Catadioptric lens system for collecting and directing light from large aperture luminescent light illuminating fixtures

A projection illumination fixture includes luminescent light tubes lined with an emulsion coating of titanium dioxide and phosphors for producing an appropriate mixture of highly scattered red, blue and green wavelengths of sustained luminescent light emission, a reflector housing for reflecting scattered rays of emitted luminescent light toward an aperture, a catadioptric lens for collecting and redirecting luminescent light rays reaching the aperture into and through a light snoot or barrel and a large area projection (magnifying) Fresnel lens at the end of the light snoot or barrel for directing and spreading the emitted light to fill an illumination field with directional divergent light ideal for dimensionally `painting` talent and objects positioned and moving within the illumination field.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to luminescent illumination systems for television,
 video and film sets and studios.
 2. Description of the Prior Art
 In U.S. Pat. Nos. 5,012,396 and 5,235,497 the Applicant, Paul D. Costa
 describes luminescent lighting fixtures and illumination systems providing
 omni-directional sustained luminescent (florescent and phosphorescent)
 light emission of desired color/chromaticity from phosphors in an emulsion
 coating the interiors of luminescent light tubes for television and film
 studios.
 It is important to understand that there are both prompt or fluorescent and
 delayed or phosphorescent luminescent light emissions excited from the
 phosphors lining the light tubes. The prompt or fluorescent light emission
 begins within 10 nsec (10.sup.-9 sec.) of the exciting stimulus and ceases
 within 10 nsec after excitation stops. The delayed or phosphorescent light
 emissions can begin after 10 nsec of the exciting stimulus but persists
 beyond 10 nsec once excitation stops [See Van Nostrand's Scientific
 Encyclopedia6.sup.Th. Ed. 1983 pp. 1237, 1788 & 2204.] The bandwidths of
 prompt or fluorescent light emissions in many instances are different than
 the bandwidths of the delayed or phosphorescent light emissions. Also, the
 phosphor compounds which fluoresce may be different from those that
 phosphoresce.
 As noted in U.S. Pat. No. 5,235,497, luminescent lighting fixtures have
 relatively large light apertures that generally frustrate efforts to
 direct and shape the emitted light. Even with the geometry for shaping the
 light from sustained luminescent lighting fixtures as disclosed in U.S.
 Pat. No. 5,235,497, the apertures can be unacceptably large, particularly
 when appropriate variations of shadows, and areas of differing luminosity,
 brightness, shade, tint and hue are required for providing a believable
 perception of dimensional depth to a two dimensional (flat) video or film
 image.
 Color television cameras, video cameras, color photography films, digital
 electron scanning cameras and the human eye each sense or perceive
 discrete bandwidths of light which are then recombined, integrated and
 interpreted in a nonlinear fashion as a particular color. In contrast to
 incandescent lighting fixtures that are characterized with reference to
 Stefan-Boltzman "blackbody emission temperatures" or `color temperatures`,
 luminescence light consists of relatively narrow bandwidths of light
 emissions which do not follow blackbody laws. (A laser is a common example
 of a luminescent light source producing a coherent amplified light
 emission in very narrow bandwidths.)
 Spectral output of luminescent light sources are better characterized in
 terms of an index which provides a comparison of colors illuminated (by
 the luminescent light) to those same colors illuminated, for example, by
 direct `white` noon sunlight. (Direct `white` sunlight typically between
 noon and 2:00 P.M. is the practical standard for determining color for
 human vision.) Manufacturers of luminescent light tubes try to blend
 phosphors to produce different bandwidth distributions of radiant energy
 usually identified with a proprietary trademark, e.g., LUMILUX.RTM..
 Descriptive terms such as cool white, warm white, daylight are also
 frequently relied upon. However, most luminescent light tube manufacturers
 ultimately resort to characterizing the distribution of different
 bandwidths of light emitted by their blends of phosphors as producing an
 effect of illumination equivalent to that produced by incandescent
 Tungsten filaments at particular temperatures expressed in degrees Kelvin
 (.degree.K), in tacit recognition of the predominance of Stefan-Boltzman
 blackbody emission standards.
 A better index for characterizing the light output of luminescent light
 tubes having a selected blend of phosphors emitting a distribution of
 different narrow spectral bandwidths of light would be the SRGB.RTM.
 standard developed by the Applicant which characterizes the relative
 radiance of respective red, blue and green primary color bandwidths of
 sustained luminescent light emanated by a blend of phosphors reflecting
 from known sets of standard gray scale charts and color band charts.
 In particular, the color of a surface is the bandwidths of light reflected
 from that surface. Such reflected light can be captured, digitally imaged
 and then sampled using conventional eye dropper tools associated with most
 computer graphics, design, and image processing software programs. The
 software eye dropper tools measure and/or characterize such parameters as
 brilliance, saturation, hue, tint, shade or whatever, in terms of the
 various color-model systems used by the particular program for specifying
 color. In a sense, the optical capture system, and associated computer and
 software tools function as a reflection meter. Diffusely reflected light
 from a standard chart can be sampled to provide a quantitative color
 evaluation of its spectral in terms of color(s) reproduced and observed by
 a human being directing the optical capture system and controlling the
 computer system.
