United States Patent 15
`Dill
`
`[11] Patent Number:
`
`[45] Date of Patent:
`
`4,724,354
`Feb. 9, 1988
`
`[54]
`
`IMAGE INTENSIFIER FOR PRODUCING A
`COLOR IMAGE HAVING A COLOR
`SEPARATION FILTER SEQUENTIALLY
`PASSING VISIBLE BLUE LIGHT AND ITS
`SECOND ORDER WAVELENGTHS, VISIBLE
`GREEN LIGHT AND ITS SECOND ORDER
`WAVELENGTHS, AND VISIBLE RED LIGHT
`Inventor:
`[75]
`James M. Dill, Pompano Beach, Fla.
`[73] Assignee:
`
`EOL3 Company,Inc., Ft.
`Lauderdale, Fla.
`
`[21]. Appl. No.: 859,423
`
`[22] Filed:
`
`May5, 1986
`
`[S51]
`
`Tint. Cheteee HO01J 31/56; HO4N 5/33;
`HO4N 9/04
`[52] US. C1. ee eccsecesessteeseseentenee 313/371; 313/474;
`313/524; 313/542; 250/213 VT; 358/41;
`358/42; 358/113; 358/211
`[58] Field of Search........... 313/103 R, 103 CM, 104,
`313/105 R, 105 CM, 112, 371, 373, 376, 377,
`379, 380, 399,400, 474, 478, 524, 525, 530, 542,
`343, 544, 527, 528; 250/213 VT; 358/42, 41, 43,
`44, 50, 55, 113, 211
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,812,526
`4,016,597
`4,085,421
`4,437,111
`
`(5/1974 Tam sseccssssscssessesereneefesteestacee 358/42
`4/1977. Dillon etal.
`oss
`
`4/1978 Gilmour.....
`ase
`3/1984 Inai et ab. oiesescsscesesnsees 358/44
`
`FOREIGN PATENT DOCUMENTS
`
`.... 313/103 CM
`0053530 6/1982 European Pat. Off.
`56850 S/1977 Japan ossecsecsesseseroersssesessceess 313/524
`
`106356
`8/1981 Japan ........sssccsseersserecepeerneeee 313/524
`
`— 10985)
`17795)
`90887
`
`1/1983) JapaneeeLensesessreeseres 358/42
`2/1983 Japan ...rsccccssssesssevssseesseneseeee 358/42
`5/1983 Japan ..ccccccsesssssrsreterereeeens 358/55
`
`OTHER PUBLICATIONS
`
`Fischer, Edward, “Obtaining Color Pictures with an
`Image Intensifier Tube”, RCA Technical Notes, RCA
`TN No. 556, Mar. 1964, 2 pages.
`Stern, M. A., et al., “Low-Light-Level Image-Ampli-
`fying Device with Full Color Capability”, Journal of
`the SMPTE,vol. 83, No. 3,. Mar. 1974, pp. 185-189.
`NHK. Technical Research Laboratories, “High-Sen-
`sitivity 3 Image Intensifier Saticon Color Camera”, Jun.
`1979, 2 pages, (Author and Publication Unknown).
`Corion Corporation, Holliston, Mass., Corion Optical
`- Filters and Coatings, Catalog, Aug. 1985, pp. 16-21,
`50-51, 84-89.
`
`Primary Examiner—James J. Groody
`Assistant Examiner—Randall S. Svihla
`Attorney, Agent, or Firm—Oltman and Flynn
`
`ABSTRACT
`[57]
`A color separation filter arrangement for an image in-
`tensifier having separate blue, green and red filters
`whichrespectively have pass bandsfor visible blue light
`and its second order wavelengths, visible green light
`and its second order wavelengths, and visible red light.
`The blue, green and red filters are interposed individu-
`ally in successionin the path of incidentvisible light. and
`infrared energy to the photocathode ofthe imageinten-:
`sifier. Use of this color separation filter produces a rela-
`tively high signal-to-noise ratio at the output of the
`image intensifier when it is used under night sky illumi-
`nation.
`‘
`
`4 Claims, 4 Drawing Figures
`
`
`
`TRANSMITTANCE
`
`
`
`400 800.
