(12) United States Patent
`Duncan et al.
`
`USOO6215597B1
`(10) Patent No.:
`US 6,215,597 B1
`(45) Date of Patent:
`Apr. 10, 2001
`
`(54) APPARATUS FOR FORMING A PLURALITY
`OF SUBIMAGES HAVING DIFFERENT
`CHARACTERISTICS
`
`(75) Inventors: David B. Duncan, Auburn; Gregory J.
`Leeson, Colfax; Judith G. Duncan,
`Auburn, all of CA (US)
`
`(73) ASSignee: Duncan Technologies, Inc., Auburn,
`CA (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/441,825
`(22) Filed:
`Nov. 17, 1999
`(51) Int. Cl." ................................................. GO2B 27/14
`(52) U.S. Cl. ............................................. 359/637; 359/634
`(58) Field of Search ..................................... 359/618, 634,
`359/640, 637
`
`(56)
`
`4,084, 180
`
`References Cited
`U.S. PATENT DOCUMENTS
`4/1978 Stoffels et al. ......................... 358/55
`
`4,444,472
`4,789,891
`4,916,529
`5,134,468
`5,221,964
`5,760,969
`2
`- -2
`5,870,228
`5,889,555
`
`4/1984 Tanaka ................................. 359/676
`12/1988 Kanayama et al. .................... 358/55
`4/1990 Yamamoto et al. ................... 358/50
`7/1992 Ohmuro ................................. 358/50
`6/1993 Chamberlain et al. .............. 358/229
`6/1998 Suzuki
`359/688
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`uzu I
`2/1999 Kreitzer et al. ...................... 359/649
`3/1999 Kawase et al. ...................... 348/336
`
`Primary Examiner-Ricky Mack
`(74) Attorney, Agent, or Firm Thomas R. Lampe
`(57)
`ABSTRACT
`
`Apparatus for forming multiple Subimages including an
`image forming lens, a color Separating prism, Subimage
`receptors for receiving Subimages from the prism, and lenses
`compensating for spherical aberrations caused by the prism
`and controlling the size of the SubimageS reaching the
`Subimage receptors. Other features include Structure for
`dissipating heat from the subimage receptors and from
`circuit boards associated with the Subimage receptorS.
`
`35 Claims, 11 Drawing Sheets
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`72
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`72
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`50
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`52-56-46
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`44
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`54 -1 56
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`5 3
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`68
`SSSSS
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`1
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`Apr. 10, 2001
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`Sheet 1 of 11
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`Apr. 10, 2001
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`Sheet 2 of 11
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`FIG. 2
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`48
`66
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`52
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`72
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`it I
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`44
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`54
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`56
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`Apr. 10, 2001
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`Sheet 3 of 11
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`US 6,215,597 B1
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`
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`a 14444444 ya442 A4444444 ZAZZAZ2AYYYZ
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`Sheet 4 of 11
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`FIG. 4
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`Apr. 10, 2001
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`Sheet S of 11
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`FIG. 6
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`108
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`102
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`60
`101
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`104
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`106
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`Apr. 10, 2001
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`Sheet 6 of 11
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`|-
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`800
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`I
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`700
`600
`Wavelength (nanometers)
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`100%
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`500
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`Wavelength (nanometers)
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`Sheet 8 of 11
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`FIG. 10
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`Sheet 9 of 11
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`RED
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`FIG. 11
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`NEAR INFRARED
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`VISIBLE (GREEN, BLUE)
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`FIG. 12
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`140
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`FIG. 13
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`VISIBLE
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`Sheet 10 of 11
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`FIG 14
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`FIG 15
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`64
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`60
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`Sheet 11 of 11
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`FIG 16
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`FIG 17
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`US 6,215,597 B1
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`1
`APPARATUS FOR FORMING A PLURALITY
`OF SUBIMAGES HAVING DIFFERENT
`CHARACTERISTICS
`
`TECHNICAL FIELD
`This invention related to apparatus for forming Subimages
`from a primary image. The invention is particularly appli
`cable to camera Systems for forming multispectral images.