 For example, in the RGB additive model, typical CRT television or computer
 monitor screens reproduce the color yellow, not spectrally present, by
 combining various brightness values of red, green, and blue light. James
 Clerk Maxwell initially demonstrated this effect to the Royal Institute in
 London in 1861. The L*a*b* (Lab) model developed by CIE.sup.1
 mathematically specifies a luminance or lightness (L) value and two
 chromatic components values (a) specifying a range from green to magenta,
 and (b) specifying a range from blue to yellow in a way that is supposed
 to be device independent. The CMY and CMYK color-model system for
 photography and printing are subtractive/multplicative models that specify
 values for cyan (C), magenta (M), yellow (Y) filters and ink which absorb
 light. Values for black (K) inks are specified in printing because
 available C, M & Y inks combine to reflect a muddy brown. [See Van
 Nostrand's Scientific Encyclopedia 7th Edition, Vol. 1, pp. 36 & 701, Vol.
 2 pp. 2203, 2714] In HSB and HLS color models, an achromatic `gray scale`
 value termed `brilliance` (B) or `lightness` (L) is specified along with
 two chromatic values specifying `hue` (H) and `saturation` (S). Saturation
 is a parameter relating to purity of the color, gray being zero. In the
 HSB model, colors having a more pronounced hue are more chromatic, i.e.,
 differ more from a gray of the same `brilliance` or `lightness`
 `Brilliance` and `hue` can in turn be related by using such terms as
 `tints` and `shades.` A chromatic color having little `hue` but high
 `brilliance` is termed a `tint`, e.g., pink, whereas color of low `hue`
 and low `brilliance` is termed a `shade`, e.g. brown.

FNT .sup.1 Centre Internationale d'Eclairage, an international organization
 which began establishing specifications for color in 1931. CIE has
 developed a number of comparable standards including CIE XYZ, CIE xyY, CIE
 L*u*v* and CIE L*a*b*. The television broadcast industry in fact specifies
 desired chromaticities in picture tube output which then relate to gamma
 corrected voltages corresponding to red green and blue signals. See 47 CFR
 .sctn. 73.682(20) (iv).
 Modern personal computers and associated graphics, design and imaging
 software programs and tools provide RGB image displays which allow users
 to manipulate and evaluate color by varying values in one or more of the
 common and proprietary color modeling schemes using side-by-side color
 comparison boxes. Such computers and software tools thus, in a very real
 sense, allow the bandwidth sensitivity of human perception to be
 integrated into the evolution of illumination standards for producing
 images of studio subjects and talent.
 Titanium dioxide also in the emulsion coatings of luminescent light tubes
 scatters and mixes the light emissions from the different phosphor
 compounds in the coating. Ad Lagendijk of the University of Amsterdam and
 the FOM-Institute for Atomic and Molecular Physics in the Netherlands at
 the American Physical Society Meeting in March 1991 held in Cincinnati,
 Ohio, reported a discovery that the velocity of light propagating through
 a highly disordered scattering medium such as a dispersion of titanium
 dioxide, appears to be one tenth of that previously assumed. [See Science
 News Mar. 23, 1991, Vol. 139, No. 12, p. 182.] Nabil M. Lawandry of Brown
 University reported in the March 1994 issue of Nature, reported that he
 and his co-workers discovered that certain dyes when dissolved in a liquid
 containing tiny particles of titanium dioxide when stimulated by an
 external energy source, amplify the (luminescent) light emitted by the
 excited dye (phosphor) molecules. In their experiment, Lawandry et al used
 a green laser to excite photoluminescent molecules of rhodamine dissolved
 in menthol. Adding titanium dioxide particles greatly amplified the
 emitted light. The surprising result was that a medium containing
 particles that reflect light in all directions can amplify emitted
 radiation. [See also Science News Apr. 9, 1994, Vol. 145, No. 15, pp.
 228-229.]
 The stability of light emission from luminescent light tubes and capability
 of blending phosphors to produce distributions of different spectral
 bandwidths of luminescent light emission permits tailoring to achieve a
 proper balance of sustained red blue and green bandwidth light emissions
 optimized for electron scanning/television/video cameras, color films and
 even two human eyes. However, electronic scanning cameras, including
 charge-coupled devices (CCDs) which record television and video color
 images do not mimic human eyes, but rather generate signals representative
 of spectral energy in separate red, blue and green light bandwidths
 reflecting off an object. This is accomplished by separating red, green
 and blue images of the object from the incoming light using, for example,
 a spilt-cube separation optical system that has appropriate Diachronic
 coatings which allow transmission of one bandwidth along the principal
 optical axis while reflecting the other two bandwidths into two adjacent
 channels typically located on opposite sides of the principal optical
 axis. The three separate color images are directed onto and converted into
 electrical image signals by three separate photosensitive or CCD surfaces.