`
`600
`1200 1300 400
`1100
`700
`800
`900 i000
`NANOMETERS
`WAVELENGTH ~
`
`INFRARED
`
`INFRAREO
`
`
`VISIGLE
`
`
`
`GREEN
`FILTER
`8a
`
`
`400 500 GOO.
`700 800.
`300 i000
`1100 1200 1300 1400
`WAVELENGTH - NANOMETERS
`
`
`
` TRANSMUTTANCETRANSMITTANCE
`
`
`
`WISIALE
`
`
`
`RED
`FILTER
`
`
` 8
`
`
`1100 1200 1300 1400
`700 800 300 1000
`400 500 600
`WAVELENGTH - NANOMETERS
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 1 of 4
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 1 of 4
`
`

`

`US. Patent
`
`—
`
`Feb.9, 1988
`
`4,724,354
`
`MIGHT SKY
`t
`~4
`
`:Gy ENERGY
`
`
`1100
`1200 1300 400
`900 1000
`800
`.700
`400 500 GOO
`WAVELENGTH - NANOMETERS
`
`
`
`
`TRANSITTANCE
`
`400 500
`
`1200 1300 1400
`1100
`900 1000
`800
`700
`600
`MAVELENGTA - NANOMETERS
`
`
`VISIBLE
`X
`ce
`x
`
`COEEN
`R
`FILTER
`S
`
`SA
`Q
`Tt
`
`.
`\
`900 1000
`1100
`1200 1300 1400
`700 800
`K 400 500 GOO
`WAVELENGTH - NANOMETERS
`VISIBLE
`RED
`FILTER
`Be
`
`/NERAREO
`
`
`
`
`1100 1200 1300 1400
`800 300 1000
`700
`400 500 600
`WAVELENGTH - NANOMETERS
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 2 of 4
`
`yy
`
`YQ
`X
`R
`S
`§
`
`=cK
`
`Fig. 4
`IF
`
`:
`
`V/S/BLE
`
`INFRAREO
`
`
`BLUE
`FILTER
`
`ESB
`
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 2 of 4
`
`

`

`1
`
`4,724,354
`
`2
`used herein is for the purpose of description and not of
`limitation.
`
`IMAGEINTENSIFIER FOR PRODUCING A
`COLOR IMAGEHAVING A COLOR SEPARATION.
`FILTER SEQUENTIALLY PASSING VISIBLE
`BLUE LIGHT AND ITS SECOND ORDER
`WAVELENGTHS, VISIBLE GREEN LIGHT AND
`ITS SECOND ORDER WAVELENGTHS, AND
`VISIBLE RED LIGHT
`
`SUMMARYOF THE INVENTION
`
`This invention relates to a novel filter arrangement
`for color separation imagery operation of an image
`intensifier under a night sky.
`Attempts to use color separation imagery with image
`intensifiers under the low illumination provided by a
`night sky have not been entirely satisfactory because of
`excessive noise in the output from the image intensifier.
`The present invention substantially overcomes this
`difficulty by taking advantage of the following facts:
`(1) night skytypically has a relatively high level of
`energy covering most of the visible spectrum and
`the infrared spectrum; and
`(2) image intensifiers generally have a sensitive re-
`sponse over the visible spectrum and much ofthe
`infrared spectrum (including specifically second
`order blue and green).
`In accordance with the present invention, the light
`image input to the image intensifier is filtered through a
`complex filter unit which passes, in succession, visible
`blue and its second order wavelengths (in the infrared
`spectrum), visible green and its second order wave-
`lengths, and visible red. The intensified visual image on
`the output screen of the image intensifier has a higher
`signal-to-noise ratio than was possible in previous at-
`tempts to use imageintensifiers in color separation im-
`agery systems.
`A principal object of this invention is to provide for
`use under night sky illumination a novel combination of
`an image intensifier and an input color filter arrange-
`ment which. produces a relatively high signal-to-noise.
`ratio at the output of the imageintensifier.
`Further objects and advantages of this invention will
`be apparent from the following detailed description of a
`presently preferred embodiment which is illustrated
`schematically in the accompanying drawings.