`
`BACKGROUND OF THE INVENTION
`In recent years, multispectral imaging has been demon
`Strated to be a useful method of evaluating features of plants,
`identifying defects in produce, or providing feature identi
`fication of other materials. Such as plastics and wood. Prism
`based multispectral cameras use a color Separating prism to
`Split an image into multiple images, each in a specific
`Spectral band. The Spectral bands can be in the ultraViolet,
`Visible, and near infrared Spectral regions. For plant
`imaging, color-infrared imaging is commonly utilized with
`imaging bands in the green, red, and near infrared regions.
`Satellite based systems are often used for this type of
`imaging in remote Sensing applications. The French-built
`SPOT Satellite acquires images in the green, red, and near
`infrared bands. The U.S.-built LANDSAT satellite acquires
`images in four spectral bands (blue, green, red, and near
`infrared). In many cases, terrestrial multispectral imaging
`has been accomplished using clusters of cameras, each
`filtered for a Specific spectral region. These cluster cameras
`have proven difficult to align and maintain. Alternatively,
`multispectral imaging can be accomplished by using a
`common objective lens and a color Separating prism to
`Separate spectral bands. The primary applications for mul
`tispectral imaging require a rugged camera not affected by
`temperature and Vibration. Applications include aerial
`imaging, produce Sorting, and advanced Surveillance.
`Color Separating prisms and lenses Specifically designed
`to work with these color Separating prisms are used exten
`Sively in electronic news gathering (ENG) cameras. Many
`color Separating prisms have been developed and patented.
`A common color Separating prism geometry is described in
`U.S. Pat. No. 4,084,180, issued Apr. 11, 1978. The dichroic
`image Separating coatings can be Selected to Separate Spec
`tral image channels throughout the ultraViolet, visible, and
`near infrared spectra.
`The color Separating prism introduces Spherical aberra
`tions and chromatic aberrations in the resulting images.
`Lenses designed Specifically to be used with color Separating
`prisms are described, for example in U.S. Pat. No. 5,760,
`969, issued Jun. 2, 1998. The color separating prism over
`corrects Spherical aberration. To compensate for this effect,
`lenses for use with these prisms are designed to under
`correct Spherical aberration thereby causing the two effects
`to cancel each other. Similarly these lenses are designed to
`compensate for longitudinal chromatic aberrations intro
`duced by the prism glass material.
`Commercial ENG lenses are corrected for chromatic
`aberrations in the visible Spectral region. Outside of the
`Visible Spectral region commercial ENG lenses commonly
`exhibit longitudinal chromatic aberrations that result in a
`shift of the focal plane location and differences in the size of
`the resulting imageS as a function of wavelength. In addition
`many ENG lenses are highly absorptive in the near infrared
`rendering them ineffective for multispectral imaging, So
`either a custom lens or a commercial lens with a long back
`focal length adapted for use with a multispectral color
`Separating prism is required.
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`Lenses for use with Single Lens Reflex (SLR) cameras are
`designed with a long flange focal length to accommodate the
`pentaprism view finder. These SLR lenses are not designed
`to correct for prism induced aberrations so the use of SLR
`lenses with color Separating prisms results in undesirable
`aberrations. However SLR lenses have a flange focal length
`adequate to physically accommodate a color Separating
`prism between the lens and image plane. Similarly mid and
`large format Still camera lenses have long flange focal
`lengths but are not designed to compensate for the presence
`of a color Separating prism.
`Multispectral imaging is best accomplished when the
`images acquired by each channel's image Sensing device are
`identical in size. It is desirable that the image Sensing pixels
`in each image channel See exactly the Same geometric region
`in the field-of-view So that the images are exactly registered.
`Achromat ENG lenses and color Separating prisms provide
`good image registration in the visible portion of the Spec
`trum but exact image registration is not feasible over a broad
`Spectral range that spans beyond the Visible region.
`In existing 3-CCD cameras, the imaging array is bonded
`directly to the prism. U.S. Pat. No. 4,916,529, issued Apr.
`10, 1990, describes a 3-CCD color separating prism. In this
`type of configuration, the thickness of the trim filters must
`be very exactly controlled and, once bonded, cannot be
`interchanged. For Specific applications, i.e., primary color
`(red, green blue) imaging this is acceptable. Multispectral
`imaging often requires trim filterS Specific for the applica
`tion. Commercial bandpass filters used for trim filters in
`multispectral cameras often do not have accurately con
`trolled thickness.
