WO2009094782A1

WO2009094782A1 - Apparatus and method for multi-spectral dual imaging

Info

Publication number: WO2009094782A1
Application number: PCT/CA2009/000122
Authority: WO
Inventors: Robert R. Parsons; James I. Symons; Ian Powell; Jonny Gauvin
Original assignee: Power Diagnostic Technologies Ltd.
Priority date: 2008-02-01
Filing date: 2009-01-30
Publication date: 2009-08-06

Abstract

A multi-spectral dual imaging apparatus producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges for delivery to an image capturing device includes first directing means for directing at least a first portion of the incident electromagnetic energy along a first path between an entrance of the apparatus and the image capturing device; first filtering means for filtering electromagnetic energy being directed along said first path; second directing means for directing at least a second portion of the incident electromagnetic energy along a second path between said entrance and the image capturing device; second filtering means for filtering electromagnetic energy being directed along said second path, wherein said first directing means reflects electromagnetic energy being directed along said first path an odd number of times greater than said second directing means reflects electromagnetic energy being directed along said second path.

Description

APPARATUS AND METHOD FOR MULTI-SPECTRAL DUAL IMAGING

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to imaging and, in particular, to an apparatus and method for multi-spectral dual imaging.

2. Description of Related Art

M u lti -spectral imaging systems produce images, such as images of objects and scenes, at more than one band or range of wavelengths of the electromagnetic spectrum. Some multi-spectral imaging systems can be used to produce two or more simultaneously captured and adjacently presented images at spectrally distinct ranges of infrared wavelengths.

For example, United States patent No. 5,926,283 to Hopkins discloses a multi-spectral two dimensional imaging spectrometer. The spectrometer of Hopkins includes an image collection subassembly comprising three distinct optical components; a spectral separation subassembly comprising several optical components which includes a prism for beam division; and a re-imaging subassembly that includes an imaging optic and a detection system. The large number of optical components of the Hopkins spectrometer through which light must pass before reaching its detection system and its need for a beam dividing prism reduces the optical efficiency of the Hopkins spectrometer and increases its size, complexity and manufacturing costs.

Thus, there is need in the art for improvements in multi-spectral imaging spectrometers by providing a novel apparatus and method. SUMMARY

The above shortcomings may be addressed by providing, in accordance with one aspect of the invention, an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum for delivery to an image capturing device. The apparatus comprises: a first filter for producing a first filtered beam by filtering electromagnetic energy of the incident electromagnetic energy having entered into the apparatus by passing within a first entry point range of entry points along an entrance plane of the apparatus within a first entry angle range of entry angles incident upon the entrance plane to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus; and a second filter for producing a second filtered beam by filtering electromagnetic energy of the incident electromagnetic energy having entered into the apparatus by passing within a second entry point range of the entry points within a second entry angle range of the entry angles to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus.

The first entry point range and the second entry point range may be any one of substantially coincident, substantially overlapping, partly overlapping and substantially non-overlapping. The first entry angle range and the second entry angle range may be any one of substantially coincident, substantially overlapping, partly overlapping and substantially non-overlapping.

The apparatus may include a first reflective device for reflecting electromagnetic energy incident on the first reflective device along a first path toward the first filter. The apparatus may include a second reflective device for reflecting electromagnetic energy reflected from the first reflective device along the first path. The apparatus may include a first reflective device angle adjuster for adjusting a first reflective device mounting angle. The first reflective device angle adjuster may be operable to permit manual adjustment of the first reflective device angle mounting angle. The first reflective device angle adjuster may be operable to automatically adjust the first reflective device angle mounting angle. The apparatus may include a second reflective device angle adjuster for adjusting a second reflective device mounting angle. The second reflective device angle adjuster may be operable to permit manual adjustment of the second reflective device angle mounting angle. The second reflective device angle adjuster may be operable to automatically adjust the second reflective device angle mounting angle. The apparatus may include the image capturing device. The image capturing device may include a first detector for detecting the first filtered beam. The image capturing device may include a second detector for detecting the second filtered beam. The image capturing device may include a lens for transmitting the first filtered beam toward the first detector and for transmitting the second filtered beam toward the second detector.

The first filter and the second filter may be adjacently mounted within the apparatus. The apparatus may include a housing for containing member components of the apparatus. The first filter and the second filter may be adjacently mounted within the housing. The first filter and the second filter may be adjacently mounted within the apparatus between the first and second reflective devices and the image capturing device.

The apparatus may include a wavelength selective component. The wavelength selective component may comprise the first filter and the second filter. The wavelength selective component may be a dichroic mirror. The apparatus may include the first reflective device and the wavelength selective component. The apparatus may be operable to reflect from the first reflective device toward the wavelength selective component electromagnetic energy of the incident electromagnetic energy having entered into the apparatus by passing an entry point within the first entry point range at an entry angle within the first entry angle range to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus. The first filtered beam may comprise electromagnetic energy having been reflected from the wavelength selective component upon being directed to the wavelength selective component from the first reflective device. The second filtered beam may comprise electromagnetic energy having been transmitted through the wavelength selective component upon having entered into the apparatus by passing an entry point within the second entry point range at an entry angle within the second entry angle range to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus.

The apparatus may be operable to reflect from the wavelength selective component toward the first reflective component electromagnetic energy having a wavelength within a reflection passband of the wavelength selective component. The apparatus may be operable to transmit through the wavelength selective component toward the image capturing device electromagnetic energy having a wavelength within a transmission passband of the wavelength selective component.

The first filtered beam may comprise electromagnetic energy having been reflected from the wavelength selective component toward the first reflective device. The apparatus may be operable to direct the first filtered beam from the first reflective device toward the image capturing device. The second filtered beam may comprise electromagnetic energy having passed through the wavelength selective component. The apparatus may be operable to direct the second filtered beam from the wavelength selective component toward the image capturing device.

The apparatus may comprise a plurality of wavelength selective components. The apparatus may be operable to direct the first filtered beam from a first wavelength selective component toward a third reflective device. The apparatus may be operable to direct the first filtered beam reflected from the third reflective device toward a fourth reflective device. The third reflective device and the fourth reflective device may be located on the same side of the first wavelength selective component. The apparatus may be operable to direct the first filtered beam from the fourth reflective device toward a second wavelength selective component. The first wavelength selective component and the second wavelength selective component may be located on the same side of the third reflective device. The apparatus may be operable to direct the first filtered beam from the second wavelength selective component toward the image capturing device. The apparatus may be operable to direct the second filtered beam, after passing through the first wavelength selective component, toward the second wavelength selective component. The apparatus may be operable to direct the second filtered beam through the second wavelength selective component toward the image capturing device.