 Single tube systems use a subtractive color process interposing an array
 of crossing filters strips to selectively pass representative bandwidths
 of light. In either case, the resultant electrical signal is then
 processed to produce signals representative of the respective red, blue
 and green light bandwidths reflected from the object. [See Television and
 Audio Handbook (1990) K. Blair Benson & Jerry C. Whittaker pp. 6.6, 6.7;
 and Television Engineering Handbook (1986) K. Blair Benson Chap. 4, pp.
 4.56-4.76, & Chaps. 11.
 The electrical images signals obtained by such electron scanning cameras
 can then be manipulated to provide color corrected or false color images
 when reproduced at a television/video monitor screen. It is even possible
 with present day CHROMAKEY videos systems to electronically subtract the
 image signal in one or more channels and substitute an image signal from a
 completely different source to produce a composite image at the monitor
 screen. The electronic systems driving the monitor screens or displays
 utilize the electrical images signals generated by the cameras for driving
 an additive color process for reproducing hues of the object imaged. [See
 Television Engineering Handbook (1986) K. Blair Benson Chap 12]
 In contrast to electronic imaging, in film, color images are reproduced
 principally by a subtractive color process using colorant filters for
 controlling the amounts of reflected red blue and green light from an
 object to create a positive or negative image of the object in a light
 sensitive chemical emulsion. [See Van Nostrand's Scientific Encyclopedia
 7th Edition, Vol. 2 pp. 2203, 2714]
 Finally, the UV radiation flashes driving luminescent light emissions from
 phosphors impart cyclic variation to the stimulated light. If the cyclic
 variation is slow as when using a 60 Hertz ballast (producing 120 flashes
 per second), rapidly moving objects illuminated produce "blurred ghost
 like" images referred to as a stroboscopic effect. The illumination
 industry characterizes cyclic variation in luminescent light emissions as
 flicker specifying a Flicker Index which is a relative measure of the
 cyclic variation in output of various sources at a given power frequency.
 Catadioptric lenses use both reflection and refraction to redirect or bend
 light and can be utilized disperse, collect, collimate and gather or
 concentrate light in a manner similar to Fresnel lenses. [See U.S. Pat.
 No. 4,755,921, Nelson, & U.S. Pat. No. 4,791,540. Dreyer et al.] However,
 as explained in U.S. Pat. No. 5,568,324, Nelson et al, because the index
 of refraction is frequency/wavelength dependant in optically transmissive
 materials, catadioptric lens systems like other refractive optical
 components, exhibit chromatic aberration, i.e., optical materials refract
 different wavelengths of light dispersively. In U.S. Pat. No. 5,568,324,
 Nelson et al presents a solution a problem of chromatic aberration in an
 over head projection (OHP) system using a light source located below and
 to one side of a planer face of a divergent catadioptric lens by utilizing
 a doublet condensing lens system where the divergent catadioptric lens has
 a planer face and a structured face of prismatic ridges in combination
 with a convergent catadioptric lens also having a planer face and a
 structured face of prismatic ridges where the respective structured faces
 of the respective catadioptric lenses are located in an aligned facing
 relationship.
 SUMMARY OF THE INVENTION
 A projection illumination fixture includes luminescent light tubes lined
 with an emulsion coating including titanium dioxide and phosphors for
 producing an appropriate mixture of highly scattered red, blue and green
 wavelengths of sustained luminescent light emission, a reflector housing
 for reflecting scattered rays of emitted luminescent light toward an
 aperture, a catadioptric lens for collecting and redirecting luminescent
 light rays reaching the aperture into and through a light snoot or barrel
 and a large area projection (magnifying Fresnel) lens at the end of the
 light snoot or barrel for projecting and spreading the emitted light to
 fill an illumination field or volume.
 A particular aspect of the invented projection fixture relates to
 positioning a `gobo" or aperture of a particular shape adjacent the
 catadioptric collector lens for shaping or tailoring cross section the
 light beam output subsequently projected and spread by the projection lens
 in the illumination field.
 A primary advantage of the invented projection illumination fixture relates
 to the fact that the titanium dioxide emulsion coating lining the
 luminescent light tubes produce, in essence, an infinite array of
 distributed omni-directional light sources each radiating a sustained
 formula of selected wavelengths of light, which when collected and
 redirected by the catadioptric lens, do not exhibit color fringes or
 moires. In particular, because the particular wavelengths of rays of
 luminescent light emissions are uniformly distributed, i.e., spread over
 an area, unlike a point or concentrated Stefan-Boltzman continuous
 spectrum or "blackbody" radiating (hot) filament, there is no chromatic
 aberration in the light collected and redirected by the catadioptric lens.
 Another primary advantaged afforded by the invented luminescent projection
 illumination fixture is that by appropriately configuring the catadioptric
 collection lens, the effective light emitting aperture large luminescent
 light tube arrays can be effectively reduced to allow for both: (i)
 magnification (projection) by appropriately located, inexpensive large
 area Fresnel lenses; and (ii) light tailoring via `gobos` and the like.