`In existing 3-CCD cameras, the thermal waste heat from
`the imaging Sensors and electronics is conducted into the
`color Separating prism. Temperature gradients in the prism
`can cause image distortion and stresses in the bond joints.
`The glass prism is a poor thermal conductor So the imaging
`array temperature is often elevated Significantly above ambi
`ent. Imaging arrays generally have a doubling in noise for
`every 10 C. rise in temperature. Linear arrays operate at
`high pixel clock rates, have large photoSite areas, and large
`pixel counts that result in particularly high heat dissipation.
`Existing cameras dissipate thermal waste heat via free
`convection using a perforated camera case or by forced
`convection using a fan. Both of these approaches provide a
`direct path for dirt to enter the camera electronics and optics,
`exposing the camera components to contaminates. U.S. Pat.
`No. 5,221,964, issued Jun. 22, 1993, shows printed circuit
`boards mounted on Standoffs, with no good thermal con
`duction path to the outside environment.
`The following patents are also of Some degree of rel
`evance: U.S. Pat. No. 4,444,472, issued April, 1984, U.S.
`Pat. No. 4,789,891, issued December, 1988, U.S. Pat. No.
`5,134,468, issued July, 1992, U.S. Pat. No. 5,870,228, issued
`February, 1999, and U.S. Pat. No. 5,889,555, issued March,
`1999.
`The patents do not teach or Suggest the invention dis
`closed and claimed herein.
`DISCLOSURE OF INVENTION
`The present invention Satisfies the foregoing need to
`correct for aberrations and image Size in camera optics for
`multispectral cameras with color Separating prisms. It pro
`vides a means of positioning Said optics relative to image
`Sensors and a means of preventing heat from the image
`Sensor and electronics from affecting the optics.
`According to one aspect of the invention, a lens with
`positive focal length is placed between a SLR camera lens
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`4
`cal interconnection between the Support boards and addi
`tional mechanical Support. Thermal conduction cooling of
`the Support boards reduces convective heating of the image
`SCSOS.
`Other features, advantages, and objects of the present
`invention will become apparent with reference to the fol
`lowing description and accompanying drawings.
`
`3
`and a color Separating prism to introduce Spherical aberra
`tions at least partially compensating for Spherical aberrations
`caused by the presence of a color Separating prism. Lenses
`with negative focal length are placed in between each
`imaging detector or Subimage receptor and the color Sepa
`rating prism. ImageSize for each channel is controlled by the
`spacings between the negative focal length lens, color Sepa
`rating prism and Subimage receptor. The power of the
`negative focal length lens can be identical for each imaging
`channel and image Size controlled only by Spacing, or the
`focal length can be different for each lens, allowing image
`Size to be controlled by a combination of lens power and
`Spacing.
`According to another aspect of the invention, one or more
`Surfaces of the positive focal length lens and one or more
`Surfaces of the negative focal length lens can be aspheric, the
`aspheric Surfaces used to correct for distortion introduced by
`the compensating lenses.
`According to another aspect of the invention, a multi
`element lens in front of the color Separating prism and a lens
`in between the color Separating prism and image Sensor or
`receptor for each optical channel is used to adjust image
`size. The image size adjusting lenses can be either positive
`or negative focal length lenses depending upon the multi
`element lens design. This multi-element lens and color
`Separating prism combination provides wide angle (>60
`degree) field-of-view with distortion under 0.05% and exact
`registration of pixels throughout the image field.
`According to another aspect of the invention, the Spacings
`between the imaging Sensors and color Separating prism are
`adjustable, allowing trim filters of various thicknesses to be
`installed and then the imaging Sensor adjusted for optimum
`focus. This removability and adjustability feature allows
`interchange of trim filters without damaging the color Sepa
`rating prism or image Sensors.
`According to another aspect of the invention, the trim
`filters can be bonded to the prism. A compensating lens
`between the prism and array is used to correct for aberrations
`caused by the prism and to adjust image size.