The apparatus may be operable to direct a first beam of electromagnetic energy having a first wavelength between an entrance of the apparatus and the image capturing device along a first path and to direct a second beam of electromagnetic energy having a second wavelength distinct from the first wavelength between the entrance and the image capturing device along a second path such that the image capturing device is enabled to capture images associated with the first beam by a first detector of the image capturing device and is enabled to capture images associated with the second beam by a second detector of the image capturing device. The apparatus may be operable to cause the first beam to be reflected along the first path an odd number of times greater than the number of times the second beam is reflected along the second path. The first path may have a first path length and the second path may have a second path length. The first path length and the second path length may be substantially equal.

In accordance with another aspect of the invention, there is provided a method for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges for delivery to an image capturing device, the method comprising: directing at least a first portion of the incident electromagnetic energy along a first path between an entrance of the apparatus and the image capturing device; filtering electromagnetic energy being directed along said first path; directing at least a second portion of the incident electromagnetic energy along a second path between said entrance and the image capturing device; filtering electromagnetic energy being directed along said second path. The method may further comprises reflecting electromagnetic energy being directed along said first path an odd number of times greater than electromagnetic energy being directed along said second path is reflected. Directing at least said first portion may comprise directing at least said first portion of the incident electromagnetic energy along said first path having a first path length. Directing at least said second portion may comprise directing at least said second portion of the incident electromagnetic energy along said second path having a second path length. Directing at least said second portion may comprise directing at least said second portion of the incident electromagnetic energy along said second path having a second path length substantially equal to said first path length. Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of embodiments of the invention in conjunction with the accompanying figures and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate by way of example only embodiments of the invention: Figure 1 is a sectional plan view of an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum according to a first embodiment of the invention, and an image capturing device; Figure 2 is a sectional plan view of the apparatus shown in Figure 1 , showing an upper first beam and a lower first beam incident upon the apparatus; Figure 3 is a sectional plan view of the apparatus shown in Figure 1 , showing an upper second beam and a lower second beam incident upon the apparatus;

Figure 4 is a sectional plan view of an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum according to a second embodiment of the invention, and an image capturing device;

Figure 5 is a sectional plan view of the second embodiment of the apparatus shown in Figure 4, showing an upper third beam and a lower third beam incident upon the apparatus; Figure 6 is a sectional plan view of the second embodiment of the apparatus shown in Figure 4, showing an upper fourth beam and a lower fourth beam incident upon the apparatus;

Figure 7 is a sectional plan view of an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum according to a third embodiment of the invention, and an image capturing device;

Figure 8 is a sectional plan view of the third embodiment of the apparatus shown in Figure 7, showing an upper reflected fifth beam and a lower reflected fifth beam being directed within the apparatus;

Figure 9 is a sectional plan view of the third embodiment of the apparatus shown in Figure 7, showing an upper transmitted fifth beam and a lower transmitted fifth beam being directed within the apparatus; Figure 10 is a sectional plan view of an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum according to a fourth embodiment of the invention, and an image capturing device; Figure 1 1 is a sectional plan view of the fourth embodiment apparatus shown in Figure 10, showing an upper reflected sixth beam and a lower reflected sixth beam being directed within the apparatus;

Figure 12 is a sectional plan view of the fourth embodiment of the apparatus shown in Figure 10, showing an upper transmitted seventh beam and a lower transmitted seventh beam being directed within the apparatus;

Figure 13 is a sectional plan view of an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum according to a fifth embodiment of the invention, and an image capturing device; and

Figure 14 is a sectional plan view of the fifth embodiment of the apparatus shown in Figure 13, showing an upper reflected eighth beam, an upper transmitted eighth beam and a lower transmitted eighth beam being directed within the apparatus.

DETAILED DESCRIPTION

An apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges for delivery to an image capturing device, comprises: first directing means for directing at least a first portion of the incident electromagnetic energy along a first path between an entrance of the apparatus and the image capturing device; first filtering means for filtering electromagnetic energy being directed along said first path; second directing means for directing at least a second portion of the incident electromagnetic energy along a second path between said entrance and the image capturing device; second filtering means for filtering electromagnetic energy being directed along said second path. Said first directing means may reflect electromagnetic energy being directed along said first path an odd number of times greater than said second directing means reflects electromagnetic energy being directed along said second path. Referring to Figures 1 to 3, the apparatus according to a first embodiment of the invention is shown in sectional view generally at 10. The apparatus 10 is operable to receive electromagnetic energy emanating from a scene or object, and produce therefrom electromagnetic energy in one or more separated beams having wavelengths in one or more distinct wavelength ranges for separated image capturing by an image capturing device, respectively.

In the first embodiment, the apparatus 10 includes a housing 12 for containing the member components of the apparatus 10. In some embodiments, the volume within the housing 12 is filled with nitrogen gas or similar, thereby reducing the likelihood of condensation within the housing 12. The housing 12 in some embodiments is permanently sealed during manufacturing. The housing 12 is preferably dimensioned to attach, including possibly removably attaching, to an image capturing device such as the camera 14 shown in Figures 1 to 3. Preferably, the apparatus 10 is attached to the camera 14 during manufacturing. However, the apparatus 10 is in some embodiments removably attachable to the camera 14. In some embodiments, some or all of the member components of the camera 14 are integrated into and form part of the apparatus 10.

Electromagnetic energy emanates toward the apparatus 10 from an object plane indicated in Figures 1 to 6 by a dashed line 16. Some of the electromagnetic energy that is incident on the apparatus 10 enters through the entrance aperture 18 of the apparatus 10. The entrance aperture 18 defines an entrance plane, such as the entrance aperture plane indicated by the dashed line 20 in Figures 1 to 6. In some embodiments, the entrance aperture 18 limits the field of view of the apparatus 10, thereby minimizing undesirable energy paths within the apparatus 10. In some embodiments, a lens (not shown) may be located in the entrance aperture plane 20 such that electromagnetic energy entering into the apparatus 10 enters through such lens, thereby permitting conditioning of incident electromagnetic energy. However, in the first embodiment where the entrance aperture 18 is implemented as a window aperture rather than a lens, the entrance aperture 18 advantageously eliminates any negative impact on quality that a lens might introduce, and advantageously lowers manufacturing costs. Preferably, the entrance aperture 18 transmits with minimal loss electromagnetic energy in the infra-red region of the electromagnetic spectrum. Some of the electromagnetic energy passing through the entrance aperture 18 into the apparatus 10 is depicted in Figure 1 as the first incident beam 22. The first incident beam 22 may be comprised of a plurality of beam rays entering the apparatus 10 within a range of entry points along the entrance aperture plane 20 at entry angles within a range of entry angles incident upon the entrance aperture plane 20, as shown in Figure 1. For ease of description, all the beam rays of the first incident beam 22 are shown in Figure 1 as being substantially parallel.

The first incident beam 22, after passing through the entrance aperture 18 into the apparatus 10, is incident upon a reflective device such as the first mirror 24. In the first embodiment, the first mirror 24 is a flat mirror that reflects electromagnetic energy, such as infrared radiation, incident upon it. Preferably, the first mirror 24 reflects substantially all of the first incident beam 22 with minimal attenuation.