 Still another aspect of the invented luminescent projection illumination
 fixture relates to its directional light output enabling lighting
 directors to cast directional arrays of shadows for providing believable
 depth to video and film images recorded in two dimensions.

DESCRIPTION OF PREFERRED AND EXEMPLARY EMBODIMENTS
 Looking at FIGS. 1 through 4, the invented projection illumination fixture
 11 includes a reflector housing 12 with internally supported reflecting
 surfaces 13 defining a trapezoidal hexahedron light cavity volume 15
 directing light emitted by a plurality of trichromatic luminescent light
 tubes 14 toward a reflector cavity aperture 16 at its base. A transmissive
 catadioptric lens 17 is disposed across the reflector cavity aperture 16
 for optically collecting the light dispersively radiating toward the
 cavity aperture and converting it into a more-or-less or directed
 "divergent" light beam. A gobo 18 with a pre-selected shaped aperture 19
 is located immediately outward from the catadioptric lens 17 for shaping
 the cross section configuration of the directed light beam from the
 catadioptric lens 17. A light snoot or barrel 21 secured to the reflector
 housing 12 tapers to a second rectangular snoot aperture 22 slightly
 smaller than the reflector cavity aperture 16. A projection lens 23,
 preferably a Fresnel type, is disposed across the snoot aperture 21 and
 projects and focuses the shaped beam of light to fill an illumination
 field or volume 24 a known distance from the fixture 12. The side walls of
 the light snoot 21 are preferably non-reflective such that escaping light
 directed by the catadioptric lens striking the snoot walls is not
 reflected into the Fresnel type projection lens 23 and projected off its
 principal optical axis 48 (See FIG. 5).
 The invented projection fixture 11 includes U-shaped rectangular
 slide-mounting frames 29 and 31 at the reflector housing aperture 16 and
 snoot aperture 22 respectively for mounting and positioning the
 catadioptric lens 17 and gobo 18 across aperture 16 and the projection
 lens 23 across the snoot aperture 22. The gobo 18 and catadioptric and
 projection lenses 17 & 23 are each mounted in rigid rectangular frames 32
 sized to be received and slide into the particular U-shaped slide-mounting
 frame 29 or 31. Conventional latches (not shown) secure the framed
 catadioptric lens 17, gobo 18 and projection lens 23 in the respective
 U-shaped slide mounting frames 29 and 31 to prevent them from sliding out
 of the fixture when it is moved.
 The U-shaped slide mounting frames 29 & 31 facilitate switching of the gobo
 18, the catadioptric lens 17 and the projection lens 23 in the invented
 fixture to meet different lighting objectives. The ease of removing and
 replacing the framed gobo 18 also allows for easy adjustment of the beam
 cross section by altering the gobo aperture 19. A skilled lighting
 director can even modify (enlarge) an existing gobo aperture 19 by simply
 cutting it to a desired shape with scissors.
 The invented projection Illumination fixture 11 also includes a typical
 pivoting bracket 37 connected to reflector housing 12 with a central clamp
 post 38 ideally extending coaxially with the principal axis 48 of the
 fixture to allow the fixture to be securely positioned on lighting rails
 and aimed in a conventional manner.
 Appropriate electronic driver circuits 26 are located in an integral bay 27
 of the r reflector housing 12 and are conventionally powered electrically,
 for example, via a conventional electrical power cord 28. The electronic
 driver circuits 27 provide high frequency current (electron) pulses from
 25 to 100 kHz for exciting UV flashes within the light tubes 14. The UV
 flashes in turn stimulate the phosphors in the emulsions lining the
 interior of the light tubes to emit sustained luminescent light having an
 appropriate (red, blue and green) wavelength distribution for correctly
 reproducing colors when reflected from surfaces and reproduced in films or
 via video signals. The light tubes 14 in turn secured to a bracket 36
 straddling the driver circuits 26 extend at the apex into the trapezoidal
 hexahedron light cavity volume defined by the reflector surfaces 13.
 Suitable collecting transmissive catadioptric lens 17 for the invented
 fixture 11 may be formed, shaped or molded from any transparent
 homogeneous material nominally having a uniform index of refraction
 ranging up from 1.3. The refracting and reflecting surfaces of such lens
 17 need not be highly precise optically, as a sharply focused light in the
 illumination field 24 is not desirable. The frames 32 need only provide
 sufficient rigidity to the lens 17 for holding it essentially in a plane
 across the reflector-housing aperture 16. Ripples or non-planar
 deformation the lens 17 should be minimized. However small deformations
 can usually be tolorated if light flux directed non-symmetrically off axis
 is not significant relative to the desired directed light flux output of
 the fixture. Such ripples and deformations essentially re-direct light
 illuminating undesired areas outside the illumination region 24.