`According to another aspect of the invention, the image
`Sensor is mounted to a low thermal expansion holder which
`is also a poor conductor of heat. Heat dissipated by the
`image Sensors is shunted away from the prisms and optics
`using a high thermal conductivity member, dissipating the
`heat into the camera baseplate rather than into the color
`Separating prism.
`According to another aspect of the invention, pairs of
`plates with flat Surfaces parallel to the prism exit Surfaces are
`used to position the arrays relative to the prism, adjustment
`providing accurate registration between the pixels in the
`imaging arrayS. Shims are used to provide axial positioning
`of the arrays for focus adjustment.
`According to another aspect of the invention, the image
`Sensor can be either an area array Sensor composed of a two
`dimensional matrix of photoSites or a linear array composed
`of 1-3 rows of photoSites. The image Sensors in the various
`Spectral channels do not need to be identical in pixel pitch
`and can be of a mixed sensor technology (CMOS, CCD,
`inGaAs, etc.). The compensating optics are used to Scale the
`image sizes to match the image Sensor providing an exact
`correspondence of pixel location between the image spectral
`channels or a numerical multiple spacing.
`According to another aspect of the invention, the camera
`electronics printed circuit boards are conductively cooled
`using a wedge type retainer to hold the boards in Slots in a
`heat dissipating base plate. A motherboard provides electri
`
`BRIEF DESCRIPTION OF DRAWINGS
`FIG. 1 is a diagrammatic side elevation view of a multi
`Spectral prism based optical assembly for an SLR or large
`format lens;
`FIG. 2 is a diagrammatic side, partial Sectional view
`showing the compensating optics of the camera mounted
`adjacent to the color Separating prism and the mounting
`System for the optical components,
`FIG. 3 is a diagrammatic top, partial Sectional view
`showing the prism and imaging array mounting rails, a prism
`retainer, and thermal shunt bar;
`FIG. 4 is a diagrammatic illustration of mounting features
`for a compensating lens and array;
`FIG. 5 is a diagrammatic illustration of mounting features
`for a compensating lens mounted in front of a trim filter;
`FIG. 6 is a simplified plan View of an imaging array of the
`invention bonded to an array mount;
`FIG. 7 illustrates the spectral bandpass for a color infrared
`3-CCD prism;
`FIG. 8 illustrates the spectral bandpass for a color infrared
`3-CCD prism with bandpass trim filters;
`FIG. 9 is a diagrammatic, perspective view of an align
`ment fixture used to align an imaging array relative to a
`prism;
`FIG. 10 is a perspective view in partial section illustrating
`a thermal conductive cooling System for the array and array
`electronics,
`FIG. 11 is an optical diagram of a color Separating prism
`configuration for a four band combined primary color and
`color infrared System using the green and blue channels
`from a color mosaic array;
`FIG. 12 is an optical diagram of an embodiment showing
`the positive and negative lenses used for image aberration
`and size compensation with a SLR objective lens;
`FIG. 13 is an optical diagram for a color Separating prism
`that has a polarization Separation coating for two channels,
`FIG. 14 illustrates an optical diagram for a five band color
`Separating prism that uses a color mosaic array for primary
`colors and monochrome arrays for near infrared channels,
`FIG. 15 illustrates the field curvature and image distortion
`for SLR lens compensation without using an aspheric com
`pensator,
`FIG. 16 illustrates the field curvature and image distortion
`for the SLR lens compensation using an aspheric compen
`Sator,
`FIG. 17 is an optical diagram of a representative multi
`element lens employed in an embodiment of the apparatus,
`and
`
`MODES FOR CARRYING OUT THE
`INVENTION
`FIG. 1 is a diagrammatic, Side elevation view illustrating
`camera components including a color Separating prism
`assembly according to the teachings of the present
`invention, the arrangement employed to convert a primary
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`image into Subimages, the Subimages having different Spec
`tral characteristics. A positive power refractive element or
`lens 10 behind an image forming lens 12 introduces aber
`rations to negate aberrations caused by the color Separating
`prism. The color Separating prism is composed of prism
`elements 14, 16 and 18. A dichroic coating 20 on prism
`element 14 reflects a spectral band, typically the shortest
`wavelength band. Often this shortest spectral band is in the
`blue and green Spectral region. A dichroic coating 22 on
`prism element 18 reflects the next spectral band (typically
`the red spectral region). An air gap 23 between prism
`elements 14 and 16 causes the band reflected by coating 22
`to be reflected at surface 24 by total internal reflection.