In the first embodiment, the first mirror 24 is mounted within the apparatus 10 to a first mirror angle adjuster 26, which is shown in the sectional Figures 1 to 3 in dotted lines. The first mirror angle adjuster 26 advantageously permits optimization of the angle of the first mirror 24 relative to the housing 12 and, in particular, relative to the entrance aperture plane 20. In some embodiments, the first mirror 24 angle is adjusted and fixed during manufacturing, and in some embodiments the first mirror angle adjuster 26 is operable to cause first mirror 24 angle adjustment during use of the apparatus 10. In some embodiments, the first mirror angle adjuster 26 includes automatic means for adjusting the first mirror 24 angle during operation of the apparatus 10.

Some of the electromagnetic energy that is reflected from the first mirror 24 is depicted in Figure 1 in association with the first incident beam 22 as the reflected first beam 28. The reflected first beam 28 is directed toward the second mirror 30. In the first embodiment, the second mirror 30 is a flat mirror that reflects electromagnetic energy, such as infrared radiation, incident upon it. Preferably, the second mirror 30 reflects substantially all of the reflected first beam 28 with minimal attenuation. Figure 1 shows the second mirror 30 mounted directly and fixedly to the housing 12. In some embodiments, however, the apparatus 10 is operable to permit adjustment of the second mirror 30 angle relative to the housing 12, such as during manufacturing, during operation of the apparatus 10 or during manufacturing and during operation of the apparatus 10. In general, the apparatus 10 is operable in some embodiments to adjust the angle relative to the housing 12 of neither, either or both of the first and second mirrors 24 and 30.

Some of the electromagnetic energy that is reflected from the second mirror 30 is depicted in Figure 1 in association with the reflected first beam 28 as the reflected second beam 32. The reflected second beam 32 is directed toward the first filter 34.

The first filter 34 is a band pass filter for passing electromagnetic energy of a first range of wavelengths to the substantial exclusion of other electromagnetic energy. The passband of the first filter 34 may be selected to be a narrow passband, thereby making the apparatus 10 highly selective of a narrow range of wavelengths. In at least one application of embodiments of the invention, the passband of the first filter 34 is selected to pass electromagnetic energy of a wavelength in the infrared region of the electromagnetic spectrum, which infrared wavelength may be selected to correspond to the electromagnetic wavelength absorption characteristic of a predetermined gas such as sulphur hexafloride gas (SF6), methane or other gaseous hydrocarbons, for example.

Some of the electromagnetic energy that passes through the first filter 34 is depicted in Figure 1 as the filtered first beam 36, which is directed toward the camera 14. The camera 14 is preferably operable to produce images corresponding to the filtered first beam 36. In the first embodiment, the filtered first beam 36 is incident upon a camera lens 38 of the camera 14, passes through the camera lens 38 and is directed toward a first detector array 40 of the camera 14. Figure 1 shows all the beam rays of the filtered first beam 36 as incident upon the first detector array 40 at a point substantially near the center of the first detector array 40.

Still referring to Figure 1 , some of the electromagnetic energy passing through the entrance aperture 18 into the apparatus 10 is depicted in Figure 1 as the second incident beam 42. The second incident beam 42 may comprise a plurality of parallel beam rays in a manner similar to that of the first incident beam 22, but entering within a second range of entry points and within a second range of entry angles. Figure 1 shows the second incident beam 42 as incident on the apparatus 10 at substantially the same angle of incidence upon the apparatus 10 as the first incident beam 22, but passing into the apparatus 10 through different entry points along the entrance aperture plane 20. In this example, the second incident beam 42, after passing through the entrance aperture 18 into the apparatus 10, passes between the first and second mirrors 24 and 30 to impinge upon the second filter 44. Where the first and second incident beams 22 and 42 impinge upon the first and second filters 34 and 44, respectively, the first and second incident beams 22 and 42 are substantially non-overlapping. The placement of the first and second mirrors 24 and 30 advantageously limit the range of incident angles of the second incident beam 42 that arrive at the second filter 44. In some embodiments, the distance between respective edges closest to each other of the first mirror 24 and the second mirror 30 is selected to prevent electromagnetic energy having an undesirable angle of incidence at the entrance aperture 18 from arriving at the second filter 44, thereby minimizing the effect of vignetting of images produced by the camera 14.

Some of the electromagnetic energy that passes through the second filter 44 is depicted in Figure 1 as the filtered second beam 46, which is directed toward the camera 14. The filtered second beam 46 is incident upon and passes through the camera lens 38 and is directed toward the second detector array 48 of the camera 14. Figure 1 shows all the beam rays of the filtered second beam 46 as incident upon the second detector array 48 at a point substantially near the center of the second detector array 48. The camera 14 in the first embodiment is operable to capture the image detected by the second detector array 48.

While the embodiment shown in Figures 1 to 3 include the first and second detector arrays 40 and 48, the camera 14 may in general include any number of detector arrays. The detector arrays 40 and 48 are typically adjacent sections of a single camera detector, for example.

In a typical application of embodiments of the invention, the passband of either one the first filter 34 or the second filter 44 is selected to pass a narrow range of wavelengths that include the absorption wavelength corresponding to the electromagnetic wavelength absorption characteristic of a predetermined gas to the substantial exclusion of other electromagnetic energy, and the passband of the other of the first or second filter 34 or 44 is selected to correspond to a similar sized range of wavelengths that substantially exclude the absorption wavelength. In this manner, the images detected by the first and second detector arrays 40 and 48, respectively, and captured by the camera 14 can be comparatively processed to reveal the presence of the predetermined gas.

Preferably, the camera 14, the apparatus 10 or both the camera 14 and the apparatus 10 are operable to permit adjustment of the distance between the camera lens 38 and the first and second detector arrays 40 and 48, thereby adjusting focus of the camera 14. In some embodiments, the camera 14 includes a manual focus mechanism (not shown) for adjusting the distance between the camera lens 38 and the camera detector arrays 40 and 48, an automatic focus mechanism (not shown) for adjusting the distance between the camera lens 38 and the camera detector arrays 40 and 48, or both manual and automatic focus mechanisms. The camera 14 may also include in various embodiments a plurality of camera lenses 38, an electronic display (not shown), storage means (not shown) for storing images captured by the camera detector 18, a controller (not shown) for controlling operation of the camera 14, a power source (not shown), or any combination thereof.

