the axis of the zoom lens by at least the radius, at the longitudinal position of the secondary mirror, of the field of view of the zoom lens, when the zoom lens is set at its minimum focal length.

23. A magnification extender according to either of claims 18 or 19, wherein the at least one part of the magnification extender comprises the secondary mirror, the structure being a rotatable arm holding the secondary mirror but not the primary mirror, the primary mirror remaining stationary.

24. A lens assembly (100), comprising: a zoom lens (150) secured to a support structure (250), the zoom lens having a zooms lens optical axis (Az); a magnification extender (300) rotatably attached to the support structure, wherein the magnification extender includes a primary reflector (340) and a secondary reflector (360) aligned along an extender optical axis (AE) and secured to an extender structure (400), wherein the magnification extender is configured to undergo a change in angular orientation around a pivot axis (Ap) from a second angular orientation having the magnification extender rotated to an angle with the zoom lens optical axis, to a first angular orientation with the zooms lens optical axis and the extender optical axis AE substantially collinear.

25. The lens assembly of claim 24, further comprising an extender actuator (450) configured to cause the magnification extender to undergo a change in angular orientation around the pivot axis between the first angular orientation and the second angular orientation.

26. The lens assembly of claim 25, wherein the extender actuator includes either a linear actuator or a rotary actuator.

27. The lens assembly (100) of either of claims 25 and 26, wherein the extender actuator includes a latching mechanism configured to secure the magnification extender to the support structure in either the first angular orientation or the second angular orientation.

28. The lens assembly of any of claims 24 to 27, further comprising a first latching mechanism (370) configured to detachably secure the magnification extender to the support structure in the first angular orientation.

29. The lens assembly of any of claims 24 to 28, further comprising a second latching mechanism (390) configured to detachably secure the magnification extender to the support structure in the second angular orientation.

30. The lens assembly of any of claims 24 to 29, wherein the zoom lens optical axis (Az) is substantially collinear with an incident light optical axis (AL).

31. The lens assembly (100) of any of claims 24 to 30, wherein the zoom lens optical axis is offset from an incident light optical axis32. A lens assembly (100), comprising: a support structure (250) having a pivot member (422) with a pivot axis (Ap); a zoom lens (150) secured to the support structure, wherein the zoom lens (150) has a zooms lens optical axis Az; a primary reflector (340) secured to the support structure (250), the primary reflector having a primary reflector optical axis (APR);a magnification extender (310) rotatably attached to the pivot member, wherein the magnification extender includes a secondary reflector (312) having a secondary reflector optical axis (ASR); wherein the magnification extender is configured to undergo a change in angular orientation around the pivot axis from a second angular orientation having the magnification extender rotated to an angle with the zoom lens optical axis, to a first angular orientation having the zooms lens optical axis, the primary reflector optical axis, and the secondary reflector optical axis substantially collinear.

33. The lens assembly of claim 32, further comprising an extender actuator (450) configured to cause the magnification extender to undergo a change in angular orientation around the pivot axis between the first angular orientation and the second angular orientation.

34. The lens assembly of claim 33, wherein the extender actuator includes a linear actuator or a rotary actuator.

35. The lens assembly of either of claims 33 and 34, wherein the extender actuator includes a latching mechanism configured to secure the magnification extender to the support structure in either the first angular orientation or the second angular orientation.

36. The lens assembly of any of claims 32 to 35, further comprising a first latching mechanism (370) configured to detachably secure the magnification extender to the support structure in the first angular orientation.

37. The lens assembly of any of claims 32 to 36, further comprising a second latching mechanism (390) configured to detachably secure the magnification extender (310) to the support structure in the second angular orientation (AO2).

38. The lens assembly of any of claims 32 to 37, wherein the zoom lens optical axis is substantially collinear with an incident light optical axis (Ai).

39. The lens assembly of any of claims 32 to 38, wherein the zoom lens optical axis is offset from an incident light optical axis.

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