`DESCRIPTION OF THE DRAWINGS
`
`FIG.1 is a schematic longitudinal sectional view of
`an image intensifier provided with the novel filter ar-
`rangement of the present invention;
`FIG.2 is a front elevation of a rotatably adjustable
`disc present presenting the different color segments of
`the filter in FIG. 1;
`FIG. 3 showsin full lines the spectral sensitivity of a
`typical image intensifier and in dashed lines the spec-
`trum of energy in the night sky, both plotted against the
`wavelength of the energy; and
`FIG. 4 shows the band-pass characteristics of the
`blue, green and red filters in the filter unit at the light
`input side of the imageintensifier of FIG. 1, in accor-
`dance with the present invention.
`Before explaining the disclosed embodiment of the
`present invention in detail it is to be understood that the
`inventionis not limited in its application to the details of
`the particular arrangement shown since the inventionis
`capable of other embodiments. Also, the terminology
`
`DETAILED DESCRIPTION
`
`Referring to FIG. 1, reference numeral 1 designates
`generally an image intensifier tube of known design
`which is shownin simplified schematic form here.It has
`a photocathode 2 at one end which is exposed to inci-
`dent light, an anode and focusing cone 3, a microchan-
`nel plate 4 having an input electrode 5 on its face
`toward the photocathode and an output electrode 6 on
`its face away from the photocathode, and a fluorescent
`output screen 7 at the opposite end. This is a typical
`“second. generation” image intensifier. The optical
`image formed on the photocathode 2 by the incident
`light is converted by it into an electron image, which is
`multiplied by the microchannel plate 4 and applied to
`the output screen 7, which produces.an optical image
`whichis an intensified replica of the optical image on
`the photocathode.
`In one practical embodiment, the photocathode2 is at
`— 1750 volts, the anode and focusing cone3 is at + 1000
`volts, the input electrode 5 of the microchannelplate 4
`is at +900 volts and its output electrode6 is at reference
`ground, and the output screen 7 is at +6000 volts. Ina
`portable image intensifier these voltages are supplied by
`an internal power supply having a three volt DC power
`source in the form of two size AA dry cell batteries.
`This battery voltage is stepped up in the internal power
`supply. to provide the different voltages for the various
`electrodes of the image intensifier.
`In accordance with the present invention, a thin film
`optical filter unit 8 is located immediately in front of the
`transparent end wall 9 of the image intensifier tube just
`ahead of the photocathode 2. As shownin FIG.2 this
`filter unit may be in the form ofa rotary disc consisting
`of a blue filter sector 8B, a green filter sector 8G and a
`red filter sector 8R, each taking up one-third ofthe disc.
`Each color sector 8B, 8G and 8R is large enough to be
`in the path ofall energy impinging on the photocathode
`- 2through the transparent end wall 9 at a particular time
`during each rotation of thefilter disc 8.
`Thefilter disc 8 is driven by a D.C. powered stepping
`motor shown schematically at 10 in FIG. 1 through a
`mechanical drive of any suitable design, indicated by
`the dashed line 11 in FIG. 1. The motor indexes the
`filter disc rapidly to successive rotational positions 120
`degrees apart in whichthebluefilter 8B, the greenfilter
`8G and the red filter 8R are positioned successively in
`front of the transparent end wall 9 of the imageintensi-
`fier. FIG. 2 showsthe filter disc in a rotational position
`in which the blue filter 8B masks the transparent end
`wail, shown in dashedlines.
`If desired, the respective blue, green and redfilters
`may be on flat panels or cards, one closely behind the
`other, which are slidably operated so that only one at a
`time covers the end wall 9 of the image intensifier and
`the other two are retracted. The three colorfilter panels
`are actuated in rapid succession, one at a time, to the
`operative position to provide blue, green and red filter-
`ing in sequence.
`Eachcolorfilter 8B, 8G and 8R is composed of semi-
`transparent layers separated in succession along the
`direction of the energy impinging on the photocathode
`2 and so arranged as to pass certain wavelength bands
`with relatively little loss and to reject the other wave-
`lengths substantially completely.
`
`20
`
`|
`
`55
`
`65
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 3 of 4
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 3 of 4
`
`

`

`4,724,354
`
`.
`
`3
`Asshownin FIG.4, bluefilter 8B has two pass bands,
`one for visible blue light and a second for blue second
`order wavelengths (i.e., infrared energy in the wave-
`length band twice that of visible blue light); the green
`filter 8G has two pass bands, one for green light in the
`visible spectrum and a second for green second order
`wavelengths (i.e., infrared energy in the wavelength
`band twice that of visible green light); and the redfilter
`8R has a single pass band in the visible red spectrum.