The apparatus 10 is advantageously operable to reduce the effect of background thermal noise on image sensitivity by cooling critical components of the apparatus 10. In the first embodiment shown in Figures 1 to 3, the apparatus 10 includes a cooler 50 for cooling the first and second filters 34 and 44. The cooler 50 may be a pettier type or other thermoelectric cooling device, for example. The cooler 50 advantageously reduces the effect of background thermal noise on image sensitivity without the need for cooling the entire volume within the housing 14. Preferably, the first and second filters 34 and 44 are adjacent to each other with minimal gap between adjacent flat edges of the first and second filters 34 and 44, respectively. In general, however, each of the first and second filters 34 and 44 may have any shape, including semi-circular, rectangular, square, etc. In some embodiments, the apparatus 10 is operable to permit the first filter 34, the second filter 44 or both the first and second filters 34 and 44 to be replaced by a user, such as by including the first and second filters 34 and 44 in a replaceable cartridge (not shown). In some embodiments, such cartridge can be slid out of and into the apparatus 10 by a user during operation of the apparatus 10. Replacing the cartridge advantageously permits use of the apparatus 10 to produce images corresponding to different predetermined gases having distinct electromagnetic absorption characteristics. In some embodiments, the first and second filters 34 and 44 are incorporated into a filter wheel that, when rotated, introduces selectable filters into the first and second paths defined by the apparatus 10. Additionally or alternatively, the apparatus 10 may be operable to permit a slide tray (not shown) to be slid along a slide tray track (not shown) of the apparatus 10, thereby selecting one or more filters, such as the first and second filters 34 and 44, from a selection of filters incorporated into the slide tray.

In some embodiments, one or both of the first filter 34 and the second filter 44 is outwardly convex in the direction toward incoming electromagnetic energy impinging upon the one or both filters. For example, the first and second filters 34 and 44 may be each mounted on a meniscus-shaped substrate such that electromagnetic energy impinges upon the first and second filters 34 and 44 at substantially a normal angle of incidence, thereby improving wavelength selectivity of the first and second filters 34 and 44. In some embodiments in which replaceable filter cartridges can be used in the apparatus 10, some such cartridges may include one or more flat filters. Additionally or alternatively, cartridges that include one or more meniscus-shaped filters may be made available.

Figure 2 shows an upper first beam 52 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle nearly or substantially perpendicular to the entrance aperture plane 20. The upper first beam 52 is incident upon the first mirror 24 at a location near the upper end 54 of the first mirror 24, reflects from the first mirror 24 toward the second mirror 30, is incident upon the second mirror 30 at a location near the second mirror upper end 56 of the second mirror 30, reflects from the second mirror 30 toward the first filter 34, is incident upon the first filter 34, passes through the first filter 34 and is directed toward the camera 14 such that the upper first beam 52 is incident upon the first detector array 40 at a point near the lower extremity 58 of the first detector array 40. In the first embodiment, the apparatus 10 is advantageously dimensioned such that an upper first beam 52 ray that is incident upon the upper end 54 of the first mirror 24, incident upon the second mirror upper end 56 and passes through the first filter 34 at its upper end will be incident upon the first detector array 40 at its lowermost detection point, as can be seen in Figure 2.

Figure 2 also shows a lower first beam 60 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle relative to the upper first beam 52. The lower first beam 60 is incident upon the first mirror 24 at a location near the lower end 62 of the first mirror 24, reflects from the first mirror 24 toward the second mirror 30, is incident upon the second mirror 30 at a location near the second mirror lower end 64 of the second mirror 30, reflects from the second mirror 30 toward the first filter 34, is incident upon the first filter 34, passes through the first filter 34 and is directed toward the camera 14 such that the lower first beam 60 is incident upon the first detector array 40 at a point near the upper extremity 66 of the first detector array 40. In the first embodiment, the apparatus 10 is advantageously dimensioned such that a lower first beam 60 ray that is incident upon the lower end 62 of the first mirror 24 at a maximum angle of incidence, incident upon the second mirror lower end 64 and passes through the first filter 34 at its lower end will be incident upon the first detector array 40 at its uppermost detection point, as can be seen in Figure 2. Such maximum angle of incidence in some embodiments is determined by the placement of the lower end 62. Additionally or alternatively, such maximum angle of incidence may be determined by the location of the lower end of the entrance aperture 18, for example.

Figure 3 shows an upper second beam 68 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle nearly or substantially perpendicular to the entrance aperture plane 20. The upper second beam 68 passes between the first and second mirrors 24 and 30 adjacent the second mirror 30, and is incident upon the second filter 44, passes through the second filter 44 and is directed toward the camera 14 such that the upper second beam 68 is incident upon the second detector array 48 at a point near the second detector lower extremity 70 of the second detector array 48. In the first embodiment, the apparatus 10 is advantageously dimensioned such that an upper second beam 52 ray that passes adjacent the second mirror 30 and through the second filter 44 at its upper end will be incident upon the second detector array 48 at its lowermost detection point, as can be seen in Figure 3.

Figure 3 also shows a lower second beam 72 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle relative to the upper second beam 68. The lower second beam 72 is incident upon and passes through the second filter 44, and is directed toward the camera 14 such that the lower second beam 72 is incident upon the second detector array 48 at a point near the second detector upper extremity 74 of the second detector array 48. In the first embodiment, the apparatus 10 is advantageously dimensioned such that a tower second beam 72 ray that passes through the second filter 44 at its lower end at a maximum angle of incidence will be incident upon the second detector array 48 at its uppermost detection point, as can be seen in Figure 3.

Referring to Figures 4 to 6, the apparatus 10 according to a second embodiment of the invention is shown in sectional view. In the second embodiment, the apparatus 10 includes a wavelength selective component such as the dichroic mirror 76 shown in Figures 4 to 6. The dichroic mirror 76 is preferably operable to reflect electromagnetic energy having a wavelength in a reflection range of wavelengths and to transmit electromagnetic energy having a wavelength in a transmission range of wavelengths. Typically, the reflection and transmission ranges of wavelengths are substantially mutually exclusive ranges. For example, the dichroic mirror 76 in some embodiments reflects electromagnetic radiation having a wavelength less than a critical wavelength and transmits electromagnetic radiation having a wavelength equal to or greater than the critical wavelength. Alternatively, the dichroic mirror 76 may in some embodiments reflect electromagnetic radiation having a wavelength greater than the critical wavelength and transmit electromagnetic radiation having a wavelength equal to or less than the critical wavelength. Typically, the camera 14 is selected to include a wide passband filter for reducing the intensity of electromagnetic radiation impinging on the first and second detector arrays 40 and 48 having wavelengths significantly greater than the critical wavelength and significantly less than the critical wavelength. In this manner, the dichroic mirror 76, in conjunction with the wide passband filter of the camera 14, is operable in some embodiments to reflect electromagnetic energy such that electromagnetic energy having wavelengths in a reflection passband range of wavelengths impinges on one of the first and second detector arrays 40 and 48 to the substantial exclusion of other electromagnetic energy, and is operable to transmit electromagnetic energy such that electromagnetic energy having wavelengths in a transmission passband range of wavelengths impinges on the other of the first and second detector arrays 40 and 48 to the substantial exclusion of other electromagnetic energy.

The dichroic mirror 76 may have any suitable thickness and be mounted to the housing 12 in any suitable manner. Additionally or alternatively, the dichroic mirror 76 is supported within a block prism, for example.