 In addition to directing light from the cavity housing 12, the catadioptric
 lens 17 also serves to diffuse the directed light such that light
 intensity or light flux within the shaped portion beam determined by the
 gobo aperture 19 is relatively uniform without `hot spots`. Suitable
 materials for such catadioptric lens include glass and transparent
 polymeric materials such as acrylic, polycarbonate, polypropylene,
 polyurethane, polystyrenes, and polyvinyl chloride.
 A catadioptric lens 17 composed of polycarbonate having a smooth surface
 facing inward toward the light tubes 14, consisting of a linear array of
 identical regular two (2) faceted triangular prismatic ridges angled at
 70.degree. available from 3M.RTM. was found by the Applicant to be
 suitable in prototypes of his invented fixture. The particular
 catadioptric lens effect provided by such 70.degree. polycarbonate film is
 refraction and reflection of light through the structured surface that for
 the most part emerges within an ellipsoidal envelope angle of 70.degree.
 in a plane perpendicular to the surface oriented perpendicular to the
 prismatic ridges and to essentially 90.degree. or so in the orthogonal
 plane parallel the prismatic ridges. [See U.S. Pat. No. 4,791,540. Dreyer
 et al. Col. 4, line 53 through Col. 5, line 17 & U.S. Pat. No. 3,712,713
 Appledorn, Col. 4, lines 10-56.]]
 The applicant observes, considering of the teachings of U.S. Pat. No.
 4,755,921 John C. Nelson, for efficiently collecting and appropriately
 redirecting light radiating into and through the aperture 16, that
 suitable designs for catadioptric lens composed of light transmissive
 materials include at least one structured surface of prismatic ridges with
 three or more faceted surfaces oriented in linear, rectilinear rectangular
 or smoothly curved parallel and concentric arrays. However, both surfaces
 of the lens may be structured. [See U.S. Pat. No. 4,900,129 D. F.
 Vanderwerf] Depending on the optical result desired, e.g., maximized
 projected light intensity/flux, the structured surface can face outward
 toward the snoot aperture 22 or inward toward the reflectors 13 and light
 tubes 14 in the reflector housing 12.
 The Applicant discovered that the light from the array of luminescent tubes
 14 radiating through the rectangular aperture 16 collected and redirected
 by catadioptric lenses 17 does not exhibit significant chromatic
 aberration or Moire patterns. This is because light emissions from the
 different luminescing phosphor compounds in the emulsions coating lining
 interior surfaces of the light tubes 14 are omni-directional, as well as
 being scattered by the titanium dioxide in the emulsion coating. In
 essence, every theoretical point in the radiating emulsion coating the
 inside of luminescent tubes 14 can be assumed to be uniformly radiating in
 every direction at each of the respective frequency bandwidths of the
 particular chosen luminescing phosphors. While chromatic aberration or
 scattering of each theoretical point source light emission would and does
 occur, because luminescent light emission is distributed over a large area
 (relatively) and radiates into each theoretical point on the input surface
 of the catadioptric lens more or less uniformly through a theoretical
 hemisphere centered on each such point, the chromatic
 aberration/scattering of the transmitted light averages. This means that
 the chromatic content of the light emerging from each theoretical point on
 the output lens surface is uniformly mixed. [See U.S. Pat. No. 2,050,429,
 W. A. Dorey et al.]
 Using the same analogy, each theoretical point on the reflecting surfaces
 13 within the housing 12 directing emitted light toward the cavity
 aperture 16 light can be also assumed to be radiating omni-directionally
 through such theoretical hemisphere centered above such point. And, as
 appreciated by Dreyer et al in U.S. Pat. No. 4,791,540 the catadioptric
 lens 17 itself reflects light back into the reflector housing 12.
 Because the light from the luminescent tubes 14 and reflectors 13 radiating
 into the catadioptric lens 17 is distributed, not concentrated or
 localized, it is not necessary for its prismatic ridges or faceted
 surfaces of the lens to be graduated relative to an emission point as with
 blackbody (hot) radiating filaments to achieve a uniform distribution of
 the transmitted light flux in the illumination field 24. [See generally
 U.S. Pat. No. 4,741,613, D. F. Vanderwerf and U.S. Pat. No. 4,859,043, P.
 Carel et al, Col. 5, line 59 through Col. 6, line 16 which discuss the
 necessity for such graduations in the faceted lens surfaces for spreading
 concentrated light sources]
 Similarly, because the purpose of the invented fixture is to provide an
 area of uniform light intensity at the illumination plane/region 24,
 precision optics is not necessary for the projection lens 23 disposed
 across the snoot aperture 21. In fact, "full page" 2.times. power page
 magnifying Fresnel sheet lens (approximately 81/2".times.11") used as a
 collector disposed across the light snoot aperture 22 14 to 15 inches
 distant from the gobo 18 was found satisfactory for projecting a shaped
 beam of light from the gobo aperture 19 to a desired illumination field or
 a volume ranging from five to fifteen feet distant from the fixture 12.