`Eachfilter 8B, 8G and the 8R rejects ail energy wave-
`lengths except those within its pass band or pass bands.
`It will be evident that the filter 8 is a spectrally sensi-
`tive beam separator for sequentially dividing the inci-
`dent energy into these components:visible blue andits
`second order wavelengths, visible green and its second
`order wavelengths and visible red.
`The photocathode 2 of the imageintensifier 1 re-
`ceives sequential color separated images and converts
`them into an electron image which is multiplied by the
`microchannel plate 4 and applied to the output screen 7
`to producea visible image which is an amplification of
`the sequential filtered inputs through the blue, green
`and red sectors offilter disc 8.
`As shownin FIG.3, a typical night sky may have the
`energy levels in the visible light and infrared spectrums
`as shown by the dashed line curve 12. A typical image
`intensifier has a response to incident energy as shown by
`the full line curve 13, from whichit will be evident that
`the response drops off sharply at about 1200 nanometers
`and higher wavelengths. The response of the image
`intensifier tube is high over the entire visible light spec-
`trum and the infrared spectrum up through twice the
`wavelength range of visible green light, but it is very
`low in the infrared spectrum in the wavelength range
`twice that ofvisible red light. Therefore, even though
`infrared energy at wavelengths twicethat of visible red
`light is substantially present in the night sky, the red
`filter 8R in the present invention rejects it because the
`imageintensifier would not respond significantly to it.
`Because of the inclusion of components of the night
`sky’s energy which are in the infrared spectrum, the
`signal-to-noise ratio of the output from the imageinten-
`sifier is substantially greater than has been possible pre-
`viously using color separation imagery in only thevisi-
`ble spectrum under a night sky.
`I claim:
`1. In combination with an image intensifier having a
`photocathode,
`a filter unit havinga first filter means with pass bands
`for only visible blue light and infrared energy in the
`
`4
`wavelength band twice that of visible blue light, a
`second filter means with pass bandsfor only visible
`green light and infrared energy in the wavelength
`band twice that of visible green light, and a third
`filter means with a pass band for only visible red
`light, said filter unit being operatively arranged to
`position said first, second and third filter means
`individually in succession in the path of incident
`energy before it reaches said photocathode.
`2. The combination of claim 1 wherein said filter unit
`is a rotatable disc with first, second and third sectors
`which respectively provide said first, second and third
`filter means.
`3. In combination with an image intensifier having:
`a photocathode for converting an optical
`image
`formed by incident energy to an electron image,
`an anode and focusing cone,
`a microchannel plate for multiplying the electron
`image produced by said photocathode,
`and an output screen for converting the multiplied
`electron image to an optical image;
`means for operating said image intensifier at a high
`signal-to-noise ratio under a night sky comprising:
`a filter unit having a blue filter with pass bands for
`only bluelight in the visible spectrum and infrared
`energy in the wavelength band twice that of blue
`lightin the visible spectrum,a green filter with pass
`bands for only green light in the visible spectrum
`and infrared energy in the wavelength band twice
`that of green light in the visible spectrum, and a red
`filter with a pass band for only red light in the
`visible spectrum, said filter unit being operative to
`position said blue filter, green filter and red filter
`individually in succession in the path of incident
`energy in the visible light and infrared spectrums
`before it reaches said photocathode.
`4. In combination with an image intensifier having a
`photocathode for converting an incident light image
`into an electron image, means for multiplying said elec-
`tron image, and an output screen for receiving the mul-
`tiplied electron image and converting it into a light
`image, spectrally sensitive filter means positioned in the
`path of said incident light image to said photocathode
`for periodically separating said incident light image,
`priorto arrival at said photocathode,into a plurality of
`differentvisible light wavelength bands and wavelength
`bands twice those of certain of said visible light wave-
`length bands.
`*
`*£
`&£
`*&
`*&
`
`10
`
`20
`
`25
`
`30
`
`40
`
`45
`
`30
`
`35
`
`65
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 4 of 4
`
`HAAG-STREIT AG - EXHIBIT 1019
`Page 4 of 4
`
`