The apparatus 10 in accordance with the second embodiment also includes the housing 12, camera 14 and first mirror 24. In the second embodiment, the apparatus 10 may advantageously be operable to provide cooling within the volume of the housing 12, including cooling specific member components of the apparatus 10, for reducing background thermal noise and thereby improving sensitivity. For example, the cooler 50 may be used for cooling the dichroic mirror 76, such as by providing cooling along one or more edges of the dichroic mirror 76 as shown in Figures 4 to 6. As also shown in Figures 4 to 6, the apparatus 10 in accordance with the second embodiment also may include the first mirror angle adjuster 26. The dichroic mirror 76 is preferably mounted within the housing 12 such that electromagnetic energy entering the apparatus 10 through the entrance aperture 18 is not undesirably obstructed from being transmitted through the dichroic mirror 76, as indicated in Figures 4 to 6 by dashed lines between the dichroic mirror 76 and the housing 12.

Figure 4 shows beam rays of a third incident beam 78 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The third incident beam 78 is incident upon the first mirror 24, reflects from the first mirror 24, is directed toward the dichroic mirror 76, and is incident upon the dichroic mirror 76. In the second embodiment, some of the electromagnetic energy incident upon the dichroic mirror 76 is reflected from the dichroic mirror 76 and is directed toward the camera 14, as shown in Figures 4 to 6. The portion of electromagnetic energy of the third incident beam 78 that is reflected from the dichroic mirror 76 is depicted as a reflected third beam 80 in Figure 4. The reflected third beam 80 preferably includes electromagnetic energy having wavelengths corresponding to the reflection passband of the dichroic mirror 76. The use of the dichroic mirror 76 advantageously provides wavelength selectivity without the use of a passband filter, such as the first filter 34 or the second filter 44 (Figures 1 to 3), thereby providing for a more compact multi-spectral dual imaging apparatus. In some embodiments, however, the apparatus 10 includes the dichroic mirror 76 and one or both of the first and second filters 34 and 44, thereby advantageously providing further wavelength selectivity. Electromagnetic energy of the third incident beam 78 that is transmitted through the dichroic mirror 76 (not shown in Figures 4 to 6) is advantageously not directed toward the camera lens 38 of the camera 14. The reflected third beam 80 rays are incident upon and pass through the camera lens 38, are directed toward the first detector array 40 of the camera 14, and are incident upon the first detector array 40 at a point substantially near the center of the first detector array 40, as shown in Figure 4.

Figure 4 also shows beam rays of a fourth incident beam 82 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The fourth incident beam 82 is incident upon the dichroic mirror 76. The portion of electromagnetic energy of the fourth incident beam 82 that is transmitted through the dichroic mirror 76 is depicted as a transmitted fourth beam 84 in Figure 4. The transmitted fourth beam 84 preferably includes electromagnetic energy having wavelengths corresponding to the transmission passband of the dichroic mirror 76 to the substantial exclusion of electromagnetic energy having wavelengths corresponding to the reflection passband of the dichroic mirror 76. The transmitted fourth beam 84 is directed toward and passes through the camera lens 38 to become incident upon the second detector array 48 at a point substantially near the center of the second detector array 48. Electromagnetic energy of the fourth incident beam 82 that is reflected from the dichroic mirror 76 (not shown in Figures 4 to 6) is advantageously not directed toward the camera lens 38.

Figure 5 shows an upper third beam 86 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle nearly or substantially perpendicular to the entrance aperture plane 20. As shown in Figure 5, the upper third beam 86 passes near and adjacent to the dichroic mirror 76 without passing through the dichroic mirror 76, impinges incident upon the first mirror 24 near its upper end 54, reflects from the first mirror 24, and is incident upon the dichroic mirror 76 at a location near the dichroic mirror upper end 88 of the dichroic mirror 76. Electromagnetic energy of the upper third beam 86 that reflects from the dichroic mirror 76 enters the camera 14 to become incident upon the first detector array 40 at a point substantially near the lower extremity 58. In the second embodiment, the apparatus 10 is advantageously dimensioned such that an upper third beam 86 ray that is incident upon the upper end 54 of the first mirror 24 and the dichroic mirror upper end 88 will be incident upon the first detector array 40 at its lowermost detection point, as can be seen in Figure 5.

Figure 5 also shows a lower third beam 90 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle relative to the upper third beam 86. The lower third beam 90 is incident upon the first mirror 24 at or near its lower end 62, reflects from the first mirror 24, is incident upon the dichroic mirror 76 at a location closer to its dichroic mirror lower end 92 than is the point of incidence for the upper third beam 86. Electromagnetic energy of the lower third beam 90 that reflects from the dichroic mirror 76 enters the camera 14 to become incident upon the first detector array 40 at a point substantially near the upper extremity 66 of the first detector array 40. In the second embodiment, the apparatus 10 is advantageously dimensioned such that a lower third beam 90 ray that is incident upon the lower end 62 of the first mirror 24 at a maximum angle of incidence permitted by the entrance aperture 18 will be incident upon the first detector array 40 at its uppermost detection point, as can be seen in Figure 5.

Figure 6 shows an upper fourth beam 94 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle nearly or substantially perpendicular to the entrance aperture plane 20, as permitted by the upper end of the entrance aperture 18. Electromagnetic energy of the upper fourth beam 94 that passes through the dichroic mirror 76 enters the camera 14 to become incident upon the second detector array 48 at a point substantially near the second detector lower extremity 70. In the second embodiment, the apparatus 10 is advantageously dimensioned such that an upper fourth beam 94 ray that is incident upon the dichroic mirror 76 at a maximum angle permitted by the upper end of the entrance aperture 18 will be incident upon the first detector array 40 at its lowermost detection point, as can be seen in Figure 6. Figure 6 also shows a lower fourth beam 96 having beam rays emanating from the object plane 16 toward the apparatus 10 at an angle relative to that of the upper fourth beam 94. At least some of the electromagnetic energy of the lower fourth beam 96 that passes through the dichroic mirror 76 enters the camera 14 to become incident upon the second detector array 48 at a point substantially near the second detector upper extremity 74. In the second embodiment, the apparatus 10 is advantageously dimensioned such that a lower fourth beam 96 ray that is incident upon the dichroic mirror 76 at a maximum angle determined by the relative locations and dimensions of the dichroic mirror 76, camera lens 38 and second detector array 48 will be incident upon the second detector array 48 at its uppermost detection point, as can be seen in Figure 6.

The apparatus 10 is preferably operable to limit the range of entry points and entry angles of incident electromagnetic energy that will follow a first path from the entrance aperture 18 to the first detector array 40 and will follow a second path from the entrance aperture 18 to the second detector array 48, as shown in Figures 1 to 6. In some embodiments, the first and second ranges of entry points along the entrance aperture plane 20 are substantially non- overlapping, and the first and second ranges of entry angles incident upon the entrance aperture 18 are substantially overlapping. The dimensions of the apparatus 10 advantageously minimize the amount of electromagnetic energy having entered into the apparatus 10 within the first entry point range and within the first entry angle range that follow a path to the second detector array 48 and advantageously minimize the amount of electromagnetic energy having entered into the apparatus 10 within the second entry point range and within the second entry angle range that follow a path to the first detector array 40.