 The Applicant found that better projected illuminating light was obtained
 by locating the plane of the gobo 18 at perpendicular distance from and
 sheet lens greater than the nominal focal length of the 2.times. power
 Fresnel magnifying sheet lens but less than twice such nominal focal
 length. The objective is looking at FIG. 4, to locate the sheet Fresnel
 magnifier lens in a plane sufficiently distant from the gobo such that the
 projected gobo aperture is inverted in the illumination field.
 The critical optical parameters of the invented fixture relate to: (i) the
 nominal focal length F.sub.L of the Fresnel projection lens; (ii) the
 f-number of the projection lens 23, i.e., the ratio of its focal length to
 its diameter; (iii) the perpendicular distance, D.sub.G between the plane
 of the gobo 18 and the plane of the projection lens 23; and (iv) the
 desired projection distances, D.sub.P, to various planes in the
 illumination field. Classically D.sub.G and D.sub.P are the so called
 finite conjugates of the Fresnel lens. The focal length, distance to gobo
 plane and a selected projection distance to any plane in the illumination
 field perpendicular to the principal optic axis of the projection lens can
 be related using thin lens assumptions by the relationship.sup.2 :

FNT .sup.2 See Halliday, Resnick, Walker Fundamentals of Physics 4.sup.th,
 (1993) Chap. 39, .sctn. 11 (pp. 1033-1035).
 ##EQU1##
 By algebraic manipulation this yields the relationship:
 ##EQU2##
 A factor significant in limiting the projection distance is the light
 intensity desired in the spatial volume to be illuminated (the
 illumination field). The skilled lighting director or illuminator should
 bear in mind that the cross section of the projected shaped beam increases
 with distance from the fixture while intensity decreases. And, from the
 point of view of the observer (a camera), it is not the intensity of the
 light in the illuminated spatial volume that is most important, but rather
 the variations in intensity of light reflecting or scattering from
 surfaces of objects and/or talent illuminated within that volume. In
 addition, the skilled optical designer optimizing the invented projection
 illumination fixture for particular applications need also consider
 tradeoffs between the desired light intensity in the illumination field
 and such inter-related factors as (i) the efficiency of the catadioptric
 lens in redirecting the scattered sustained luminescent light into a
 desired divergent ellipsoidal cone, (ii) the length of the light
 snoot,(iii) the f-number of the Fresnel type projection lens, (iv) the
 number (volume) of luminescent tubes that can be mounted within reflector
 cavity and (v) reflectivity of the reflectors directing light out the
 reflector cavity aperture.
 In the example given above, using a 2.times. power page magnifier Fresnel
 lens as collecting projection lens 23, locating the gobo approximately 14
 to 15 inches from the plane of the lens 23 produced acceptable levels of
 illumination in a volume ranging 5 to 15 feet from the fixture.
 Concentrating now on FIG. 4, the boundary optical paths through the optical
 components of the invented projection fixture 11 are primarily determined
 by the catadioptric lens 17 which predominantly confines light emerging
 from each theoretical point on its structured surface to an elliptical
 cone ranging from 70.degree. in a plane .perp. to the prismatic ridges
 (also angled at 70.degree.) and to approximately 90.degree. in a plane
 .parallel. the prismatic ridges (a function of the relative refractive
 index parameters establishing total internal reflection of light within
 the lens). Assuming the cross section of figure is .perp. to the prismatic
 ridges, within the gobo aperture 19, boundary rays 41 and 42 radiating at
 angles of 55.degree. and 125.degree., respectively, relative to the plane
 of the lens 17 reach the snoot aperture 22 and are projected by the
 projection lens 23. Boundary rays 43 and 44 radiating at angles greater
 than 55.degree. and less than 125.degree. from the surface of the lens 17
 will also reach the snoot aperture 22 and be projected by the Fresnel type
 projection lens 23. Boundary ray 46 and 47 radiating at angles of
 125.degree. and 55.degree., respectively strike the walls of the snoot 21.
 The portion of the light radiating from the surface of the lens 17 from
 55.degree. to approximately 90.degree. between boundary rays 41 & 47 and
 from approximately 90.degree. to 125.degree. between boundary rays 42 and
 46 will strike the walls of the snoot 21. Preferentially, light rays
 striking the walls of the snoot 21 are redirected or absorbed in a manner
 to prevent collection and projection off the primary projection axis 48 of
 the projection lens 23.
 The projection lens 23 collects the directed light rays radiating more or
 less conically from the catadioptric lens 17 out the gobo aperture 19
 through the snoot aperture 22 along its principal optical projection axis
 48, and directs the collected light rays though a focal region indicated
 at 51 into the illumination field.24. Because the light directed by the
 catadioptric lens 17 is diverging within an ellipsoidal cone from
 70.degree. to 90.degree., light within the shaped beam arriving at the
 illumination region 24 is fuzzy or `soft`. This means in essence that
 light rays simultaneously emerging from each theoretical point on the
 surface of the catadioptric lens collected and projected by the projection
 lens 23 continue to diverge within that 70.degree. to 90.degree.
 ellipsoidal cone relative to each other in the illumination region 24.