`Prisms 16 and 18 are bonded together using an optical
`adhesive of any suitable type. A third band is transmitted
`through dichroic coating 22. Negative power compensing
`lenses 26, 28, and 30 are used to adjust image size of
`Subimages imaged at image receptors in the form of elec
`tronic imaging arrays or image Sensors 32, 34, and 36
`respectively, by controlling the Spacing between the image
`sensors and compensating lenses. Trim filters 38, 40, and 42
`are used to accurately regulate the Spectra of the Submim
`ages incident on the imaging arrayS.
`FIGS. 2 and 3 are, respectively, diagrammatic, Side,
`elevational, partial cross-sectional and diagrammatic, top,
`partial croSS-Sectional views of a multispectral 3-CCD cam
`25
`era embodiment constructed according to the teachings of
`the present invention and having the general overall layout
`shown in FIG.1. An SLR lens 44 attaches to bayonet mount
`46 which is attached to front mounting plate 48 by lens
`retainer 50. Front mounting plate 48 is made from low
`expansion coefficient 416 Stainless Steel or a titanium alloy
`or other suitable material. Lens retainer 50 holds plano
`conveX compensating lens 52. The color Separating prism 53
`composed of prism elements 54, 56, and 58 separates the
`primary image into three spectral regions and directs the
`Subimages to image Sensing arrayS 60. Trim filterS 62 block
`all light outside of the Spectral band Specified for each
`imaging array 60. A holder 66 positions each image array 60
`relative to the color Separating prism. A holder 68 positions
`each image compensating lens 64 relative to its associated
`imaging array 60. A printed circuit board 70 is soldered to
`each imaging array 60 to provide ancillary circuitry required
`for imaging array operation.
`In FIG. 2 printed circuit boards 72 provide the remainder
`of the camera circuitry not on array driver printed circuit
`boards 70. These boards are mounted using wedge-type
`thermal conducting mounts 74 providing good thermal con
`tact between the printed circuit boards 72 and a base plate 76
`of camera body or case 78. These mounts also provide
`rugged mechanical fixing of the printed circuit boards. By
`providing good thermal conduction cooling of printed circuit
`boards 72, the thermal convection heat load into the camera
`optics and imaging arrayS is reduced, improving the perfor
`mance of these components.
`In FIG. 2 an array mounting bar 80 is attached to left and
`right Side rails 82, 84 as is the color Separating prism
`assembly. The array mounting bar is made from a low
`expansion coeficient metal (416 stainless Steel or titanium,
`for example). The mounting rails 82, 84, prism assembly 53
`and array mounting bar 80 are nearly identical in their
`expansion coefficient, minimizing Sensitivity to temperature
`changes. Prism mounting plates 86 and 88 are bonded to
`opposite sides of prism assembly 53. Mounting rails 82,84
`are attached to front plate 48. Screws 90 are used to anchor
`the prism assembly to the mounting rails and ScrewS 92 are
`used to apply a load to mounting plate 88 keeping bond
`joints between prism 53 and mounting plates 86 and 88 in
`compression.
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`In FIG. 3 support electronics printed circuit boards 72 are
`connected to a motherboard 94 providing a digital and
`analog bus between boards and providing mechanical fixing
`of the boards.
`The camera body or case 78 contributes to formation of a
`hermetic enclosure protecting the internal camera compo
`nents from environmental elements. Camera case 78, rear
`panel 96, front mounting plate 48, lens retainer 50, and
`compensating lens 52 form a contiguous enclosure. This
`Sealed enclosure can protect the camera optics and electron
`ics from moisture and dirt contaminates. The conduction
`cooling features dissipate waste heat through the camera
`case, eliminating the need for performations in the camera
`case. The compensating lens provides a means of forming a
`contiguous barrier not found in conventional cameras with
`removable image forming lens.