Referring to Figures 7 to 9, the apparatus 10 according to a third embodiment of the invention is shown in sectional view. In the third embodiment, the apparatus 10 includes the housing 12, camera 14, dichroic mirror 76 and first mirror 24 and may include the first mirror angle adjuster 26 and the cooler 50 as shown in Figures 7 to 9.

Figure 7 shows beam rays of a fifth incident beam 98 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The fifth incident beam 98 is incident upon the dichroic mirror 76.

The portion of the electromagnetic energy in the fifth incident beam 98 having wavelengths within the reflection passband of the dichroic mirror 76 is reflected from the dichroic mirror 76 toward the first mirror 24 as a reflected fifth beam 100. The reflected fifth beam 100 is reflected by the first mirror 24 toward the camera lens 38. The reflected fifth beam 100 passes through the camera lens 38 and is directed toward and becomes incident upon the second detector array 48 at a point substantially near the center of the second detector array 48.

The portion of the electromagnetic energy in the fifth incident beam 98 having wavelengths within the transmission passband of the dichroic mirror 76 passes through the dichroic mirror 76 toward the camera lens 38 as a transmitted fifth beam 102 The transmitted fifth beam 102 passes through the camera lens 38 and is directed toward and becomes incident upon the first detector array 40 at a point substantially near the center of the first detector array 40 Figure 8 shows upper and lower reflected fifth beams 104 and 106 reflected from the dichroic mirror 76 toward the first mirror 24, reflected from the first mirror 24 toward the camera lens 38, passing through the camera lens 38 and impinging upon the second detector array 48 at lower and upper extremities thereof, respectively Figure 9 shows upper and lower transmitted fifth beams 108 and 1 10 transmitted through the dichroic mirror 76 toward the camera lens 38, passing through the camera lens 38 and impinging upon the first detector array 40 at lower and upper extremities thereof, respectively

Still referring to Figures 7 to 9, the dichroic mirror 76 is preferably mounted within the housing 12 such that electromagnetic energy entering the apparatus 10 through the entrance aperture 18 is not undesirably obstructed from being transmitted through or reflected from the dichroic mirror 76, as indicated in Figures 7 to 9 by dashed lines between the dichroic mirror 76 and the housing 12 In some embodiments, the apparatus 10 includes a first field stop (not shown) located between the first mirror 24 and the camera lens 38 defining an aperture through which the reflected fifth beam 100, upper reflected fifth beam 104 and lower reflected fifth beam 106 can pass, while inhibiting electromagnetic energy beams not reflected from the first mirror 24 from being incident upon the camera lens 38 Similarly, the apparatus 10 includes in some embodiments a second field stop (not shown) located between the dichroic mirror 76 and the camera lens 38 defining an aperture through which the transmitted fifth beam 102 can pass, while inhibiting electromagnetic energy beams not transmitted through the dichroic mirror 76 from being incident upon the camera lens 38 In a variation, the apparatus 10 may include a third field stop (not shown) located between the camera lens 38 and the first mirror 24 and dichroic mirror 76 defining an aperture through which electromagnetic energy beams emanating from the first mirror 24 and the dichroic mirror 76 toward the camera lens 38 can pass. In general, the apparatus 10 may include any of the first, second and third field stops. When included, the first, second and third field stops may be mounted to the housing 12, for example. Additionally or alternatively, the first field stop may be mounted to the first mirror 24, including being integrally mounted thereon, and the second field stop may be mounted to the dichroic mirror 76, including being integrally mounted thereon. By way of further example, any one or more of the first field stop, second field stop, third field stop, mounting hardware (not shown) for the first mirror 24 and mounting hardware (not shown) for the dichroic mirror 76 may be integrally formed within the housing 12.

The third embodiment advantageously minimizes the number of optical components required to produce, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges for delivery to an image capturing device, thereby permitting the apparatus 10 to have compact dimensions. Furthermore, the third embodiment minimizes the difference in path length between the separate paths travelled by the separated beams of wavelength distinct electromagnetic energy, thereby minimizing magnification errors of the apparatus 10.

Parallax error is advantageously minimized by the geometric arrangement of components and dimensions thereof of the third embodiment. More generally, embodiments of the invention including the third embodiment in which electromagnetic energy beams entering the apparatus 10 through the entrance aperture 18 first impinge upon a wavelength selective component, such as the dichroic mirror 76, permit a reduction of parallax error through appropriate geometric arrangement of components and dimensions thereof, such as the geometric arrangement of components and dimensions shown in Figures 7 to 9. Referring to Figures 10 to 12, the apparatus 10 according to a fourth embodiment of the invention is shown in sectional view. In the fourth embodiment, the apparatus 10 includes the housing 12, camera 14, dichroic mirror 76, first mirror 24 and second mirror 30. The apparatus 10 also includes in the fourth embodiment a second dichroic mirror 1 12 and may include the cooler 50 as shown in Figures 10 to 12. Either or both of the first and second mirrors 24 and 30 may be mounted within the housing 12 such that angle adjustment is permitted. By way of example, Figures 10 to 12 show the first mirror 24 fixedly mounted to the housing 12 and the second mirror 30 adjustably mounted to the housing 12 via a second mirror angle adjuster 114. The second mirror angle adjuster 1 14 may be identical, similar or different from the first mirror angle adjuster 26 (Figures 1 to 9).

Figure 10 shows beam rays of a sixth incident beam 1 16 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The sixth incident beam 116 is incident upon the dichroic mirror 76. The portion of the electromagnetic energy in the sixth incident beam 1 16 having wavelengths within the reflection passband of the dichroic mirror 76 is reflected from the dichroic mirror 76 toward the first mirror 24 as a reflected sixth beam 1 18. The reflected sixth beam 1 18 is reflected by the first mirror 24 toward the second mirror 30, impinges upon the second mirror 30 and is reflected from the second mirror 30 toward the second dichroic mirror 1 12, and is incident upon the second dichroic mirror 112. Due to the reflection from the dichroic mirror 76, the reflected sixth beam 118 is formed of electromagnetic energy having wavelengths substantially within the reflection passband of the dichroic mirror 76. Preferably, the dichroic mirror 76 and the second dichroic mirror 1 12 have substantially the same reflection passbands such that substantially all of the reflected sixth beam 1 18 is reflected from the second dichroic mirror 1 12 toward the camera lens 38. The reflected sixth beam 1 18 passes through the camera lens 38 and is directed toward and becomes incident upon the first detector array 40 at a point substantially near the center of the first detector array 40.