 Further, it should be appreciated that a higher intensity or flux light
 radiates from the fixture before within the volume defined by boundary
 rays 43 & 44 which after inverting at the focal region of the projection
 lens spreads or projects over a larger area in the illumination field. The
 converse is true for light falling within the envelope of boundary rays 41
 and 42. Accordingly, the transition from light inside the shaped beam to
 dark outside the shaped beam in the illumination region 24 is not a sharp
 transition but more of a gradual transition. The sharpness of the
 transition between light and dark regions of the shaped projected light
 beam is also a function of the projection lens focal length F.sub.L and
 the conjugate distances D.sub.G and D.sub.P from the projection lens to
 the gobo and the projection plane respectively. Accordingly, a consummate
 lighting director can manipulate the transition between light and dark
 regions of the shaped light beam in the illumination field by using
 projection lenses with different focal lengths and by moving the fixture
 toward and away a particular reference plane in the illumination field.
 The skilled lighting director or illuminator must also remember in using
 the invented projection illumination fixture that the light sensitivity of
 the human eye is not straight forward, nor linear. For example, personal
 computers can reproduce literally millions [(2.sup.24)=16,777,216] of
 different colors using only mixtures of red blue and green light
 frequencies each being assigned 8 information bits, tens of thousands of
 which may be differentiated by the human eye and brain. Further, the human
 brain interpreting what the eyes senses, responds to variations in
 intensity, relative brightness and darkness to provide perceptions of
 depth. Divergence in the illuminating light likewise provides essential
 data for human depth perception. For example, gradations of hue of a
 hanging green leaf scattering diverging sunlight allows a human being to
 determine the orientation of the leaf in space. Similarly, the curvature
 of smooth surfaces such as automobile fenders is revealed by highlights
 and gradations in tints and hues perceived in light scattering from such
 surfaces typically radiating from divergent sources such as sunlight.
 The beauty of the catadioptric lens 17 in the invented projection system,
 looking at FIGS. 7, 8 & 9, is that light 79 enters the lens 17 (via the
 reflector housing aperture 16) essentially hemispherically divergent at
 every theoretical point on the entrant surface 78 of the lens 17, but
 predominantly radiates or exits from the lens from each theoretical point
 on the exit surface 79 of the lens 17 in a ellipsoidal cone. A small
 percentage of light also emerges from the exit surface 79 of the lens in
 regions 84 of the theoretical exit hemisphere (FIG. 8). The angle of the
 faceted prismatic ridges 81 primarily determines the angle of divergence
 of the radiating light in a plane 82 oriented perpendicular (.perp.) to
 the ridges 81. The index of refraction of the material composing the lens
 determines the angle of divergence of the radiating light in a plane 83
 parallel to the ridges 81. The chromatic content of such entrant and
 radiant light (determined by the luminescing phosphors of the light tubes)
 is a homogeneous mixture of desired ratios of red blue and green light
 frequencies. The projection Fresnel type lens 23 projects such chromatic
 diverging light to the illumination field 24 where in essence each
 theoretical point in plane perpendicular to the principal optical axis of
 the projection lens likewise is divergent in an ellipsoidal cone
 (70.degree. to 90.degree.) since the illuminating beam at such plane is
 essentially an enlarged inverted image of the gobo aperture 19.
 Lighting and illumination directors lighting sets and stages can literally
 `paint` both talent and surfaces located within the beam cross section of
 the invented projection fixture with the selected ratios of red blue and
 green light frequencies such that the surfaces so `painted` scatter
 (reflect) it in a manner which creates a distribution of hues, shades
 tints and brights capable of being recorded by film or by video systems
 sensitive to those light frequencies. Images reproduced from such recorded
 films and video signals will present a similar distribution of hues,
 shades, tints, and brights determined by the limits of the particular
 recording/sensing mechanism.
 For example, looking at FIG. 5, without directional illumination a
 reproduced image of talent 51 and objects 52 located within an
 illumination region 24 otherwise adequately lite, will appear flat or
 `cartoonish` with planar regions of different colors not having any
 visually apparent dimensional differentiation. Adding directional
 divergent light using one or more of the invented projection illumination
 fixtures (FIG. 6) adds a distribution of hues, shades, tints and brights
 to the reproduced image which in turn provide visually apparent
 dimensional differences to the different colored areas composing the
 image. Skilled lighting directors use such directional divergent light to
 create highlights (brights & tints) with related shadows (hues and shades)
 to provide definition. For example, an image of a talent presenting the
 latest news becomes believable and recognizable because of a highlighted
 cleft chin above a chin shadow, or a bright forehead shaded by elegantly
 or not so elegantly coifed hair, or because of a determined nose, or full
 (sensuous) lips.