`In FIG. 4 details of the prism assembly and one of the
`asSociated image arrayS 60 and related Structure are illus
`trated. Trim filter 62 is bonded to prism assembly 53.
`Bonding the trim filter 62 to the prism eliminates two
`air-glass interfaces, decreasing reflective losses. Compen
`sating lens 64 is bonded into lens retainer 68 which fixes the
`position of the compensating lens relative to the imaging
`array 60. The imaging array is bonded into array holder 66.
`A thermal conductive medium 98 of any suitable commer
`cially available type between the imaging array and array
`Support electronics printed circuit board 70 dissipates heat
`generated by the imaging array.
`In FIG. 5 a trim filter 100 is shown as being mounted
`between the compensating lens 64 and the imaging array 60.
`This configuration allows commercial mounted narrowband
`filters to be used for trim filters. The FIG. 4 configuration
`with the trim filter bonded to the prism is best Suited for use
`with unmounted Single layer glass trim filters.
`In FIG. 6 an imaging array 60 is shown as being bonded
`using an adhesive 101 into an array holder 102. The imaging
`array mounts in the array holder Such that the glass window
`(not shown) incorporated on the array is flush with an array
`holder planar Surface and the image Sensor of the array is
`perpendicular to the array holder. A rectangular hole in the
`array holder 102 provides accurate positioning of the imag
`ing array 60 while having relief regions to preclude electri
`cal contact between the array holder and array electrical
`terminals. Adhesive potting between the array holder and
`array provides good mechanical Support without relying on
`the array electrical leads for mechanical Support and posi
`tioning. Holes 104 and 106 may be used to mount additional
`hardware. Slots 108 are provided for the purpose which will
`be described below with reference to FIGS. 9 and 10.
`In FIG. 7 the dichroic nature of a representative color
`Separating prism is illustrated, showing nominal Spectral
`bands Separated by the prism dichroic coated elements. In
`this example the spectral bands for Channels 1-3 are nomi
`nally green, red, and near infrared, respectively. Broad
`Spectral bands are Separated by the prism assembly.
`In many applications it is desirable to use trim filters to
`block out-of-band radiation transmitted by the prism dich
`roic coatings. The trim filters can also be used to decrease
`the Spectral band transmitted to the imaging detectors. The
`cross-hatched regions in FIG. 8 illustrate the Spectral nar
`rowing of the image channels.
`In Some applications it is desirable to Separate one spec
`tral band into two different polarizations. In this case coating
`22 in FIG. 1 would be a polarization Separating coating.
`Imaging arrays 32 and 34 receive the S and P polarizations
`of otherwise spectrally identical images. Trim filters 38 and
`
`
`Ex.1041 / Page 15 of 19Ex.1041 / Page 15 of 19
`
`TESLA, INC.TESLA, INC.
`
`

`

`US 6,215,597 B1
`
`15
`
`25
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`7
`40 can be used to independently regulate the Spectral bands
`received by arrays 32, 34 or the trim filters can be identical.
`In FIG. 9 an approach used to adjust the alignment of an
`image array 60 relative to the color Separating prism 53 is
`shown. Focus is adjusted using Shims Such as Shim 110
`between the mounting rails 82, 84 and the array holder 66.
`Rotation and horizontal and vertical alignment are adjusted
`using micrometers 112 or other fine adjustment devices.
`Slotted holes 108 in the array holder allow motion of the
`array holder relative to the mounting rail when not tightened
`down and fixed in place. Screws (not shown) passing
`through the Slotted holes into the mounting rails are used to
`fix the position of the array relative to the prism once the
`array is in the desired position.
`In the arrangement of FIG. 10, the array printed circuit
`boards 70 are bonded to imaging sensors 60 which are
`bonded into array holders 102. The prism unit 53 is mounted
`to the mounting rails 120 which in turn are anchored to the
`camera front mounting plate 48. Heat dissipated in the
`imaging array is conducted to the array printed circuit board.