Figure 10 also shows beam rays of a seventh incident beam 120 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The seventh incident beam 120 is incident upon the dichroic mirror 76. The portion of the electromagnetic energy in the seventh incident beam 120 having wavelengths within the transmission passband of the dichroic mirror 76 passes through the dichroic mirror 76 toward the second dichroic mirror 1 12 as a transmitted seventh beam 122. The transmitted seventh beam 122 is incident upon the second dichroic mirror 1 12. Due to the transmission through the dichroic mirror 76, the transmitted seventh beam 122 is formed of electromagnetic energy having wavelengths substantially within the transmission passband of the dichroic mirror 76. In the fourth embodiment in which the dichroic mirror 76 and the second dichroic mirror 112 have substantially the same transmissions passbands, substantially all of the transmitted seventh beam 122 passes through the second dichroic mirror 112 toward the camera lens 38. The transmitted seventh beam 122 passes through the camera lens 38 and is directed toward and becomes incident upon the second detector array 48 at a point substantially near the center of the second detector array 48.

Figure 11 shows upper and lower reflected sixth beams 124 and 126 reflected from the dichroic mirror 76 toward the first mirror 24, reflected from the first mirror 24 toward the second mirror 30, reflected from the second mirror 30 toward the dichroic mirror 1 12, reflected from the second dichroic mirror 1 12 toward the camera lens 38, passing through the camera lens 38 and impinging upon the first detector array 40 at lower and upper extremities thereof, respectively.

Figure 12 shows upper and lower transmitted seventh beams 128 and 130 being transmitted through the dichroic mirror 76 toward the second dichroic mirror 1 12, transmitted through the second dichroic mirror 1 12 toward the camera lens 38, passing through the camera lens 38 and impinging upon the second detector array 48 at lower and upper extremities thereof, respectively. The fourth embodiment advantageously provides flexibility of geometric placement of the first and second dichroic mirrors 76 and 1 12 and the first and second mirrors 24 and 30 such that parallax error can be significantly reduced by appropriate placement of components within the apparatus 10 and dimensions thereof, such as shown in Figures 10 to 12.

Still referring to Figures 10 to 12, the dichroic mirror 76 and the second dichroic mirror 1 12 are preferably mounted within the housing 12 such that electromagnetic energy entering the apparatus 10 through the entrance aperture 18 is not undesirably obstructed from being transmitted through or reflected from the dichroic mirror 76, as indicated in Figures 10 to 12 by dashed lines between the housing 12 and the dichroic mirror 76 and second dichroic mirror 112, respectively. In some embodiments, the apparatus 10 includes a first field stop (not shown) located between the first mirror 24 and the second mirror 30 defining an aperture through which the reflected sixth beam 118, upper reflected sixth beam 124 and lower reflected sixth beam 126 can pass, while inhibiting electromagnetic energy beams not reflected from the first mirror 24 from being incident upon the second mirror 30. Similarly, the apparatus 10 includes in some embodiments a second field stop (not shown) located between the dichroic mirror 76 and the second dichroic mirror 1 12 defining an aperture through which the transmitted seventh beam 122 can pass, while inhibiting electromagnetic energy beams not transmitted through the dichroic mirror 76 from being incident upon the second dichroic mirror 112. In general, the apparatus 10 may include either, both or neither of the first and second field stops. When included, the first and second field stops may be mounted to the housing 12, for example. Additionally or alternatively, the first field stop may be mounted to one or both of the first and second mirrors 24 and 30, including being integrally mounted thereon, and the second field stop may be mounted to one or both of the dichroic mirror 76 and the second dichroic mirror 1 12, including being integrally mounted thereon. By way of further example, any one or more of the first field stop, second field stop, mounting hardware (not shown) for the first mirror 24, mounting hardware (not shown) for the second mirror 30, mounting hardware (not shown) for the dichroic mirror 76 and mounting hardware (not shown) for the second dichroic mirror 112 may be integrally formed within the housing 12.

Referring to Figures 13 and 14, the apparatus 10 according to a fifth embodiment of the invention is shown in sectional view. In the fifth embodiment, the apparatus 10 includes the housing 12, camera 14, dichroic mirror 76, first mirror 24, second mirror 30. The apparatus 10 in the fifth embodiment may also include mirror angle adjustment means, such as the first mirror angle adjuster 26, for any one or more of the first mirror 24, second mirror 30 and the dichroic mirror 76. The apparatus 10 may also include the cooler 50 as shown in Figures 13 and 14.

Figure 13 shows beam rays of an eighth incident beam 132 emanating from the object plane 16 toward the apparatus 10, and passing through the entrance aperture 18 into the apparatus 10. The eighth incident beam 132 is incident upon the dichroic mirror 76. The portion of the electromagnetic energy in the eighth incident beam 132 having wavelengths within the reflection passband of the dichroic mirror 76 is reflected from the dichroic mirror 76 toward the first mirror 24 as a reflected eighth beam 134. The reflected eighth beam 134 is reflected by the first mirror 24 toward the second mirror 30, then reflected by the second mirror 30 toward the camera lens 38. The reflected eighth beam 134 passes through the camera lens 38 and is directed toward and becomes incident upon the second detector array 48 at a point substantially near the center of the second detector array 48. The portion of the electromagnetic energy in the eighth incident beam 132 having wavelengths within the transmission passband of the dichroic mirror 76 passes through the dichroic mirror 76 toward the camera lens 38 as a transmitted eighth beam 136. The transmitted eighth beam 136 passes through the camera lens 38 and is directed toward and becomes incident upon the first detector array 40 at a point substantially near the center of the first detector array 40. Figure 14 shows an upper reflected eighth beam 138 reflected from the dichroic mirror 76 toward the first mirror 24, reflected from the first mirror 24 toward the second mirror 30, reflected from the second mirror 30 toward the camera lens 38, passing through the camera lens 38 and impinging upon the second detector array 48 at an upper extremity thereof. The upper reflected eighth beam 138 is reflected three times on its path between the entrance aperture 18 and the camera lens 38 and, thus, is reflected three times on its path between the entrance aperture 18 and the first detector array 40.

Figure 14 also shows upper and lower transmitted eighth beams 140 and 142 transmitted through the dichroic mirror 76 toward the camera lens 38, passing through the camera lens 38 and impinging upon the first detector array 40 at lower and upper extremities thereof, respectively.