 An example of the visual impact the above phenomenon on human beings, can
 be easily appreciated by comparing early `flat` Graphical User Interface
 (GUI) Qperating System (OS) programs for personal computers with the
 dimensionally shaded, window frames and icons which typify present day GUI
 OS programs for those same personal computers. Today graphical computer
 programs are typically capable of providing dimensionality to
 computationally created images by locating a divergent radiating light
 source relative to an image, calculating and then displaying shaded and
 bright areas of the image as illuminated by the light source. Computer
 game and simulation programs are even capable, to a degree, of presenting
 moving computational images with a dynamic play of shadows and brights to
 enhance the reality of the virtual environment presented visually on a
 screen to the human being playing the game or experiencing the simulation.
 The areas of tints, brights, hues and shades created by directional
 divergent light also enable artists to touch up their reproduced images.
 For example, the dimensionality, visually apparent in quality, black and
 white still images produced by such famed artists as Ansel Adams, is first
 a function of the skill of the photographer in recognizing recording
 negative images in light that provides adequate gradations of grays to
 provide dimensional differentiation between light and dark areas in the
 (negative) image; and second a function of the artistic skill of the
 photographer (or developer) in developing prints from such negative images
 adding and subtracting light (burning and dodging) as necessary in the
 differentiating gray areas to provide a realistic illusion of dimensional
 depth to the reproduced (print) image. The shapes and distributions of the
 different gray areas in the negative, are a function of the shadows cast
 by divergent directional light illuminating the object or talent, is the
 information used by the artist in developing the prints.
 Today, graphics software programs such as ADOBE.RTM. ILLUSTRATOR,
 ADOBE.RTM. PHOTOSHOP.RTM. and QUARK EXPRESS.RTM. enable the skilled artist
 even more freedom to idealize (amend) a recorded or digitized (video)
 still image to emphasis or de-emphasis illusions of dimensionality. Such
 computational sampling tools as the eyedropper tool for sampling `color`
 of an area of a particular tint or hue, the magic wand tool defining areas
 of a particular color value, the lasso tool and the like are potent tools
 in the hands of a competent artist who grasps and can render distributions
 of hues, shades brights, and tints to give an impression or illusion of
 depth to a planar image. With such software tools areas of a particular
 hue, shade, tint or bright can be sampled and amended to enhance or
 mitigate visually apparent dimensionality. The shapes of such particular
 areas of hue, shade, tint or bright are again determined by the
 directionality and divergence of the light illuminating the talent or
 object when the image was originally captured.
 Moving images, i.e., successive still images of relatively moving talent
 and objects, are not as easily manipulated as single still images to
 provide an illusion of dimensionality because the dynamic distribution or
 play of shadows (hues and shades) and highlights (tints and brights) on
 non flat moving surfaces are perceived by the human eye and brain as
 indicia movement in three dimensional space. Such distributions change
 with every change in relative position. Accordingly, even with the
 computational aid of computers systems, it is not usually feasible to
 routinely retouch a moving sequence of images to provide a believable
 illusion of depth or dimensionality not present in the light distribution
 when the images were recorded. This is in contrast, to the film and video
 entertainment industry where successive images with each with
 distributions of dimensional hues, shades, tints and brights are
 routinely, and believably `morphed` or transformed into other dimensional
 images. A point of commonality, helping the plausibility of such scenes is
 a common relative position of a directional divergent light source
 (virtual or real) creating the dynamic dimensional play of the
 distributions of hues shades tints and brights in the successive images.
 The invented projection fixture enables lighting directors to cast directed
 shaped beams of divergent light from reference positions into an
 illumination field or region for the purpose of creating dimensional
 distributions of highlights (tints & brights) and shadows (hues and
 shades) to images of talent and objected moving relatively in such space.
 The ability to manipulate (change) the cross section a directed divergent
 beam in that illumination field by changing the gobo aperture in the
 invented projection fixture allows skilled lighting directors to
 creatively conceal or transform undesired surfaces and areas. For example,
 in a uniform flat luminescent illumination field without shadows, using a
 CHROMAKEY video set, a moving `blue or green` carrier may be effectively
 transformed, visually, into a magic carpet bearing objects/talent
 positioned for dimensionality `painting` in directed divergent luminescent
 light from one or more of the invented projection fixtures in an
 illumination field. In such a suggested CHROMAKEY video set, both the
 primary illumination and dimensionality illumination should be provided by
 luminescent light tubes with the same formulas or blends of phosphors for
 producing essentially identical ratios or mix of red, blue and green light
 frequencies. The ability to tailor the directed divergent beam to avoid
 dimensionally `painting` the `blue or green` carrier, allows for
 subtraction and substitution of a different image signal for the carrier.
 The invented projection fixture for providing directed divergent
 luminescent light suitable for television, video and film production
 application has been described in context of representative, exemplary and
 preferred embodiments. Many modifications and variations can be made to
 the invented projection illumination fixture, which, while not exactly
 described or suggested in the foregoing specification, fall within the
 spirit and the scope of the invention as described and set forth in the
 appended claims.