`Heat from the board is conducted through a high thermal
`conductivity flexible ribbon 122 to a thermal shunt plate
`124. The thermal shunt plate 124 conducts heat into the
`camera base plate 76. This shunt plate also provides
`mechanical Support between the front plate 48 and base plate
`76. Cooling the imaging array by shunting heat reduces the
`temperature of the imaging array. Temperature induced
`noise in the array generally doubles for every 10 degrees
`centigrade temperature rise. Shunting thermal energy
`decreases temperature gradients in the prism thereby reduc
`ing temperature induced refractive behavior in the prism.
`Commercial color Separating prisms commonly Separate
`an image into primary color components (red, green, and
`blue). Multispectral cameras have been built that use a color
`Separating prism to Separate green, red, and near infrared
`Spectral bands. With each of these configurations three
`monochrome imaging arrays are used to capture the three
`Spectral band images.
`In FIG. 11 a color Separating prism is used to Separate a
`blue-green band, a red band, and a near infrared band. A
`40
`color mosaic array is used in the blue-green channel to
`image the blue and green imageS. Color mosaic arrays are
`used in Virtually every Single array camcorder and digital
`Still camera. The Bayer pattern mosaic consisting of alter
`nating rows of red-green-red-green pixels and blue-green
`blue-green pixels is one of the most common color mosaic
`patterns. Monochrome arrays are used in the red and near
`infrared channels. Digital Signal processing is used to extract
`the data from the color mosaic array to provide blue and
`green images. These four color planes (blue, green, red, and
`near infrared) are combined to form a normal primary color
`image (red, green, blue) and color infrared (green, red, near
`infrared) image combining the functionality of what would
`otherwise require two cameras into a single camera.
`In FIG. 12 the color Separating prism Separates the visible
`image from the near infrared. A color mosaic imaging array
`images the primary color components (red, green, blue). A
`dichroic coating 130 Separates the near infrared into two
`different Spectral bands which are imaged by two mono
`chrome arrayS.
`In FIG. 13 the color separating prism separates the visible
`color image from near infrared at coated Surface 140. The
`near infrared is separated into two different polarizations at
`coated Surface 142. This prism configuration provides two
`Spectrally identical near infrared channels with one channel
`imaging the S-polarization and the other imaging the
`P-polarization components.
`
`8
`FIG. 14 is an optical diagram of the color Separating prism
`and compensating optics according to the first embodiment
`(the embodiment of FIG. 2) of the invention. The SLR lens
`is represented by a paraxial element with a focal length of 60
`mm. This value was Selected based on laboratory measure
`ments of commercial SLR lenses. Measurements of image
`Size as a function of wavelength were used to determine the
`required image size compensation. A plano-convex lens 52
`is placed between the SLR lens 44 and color sorting prism
`53 with the convex surface toward the SLR lens. A plano
`concave lens is placed between color Sorting prism 53 and
`image sensor 60. Trim filters 62 can be mounted next to the
`prism. The distance between the negative focal length lens
`44 and image Sensor 60 is used to adjust imageSize and the
`distance between the prism 53 and negative focal length
`lens/image Sensor assembly is used to control focus in each
`imaging channel.
`Numerical values for the working example shown in FIG.
`14 are provided in TABLE 1. In this table, S represents the
`Surface number. R represents the optical Surface radius of
`curvature in millimeters units. The values tabulated in
`column D are the distances between Surfaces in units of
`millimeters. The columns V and N show the index of
`refraction and Abbe number for optical materials used in this
`working example. FIG. 15 shows the image distortion for
`this working example. The compensating optics reduce the
`RMS spot size to approximately 10% of the RMS spot size
`for an uncompensated f/1.4 optical System based on an SLR
`lens and a color Separating prism.
`
`TABLE 1.
`
`D
`
`25.0
`2.5
`1.5
`28.17
`2.O
`D6
`2.O
`D8
`
`R
`
`Infinite
`77.52
`Infinite
`Infinite
`Infinite
`Infinite
`Infinite
`43.776
`
`S
`
`1.
`2
`3
`4
`5
`6
`7
`8
`
`V
`
`N
`
`1517
`
`64.17
`
`1603
`1785
`
`38.03
`25.76
`
`1785
`
`25.76
`
`TABLE 2 lists the Spacings between the prism and plano
`concave compensating lens (D.6) and the plano-concave
`compensat