The dichroic mirror 76 is preferably mounted within the housing 12 such that electromagnetic energy entering the apparatus 10 through the entrance aperture 18 is not undesirably obstructed from being transmitted through or reflected from the dichroic mirror 76, as indicated in Figures 13 and 14 by dashed lines between the dichroic mirror 76 and the housing 12. Additional field stops (not shown), such as a field stop located between the first mirror 24 and the second mirror 30 or following the dichroic mirror 76, for example, may be used in a manner described herein. The fifth embodiment advantageously provides greater flexibility of geometric placement of the first and second mirrors 24 and 30 such that parallax error can be significantly reduced by appropriate placement of components within the apparatus 10 and dimensions thereof, such as shown in Figures 13 to 14. Simulation studies of the fifth embodiment using dimensions scaled to those shown in Figures 13 and 14 have produced results indicating no or negligible parallax error associated with the reflected eighth beam 134 and the transmitted eighth beam 136, and minimal parallax error associated with the upper reflected eighth beam 138 and the upper transmitted eighth beam 140. As shown in Figures 13 and 14, a beam of electromagnetic energy that is reflected by the dichroic mirror 76 on its path between the entrance aperture 18 and a detector array of the camera 14 is reflected a total of three times. A beam of electromagnetic energy that is transmitted through the dichroic mirror 76 on its path between the entrance aperture 18 and a detector array of the camera 14 is not reflected on such path. In the eighth embodiment, dichroic mirror 76 reflected beams are reflected three times more than dichroic mirror 76 transmitted beams. Reflecting dichroic mirror 76 reflected beams an odd number of times greater than the number of reflections for dichroic mirror 76 transmitted beams advantageously permits respective images associated with the dichroic mirror 76 reflected beams and the dichroic mirror 76 transmitted beams to become mirror imaged relative to each other at the first and second detector arrays 40 and 48 of the camera 14. Causing respective images associated with electromagnetic energy beams impinging on the first and second detector arrays 40 and 48 to be mirror-imaged relative to each other advantageously permits cancellation of image distortion due to non-uniformity of beam intensity across each detector array of the camera 14, such as in the case of vignetting for example, by subtracting one image from the other image after detection by the detector arrays of the camera 14. Such subtraction of images can be performed by digital computation, for example. In some embodiments, the apparatus 10 is operable to direct beams of electromagnetic energy between the entrance aperture 18 and the first detector array 40 along a first path and to direct beams of electromagnetic energy between the entrance aperture 18 and the second detector array 48 along a second path such that the respective path lengths of the first and second paths are substantially similar, thereby advantageously minimizing differences in path length of the respective beams impinging on the first and second detector 40 and 48. For example, in a variation of the fifth embodiment with reference to Figures 13 and 14, additional reflective mirrors, such as mirrors similar to the first mirror 24 or the second mirror 30, may be introduced into the path of the transmitted eighth beam 136 between the dichroic mirror 76 and the camera 14 such that the path length of the path travelled by the transmitted eighth beam 136 becomes the same length as that of the reflected eighth beam 134. By way of particular examples, an even number of mirrors, such as two or four mirrors, may be introduced into the transmitted eighth beam 136 path such that the odd number of difference in reflections of the reflected eighth beam 134 and the transmitted eighth beam 136 is preserved. Alternatively, an odd number of mirrors, such as three mirrors, may be introduced.

Where an odd number of mirrors, such as three mirrors, are introduced into the path of the electromagnetic energy beams transmitted through the dichroic mirror 76, an odd number of mirrors can be used in the path of the electromagnetic energy beams reflected from the dichroic mirror 76, such as one mirror 24 (Figures 7 to 9 for example) or three mirrors (not shown), thereby preserving the mirror-imaging of respective images associated with electromagnetic energy beams impinging on the first and second detector arrays 40 and 48 while minimizing the difference in path lengths between the respective beams impinging on the first and second detector arrays 40 and 48.

Where an even number of mirrors, such as two mirrors, are introduced into the path of the electromagnetic energy beams transmitted through the dichroic mirror 76, an even number of mirrors can be used in the path of the electromagnetic energy beams reflected from the dichroic mirror 76, such as the first and second mirrors 24 and 30 (Figures 13 and 14 for example), thereby preserving the mirror-imaging of respective images associated with electromagnetic energy beams impinging on the first and second detector arrays 40 and 48 while minimizing the difference in path lengths between the respective beams impinging on the first and second detector arrays 40 and 48.

Minimizing the difference in path lengths between the respective beams impinging on the first detector array 40 and the second detector array 48 advantageously minimizes differences in magnification of images associated with such respective beams.

In some embodiments, the apparatus 10 includes a notch filter (not shown) to reduce the intensity of electromagnetic energy impinging on the first and second detector arrays 40 and 48 having wavelengths between the desired first passband and the desired second passband. The first desired passband may be the passband of one of the first filter 34 or the second filter 44, or one of the reflection passband or the transmission passband of the dichroic mirror 76, for example. Similarly, the second desired passband may be the other of the first or second filters 34 or 44, or the other of the reflection or transmission passband of the dichroic mirror 76, for example. In some embodiments, the notch filter is constructed from a highpass edge filter and a lowpass edge filter such that the cutoff wavelength of the lowpass filter is higher than the cutoff wavelength of the highpass filter. In general, the notch filter may be appropriately located anywhere between the entrance aperture 18 and the first and second detector arrays 40 and 48. In a variation of the fifth embodiment, a notch filter may be located between the camera lens 38 and the dichroic mirror 76 and first and second mirrors 24 and 30, for example.

Thus, there is provided an apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges for delivery to an image capturing device, the apparatus being operable to direct a first beam of electromagnetic energy having a first wavelength between an entrance of the apparatus and the image capturing device along a first path and to direct a second beam of electromagnetic energy having a second wavelength distinct from the first wavelength between the entrance and the image capturing device along a second path such that the image capturing device is enabled to capture images associated with the first beam by a first detector of the image capturing device and is enabled to capture images associated with the second beam by a second detector of the image capturing device. The apparatus may be operable to cause the first beam to be reflected along the first path an odd number of times greater than the number of times the second beam is reflected along the second path. The first path may have a first path length and the second path may have a second path length substantially equal to the first path length. While embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only. The invention may include variants not described or illustrated herein in detail. For example, embodiments other than the first embodiment, including the second embodiment, may be varied by replacing the dichroic mirror with a beam splitting device such as 50/50 mirror that is not wave selective and introducing the first and second filters as described in respect of the first embodiment. By way of further example, the first mirror angle adjuster 26 may be used with any one or more of the mirrors, including dichroic mirrors, of the embodiments described herein. By way of further example, housing 12 may have an orientation relative to the camera 14 suitable for portrait display of images, landscape display of images, or any combination thereof. Thus, the embodiments described and illustrated herein should not be considered to limit the invention as construed in accordance with the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for producing, from incident electromagnetic energy, a plurality of separated beams of electromagnetic energy respectively associated with distinct wavelength ranges of the electromagnetic spectrum for delivery to an image capturing device, the apparatus comprising:

(a) a first filter for producing a first filtered beam by filtering electromagnetic energy of the incident electromagnetic energy having entered into the apparatus by passing within a first entry point range of entry points along an entrance plane of the apparatus within a first entry angle range of entry angles incident upon the entrance plane to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus; and

(b) a second filter for producing a second filtered beam by filtering electromagnetic energy of the incident electromagnetic energy having entered into the apparatus by passing within a second entry point range of the entry points within a second entry angle range of the entry angles to the substantial exclusion of electromagnetic energy having otherwise entered into apparatus.